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Tried three different MAP sensors, but 2.5 engine still bogs badly when accelerated by Patrick
Started on: 01-26-2014 11:33 PM
Replies: 35 (1173 views)
Last post by: Patrick on 07-25-2014 07:07 PM
Patrick
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Report this Post01-26-2014 11:33 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post


Fortunately I have another Fiero to drive, but my trusty '84 5-spd is acting up. I noticed it started running very rough when first started. It will improve somewhat after running for a couple of minutes, but something is still screwey. The engine will rev high and stay there easy enough with good power (that indicates to me that the ignition system and fuel supply are probably fine), but the engine will stall unless it's acceleratred very slowly.

There are no trouble codes.

If I disconnect the MAP sensor's electrical connection, the engine will idle and rev up just fine... no bogging.

There is plenty of vacuum (22 in Hg) from the TB to the MAP at idle.

I figured it must be the MAP sensor then. Tried one from another Fiero. Back to the bogging again.

Tried a MAP sensor from a third Fiero. Back to the bogging again.

I doubt that all three of these MAP sensors are faulty.

I haven't checked the voltage readings at the MAP yet, but with what I've reported so far, has anyone got any ideas?

(In case it might have any bearing on suggestions, this engine has always had rather poor gas mileage. Never been above 25 MPG. Kind of lousy for a duke with a 5-spd.)

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phonedawgz
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Report this Post01-27-2014 07:31 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post

I would suspect low fuel pressure under load.

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Report this Post01-27-2014 08:10 AM Click Here to See the Profile for KurtAKXSend a Private Message to KurtAKXEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by phonedawgz:

I would suspect low fuel pressure under load.


^ What he said. I've had two do the exact same thing, one with a leak in the rubber coupler tube between the pump and sender, and one with a bad pump.

If you pick up a TBI fuel pressure test adapter and a fuel pressure gauge with a hose, you can temporarily tape the gauge to your back window. I bet your fuel pressure under hard acceleration drops down below 7 psi.

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conan469
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Report this Post01-27-2014 08:21 AM Click Here to See the Profile for conan469Click Here to visit conan469's HomePageClick Here to Email conan469Send a Private Message to conan469Edit/Delete MessageReply w/QuoteDirect Link to This Post

i agree with fuel pressure. cheap test would be to pinch of the return line (rubber hose somewhere?) and drive it.
don't leave it clamped for long time.
have done this to get cars back to the shop.

could also be ignition module. have had them get weak and still run.
replaced one few months back, after car died, thern customer came back to thank me for the power increase while driving,
he said it had been bogging down and slow for a while, then it finally died.

remember under load cylinder pressure rises A LOT higher than in neutral.
fuel demands are higher and more spark is needed.

[This message has been edited by conan469 (edited 01-27-2014).]

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armos
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Report this Post01-27-2014 11:05 AM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post

I would want to check the fuel pressure just on principle (it's certainly important and it's good to know the info), but I don't think that can explain why it accelerates better when the MAP is unplugged. Unless it's only a minor difference, but it sounds like the change was significant.
I'm confused by the statement that it makes good power, but stalls unless you accelerate slowly. That seems like a contradiction - do you mean it makes good power when the MAP is unplugged?

Does it seem that colder weather corresponds to when the cold idle issue surfaced?

When the MAP is unplugged, the ECM will run more rich. I've seen this when datalogging a V6 car, and I assume the 4cyl has similar programming. That rich condition might be helping to compensate for whatever the problem is. Perhaps the mixture is truly lean for some reason.
Or perhaps the mixture is good, but it's a marginal ignition problem, such that it breaks down under load unless it's running extra rich.

Have you investigated the TPS? A bad TPS could easily cause a lean stumble when accelerating, but I don't know if it can be bad enough to cause a stall. The ECM's logic for the check engine light is really simplistic and can easily miss a fault.
This doesn't really fit the idling problem though - a bad TPS shouldn't affect idle as far as I know.

If you have a meter then definitely check the voltages at the MAP sensor connector. I'd also probably change plugs and check compression while you have them out.

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Boostdreamer
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Report this Post01-27-2014 11:48 AM Click Here to See the Profile for BoostdreamerClick Here to Email BoostdreamerSend a Private Message to BoostdreamerEdit/Delete MessageReply w/QuoteDirect Link to This Post

Checked the timing? Power off idle is greatly affected by the timing.

Jonathan

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AL87
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Report this Post01-27-2014 12:08 PM Click Here to See the Profile for AL87Click Here to Email AL87Send a Private Message to AL87Edit/Delete MessageReply w/QuoteDirect Link to This Post

My question here is: What would cause the fuel pressure to drop or remain consistent (but not enough for the demand)?

bad fuel pump? low charge on battery? bad regulator? (if a 2.5 has one)

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Report this Post01-27-2014 12:13 PM Click Here to See the Profile for CsjagClick Here to Email CsjagSend a Private Message to CsjagEdit/Delete MessageReply w/QuoteDirect Link to This Post

Is the fuel filter fairly new? Is the exhaust system flowing freely without any obstructions like a clogged cat?

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Patrick
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Report this Post01-27-2014 02:22 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

Lots of questions and suggestions to respond to, but I'm just going out the door. I'll touch upon the following before I have to go...

 
quote
Originally posted by armos:

I would want to check the fuel pressure just on principle (it's certainly important and it's good to know the info), but I don't think that can explain why it accelerates better when the MAP is unplugged. Unless it's only a minor difference, but it sounds like the change was significant.

I'm confused by the statement that it makes good power, but stalls unless you accelerate slowly. That seems like a contradiction - do you mean it makes good power when the MAP is unplugged?


The change is very significant with the MAP unplugged.

With the MAP still connected... If the throttle is cracked open quickly, the engine will stumble badly and sound like it's running on two cylinders. However, if the throttle is opened very slowly, the engine can reach and maintain a high RPM and it sounds fine. This is what I was describing below.

 
quote
Originally posted by Patrick:

The engine will rev high and stay there easy enough with good power (that indicates to me that the ignition system and fuel supply are probably fine), but the engine will stall unless it's acceleratred very slowly.



As I say, unplugging the electrical connection of the MAP results in the engine appearing to run "normal". The throttle can be quickly cracked open and the engine will accelerate fine.

Okay, I've got to go. Thanks everyone for the suggestions so far. I'll respond further later today.

[This message has been edited by Patrick (edited 01-28-2014).]

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carbon
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Report this Post01-27-2014 03:04 PM Click Here to See the Profile for carbonSend a Private Message to carbonEdit/Delete MessageReply w/QuoteDirect Link to This Post

If you're checking voltages be sure to check TPS as well... the throttle position is used by the ECM for accel enrichment. It just pops into my head when you say you can slowly reach any RPM and it runs fine once it gets there.

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Report this Post01-27-2014 03:18 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by phonedawgz:
I would suspect low fuel pressure under load.

Could be.
need right tool for doing this w/o cutting etc.
See my Cave, TBI Test Adaptor

Check FP power and ground before thinking FP is bad. Why?
See my Cave, Electric Motors

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)


The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

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Report this Post01-27-2014 09:06 PM Click Here to See the Profile for Custom2M4Click Here to Email Custom2M4Send a Private Message to Custom2M4Edit/Delete MessageReply w/QuoteDirect Link to This Post

I would check fuel pressure, your cat converter, and change the fuel filter and air filter.

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Report this Post01-27-2014 10:12 PM Click Here to See the Profile for CsjagClick Here to Email CsjagSend a Private Message to CsjagEdit/Delete MessageReply w/QuoteDirect Link to This Post

My 85 duke was doing the same thing and after checking a lot of things it turned out that the timing was way off. After I fixed the timing and drove it for awhile to reset the ecm it was fine.

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Report this Post01-28-2014 12:01 AM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post

This is a long shot, but try disconnecting the EGR (and cap off the vacuum line) and see if that helps. When the EGR valve goes bad, it can sometimes cause a stumble on acceleration.

Edit to add: I would also suggest checking the timing, just to be thorough. Also, take a look at the electrical plugs on the ignition module. I once had an electrical plug fall apart, which broke the connection to the spark advance line... had to drive *really* conservatively, because the engine didn't want to accelerate.

[This message has been edited by Blacktree (edited 01-28-2014).]

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Patrick
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Report this Post01-28-2014 02:12 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

Thanks guys, for all the suggestions of things to check. So far we have...

 
quote

low fuel pressure

ignition module

bad TPS

ignition timing

clogged cat

fuel filter

air filter

bad ground

low battery

fuel regulator

faulty EGR



I'm hoping if it's not raining tomorrow that I'll be able to check over all these things (as the car is out in the open), although it's a heck of a nuisance checking fuel pressure on a duke. No schrader valve like the V6 has. I have a fuel pressure gauge but no adapter thing for the duke's fuel line. I'll worry about that tomorrow.

However...

It's still not clear to me how ANY of those suggestions can be responsible for the "bogging" on acceleration, when simply unplugging the MAP seems to correct the issue!

Stranger still is the fact that three different MAP sensors (when connected) all behave the same... bog city.

Disconnecting the MAP obviously sets a default value for something. Does anyone know exactly what-all is set to a default value when the MAP is unplugged? Is it a default value just for the MAP itself, or is it an all inclusive default for all the sensors... O2, CTS, etc?

It would be very helpful to know. If it's a default value just for the MAP which is set, then it seems to me that the MAP itself (or perhaps wiring to it) must be bad if the engine runs better. If it's an "all inclusive" default value for various sensors, then unplugging the MAP might be masking a problem sensor elsewhere.

Again, there have been no trouble codes stored, but I understand a sensor can be flakey without actually setting a code.

So... any feedback on what I've brought up in this post?

[This message has been edited by Patrick (edited 01-28-2014).]

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Report this Post01-28-2014 10:24 AM Click Here to See the Profile for BoostdreamerClick Here to Email BoostdreamerSend a Private Message to BoostdreamerEdit/Delete MessageReply w/QuoteDirect Link to This Post

My V6 won't run at all without the MAP so I don't have a clue. It will die if I unplug it.

Jonathan

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Report this Post01-29-2014 12:00 PM Click Here to See the Profile for conan469Click Here to visit conan469's HomePageClick Here to Email conan469Send a Private Message to conan469Edit/Delete MessageReply w/QuoteDirect Link to This Post

the map is one of the sensors gm used to calculate fuel mixture.
it also uses the O2 sensor, did you try unplugging the O2 but leaving the map plugged in?
it is possible for an O2 to shift and give an ok signal pattern but too high or too low of a voltage and still be within ecm parameters.

basically unplugging the map should cause the ecm to go open loop and fuel/spark the engine with base programmed values not the current
live values of closed loop.

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Report this Post01-29-2014 12:12 PM Click Here to See the Profile for CsjagClick Here to Email CsjagSend a Private Message to CsjagEdit/Delete MessageReply w/QuoteDirect Link to This Post

Often when you disconnect sensors the ECM has to learn the new input, I am told you have to drive the car over 35 mph for a few miles and every time you turn it off and drive it again the car runs better and better. I have noticed on my 85 duke that I have been tuning that sometimes after I adjust something or change something it runs crappy for a few minutes until the ecm adjusts.

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Report this Post01-30-2014 12:22 AM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post

I'm looking at an old datalog I recorded when I had an idling problem, and tried unplugging my MAP. It did "fix" the idling problem, but only because it made the car run rich. The MAP wasn't actually faulty.
I'm trying to see what the ECM did differently without the MAP connected.

I should note that the log was from an 86 V6, not a 4cyl.
The log only has the car running for about 85 seconds, but it was already fully warmed up at the time (~200-210F coolant temperature).
It recorded a constant low reading of about 10.7kPa from the MAP and set the "MAP low" error flag.
The ECM reported that it was in closed loop for the whole log.
The O2 was almost constantly reading rich. It was active, but reading over 1.0V most of the time. It only blipped quickly to the lean side (low voltage) 3 times in 85 seconds. The sensor was good, it only behaved like this in the "MAP low" error state.
The BLM was at 120 and the INT was at 20.

Low INT/BLM numbers had already been a problem, but the INT was even worse in this log with the MAP unplugged. This is consistent with the rich readings from the O2 sensor.
In spite of the O2 readings, and that it was claiming to be in closed loop, there was still no "rich exhaust" code set. The only code was "low MAP". By my reading of the "rich exhaust" (code 45) parameters in the service manual, it looks like I met the conditions to set that code, except it also requires a minimum run time of 1 minute. If I had left it running longer, maybe the code would have set. I don't remember if I had it running for long prior to hitting the record button.
The way the O2 reading behaved during that log, I actually wonder if the ECM was deliberately trying to run near the threshold for code 45.

I don't see any values being substituted, at least not in a way that's visible through the diagnostic connector. The MAP has a constant low value, which if it were being observed, would cause it to run lean, not rich. Other sensors appear to have continued working normally.
I think it's reasonable to say that the MAP is being substituted (or just ignored) in the internal code, but there's no indication of any other sensors being affected.

Based on all this, I believe that in the "low MAP" error state, the ECM ignores the MAP and adds extra fuel to it's internal calculations. It's idle mixture is near the threshold for a rich exhaust error, but at least in my case it did not set one.
I did not test or log the "low MAP" state while driving. My log was only at an idle.


If you leave the MAP connected and unplug the O2 sensor instead, it should have the same effect of making it run rich. If it still runs better when you do this, then it might further suggest that the MAP signal isn't really the problem.
However, I still wouldn't say it can be completely ruled out. Whatever is wrong, whether it's MAP or something else, the engine/ECM may simply be less sensitive to it when it's already on the rich side.
These newfangled 1980s fuel injected computer cars are basically designed to run as lean as they can. I believe this combined with the primitive computer controls lends to their finicky nature.

[This message has been edited by armos (edited 01-30-2014).]

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Patrick
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Report this Post01-30-2014 02:56 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by conan469:

basically unplugging the map should cause the ecm to go open loop and fuel/spark the engine with base programmed values not the current live values of closed loop.


That's what I thought was happening as well when I unplugged the MAP, but from what armos has reported, perhaps that's not the case.

 
quote
Originally posted by armos:

I'm trying to see what the ECM did differently without the MAP connected.
The ECM reported that it was in closed loop for the whole log.

I don't see any values being substituted, at least not in a way that's visible through the diagnostic connector. The MAP has a constant low value, which if it were being observed, would cause it to run lean, not rich. Other sensors appear to have continued working normally.
I think it's reasonable to say that the MAP is being substituted (or just ignored) in the internal code, but there's no indication of any other sensors being affected.


That's surprising to hear, but very good to know!

 
quote
Originally posted by conan469:

it also uses the O2 sensor, did you try unplugging the O2 but leaving the map plugged in?


 
quote
Originally posted by armos:

If you leave the MAP connected and unplug the O2 sensor instead, it should have the same effect of making it run rich. If it still runs better when you do this, then it might further suggest that the MAP signal isn't really the problem.


Yes, I should definitely try unplugging the O2 sensor instead and see what happens.

 
quote
Originally posted by armos:

Whatever is wrong, whether it's MAP or something else, the engine/ECM may simply be less sensitive to it when it's already on the rich side.


I guess that's what other fellas were saying earlier in the thread as well. I suppose I was hesitant to believe that simply creating an extra rich mixture (by unplugging the MAP) might possibly be masking the actual problem.

Well, thanks everyone... I certainly appreciate these ideas and suggestions. I'll poke away at this when I get an opportunity over the next few days and report back what progress I may (or may not) have made.

It really frustrates me that I can't find my ALDL cable (made by Dodgerunner) that I use when running WinALDL. I think the last time I used it was when I was working on This car. I tucked the cable away in a safe spot afterwards, and it's still tucked away safely... wherever it is! If anyone has an ALDL cable that's not being used anymore, and you wish to sell it, I just might be interested!

[This message has been edited by Patrick (edited 01-30-2014).]

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carbon
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Report this Post01-30-2014 09:03 AM Click Here to See the Profile for carbonSend a Private Message to carbonEdit/Delete MessageReply w/QuoteDirect Link to This Post

With a MAP sensor and IAT sensor you can run speed density calculations based on RPM, manifold pressure and air temperature. This is how the Fiero operates under normal circumstances.

If you unplug the MAP, there is really no way to continue running speed density.

With a only TPS sensor and RPM you can run Alpha-N calculations, setting fueling and igntion with only throttle position(Alpha) and engine speed (N)... and it is set very conservatively, hence the running rich with the MAP unplugged as the computer is flying blind not really knowing how much air is actually coming in. So it better be enough fuel for colder air and significant load as the ECM no longer has MAP to tell it that load is increasing, like climbing a hill. AKA Limp Home Mode.

If you are running speed density with no TPS you'll have fairly poor throttle response but it will run decently if throttle changes are slow. If you run in Alpha-N, with no MAP, you'll run rich with OK throttle response, but never quite right.

Speed density with the addition of TPS for acceleration enrichment is going to give the best drivability.

Edit: Yes the ECM also takes into account the intake air temperature and coolant temp. You'll notice that if either of those sensors die, the ECM goes rich to compensate as well. If it doesn't know what is going on, it assumes the worst.

[This message has been edited by carbon (edited 01-30-2014).]

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Patrick
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Report this Post04-08-2014 01:58 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

I don't know where the time has gone , but I finally got back to working on this Fiero today. (I've been driving a different one.)

Discovered something very very interesting.

First, I tried a couple of different things. I reconnected the MAP but disconnected the O2 sensor, to see if that would also allow the engine to run in a "default" mode. No dice, the engine wouldn't start. Disconnected the MAP and the engine started right up. After the engine had warmed up, I was able to start it with the O2 sensor disconnected, but the engine ran like crap (unless I also disconnected the MAP).

I then connected a spark tester (with a special light bulb) to one of the spark plugs. While the engine was running, I could see that the spark was consistent at every RPM range, with or without the MAP connected. To me this indicated that there was no ignition problem.

It was obvious that the only "tweak" that would allow the engine to run semi-normal was to unplug the MAP. Because I had the air filter can removed, I could easily see that when the MAP was unplugged, the spray pattern was heavier from the injector. When I plugged the MAP back in, the spray pattern would lessen.

I decided to disconnect the fuel return line to see how much fuel was being circulated. I ran a hose from the TBI to a gas can. My plan was to plug the line temporarily (after I checked the flow) to see if a higher fuel pressure might make a difference. I never got that far.

To my great surprise...there was absolutely NO fuel coming out of the fuel return line. Either the fuel pump is barely working, or there's a problem with the fuel supply line in the tank., or... or... or... the fuel filter is almost completely plugged. I'm really REALLY hoping it's just the fuel filter, but I'm not counting on it.

Ran out of time today. Hopefully on Wednesday I can at least determine if it's the fuel filter which is to blame. My fingers are crossed!

[This message has been edited by Patrick (edited 04-08-2014).]

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phonedawgz
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Report this Post04-08-2014 01:40 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post

So perhaps with the MAP connected the fuel requirements are going way up (correctly perhaps) but fuel system can't keep up and the engine leans out?


Maybe - lets see what happens with the correct fuel pressure to the TB.

[This message has been edited by phonedawgz (edited 04-08-2014).]

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Report this Post04-08-2014 03:08 PM Click Here to See the Profile for mckaymotoworksClick Here to visit mckaymotoworks's HomePageSend a Private Message to mckaymotoworksEdit/Delete MessageReply w/QuoteDirect Link to This Post

Some of your symptoms sound similar to mine. The car did sit for 17 years, and the PO dropped the tank, cleaned, replaced fuel pump but there might be crud all in the lines he didn't fix. I also suspect he put a cheap FP in along with the other cheap stuff from Autozone I have found along the way.

I bought a vintage vacuum gauge, how can I permanently fit a valve in line so I can easily check it when needed? The link on Ogre's page no longer shows the valve itself available, but a new model with the gauge. Would be nice to have the valve inline to be able to tap into when needed.

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Report this Post04-08-2014 03:18 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by phonedawgz:

So perhaps with the MAP connected the fuel requirements are going way up (correctly perhaps) but fuel system can't keep up and the engine leans out?


With the MAP connected, it appears the ECM reduces the amount of fuel that the injector is spraying... even though the end result (due to the low fuel pressure) is that the engine starves. I suspect the ECM is designed to work within a defined range of fuel pressure, and can't correctly cope when the pressure falls below a minimum level.

This is all conjecture on my part as I understand very little about EFI.

I'm hoping on Wednesday that I'll at least be able to find out if a new fuel filter helps to resolve this issue. It's doubtful, but I'm not all that excited about dropping the fuel tank (as I don't have a good place to do it here).

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phonedawgz
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Report this Post04-08-2014 03:28 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post

I misread it and thought the higher spray was with the MAP connected. This makes sense now.

Having the MAP connected allowed the GM engineers to have the ECM inject the correct precise amount of fuel. Without the MAP they just have to guess. Since they were guessing and they didn't want the engine to lean out it would make sense that the ECM was programmed to inject a richer mixture to allow the vehicle to limp home.

With the suspected marginally low fuel pressure the higher injection rates allowed the engine to run.

I'd say 50/50 on the fuel filter vs fuel pump.

[This message has been edited by phonedawgz (edited 04-08-2014).]

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Report this Post04-08-2014 03:28 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by mckaymotoworks:

Some of your symptoms sound similar to mine. The car did sit for 17 years, and the PO dropped the tank, cleaned, replaced fuel pump but there might be crud all in the lines he didn't fix.


Interestingly enough, this Fiero sat for at least eight years or so before I resurrected it four years ago. Although I did a LOT to this car, dropping the fuel tank and replacing the fuel pump is something I didn't need to do at the time. Maybe I'll be lucky and it's just crud (that had developed from sitting all those years) that's eventually plugged the fuel filter (which I had replaced four years ago).

 
quote
Originally posted by mckaymotoworks:

I bought a vintage vacuum gauge, how can I permanently fit a valve in line so I can easily check it when needed? The link on Ogre's page no longer shows the valve itself available, but a new model with the gauge. Would be nice to have the valve inline to be able to tap into when needed.


I really don't think it should be all that difficult to make up some kind of a "T" for a fuel pressure tester (perhaps using off-the-shelf brass fittings) that could be placed temporarily in the fuel line by the filter or TB. Another project to do... they never end!

[This message has been edited by Patrick (edited 04-08-2014).]

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Report this Post04-08-2014 03:37 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by phonedawgz:

I'd say 50/50 on the fuel filter vs fuel pump.


You think there's that much chance that it's the fuel filter, eh? I'm feeling a bit better about this now.

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Report this Post04-09-2014 09:29 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post


Okay, here's what I found today...

I disconnected the fuel filter (it was very clean inside) and connected a fuel pressure gauge onto the end of the fuel supply line. I then jumped terminal "G" at the ALDL connector with 12v from the cigarette lighter to run the fuel pump. The gauge showed a grand total of 4 lbs pressure while the pump was running, and immediately dropped to zero when the power was cut.

I suspect that short chunk of flexible hose inside the tank has rotted. Whether it's that or the pump itself which is to blame, it looks like the tank needs to be dropped. Damn.

Any other suggestions after reading what I've found?

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Report this Post04-10-2014 02:55 PM Click Here to See the Profile for logical1Send a Private Message to logical1Edit/Delete MessageReply w/QuoteDirect Link to This Post

You shoud jump the relay to power fuel pump. I dont think the cigarette lighter is strong enuff to push the pump. I think the relay is light a 40 amp push

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Report this Post04-10-2014 03:24 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by logical1:

I dont think the cigarette lighter is strong enuff to push the pump.


This is the first time I've ever heard anyone mention that, but I'm open to more feedback on this.

The pump appeared to work fine connected in this manner. (Made the same "hum" as usual.) No fuses were blown. This method of checking the fuel pump has quite often been recommended here.

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Report this Post04-10-2014 07:16 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post

The cigarette lighter is 12V. If the amperage were insufficient to run the pump, it would blow the fuse. ??

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Report this Post04-11-2014 10:38 AM Click Here to See the Profile for logical1Send a Private Message to logical1Edit/Delete MessageReply w/QuoteDirect Link to This Post

A while back i had an issue with my fuel pump prim feature. P.o did a hack job on relay wiring. I used 12 volts to make my own prime feature that was button driven. Took forever to prime. Like 20 secs to get a suffixent prime when hooked to 12 volts. Eventually a good aet of fellow pff ers guided me through the relay process. Grounding it on black and power to green and it fires immediately every time. I thought the 12 v should have been sufficent to but its not. Thats the whole point of the relay. The same reason y everything strong in the car has a relay. Lock, headlights, etc. Just providing my hands on experience. Plus when you jump from relay in my case it was noticeably louder. B4 i had to listen for the hmm and at the relay it was apparent as well as the immediate cranking from then on.

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Report this Post04-11-2014 05:01 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by logical1:

I thought the 12 v should have been sufficent to but its not.


I'm no wiring expert, but as long as the ground is good, isn't the voltage being sent to whatever device requires it 12v no matter what? If the amperage required is too much for the wiring, a proper fuse should prevent a wiring meltdown.

 
quote
Originally posted by logical1:

The same reason y everything strong in the car has a relay.


I was under the impression that a relay prevented the need for heavy amperage to go through the switch.

As I say, I'm definitely no wiring expert, so I appreciate the discussion.

[This message has been edited by Patrick (edited 01-22-2017).]

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Report this Post07-17-2014 03:26 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

I had to put this project on the back-burner as I had an '88 Formula that I wanted to tweak for autocross this year. That Fiero is basically done for now (performs great at autocross), so I returned to the Mighty Duke today.

To bring us up to speed from when this was put on hold...

 
quote
Originally posted by Patrick:

I disconnected the fuel filter (it was very clean inside) and connected a fuel pressure gauge onto the end of the fuel supply line. I then jumped terminal "G" at the ALDL connector with 12v from the cigarette lighter to run the fuel pump. The gauge showed a grand total of 4 lbs pressure while the pump was running, and immediately dropped to zero when the power was cut.

I suspect that short chunk of flexible hose inside the tank has rotted. Whether it's that or the pump itself which is to blame, it looks like the tank needs to be dropped. Damn.



I dropped the tank today. What I found was very interesting. Keep in mind this was a car that I bought non-running and which ended up sitting for eight years before I swapped in a 5-spd and did a hundred other things... but I had never dropped the tank. I was rather curious what I was going to find.

Here's the short chunk of flexible hose that I suspected was going to be rotted. It isn't.



So what was the problem? Was the pump bad? Hold on, I want to post a shot of the pump assembly before I removed the hose.



Other than the fact that there were no clamps on the hose , it looks okay, right? But hold on (again), look at this now...



So, are you able to figure out what possibly happened? One last image to show.



If you look carefully at that last shot, you'll notice where the rubber hose was located on the upper tube. You'll also notice a slightly blacker area just a little lower on that same tube. I suspect that was where a previous rubber hose had been located. Starting to get the picture yet?

It looks to me that either the hose was pushed up too high on the upper tube, and always just barely touched the pump... or the pump was originally pushed up into the hose, and was suspended by the hose, until the pump over time slowly pulled out of the hose (because of there being no clamps) and slid downwards (as there is some up and down play in the pump assembly).

It's possible I've totally lucked out and all that's required to fix this issue is two hose clamps. I'm also pleased with how clean the inside of the tank is. And look at that perfect sock-strainer thing. Pretty good considering this car had sat for many years at one time with old gas in the tank.

I'll get it all back together and report what happens.

[This message has been edited by Patrick (edited 07-23-2014).]

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Report this Post07-25-2014 07:07 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post


Yes, it takes me a long time to finish a project (as I'm usually involved in more than one at a time), but I'm very happy to report... The Mighty Duke rides again!

That's all the problem was... just the lack of a couple of clamps on the fuel pump hose in the tank.

My thanks to everyone who contributed to this thread. Much appreciated.

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