Hello All,

My buddy has a 1987 Base Coupe with the 2.5 and Automatic Transmission. Since the day he bought it a year ago, it's had an immediate hesitation when taking off from a stop and sometimes when putting the pedal down at various speeds. It acts almost as though it gets too much air and no fuel initially, then gets going after that (albeit sluggishly). Now, here is what has occured with our attempts to "fix:"

First time around, we did the following:

New Plugs

New Wires

New Fuel Filter

Checked vacuum lines

New Throttle Position Sensor (had code so tried new one)

Cleaned up EGR opening
These things did NOTHING to improve the problem. So he continued driving for a while. This past December, I bought a coil pack off e-bay, and we tried swapping that out. WHILE doing this, we found a crack in the crank sensor tube that goes through the engine block. So I replaced the cracked one with the "new used" one and put it all back together. The hesitation was GONE and the car ran like it never had before (well, since he had it anyway)! But then about a week later, the hesitation is BACK!

I am at a loss as to what "fixed" an issue like this temporarily only to have it return? As a side note, I posted this on the YAHOO FIERO GROUP and Ed Parks at the Fiero Factory though the culprit was likely a fuel delivery issue, possibly the pump or the line inside the tank being ruptured/cracked. But then I tried the coil pack and sensor deal and it seemed fixed but came back.

ANY help would be appreciated!

Regards,

Gary

hmmm, have you searched for threads about it? I know I have seen it mentioned before here. I don't have thoughts since you replaced most things I would have.

Nobody on here has any real advice on this question?

-Gary

If the fuel pump is weak, the fuel pressure regulator is dirty/weak, or the injector is dirty it can cause hesitation as well.
Are you sure the hesitation is from not enough fuel or possibly a little too much fuel?
With weak pressure or a dirty injector it will spit rather than spray.
Does it smell like it's running rich?
https://www.fiero.nl/forum/Forum2/HTML/088997.html

I know you said you checked vaccum lines but maybe they are worth checking again. Just my 0.2

The first time I did work on my 4cyl (exhaust manifold gasket replacement) I lost one of the vaccum tubes that connects to the little black box on the right of the air filter housing. (Sorry I dont have a better description) and I replaced it with some random hosing that I had in the garage. My car did exactly what you are describing and it drove me absolutely insane, I checked everything over and over, problem was it was always cold when I looked.
One day I got so frustrated driving on the road that I pulled over and popped the decklid. When I checked everything this time I found that my cheap garage fix didnt work. When the cheap hose got hot, it would kink and loose its form. I went to autozone and bought a new vaccum hose for that purpose and havnt had that problem since.

Just some thoughts.

Since it ran great after replacing the coil pack and crank sensor I would double check them. Possibly the bolts vibrated loose and you are loosing connection. While checking I would clean the area up and make sure all grounds are good.

Even though they only seem to recommend the extra ground strap from the engine to the frame for the 2.8l. I added one to my duke and it did smooth out the idle. May have something to making sure the ECM gets enough current.

Sometime hesitation is caused by a vacuum leak. I know you checked all the vacuum lines and the EGR gasket. Could something beyond the vacuum lines be leaking? Maybe for a test drive try blocking a couple. Also those EGR bolts vibrate loose.

Does it also hesitate before the going into closed loop or after?

My 87 idles at 1200-1500 in cold start mode and then at 1000 after the O2 gets up to operating temperature.

Any codes now?

Next question: Does it hesitate in neutral also or just in gear. Sometimes if the TCC solenoid is stuck the transmission can drag.

ON THE VAC LEAK:
I've got no codes presently and the check light hasn't come on at all over the past year since replacing those initial parts. I have my doubts about a vacuum leak because of the coil pack and sensor change out incident where it suddenly ran great.

OREIF- I doesn't seem to get decent gas mileage at this point, so it could be TOO much fuel as opposed to not enough? Doesn't "smell" rich really though except at start up when cold.

All in all if it were the fuel deliver or a vacuum issue I don't get why it would have been better IMMEDIATELY after changing that sensor/coil pack? But still, how did it go back to the same issue?

ARRRGH! I will look at the link you posted OREIF. THANKS!

-Gary

I second that

quote Originally posted by mike-ohio: Since it ran great after replacing the coil pack and crank sensor I would double check them. Possibly the bolts vibrated loose and you are loosing connection. While checking I would clean the area up and make sure all grounds are good.

Your "new used" crank position sensor might have cracked.

Another common cause of hesitation in the Duke is the EGR valve. Here are 2 tests you can perform on it:

1) Detach the vacuum hose from the EGR valve. Then use your fingers to manually push up the diaphragm. Use a finger to cover the vacuum port, and let go of the diaphragm. The diaphragm shouldn't move. And when you remove your finger from the vacuum port, the diaphragm should pop back to its resting position. If the diaphragm drops while you're covering the vacuum port, or doesn't drop after you uncover the port, the EGR valve is faulty. Both these conditions will cause a vacuum leak.

2) Detach the vacuum hose from the EGR valve and plug the hose. Now drive the car around the block, and see if the engine still hesitates. If the hesitation stops, you have a faulty EGR valve. If it doesn't, then your problem lies elsewhere.

Best of luck!

Blacktree,

Your EGR idea is intriguing- we DID do the EGR cleaning basically the same time we did the coil pack/sensor, so maybe we made the EGR work for a bit by playing with it and it's now faulty again. I will look into this.

Thanks!

-Gary

The Duke EGR does not work like the V6 EGR valve. It will not hold vacuum. Just block off the EGR port and plug the vacuum line to eliminate it as an issue.

From Ogre's Cave:

The EGR, Exhaust Gas Recirculation, valve is used to limit emissions and to prevent engine knock. On V6 the valve is ECM controlled but on the L4 it is operated by a combination of engine vacuum and exhaust back pressure.

[This message has been edited by Hudini (edited 01-23-2008).]

Also make sure you have a good engine to body ground. When I had my 87 blue coupe, that little braided strap cured a lot of issues. Go from where the negative battery post terminates on the head to one of the deck hinge studs.

I got mine out of the HELP! section at Auto Zone for $2-3.

Matt85GT,

Also a good thing for us to check out.

Thanks!

-Gary

quote Originally posted by Hudini: The Duke EGR does not work like the V6 EGR valve. It will not hold vacuum.

Where did you get this information? If the EGR diaphragm doesn't hold vacuum, it won't work.

quote Originally posted by Blacktree: Where did you get this information? If the EGR diaphragm doesn't hold vacuum, it won't work.

Not to mention cause a vacuum leak

Also, as for working after the coil pack was changed, sometimes stronger spark will momentarily overcome the problem, untill the problem becomes worse enough to overcome the increased spark. If you get my drift....

I get the drift- though I'm not sure that would be the case here. I'll be looking into all of it at this point it seems...

-Gary

What type of spark plugs are installed ? Some Forum posts report problems with Platinum plugs in a car with DIS ignition.
Was the air filter replaced ?
Have you considered using fuel injector cleaner with the next fill-up ?

quote Originally posted by StockGT: What type of spark plugs are installed ? Some Forum posts report problems with Platinum plugs in a car with DIS ignition. Was the air filter replaced ? Have you considered using fuel injector cleaner with the next fill-up ?

Plugs are ac/delco as listed in the manual

Air filter is new

Tried injector cleaner through at least 4 tanks of gas over past 5,000 miles

I might have to lean with Ed on the fuel issue thing. When I first got my 88 it had been sitting parked for a while. Sometimes when you took off from a stop or something it acted like you described, bogged down, then if you backed off and slowly increased throttle it evened out. After about 2k miles of that or so I got off a highway, stopped for a light, and then when I went to start moving it died. Fuel pump was humming but ony a little fuel would trickle out, and then only if the injector was pulled. Wasnt making enough fuel pressure. I replaced everything at once for good measure - pump (upgraded bosch with LLT from autozone), sock, filter, and even the injector since I had a spare, took care of the problem. Now I cant say why the work you did temporarily fixed the problem, but I had that symptom and eventually it was pump related for me.....

Instead of guessing at the Fuel pump / pressure, why not put a gauge on it? injector cleaner won't help you if you have an in tank filter sock full of crud. It's a PIA to drop the tank for a visual, so'd I'd buy or borrow a gauge to see where the fuel pressure is. To answer the next question...my clogged up fuel system would drive find for the first xx minutes and then bog down. I could turn it off and on and it'd run fine for a few more minutes, almost as if it were sucking up some crud against the sock and dropping it when the demand was off. Gradual acceleration was ok, but kind of elusive the way it presented itself. I think worth a check of the fuel pressure. Good luck

ApexNC,

That's what ed parks said to do- he gave instructions on how to do a pressure test, etc... I might have to do that.

-Gary

Check the spark gaps

Just give it a tune up, wires, plugs, filters, etc.

Unplug the MAP wire and take it for a drive, see if that helps.

[This message has been edited by 84Bill (edited 01-25-2008).]

quote Originally posted by Blacktree: Where did you get this information? If the EGR diaphragm doesn't hold vacuum, it won't work.

As said by Ogre's Cave and by my own experience. Try it sometime. Pull a vacuum on a Duke EGR and see. It will not hold. I thought I had a bad EGR until I tried it on a new one.

EDIT: I'm heading to the parts store this morning so I'll check again. Just want to be sure.

[This message has been edited by Hudini (edited 01-26-2008).]

You said it's not giving any codes, but it sounds just like the behavior with code 42. When you get that code, the ECM is not controlling timing, but instead the ignition module is using a default timing.

I'm having almost the exact same problem with the '84 pace car (mtx) I recently bought. The shop did a tune-up and replaced the O2 sensor, then determined the fuel injector was bad. So I replaced the fuel injector and fuel filter, but then the car wouldn't idle without stalling and ran way too rich. Today we figured out the IAC was all gummed up, cleaned that out and it now idles great but the hesitation is still there.

From reading this thread, it sounds like it's probably one of two things: a vacuum leak, or an issue with the fuel pressure.

The car had been sitting for a while (not sure how long) before I bought it, so it could be bad gas or gunk in the tank. The thing is, the hesitation only happens when starting out in gear, not in neutral, so it would be pretty tough to test the fuel pressure under load. Would the TCC solenoid thing apply to manual transmission too?

------------------
Marc Lieberman
Webmaster, Indypacecars.com
http://www.indypacecars.com

I finally own a Fiero pace car!

TCC selinoid is in Automatic Transmissions only.

The 84-86's also used a standard distributor, though I'm not sure how much, if any, differently the car might react to the same issues (vacuum leaks, etc.).

I am not getting any codes at all, and never got a code 42 even when the light had been set on. Only the oxygen sensor codes and the throttle position sensor codes were ever set and stored.

It ran the same BEFORE & AFTER new plugs. On SECOND set of plugs actually and they were gapped correctly both times so I can't imagine those to be the issue.

This is aggravating, as setting up a pressure test is a PIA in my opinion...

-Gary

I tried the remove the egr thing and on my 88, the car would not run properly. It needs the egr. Have you looked at the crank sensor?
New crank sensors arent to bad in price. I have a spare just in case. Did you follow the procedure that the Ogre suggests when installing coil packs and sensors? I found a similar problem with of all things fairly new ac delco wires. They were less than a two years old, so I thought it had to be something else. Took the intake manifold off because sometimes they leak. Nope that wasnt it. It was the wires.

Steve in Michigan

[This message has been edited by solotwo (edited 01-27-2008).]

I'll check out the Ogre's site...

Working on my '84 a bit today, we found upon removing the vacuum line to the EGR (with the engine running), there was no vacuum pressure at all on that line. Is there supposed to be? Would this indicate a vacuum leak or a bad throttle body?

In addition to the hesitation, the car is also misfiring at idle. Would a vacuum leak cause that as well? And the car is still running very rich, although not as bad as it was before cleaning the IAC, and at least it doesn't stall any more when idling.

The next thing we'll be checking is the fuel pressure and also the vacuum pressure. Just found out tonight that my neighbor has both gauges.

------------------
Marc Lieberman
Webmaster, Indypacecars.com
http://www.indypacecars.com

I finally own a Fiero pace car!

quote Originally posted by Indypacecars: Working on my '84 a bit today, we found upon removing the vacuum line to the EGR (with the engine running), there was no vacuum pressure at all on that line. Is there supposed to be? Would this indicate a vacuum leak or a bad throttle body?

No, there is only vacuum when the throttle is opened.

quote Originally posted by 84Bill: No, there is only vacuum when the throttle is opened.

There is only intake manifold pressure when the throttle is closed. Vacuum(negative pressure) will drop off as the throttle is opened.

My 84 with 4cyl auto had the hesitation. I changed many things, including EGR. Still there. Then I started replacing things again. The new plugs helped some (but then again, we had 20k on the old ones and we use a bit of oil so it was time). Problem still there. Swapped an EGR from another Fiero 4 cyl.. same problem.

Ordered a new AC/Delco EGR from rockauto.com, installed it in about 30 mintues, rough idle for a minute or two, then settled down and has run fine without problems for a couple of months now.

Lesson learned. EGR is sensitive and needs a factory part, not an aftermarket or used part.

I think my problem is a little more serious than just hesitation. I'm talking about trying to start out in first gear and having the car sputter, backfire, and want to stall. It's nearly impossible to start out even on the slightest uphill incline unless I give the car a whole lot of gas before attempting to let the clutch out (which, on a hill, is a bit tricky).

Also, the car seems to run better when first started, with only a minor misfire here and there, but will idle rougher as it gets warmed up. And when I first drove it around the block today I didn't have any hesitation/dead spot, but on a drive 20 minutes later, it started acting up again. So I'm wondering if it is an issue with crud in the gas tank perhaps? It could also be that the car's been sitting with this gas for who knows how long... which is why I'm trying to run it and burn off the gas, rather than worrying about trying to drain it. Although it might not be a bad idea anyway.

Thoughts?

[This message has been edited by Indypacecars (edited 02-03-2008).]

quote Originally posted by turboguy327: There is only intake manifold pressure when the throttle is closed. Vacuum(negative pressure) will drop off as the throttle is opened.

Not trying to argue here but I dont want this guy chasing dead ends.
There is NO VACUUM to the EGR port when the engine is at idle.

[This message has been edited by 84Bill (edited 02-04-2008).]

quote Originally posted by scotkb75: My 84 with 4cyl auto had the hesitation. I changed many things, including EGR. Still there. Then I started replacing things again. The new plugs helped some (but then again, we had 20k on the old ones and we use a bit of oil so it was time). Problem still there. Swapped an EGR from another Fiero 4 cyl.. same problem. Ordered a new AC/Delco EGR from rockauto.com, installed it in about 30 mintues, rough idle for a minute or two, then settled down and has run fine without problems for a couple of months now. Lesson learned. EGR is sensitive and needs a factory part, not an aftermarket or used part.

Interesting...

i have the same car. when changing the coil pack and sensor , did you add teflon tape to the bolts that hold the pack to the block? because at least one bolt goes through the block and will cause a oil and or vacuum leak leak . also did you change the o-ring on the sensor? remember, seals that leak oil will also create vacuum leaks.

quote Originally posted by FieroFanatic13: Hello All, My buddy has a 1987 Base Coupe with the 2.5 and Automatic Transmission. Since the day he bought it a year ago, it's had an immediate hesitation when taking off from a stop and sometimes when putting the pedal down at various speeds. It acts almost as though it gets too much air and no fuel initially, then gets going after that (albeit sluggishly). Now, here is what has occured with our attempts to "fix:" First time around, we did the following: New Plugs New Wires New Fuel Filter Checked vacuum lines New Throttle Position Sensor (had code so tried new one) Cleaned up EGR opening These things did NOTHING to improve the problem. So he continued driving for a while. This past December, I bought a coil pack off e-bay, and we tried swapping that out. WHILE doing this, we found a crack in the crank sensor tube that goes through the engine block. So I replaced the cracked one with the "new used" one and put it all back together. The hesitation was GONE and the car ran like it never had before (well, since he had it anyway)! But then about a week later, the hesitation is BACK! I am at a loss as to what "fixed" an issue like this temporarily only to have it return? As a side note, I posted this on the YAHOO FIERO GROUP and Ed Parks at the Fiero Factory though the culprit was likely a fuel delivery issue, possibly the pump or the line inside the tank being ruptured/cracked. But then I tried the coil pack and sensor deal and it seemed fixed but came back. ANY help would be appreciated! Regards, Gary

Hadn't thought about the teflon tape thing or the o-ring really- it seemed like it would primarily be a little bit of an oil leak is all...