Hello everyone. ..I have a 89 corvette 6speed..I presented this issue a week ago and felt the need to put this issue through again..I have posted about an off 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
-NEW OXYGEN SENSOR
-NEW IGNITION COIL
-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 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 FOR ABOUT HALF THAT....THE END RESULT IS ...THE PROBLEM REMAINES
for some reason he didn't check my timing, vacuum lines, ohm my injectors, voltage for serveral sensors, check ignition or other things related....he stated he couldn't get his diagnostic scanner to connect with my ecu...I think he blew me off
please excuse my LARGE letters it is to show fustration....HELP ME!!!!

 

Was looking for people that beat this issue. ...tell me what you found to be the culprit(s)....

 

If the injectors are original, ohm them. Common problem with the 89's.

 

The injectors are supposedly replaced they look aftermarket ...not sure if they are malfunctioning or just dirty......but i clearly have a lean issue

 

Injectors can cause the problem your having....It could be injectors even if they aren't the originals, but the Multecs were known to cause problems because of newer fuels with ethanol..If you pull the injectors and send them to Jon at "Fuel Injector Connection" , he can test them to see if they're working properly and also clean them while he has them....WW

 

Or just cut to the chase and get some new Bosch III injectors... they have a better spray pattern, among other upsides.

There is one facet to the older C4s that most people are unaware of:

THE WIRING HARNESS SUCKS.

In 1990 (or 91, can't remember exactly which MY), the SAE changed the requirement for wiring insulation. This change was epic... it has allowed the newer harnesses to last 25 years without failure. The downside, pre-updated harnesses are prone to failure to chemical, heat and time. Add in chaffing and the wiring harness will fall to **** in no time flat.

Check the core of the harness... it might be a pain to do, but make sure that you don't have two wires bare in there grounding each other out. Also check the wiring at the fuel pump, make sure it's up to snuff.

Finally, remove the battery, and replace the main power leads to said battery. Over time, the corrosion will work down the wiring and create more problems than you can imagine. New ones are not expensive and are better insulated against said corrosion.

Check the frame under the battery for rust. I am sure it has rusted (My '92 coupe did it in under 15 years). This is due to battery acid leaking and the general location of the ground and such... essentially, the frame rail becomes something of a sacrificial anode... However, clean the area thoroughly with (preferably) a pneumatic grinder with a steel brush on the end. this will remove all rust and debris. Then prime and paint. I used Dupli-Color engine paint and it has held up EXCELLENTLY (did my fix in 2005). They have a semi-gloss black that matches pretty well.

While the battery and its bracket are out, also check the junction block on the fire wall. Make sure everything is clean. Take it apart, hit the ring connectors with a light touch from a Scotch-brite pad and then use some battery terminal spray on them before reassembly.

Under the car is the main grounding point. Check that. You can't miss the damned thing, it's on the transmission and has about 8 or 9 wires going to it. Make sure nothing is frayed or simply broken. It's a stud, so remove the bolt and washer, then remove the wires, cleaning all of them with brake cleaner. No need for the terminal protectant, it will only attract more dirt under there.

If you have bad or dirty connections and/or grounds, these cars will run like ****... this is simple and cheap stuff to do to make sure all is good.

 

Are you reading the data when the engine is running with the Snap-On scanner???

DUB

 

when we connected the scanner I saw the different numbers and readings but didn't know what I was looking at or what to look for ...can anyone chime in to tell me what I should be looking for


by the way ....as of today I also replaced the oxygen sensor, engine coolant temp sensor and coil(see my first post on this thread for other things replaced/swapped).......I wont lie....the car is still doing it but not as bad .....I also will note that I added a bottle of stp injector cleaner.. I thought back to when I first bought the car in feb and it has gotten better since.. also I don't get gas from crappy stations anymore ..is it possible I may be slowly driving the injectors clean...adding fuel injector cleaner has been the only thing giving noticeable improvement ..all the other things needed to be replaced anyway

 

did you check fuel pressure at rails valve?you have changed most of critical sensor and parts injection related,with minor results.Check your timing too.Good advice is to check your injectors Ohms ( at least 16 ohms),and with a noid light too.i think issue is wire/harness related...

 

you need an aldl cable to connect to the ALDL link under the steering wheel.Using tunerpro (software free tuning/datalogging/codes scanning) and a cheap laptop.you can buy a cable for 60 bucks....

 

We did check fuel pressure and its weak....30-32ish and with pressing throttle to accelerate the gage sits 35-36...I know the pressure should be much higher.....
ALSO TODAY !!...the stumble has started to improve more and more weather was 75 degrees BUT...now the car has trouble keeping an idle where it wants to stall ..and has two or three times today..starts right back up ..sometimes it immediately starts to fight to stay alive again or the idle is fine ....the issue is it seems to now have trouble holding an idle....
SOMETHING ODD HAPPENED THOUGH....I went to get gas and upon opening the gas cap there was alot of pressure unleashed. .. <that hasn't happened before today ...I just read on another site of a guy that discovered his gas cap was clogged?.....let me know what you guys think....im fighting for my life here

 

i would buy a cable and download Tunerpro rt, datalogg that car and see what happen...if you are running lean you have high BLM's (read block learn multiplier)the O2 sensor is reading more oxygen than expected by your tune...high BLM's are usually in the 140-150-160 range in Tuner pro.Tunerpro has a section for trouble codes too,it says for example code 33,or code 44 if you have codes stored in memory...
here two pics for the minimum/maximum range of BLM's in a 85' tune.

 

It has been mentioned that the injectors can be the culprit. Checking the OHMS is one thing...but watching your base Pulse Width (PW) on the scanner can be helpful also. You might see 2.2 to 2.4 milli seconds (Ms) on the scanner..... and when it gets hotter should get to about 1.6 Ms (ish).

And without a special tool...performing a injector balance test is helpful to make sure each injector is the same ( or really close to) the pother injectors.

DO you have GM Corvette Service manual????

You INTEGRATOR value should be at or very near 128. If not...it can be letting you know you have a vacuum leak AFTER the Idle Air control valve.

Watching your Mv ( millivolts) of your Oxygen sensor when you crank it and when it goes into CLOSED LOOP and see that when you go into CLOSED LOOP you problem begins.

WATCH OUT for you adding too many additives in your fuel.

HOW old is your fuel????

Be CAREFUL in ASSUMING that the notch on your harmonic balancer is CORRECT when you go and check your timing. The outer ring of a harmonic balancer can SPIN....thus...using a timing light can be futile due to setting the timing to a notch that is NOT correctly positioned on the balance to give to the ability to correctly set your timing. AND you have to disconnect the EST wire to set your timing.

If you replaced the coil in the distributor cap...WATCH out for some crappy coils that are painted black....so the ground strap UNDER the coil...and the wire that gets secured to it on the top are NOT actually doing there job...because the paint is not allowing for good contact. The factory service manual will tell you how yo check you coil....and ALSO the pick up coil also.

Verify that your 'burn-off' function is working correctly by looking into the front of the Mass Air Flow sensor AFTER you turn your engine off after it has gotten hot and went into CLOSED loop. I VISUALLY check this...even though eh scanner will show that it is ON...I have to see it for myself....and you have to be QUICK and get to it after you turn off the key.

Possible EGR issue....sticking can possibly be a culprit.

DUB

 

Parts companies love it when people simply throw parts at the problem...

 

Im afraid you ARE correct. ......but I did make an appointment to attempt to allow a very popular(according to people on here) chevy -Corvette only- tech from bryner Chevrolet in jenkintown Pa. About 10 minutes away from me take a look at my car ...he was supposed to go over the whole car but also point out anything relevent to my primary issue(low throttle stumble)(code 44 -lean exhaust)...i was expecting him to look up all these things that you are pointing out to me....he stated he couldn't get his diagnostic scanner to connect with my ecu...he asked if anyone has ever been able to connect with my ecu. I told him my mechanic has connected his snap-on tools data logger/scanner with no problem. ...he looked at me like I was f@#king lying....I wish there was a place in the Philadelphia area who I could spend the day and tackle this problem properly. ...because im sure the chevy tech (though a nice guy) blew me off...so he can work on the newer vettes waiting for appointments ....can anyone out there who had this problem tell me what there culprit(s) was....also I will check the things mentioned

 

DO you have a GM Corvette Service Manual??????

DUB

 

i'd maybe look harder at that low fuel pressure. should be 43.5psi. i couldn't get mine to run with a brand new NAPPA pump. granted it's a 383, but it would start, no run with pressure around 35 psi. Also maybe look at the Idle Air Control valve/motor. it may be sticking part open or moving slowly.

 

That fuel pressure is unacceptably low. No question.