I have solved the alternator belt problem and successfully run the engine, but I keep getting a code 34 and the engine runs extremely rich. The code is stored as soon as the ignition is turned on, and I am receiving no other trouble codes. I have checked MAF and relay connections, and reversed the relays with no response, so that would not seem to be the direct cause. Upon reading that code 34 could be stored as a result of improper adjustment of the TPS, I followed procedures available on the Thirdgen website to adjust it properly. I found that the voltage change is linear and there are apparently no defects in the TPS itself, but that the voltage is around 4.0 at closed throttle and 0.8 at wide open throttle. I took the voltage between terminals "B" and "C" using jumper wires and determined that terminal "C" (the gray wire) was hot. I then took the voltage between terminals "A" and "B" and found that the voltage curve was reversed, with 0.8 V at closed throttle and 4.0 V at wide open throttle with terminal "B" (the blue wire) hot. By rotating the TPS, I was able to calibrate it at 0.54 V as specified. Also, I got a constant reading of 4.67 V across terminals "A" and "C", with terminal "A" hot. Apparently, this is the power supplied to the CTS and MAT sensors.
The improper TPS voltage curve would seem to be the most likely cause of the engine's running so rich. I'm not so sure what it has to do with a code 34 stored before startup, though. Also, strangely, there is actually throttle response, and the engine will rev somewhat naturally, but sometimes has difficulty maintaining a contant RPM above idle, and occasionally stumbles even at idle. I simply do not understand the reversal of TPS voltage. The wires are not shorted and go to terminals C13, C14, and D2 on the ECM as they should according to the wiring diagram and are consistent with the configuration I have observed on other GM vehicles of the era. Would it be possible that the source of TPS voltage which runs through the ECM is of the wrong polarity? I would have expected such to have more adverse effects. I would appreciate any suggestions, and will abstain from further operation until I determine something definite. Thanks

 

Ok this is a little off the wall, but it IS possible to install the tps backwards...I'm not sure how the lever on the tps would engage the throttle but it would explain the problem.

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89 Iroc-Z LB9 305 TPI auto 2.73 posi:
3" Dynomax "cat" back,K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, 180' thermo, mild ignition mods, synthetic oil, kicker sound system, soon to attempt engine swap...

 

Also, the computer knows from the maf (if the tps is indeed reversed) that it's not at wot so it probably overrides the tps and thinks the maf is bad - i.e. it thinks you really are at WOT and the maf isn't reading correct flow. But code 33 would make a lot more sense in that case. That's all I can think of.

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89 Iroc-Z LB9 305 TPI auto 2.73 posi:
3" Dynomax "cat" back,K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, 180' thermo, mild ignition mods, synthetic oil, kicker sound system, soon to attempt engine swap...

 

Well, I'll take a stab at this one. What I've researched applies to the 86 L98, but I hope it applies to your engine too. You didn't indicate which engine you're running so I hope it's an 87 or 88 L98.

I've recently been doing a lot of adjustments to my TPS on my 86 Vette just to see what setting gave me the best performance.

The voltage readings are taken from the top and center wires (terminals A and B)with a digital voltmeter. It doesn-t matter which lead of the voltmeter goes into which TPS terminal. If you cross them, your meter will just show you a negative sign (-) next to the voltage reading.

GM's Service Manual states that those voltage readings should occur with the throttle closed and ignition on or at idle (page 6E3-A-40.)

Code 22 will be set if the (1) engine is running and (2) TPS signal voltage is less that about .2 for 3 seconds.

Terminal "C" should have 4-6 volts.

Terminal "A" is #452 and is black and "B" is 417 which is Dark Blue. "C" is 416 and Gry

For the 86, the reading should be .54 +/- .075 which means anything between .465 and .615 is withing spec. I've taken mine all the way to .67 without getting a code, but once you go too far, the ECM with set a high voltage code.

The bottom most wire, is terminal "C" and is simply a reference voltage and isn't used for setting the TPS voltage, only the top two terminals are used.

To test for any bad/dead spots in the TPS, you really need an analog meter with a sweeping hand. Attach it as you did the digital job and slowly open the throttle by hand while watching the meter. The indicator should smoothly move across the dial as you open the throttle, with no sudden dips or jumps.

Code 21 is set when (1) engine is running (2) TPS voltage signal is greater than 2.5 volts, (3) air flow in grams/second is less that 12GM/sec, (4) all conditions are met for 3 seconds OR TPS voltage is over 4.5 volts with ignition "on" or engine running. (Page 6E3-A-38).

So, I just went back and re-read your post and I see that you don't have a problem with the TPS other than the .8 voltage reading. Just use A and B, forget C; keep the WOT voltage under 4.5 volts (that's another story about the WOT PE problems that causes).

Clear and stored codes by disconnecting the battery for at least 30 seconds, then fire her up. If you stilL get a MAF code, I'd direct my attention there and use the MAF trouble shooting procedure, like unplugging it, etc.

If you need the MAF trouble shooting procedure shoot me an email and Chippy266@aol.com

Hope this helps,

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

[This message has been edited by JakeJr (edited January 10, 2001).]