88 Drivability Problem

[ELKYNUT]

I was wondering if any of you could give me some advice on a problem I am having.

Some days my vette will run great, other days the check engine light comes on and it still runs great. If you turn off the car, the light usually goes away. Well, now it started to hesitate. You give it gas and nothing happens, the idle jumps up to about 1500 RPM, and it just doesn't go once your in gear. You can rev it up and it is fine, but as soon as you let the clutch go, nothing happens, it just falls on its face. My mechanic friend threw a code reader on there, and it pulls up a code for that MAT sensor, MAF sensor and a tps sensor. The local chevy garage isn't all that good, so I asked my friend who has access to a GM computer and that is what it pulled up. He is doing some homework on it, but I just wanted to check around with you guys as well.

The car does have a D.A.M. air intake on it, a BBK T.B. and a Casper's T.B. interface. The fuel pressure guage for some reason was reading almost 50 psi, we turned it down to around 38 psi.

Any help would be greatly appreciated.

Thanks,
Bill

 

[Ken]

All I can add is that it sounds like you are on the right track. You say your friend pulled codes for MAT, MAF and the TPS sensor?

What codes specifically?

 

[afree]

I agree with Ken but specific codes would be helpful. I have an 88 as well and ran into a similiar problem. It just so happens that it occurred at a time when I was about to park the car for a while to do a few mods. Unfortunately I can't tell you which thing I did corrected the problem but I suspect it was fuel delivery problem. I did change a few things in this area, new regulator, new filters, cleaned injectors and replaced injector o-rings. I also did a few others mods. After everything was back together she ran great.
I know this doesn't help much but with a little more info we might be able to steer you more precisely to the problem.

 

[ELKYNUT]

OK GUYS. I talked to my buddy and he said it pulled up code #'s 21,22,33,34. He thought the codes 21 and 22 were due to the Casper's Throttle Body interface and so we yanked that off. What do you think? Anybody want a Casper's unit?:d

 

[Edmond]

OK GUYS. I talked to my buddy and he said it pulled up code #'s 21,22,33,34. He thought the codes 21 and 22 were due to the Casper's Throttle Body interface and so we yanked that off. What do you think? Anybody want a Casper's unit?:d

According to my book:

21-TPS voltage high, idle above 0.9v

22-TPS voltage low, idle 0.3-0.9v

33-MAF '85-89 circuit-voltage high

34-MAF '85-89 circuit-voltage low

Taken directly from Corvette Fuel Injection & Electronic Engine Management by Charles O. Probst.

 

[afree]

Somewhat contradicting aren't they. Well by now you probably already know that if it's the MAF Sensor it is going to cost you some bucks about $150 or so with a core return BUT I would not jump to that conclusion just yet.
I know for a fact that the car will actually run pretty good with the MAF completely disconnected. I have done expirements to prove this. Don't get me wrong it does not run great just OK.
I would actually suggest that you disconnect the MAF sensor and see if you have the same symptoms. I actually bought a MAF sensor once only to discover the I had a clogged fuel filter.
I have a MAF sensor tester that I bought from Mid-America that will definetly tell you if the MAF is working right or not. Basically it is a plug that allows you to monitor the MAF output while driving the car. I had to tape my Digital Volt Meter to the windshield to use it but in this particular case it actually allowed me to see that the MAF was not outputting the correct voltage under WOT.
BUT yet another BUT...with the codes contradicting themselves I might be tempted to look for some common element.
Will think on this one and let you know what if anything I come up with...hmmmmmmmmm

 

[ELKYNUT]

THANKS, THAT WOULD BE GREAT. OH BY THE WAY, WHERE IS MY PCM ON THIS THING?

 

[Edmond]

THANKS, THAT WOULD BE GREAT. OH BY THE WAY, WHERE IS MY PCM ON THIS THING?

If you're referring to the computer chip, it is located in the dash on the passenger side. It is accessible by removing the bottom panel (where the passengers knees are facing) with only a few screws. Look up and you'll see two nuts holding the bracket that holds the housing unit of the computer.

 

[afree]

Since you have removed the Casper unit I would suggest that you clear the codes by disconnecting the battery for a few seconds, re-connect battery, start the car, note symptoms and then re-check codes just to see if they are repeatable.
By the way the 50 pound pressure reading is a little high so turning it down a grunt was probably not a bad idea but I think somewhere in mid 40's would be a better setting. After I installed my adjustable regulator I did find that my car did not peform as well above about 47 although these are only results from 0-60 times and not from actual Dyno pulls.
I realize I'm still not helping much but I am still thinking on it...

 

[Bonnell]

I had very similar symptoms when I first purchesed by '88. It turned out to be the PCM. The dealer changed it for $314 but I later joined this forum and found taht I could have done it myself for $144.