inimeg6482

Hello everyone. ..I have a 89 corvette 6speed....I have posted a few weeks ago about an of idle studder/stumble/hesitation/ or whatever you prefer.. IT IS DRIVING ME INSANE!! ....I have been tackling this in the most perfect manner .....here's what I've done.......
I HAVE REPLACED OR SWAPPED IN/OUT THE FOLLOWING

-NEW PLUG WIRES(PLUGS LOOKED OK)
-NEW TPS(set to .54)
-NEW CAP AND ROTOR
-NEW FUEL PUMP
-NEW FUEL FILTER
-NEW FUEL PRESSURE REGULATOR
-NEW IAT SENSOR
-SWAPPED IN NEW MAF = PROBLEM REMAINED = PUT OLD ONE BACK ON
-SWAPPED IN NEW ECU = PROBLEM REMAINED = PUT OLD ONE BACK ON

***PULLED CODES VIA SNAP-ON TOOLS SCANNER****
CODE 44 LEAN EXHAUST

***WENT TO APPOINTMENT AT BRYNER CHEVROLET YESTERDAY AND HAD STEVE SPENCER CHECK MY CAR ...OTHER THAN COMMON THINGS FOUND WRONG IN A CAR THIS OLD HE STATED THAT HE THOUGHT MY FUEL PRESSURE REGULATOR
(THAT I HAD REPLACED TODAY) WAS THE ISSUE. HE WANTED OVER $800 TO REPLACE. I HAD MY MECHANIC DO THE SAME JOB TODAY FOR ABOUT HALF THAT....THE END RESULT IS ...THE PROBLEM REMAINES
please excuse my LARGE letters it is to show fustration....HELP ME!!!!

gerardvg

Hi

You will find it eventually.

Start with this good test, start the car from cold and run for 10 or 20 seconds and turn it off. Check each exhaust port on the headers or exhaust manifold an inch from the head, if one is cold that is your problem cylinder.

Common problems.

Tugging the injector wires to remove the harnes from injector, i had a broken strip of metal in the connector. It would show 12 volt pulses when flipped over and checking with a multimeter, but it would not operate the injector.

Valve lash too tight. Check your compression on all cylinders, if one is down that will cause rough running.

Head gasket blown. That will show up with the compression test and your engine will run rough.

EGR Valve sticking open. The exhaust gas recirculation valve needs to be closed at idle, they can stick open with carbon build up.
Use a flashlight and check, you can suck on a vacuum hose to the egr valve to see if it rises and if it closes.

Good luck.

Tom400CFI

Have you checked for false air/vacuum leaks?

Have you confirmed base ignition timing?

Have you checked fuel pressure while the symptom is occurring? I know you replace pump, filter, regulator...but have you looked at the pressure, while the symptom is occurring? Those are three things that *I* would start with.

inimeg6482

We did this today ...well i guess now yesterday (after 1am now)Fuel pressure before fuel pressure regulator swap was unreadable (needle was zipping back and forth) now it is readable hangs around 32psi at idle and moves up to about 40 while pushing the throttle when driving.....the funny thing is when this studder is happening the fuel pressure hangs around 35psi ....we disconnected the vacuum from the fuel pressure regulator and it shot to around 40-41psi....my mechanic wanted me to drive around the block like this and if the problem was gone he felt that it means I need to buy an adjustable fuel pressure regulator and turn up the pressure. ..BUT ...even with the pressure at 40 the problem REMAINED. ...also please note...the EGR has been deleted by the previous owner. ...ALSO ...the car does not do this until I get a few blocks away ( about 180-200 degree engine temp)....why would I have a blown head gasket... wanna know something ....I asked Steve Spencer if he checked my timing when I took it to him and he said he didn't check it..I was expecting him to check everything at least related to my issue. ...he also said my ecu wouldn't communicate with his scanner(I honestly feel he didn't bother doing much else at that point)..I won't bash him...he was a nice guy...he was confident in it being the fuel pressure regulator (would've been a $800-900 mistake. ..glad I went to my mechanic ...even though the fuel pressure regulator was done since it didn't solve the issue my mechanic charged me $300.... <great guy

Silver96ce

Since you are OBDI, I did a quick search and came up with this -
http://www.misterfixit.com/code44.htm

You seem to have dealt with a lot of the suggestions but if I were you I would look at the following -
1. Oxygen sensor wiring.
2. Oxygen sensor itself - how many miles on the car and was the sensor ever changed? IIRC - oxygen sensors on OBDI were supposed to be done @ 60k miles.
3. fuel injectors. You can pull and send for cleaning and testing.

Good luck - you'll get it fixed.

inimeg6482

I will say this....the guy I bought it from said the injectors were just done and he said they are ls1 ...but from talking to people on here i know that is incorrect....probably
lt1 injectors.....and he said the oxygen sensor was new so we didn't change it ..I thought if it was not working properly I would get a direct code for it ....right?

89onlyZ51

If the injectors are original (gray multecs), I bet that's your issue. Put an ohm meter across each injector's terminals with the engine warm, and look for 15+ ohms. If you see any in the single digits, that's your problem.

Dt86

You took it to a dealer and they didn't even put it on a scanner to look at the live data?

blackozvet

if you have a stumble and fault shows lean exhaust, then it's probably fuel related ,
I would be looking long and hard at the injectors (and dont take the previous owners word) especially if you have changed just about everything else !

can you show us a picture of the injectors as they are sitting in the engine now , that might help with an ID of them.

Lloyd Smale

id change the plugs even if they looked good and id change the 02 sensors to start with.

_ski_dwn_it

Does it have the stock tune (chip) in it or did someone screw with the tune that didnt know what they were doing. Going to have to pull the ECM down and check that. If it looks all stock with the stock sticker on the Eprom you are probably dealing with a stock chip.

My fathers 86 had an issue....we changed the ECM and it ran like a top since. That is easy to do if you are friends with the local Autozone or equivalent - have them order it in for you. Unplug your try it if it doesnt make a difference have them return it the next day.

Churchkey

As suggested ohm test the injectors when they are hot a reading below 14ohms = a failing injector(s).

Disconnect the EST weather-pack connector & set the timing @ 6* BTDC. The EST connector is a single black weather-pack in line connector, wire color is tan with a black stripe, location should be above the brake booster.


Remove the base idle plug.
Connect a paper clip, to your diagnostic terminal under your dash connect to terminal A and B (the top right two pins).
Turn on ignition but don't run the engine.
wait at least 30 seconds and then remove the idle air valve connector (IAC) (the square plug) then turn off ignition and unplug the paperclip.
Now unplug the EST connector.
Start your vette and set the idle speed to 400 rpm in neutral (auto trans) 450 rpm (manual trans) then check your throttle position sensor,
the top two wires it should be set to 0.54volts dc, also confirm with engine off that the tps rises to 4.5 volts at full throttle.
Turn of the ignition and reconnect the iac valve connector and timing connecter and start your vette.
it should go to 1200 rpm then drop slowly to 600 rpm, take the car for a 15 minute drive with the usual stop lights.
It is normal for a little hunting while the ecm relearns, also do a few spirited take offs.
All should settle after 15 to 30 mins normal driving and have a stable idle.

Good luck

antfarmer2

My 94 would bog and backfire under the hood no codes changed the o2's never ran better

Kevova

you were able to access codes with scanner are you able to use it to monitor data? Do you have access to diagnostic charts. If not you need access. If so I would look at MAF, o2, and fuel trim. Fuel quality also should be checked. good luck

mike100

how many cross-counts does the o2 sensor(s) get? that's how many times a second the voltage swings from rich to lean- usually two or three times for a good sensor.

It sounds like the car only runs bad in closed loop (when the computer uses the o2 feedback after warmup). O2 sensors are pretty cheap- I'd probably replace it since it could be more than 20 years old even if the car ran good. It is at the heart of the issue imo. could be a lazy o2 sensor stuck at a certain voltage output fooling the ecm.

inimeg6482

You guys on here are the best......I didn't expect so much responses.....truthfully I thought going to bryner Chevrolet and having steve spencer check my car would've been the end of this issue. ......he chose NOT to check pretty much most of the things all of you mentioned even timing and said his scanner wouldn't communicate with my car...but I told him that my mechanics snap-on scanner worked and gave the code 44....steve Spencer did say he manually checked codes and got a 44.....now he is supposed to be THE vette person in this area ...I feel he is a great guy but didn't want to be bothered with my car ....I will change the o2 sensor on my next day off (Saturday)....he said he wasn't familiar with my fuel injectors too...for some reason he didn't ohm them either....when he pulled me to the side he pointed out other obvious things that need to be done and kind of just said he thought it was the fuel pressure regulator and then presented me with a $800-900 quote to do it.....my throttle right now is basically an on/off switch the only related things not touched is plugs, o2, timing, injectors, engine coolant temp sensor I just don't understand why he wouldn't check these things all of you mentioned

antfarmer2

He wants the $800 to $900 if still bad he can put in the $20 o2 sensor

xrav22

Change out o2 sensors and clean EGR solenoid connectors. Check air pump is not pumping always into exhaust.

inimeg6482

Egr was deleted by previous owner. .......and as far as checking air pump...i was expecting bryner Chevrolet to know to check these crucial things but he never mentioned checking any of this stuff.....is there anyone in the Philadelphia area that yall can think of that will TRUELY be willing to check my car out...my mechanic is honest with me and he has admitted he is stumped .....he feels it must be fuel related but after replacing fuel pump, fuel filter, fuel pressure regulator, cap and rotor, plug wires, TPS, incoming air temp sensor, the fuel issue should be gone.....

inimeg6482

Any other ideas fellas?.......I seen that this has been an issue with ALOT of us can anyone share what they did to remedy this issue