383 in 1989 automatic. TPIS intake and throttle body, but a mild build with new bosch 24# injectors. This engine was virtually new and then sat in storage for three years. It was never properly tuned and I am trying to get it running as well as I can before a tune and prom burn, but it will not idle and I cannot get rid of the code 34 error. I swapped in some spare relays for the MAF/Burn Off, and am getting the correct .4 to 1 volt MAF input at the PCM pin when running, but its not showing 2.5 volts when keyed on...only gets about .15-.30 volts.

9 out of 10 times it throws the code within 3 seconds-the other time it takes about 30 seconds. Throttle body was checked and it clean, no apparent vacuum leaks. TPS sweeps goof from .5 to almost a full 5 volts. Fuel pressure set 43 PSI, and small timing adjustments at the distributor made no helpful differences.

Only sets code 34, swapped with spare ECM and did the same thing.

I had a gutted (definned and descreened) prior working spare MAF I swapped in also-and ran the same.

The smell tells me its definitely burning rich-but seems to level out at run well at over 1500 RPMS.....no road test drive yet.

I did notice some erratic fuel pressure readings at the intake mounted oil filled gauge (43 and dropping into the high 20's), and will be checking with an external gauge at my next round of troubleshooting (has brand new adjustable fuel regulator). Not sure if code 34 can be related to fuel pressure?

Throw my any bones you can think of...getting to the end of my rope on this one...

 

If it were me I would have someone burn a chip to at least get closer to the correct tune, most tuners charge one fee and will reburn until the tune is correct. So you can pay now and do multiple datalogs later on to get the best tune for your new motor.....Here is the info for a code 34 (1985-1990) Clean the throttle body. Check MAF connections. Replace MAF relay. Replace MAF Sensor. Possible ECM failure..WW

 

Thanks-I ran the code through alldata, identifix and google, and did what I though was a good amount of homework. Will probably just take it in for a tune/burn, was hoping to eliminate that MAF error first.

The only issue I found with the MAF is that the signal is much less than the referenced 2.5 volts at the Keyed on position....can this be relay related?

 

I no longer have my Vette or the shop manual,but what voltage is the MAF should be at with key on? Is it 2.5 or 5?I cannot recall.

Have you checked,cleaned the MAF harness connectors and ensure they plug in correctly?If you get the car running some,when the car is turned off,does the MAF wire glow red for a few seconds?

(If you had a snap on scanner it would tell you if the burn off is working or not)
Im also curious if the IAC counts is reading normal with key ON then started...again a scanner will show this.

Will your car start and idle with the MAF unplugged?

If so,try that and we can go from there.


One more thing,it may have nada to do with,but did you set and adjust the minimum air speed screw and tps correctly on that TPIS TB unit?Your engine is much larger now,so you may need to increase it flow properly at idle,not just put it at stock settings if thats where it is at now.

 

The main MAF reference should be at 5v but the signal wire should be at 2.5v according to my pinout chart....this is the dark green signal wire feeding the ECM.

 

Set you're minimum air speed like mentioned above, My setup does not like to idle under 1100 rpm.

 

Couple small progression steps:

My erratic fuel was simply getting very low on gas...wish they were all that easy.

My MAF signal seems within range (.4 to 1 volts at ECM), but it's not glowing (burning off). Burn off wire has good continuity back to relay and both MAF and BURNOFF relays are brand new, as well as swapped with other know good relays now, connections are clean.

Looks like burn off is fed through the fuel pump relay circuit? I will study the diagrams and dive into that as well as try to set the idle and double check IAC/TPS.

I also noticed that my TECH1 one scanner plugged into the OBDI gives me a connect pin E error....will double check to make sure pin E is connected to the correct pinout at the ECM tomorrow. Hoepfully the scanner can give me some useful live data. Car is running rich, but running, sometimes stalling out but still likes anything over 1500RPM and setting code 34 in 3 seconds after clearing.

 

Does anyone know how long the ecm must see a closed loop cycle prior to prompting the MAF element burnoff flash?

 

Try changing the MAF relays. They are relatively inexpensive.

 

I swapped in some good used ones and some new ones with no difference.

 

This is quoted from my "How to Tune and Modify Chevrolet Fuel Injection" by Ben Watson.

For a code 34 fault


" Clear the codes and run the engine until the check engine light comes back on or until you are satisfied it will not. If Code 34 returns, disconnect the the MAF and run for 3 minutes. Does it set a Code 33? If it does not, the MAF signal is shorted to the ground or the ECM is faulty. If Code 33 is set, check for 12 volts available to the MAF sensor. If the MAF is receiving 12 volts, replace the MAF."

(It also says a code 34 can be set from a false air leak)