Hey all, I have a 1996 Firebird Formula I'm trying to diagnose a P0100 trouble code on.

The code seems to set when accelerating/revving the engine. Based on the freeze frames, the code seems to set when the MAF sensor signal drops down to 2.36 gm/s momentarily.

Had a no-start condition that was solved by replacing the ignition coil. Now I've got a P0100 Isufficient MAF sensor activity code that I can't figure out.

Currently, the car seems to run better in speed-density mode with the harness unplugged. With the harness plugged in, my scanner is reading the MAF at 15 grams/second. Running in SD, I'm getting 2.36 gm/s.

Here's the diagnostics I've done:

1. Replaced the Delphi MAF with a Blue Streak MAF with little improvement.
2. I have 5V with key on between the yellow and black/white wires.
3. I have 12V with between the pink and black/white wires.
4. I have continuity between the sensor harness and PCM harness.

Any ideas? Thought about buying a remanufactured AC Delco unit. I don't THINK it's an issue with the harness or PCM, but I'm not sure. Any ideas are appreciated!

 

Are you sure both MAF and SD readings are both in grams/second? Could SD possibly be reporting in pounds/minute? The conversion factor is 7.56. 2.36 pound/min = 17.8 gram/sec. The SD calculation can be “off” if engine breathing has been modified but VE tables have not been updated. Can also be skewed by the accuracy of the MAP and IAT sensors, which are primary inputs to the SD calculation.

P0100 typically sets if the MAF signal goes to 0 Hz. Can’t remember now, but it’s either the 96 or 97 that has a tendency for the MAF wiring to break somewhere in the harness. Having 5 volts on the sensor wire means the PCM is supplying the 5 volts reference to the MAF sensor. But the MAF sensor signal is not a voltage. It is a variable frequency (Hertz) riding on the 5 volt reference. At idle, using a frequency counter you should see about 2,200 Hz.

 

Very certain, when plugging the harness in the gm/s reading would immediately jump from 2.36 to ~15. The engine would then bog down and drop from ~1000 RPM to ~500 RPM, then jump back up after 6 or so seconds (I'm assuming running very rich with sensor)

I've seen some of your other responses, I believe it's the 97 that has a tendency the break in the harness. I can check frequency tomorrow, but so I understand: frequency drops to 0 = potentially bad harness, if it doesn't, bum MAF sensor?

One detail I'm not sure that I added, is that the car seems to bog down if you rev it from idle or start accelerating- once you get above, say, 2000 RPMs it clears up.

 

What RPM does the fully warmed up engine idle at with the MAF connected, and showing 15 gr/sec?

What RPM does the engine idle at with the MAF disconnected, showing 2.36 gr/sec?

Is engine and programming stock? Which transmission?

If the signal drops to 0 and the code sets, could be the sensor or the wiring. I'm just trying to see if there is still a signal when the mass flow drops to 2.36 gr/sec, or if that number is the result of the SD calculation.

This is nothing I've ever run across in 20+ years doing this.

 

Scanner showed that the engine dropped to ~500 RPM upon the sensor being plugged in, and then settling between 850 to 1000 RPM.

Scanner reads 900 RPM with sensor unplugged and reading 2.36 gm/s

Neither are stock, engine internals have been moderately modified (cam, etc.) The engine also has 30lb injectors. A tune was done by TPI Specialties in MN, but I'm not sure what was done as that was before I bought the car. Transmission is a M6.

A few other details that might matter:

This code showed up after replacing the coil (which was the problem) and injectors (which I thought were the problem). The injectors I swapped out and swapped in are all 30lbs, the only difference is the old ones are Bosch F1SE-E9A Ford injectors (don't ask me how) and the new ones are ACCEL GM injectors. My logic says that the injectors should not affect it at all, but I have no clue.

The car also came stock with ram air, not sure if that affects MAF readings.

Unfortunately I don't have access to a meter that can do Hz at the moment, so that is TBD.

 

Idle seems high, but that’s probably the result of the tune setting the target idle higher than stock (800 RPM) with a T56. MAF grams/Secseems about 50% higher than normal, but again could be the result of the tuner altering the MAF calibration table (RPM vs.Hz). And the tuner may have altered the VE tables, which alters the results of the speed-density calculation.

TPIS is/(was?) a reliable source of LT1 tech, so tunes should be done well. Might be worth asking them for input on the problem.

Injectors aren’t the cause. But Accel hasn’t proven to be the best choice. The Bosch III injectors seem to be current favorites.

 

Appreciate all the time and input. What do you recommend as the next best course of action? Try a 2nd new sensor? Try a new sensor harness? Look into a possible re-tune (Solomon perhaps?)

 

Ummmmm….. no Solomon.

In the morning I'm going to dig into the wiring details of the 12 volts and ground to the MAF. Could something else in the circuit (assuming there are other sharing devices) be affecting the MAF sensor.

I've been working on Firebird Nation with a guy who had his 97 LT1 built up - LE heads and cam, etc.. - and has been plagued ever since with an inability to eliminate trouble codes (he lives in strict California) for the crankshaft position sensor (used only for misfire detection) and P1351 for an open circuit on the ICM, accompanied by loss of power. After staring at the ignition wiring diagram I finally realized the coil, the ICM, and the CKP sensor all get 12 volts from the same fuse. Could a problem with one cause the excessive voltage on the ICM trigger wire, trip P1351 and cause issues with the coil? Boggles my mind. Then the light bulb went on for your MAF issues.

 

Like I said, I really appreciate all the effort. One thing that came to mind when you said that is, when I was removing the ignition coil bracket off of the block, there were, what I assume were ground wires, that were being held in place by the coil bracket- possible I re-installed with a poor ground? I doubt those have anything to do with it, but that was something that was worked on before this issue appeared.

 

Just wanted to give some updates:

Changed how the ground wires behind the ignition coil were set up, it predictably Changed nothing. I also tried hard wiring a new wire between the harness and PCM, which also changed nothing. So all I've determined at this point is that the sensor wire is probably fine. I'm at my wits end with this project, any other ideas Injuneer? Thanks

 

Why the ground wires at the coil? Hopefully I didn’t mislead you with my comments about someone else's ICM problem. I only mentioned the ICM to illustrate that we need to look at the opportunity for similar problems with multiple devices on the MAF circuits.

I still want to look at the MAF wiring diagrams. Didn’t get a chance today. Trying to get Midland-National to send me the money from an IRA annuity that matured a couple weeks ago. Have to pay my outrageous quarterly NJ property taxes on August 1.

 

Just wanted to try it for the hell of it at this point, that was one other thing I changed between start of problem and end of problem.

 

Update Number 2:

Took the car to a performance shop, good news is that they took a look at it and confirmed that the electronics and sensor are all working as intended and that shouldn't be an issue.

Bad news is that they think it's something mechanical in the engine on the drivers side - lifters, push rod, something that's causing it to run like dog and pop/backfire. They don't have the time or space to dig into the engine and referred me to a different performance shop that's a month out on work.

Normally I'd take a swing at it but I know NOTHING about doing internal work like that so I'm not sure. Might pay to get it straightened out and then get rid of the damn thing, it's been a headache since I bought it.

 

Update #3:

3rd mechanic essentially told me "we have no idea why mechanic #2 told you it was a mechanical issue on bank 1, there is no indication of broken springs/burnt valves/etc." They also disagreed with the assertion that the MAF signal is fine, as they said they kept getting P0100 as well.

Mechanic 3 suspects a possible tune issue and told me to go somewhere else, so now I have to try and track down a performance shop who will even look at (out of the 6 performance shops I've called so far, no will look at it due to it being an LT1 car).

So pretty much back to square one with zero progress and $250 less in my bank account. Only thing I can think of at this point is try a remanufactured AC Delco unit or try to find SOMEBODY who will tune the car...