I have an 85 tpi. I have a 222 234 at 50 thousandths 494 494 cam, ported plenum, air foil with ported L98 heads, Vortex Rammer, and a 150 hp N.O.S. kit. I have a reoccurring code 34. I did find some vacuum leaks, and as far as I know all of these have been fixed. I purchased a used, supposedly functional, mass air flow sensor and a new aftermarket mass air flow sensor, and I am still getting a code 34. The car is stumbling badly under acceleration, backfires when I let off the gas to slow down, when revving under no load it backfires through the intake, when I disconnect the battery and reset the computer the car runs strong with no problems for approximately 30-45 minutes. Before the code appears after resetting the computer burnoff is visible; once the code occurs I have yet to see the burnoff cycle. I bought a 165 computer and have converted an LT1 intake for a 383 planned to be transplanted Winter of 2005. I would like to drive my car the remainder of this year and the Summer of next year, however, I can't seem to lick this problem. I'd like to get it taken care of before I store the car for the Winter. Any help and/or suggestions would be greatly appreciated.
Thanks,
Ashley

 

You're on the right track in that it's a MAF code and if you're confident you have a good MAF between the two you've tried then I'd re- check vacuum and inspect all around intake for air leaks. One of my books also says a code 34 can be set if the MAF relays and or ECM are malfunctioning. I'd suspect/check relays first for the obvious.

 

I replaced MAF relays last Summer and at the moment I am unsure of the condition of the MAF that was on the car and the used one I purchased, but I do know the new one I bought didn't help. I have tried looking for vacuum leaks by plugging all vacuum lines out of the intake manifold except fuel pressure and brake booster. I also started the car and sprayed starting fluid anywhere I suspected there might be a leak. I found one doing that which ended up being a dry rotted piece of hose between the driver side evacuation tube from the valve cover to the intake.

 

Go ahead and finish the job of looking for vacuum leaks. The diaphragms in either of those items can rupture and cause a vacuum leak. I'm not saying one or the other is the cause, but since you're so close, it pays to eliminate them as possibilities.

RACE ON!!!

 

I don't believe there is a problem with the fuel pressure regulator. I have an aftermarket fuel pressure gauge and fuel pressure rises during acceleration as it should. Brake booster on the other hand I am uncertain of. Does anyone know why the symptoms seem to go away when I reset the computer? I would think a vacuum leak would consistently be a problem regardless of reseting the computer.

 

It is possible that the code puts you in a "limp home mode", deteriorating performance. It runs OK until the code sets. I'm not sure this is true in YOUR case, but it is a possibility, and a good explanation.

RACE ON!!!

 

Vetteman I have the exact same symptoms/problem with my 85! The best I can figure is It has to be a 85 only problem.
I too tried new MAF and my burnoff module is working, but after engine
gets hot code 34 again.
Try to stay in touch maybe we can figure it out.

 

I am having the same problems with mine. It has had those symptoms ever since I put the TPI in and I haven't been able to fix it. Anything you guys find would be great seeing as I am very new to the TPI game.

 

Anyone else having this problem?
I'm curious mean8t where did you get your tpi setup?
I tried replacing the idle speed control some have suggested that
didn't seem to help.

 

I got the plenum, TB, MAF, computer and wiring harness off of ebay and the rest is aftermarket, SLP runners, Scoggin dickey base, accel injectors, etc. It works really well, execpt for the same symptoms as listed above. I have to install an ALDL and pull the codes, but I am sure that it will be a 34.

 

I am trying to find wiring diagraams for 1985 [all by itself]
between the MAF, burnoff module and pocessor.
I figure it has to be wiring or a bad burnoff module. although the MAF wire does glow red after shut off. I read the processor checks the MAF and sets code 34 on startup. Then after check light comes on runs like MAF is disconnected.
If wiring tests ok and its a bad burnoff module I'd like to update to 86 up processor and eliminate burnoff module for later setup with relays.
If anyone has any ideas/info it would be greatly appreciated.

 

So, I completely plugged off all vacuum lines including fuel pressure and brake booster, and this did absolutely nothing. I spent the weekend replacing all intake manifold gaskets and rebuilding the throttle body, of course as I suspected this did nothing. I am now looking into the possibility of some computer problem, does anyone have an 870 computer in good operating condition? For those of you who are experiencing the same problem what steps have you taken to solve it, so that I can eliminate those as possibilities.

 

Sounds like you have the exact sa\me symptoms I have!
you can use the following links to check your pin-outs. Remember 85 is all by itself.
I too checked for vacuum leaks none found.
I am going nuts, still have intermittant code 34 on hot restart only! when CEL on it runs like the MAF is unplugged. I did the diag routine where you disconnect the MAF and if the code changes to 33 you have a bad MAF, WRONG I tried a new MAF, now I have 2 MAF's.
I tried my MAF in a friends 87 no check engine light so MAF is good.
I found a wiring diagram at:
http://chevythunder.com/1226870_ecm.htm.
I checked all "a,b,c,d,e" MAF wires for continuity to the ECM/shorts to power or ground . I found pin "A" had continuity to ECM but was not grounded, so I made a ground wire to engine, no change did not help.
I checked Burnoff module wires all checked ok. Buroff wire heats up MAF after shutdown.
I found ECM pinouts at:
http://chevythunder.com/fuel%20injec...%20pinouts.htm
All seemed to check ok.
I cheched voltage at MAF pin C/ ECM pin B11 .5 to .7 volts at idle just like its should.
I do not undestand what MAF pin B/ ECM pin 13 analog ground is
for? but it has cotinuity to ECM, no shorts.
It seems like if the MAF and the wiring is good then:
I am leaning to a bad ECM but I have not been able to find GM diag test for 85 Corvette,I would like to find a 85 only diag procedure before I guess again[spend more money on parts]. I do have a Hypertech Chip but I don't see how that could be bad, all seemed well till acouple weeks ago.
I am fast learning to HATE TPI, give me a CARB anyday!

 

Thank you for the wiring diagrams, they were quite helpful, but as in your case I have yet to solve my problem. So it seems here we've eliminated all other possibilities. We have three people experiencing the same symptoms who have pursued all options unsuccessfully with the exception of the computer. Looks like I'm in the market for an 870. If anyone has one please let me know.
Thanks,
Ashley

 

I installed a new computer; since then I have had no code, no hesitation, no problems what-so-ever. Car runs like a scalded dog. Seeing as how this was a suspected problem from early on, I wish I would have just bit the bullet and replaced it at the beginning of the Summer. Now I have two-three weeks tops of decent weather. I hope this helps with the problems some of you are experiencing as well.
Thanks,
Ashley

 

Boy do I agree! I could've should've just started replacing parts.
After trying a new MAF, then trying my MAF on a freinds
car and his on mine, and spendings hours checking wiring etc. I finally gave in and ordered a new ECM the other day. I know it will fix it, everything else checks good! But now its too late to enjoy it till next year.
Thanks for all the info.