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VERY Confusing! Not common either I bet. by 87FieroSport
Started on: 01-27-2014 06:06 PM
Replies: 19 (505 views)
Last post by: lou_dias on 01-30-2014 09:37 PM
87FieroSport
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Report this Post01-27-2014 06:06 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
So, I have a 1986 Fiero GT, Automatic.

~15-17MPG
~Temp never past 190 or so (Common?)
~TCS unplugged, No CEL, (No more bogging down though.)

From day 1 I have gotten 15-17MPG (17 on a REAL good day.)
P.O said Y-pipe might have a crack (I accidentally left the part there.. new one coming soon.)
The front manifold was cracked, replaced it along with head gasket.
Car bogged down at 30mph, would jump to 4500rpm and climb in MPH when I actually hit the gas.

So.. since I have owned this car, it has gotten 15-17MPG on the highway and in the city, now I drive mostly highway to work.. so 15MPG isn't efficient.

But! I have gone through a ton of things, and determined no change in mileage.

Replaced throttle body with capped screw (Incase it was messed with)
Replaced front manifold with cracks.
Replaced throttle cable
Replaced kickdown cable
Unplugged TCS due to bogging down at 30mph then shooting up to 4500RPM and accerlating rapidly. (No CEL ever came on, MPG did not change)
Removed cold start injector.
Added CAI

Would a CEL come in with the TCS unplugged? Ive had it unplugged for a while, no CEL, no change in MPG, no more bogging.
These are values from Tunerpro,

My o2 sensor bounces back and forth (between 100-900mv.)
My INT and BLM seems to stay in the 140's consistently. Sometimes 120, then to 139-140.
My INT and BLM were between 128-144 (Jumped together at the same time from 120-142 a few times. Max 146 I think. (INT was 146 too.)
Coolant temp never rose above 200.

I get a whole lift to myself on Thursday, so I plan to replace my Y-pipe and TCS/Pressure switch.
Whatelse should I look for? I plan to bring my laptop so I can record data on TunerPro aswell.

Added: When I tromp on the gas, I can hear some ticking (Like a very small leak. Also ticks louder when cold started.)
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87FieroSport
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Report this Post01-27-2014 06:13 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
Also, I did happen to catch a glimpse of Tunerpro while driving to work.

The computer said my TC was "engaged" at 65MPH, but I unplugged the TCS, would it still engage?
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tebailey
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Report this Post01-27-2014 06:36 PM Click Here to See the Profile for tebaileyClick Here to Email tebaileySend a Private Message to tebaileyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Could just mean the ecm is sending a lock-up signal.
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lateFormula
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Report this Post01-27-2014 06:36 PM Click Here to See the Profile for lateFormulaSend a Private Message to lateFormulaEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you're going to replace the Y pipe, put a new O2 sensor in it. While the Y pipe is out, try to rig up a cap on the intermediate pipe (going to the cat) and apply air pressure from a compressor to see if you get backpressure, or if the air will flow through to the tailpipes. Do you have a catalytic converter on the car? I might suspect a clogged converter, but if that was the problem the engine would bog across all RPM and might not be able to get to 4500 RPM. If you have a converter on the car it might be partially obstructed.

And if you unplugged the TCC solenoid at the trans, it could not lock up unless it was frozen in a locked position. But if it were unplugged Tunerpro could not tell you if it were locked up.

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

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87FieroSport
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Report this Post01-27-2014 06:48 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
It's a 4 prong circle connector, near the back of the engine near the firewall, in the trans.

Yea.. It's definitely been unplugged, for a while now haha!

I wouldn't suspect a clogged converter either, the car performs GREAT! Just lacks in the mileage aspect..

I would note that while cruising, (And hitting the brake around 30mph) the rpm would fall, skip back up and drop again (Car feels like it lurches a little), Is this the torque converter acting upon braking? I've read that if it Doesn't do this, that it should be replaced.
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Arns85GT
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Report this Post01-27-2014 06:50 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
first thing to suspect is that CAT.

Arn
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87FieroSport
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Report this Post01-27-2014 06:50 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
And Tunerpro does tell me that it's engaged, at HWY speeds and when I drop down, it'll say "Disengaged"
So it is telling me those two things, but it doesn't mean it's happening actually.

But in any case, since I got the car it was bogging down.
I unplugged the TCC, and it has NEVER bogged again.

So I suspect that was faulty from Day 1, and will be replaced.
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87FieroSport
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Report this Post01-27-2014 06:51 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post

87FieroSport

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quote
Originally posted by Arns85GT:

first thing to suspect is that CAT.

Arn


I wouldn't jump to the Cat because of what I said with bogging down.

The great performs great, If it were the Cat, I'd notice something throughout my daily driving. But I sadly have nothing to report on that.
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Report this Post01-27-2014 06:52 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post

87FieroSport

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I've also diagnosed and witnessed my fair share of clogged cats aswell,
And this is why I haven't suspected it, Just no symptoms of it.
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Report this Post01-27-2014 07:52 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
Normally the TCC sticking stalls the car when it comes to a stop. Doesn't really cause any other issues as the transmission can up shift and downshift with it locked.

The lack of TCC will impact your fuel economy - especially on the highway.

Any "ticking" in the exhaust is usually a crack in a primary tube or an exhaust gasket leak at the head. Since it is upstream of the O2, the ECM will see this as a lean condition and add fuel. You BLM readings are indicating the ECM seeing a lean condition and adding fuel. A BLM of 140 means the ecm is calling for 9% more fuel - which will hurt your fuel economy.

Never have you mentioned checking the timing and verifying the balancer TDC mark is actually TDC. Since you had the heads off, the timing will need to be reset and if the outer ring on the balancer moved, it could have been set wrong. If the timing it too retarded, you will see less power, the engine will feel like it is bogging (especially after gear upshifts or when the TC locks up), and the incomplete burn will show lean on the O2 sensor and add more fuel.

Fix the exhaust leak(s), fix the TCC, check the timing mark, and set the timing, and replace the O2 sensor for good measure and you will probably see a significant improvement in power and fuel economy.

------------------
fieroguruperformance.com

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

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87FieroSport
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Report this Post01-27-2014 08:05 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
I did the timing over again after I replaced the gaskets and manifold.
It doesn't feel like it has any less power than it should, acceleration is superb.

I just ordered everything I need to replace:

Y-pipe, and gaskets.
TCS and pressure switch.
Distrib O'ring (Mine leaks.)

I'll re-check timing when I do all of this, it is really hard to see down there sometimes though...
But I KNOW I should be getting better mileage, 15-17MPG across the board and Tunerpro values indicate something is at fault.

But it's not throwing a CEL, so it must be on the borderline of faulty and non-functional.

So, let me re-cap; Unplugging the TCC solenoid will NOT throw a CEL? It was the reason for bogging down at random times. That's for sure, since it doesn't happen at all anymore, not even once.

Edit to add: Is it possible, that the TCC has been bad since I bought the car? Which is why mileage has also been so bad? I know there is a leak too but I REALLY want to know about the TCC. Running with it unplugged has been so.. calming and nice. But I want to know that replacing it would help fuel economy too. I'd like to see 200 miles out of a tank.. All I do is highway drive to and from work and don't go out other than that.

[This message has been edited by 87FieroSport (edited 01-27-2014).]

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Report this Post01-28-2014 03:15 AM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 87FieroSport:
So, let me re-cap; Unplugging the TCC solenoid will NOT throw a CEL?

Correct. The ECM will keep commanding it but it has no idea if it's actually working. I drove with it unplugged for years.

 
quote
Is it possible, that the TCC has been bad since I bought the car? Which is why mileage has also been so bad? I know there is a leak too but I REALLY want to know about the TCC. Running with it unplugged has been so.. calming and nice. But I want to know that replacing it would help fuel economy too. I'd like to see 200 miles out of a tank.. All I do is highway drive to and from work and don't go out other than that.

It makes a small difference to the cruising mileage, like maybe 1-2mpg. It's good to have but it shouldn't be the cause of a major drop.
I'm an advocate of replacing old O2 sensors, but there's no predicting how much difference it will make. On my car it was 10%, but it just depends how bad the old one is. They're very cheap for this car. Denso and Delco brands are usually recommended, many people complain about Bosch.

BLMs in the 140s is a sign that something is out of tune, and it won't likely run at it's best in that state. Exhaust leak and O2 sensor might be contributing to the high BLM. The lockup TCC would not be.
If you have a gauge, you might as well check the fuel pressure. If it's weak that would also explain havoc with the BLMs. Pressure should be around 42psi key on engine off, and with engine running it should be in the high 30s. If you watch the gauge while moving the throttle, you should see the fuel pressure vary along with it. The regulator is supposed to maintain a constant differential versus manifold pressure. Lastly, after turning the key off, the lines should hold pressure. It shouldn't lose more than a few psi in 15-20 minutes.

Since you're datalogging - have you noticed if the incoming air temperature reading is reasonable? The IAT sensor sometimes reads way off due to getting dirty. Mine recovered after being soaked in CLR, so that's worth a try before replacing it.

I don't know what speed you cruise on the highway, but that could be another factor. The 3spd automatic has no overdrive gear so it's really inefficient at high speeds. I have the same model (86GT auto) and based on the overall mileage I get with certain trips, I think I can reasonably estimate that highway mileage at 65mph cruise is roughly 25mpg (I usually get 22-23 overall). If you drive 80, it would be a lot worse but I don't know how much.
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Report this Post01-28-2014 08:59 AM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'll check the IAT, and let you know.
I replaced my o2 back in school (Beginning of 2013).

I cruise 70 on the highway, but between 55-75 it doesn't matter, it's alwys the same.

I remember doing fuel pressure last year and it was up to par the whole way.

My tach is a little off (reads higher than what tuner pro tells me.)
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Report this Post01-28-2014 09:00 AM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post

87FieroSport

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I'm very light on the gas around town, and still the same outcome too.
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Report this Post01-28-2014 12:51 PM Click Here to See the Profile for jschmidt95Click Here to Email jschmidt95Send a Private Message to jschmidt95Edit/Delete MessageReply w/QuoteDirect Link to This Post
it might be a long shot, but how does your trans fluid look? I know if the fluid is old/leaking you would have maybe a permanent slippage condition and it might be whats sucking up your gas...
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87FieroSport
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Report this Post01-28-2014 01:59 PM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
It'll get a fluid and filter change after
My TCC Solenoid goes in. So we'll see

My Trans doesn't slip at all (only if I have to gun it on an entrance ramp and then ease off/get back on it.)
Very rarely though.
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Report this Post01-29-2014 10:24 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 blm and int readings mean that the ecm is adding fuel. 128 is considered perfect for both (+-5 or so from that is still ok)
You might want to look at the map sensor or a vacuum leak causing the map to get an incorrect reading.
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Report this Post01-30-2014 08:54 AM Click Here to See the Profile for peterhClick Here to Email peterhSend a Private Message to peterhEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have a 1986 SE v6 and I get approx. 17 mpg driving in rush hour traffic (27 lights for a 15 mile trip!).
I have not done much highway driving but I woul estimate low 20's on my car.
So, yes you should get better gas mileage.
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87FieroSport
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Report this Post01-30-2014 11:06 AM Click Here to See the Profile for 87FieroSportSend a Private Message to 87FieroSportEdit/Delete MessageReply w/QuoteDirect Link to This Post
I went through some recorded data yesterday.

@197* Coolant temp.
49-53 miles per hour this run.

I noticed that when I stepped on the gas (TPS indicating more throttle.)
My BLM and INT went to around 135-140's, and when letting off from that, it stayed for a bit and then went to normal.
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lou_dias
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Report this Post01-30-2014 09:37 PM Click Here to See the Profile for lou_diasClick Here to Email lou_diasSend a Private Message to lou_diasEdit/Delete MessageReply w/QuoteDirect Link to This Post
my 5 speed formula averages 26mpg, don't expect more than 23mpg with an auto, hence:

9% extra fuel accounts for most of your issue, fix that manifold
check tires pressures
check that your tires move freely with the car jacked up
get rid of any extra weight you're carrying around in your trunk and passenger seat
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