I have some odd behavior with the MAF that seems to point me to the ECM and wanted to see if there was anything I was missing before trying to replace:

With the MAF plugged in, the car is hard to start and once it gets started you need to pulse the throttle to keep it running, it runs at pretty much WOT or stalls out, can’t find anything in the middle

• Unplug the MAF, car starts pretty easily, idles high (maybe ~2,000RPM if we believe the Tach) but otherwise isn’t too bad
• Plug the MAF back in while it’s running and it dies quick unless you pulse throttle

Obviously it seemed like MAF was to blame, ordered one up (refurbished), it came in with the plastic pin housing not really installed so didn’t instill confidence, but plugged it in, same result, maybe it isn’t the MAF???

• Returned MAF because it arrived “broken” and started more troubleshooting
• Checked continuity to all wires from MAF to relays, MAF to ECM, relays to ECM, all seem fine
• Thinking I am as likely to burn up a relay as I am to actually test one, I bought two new relays, MAF and Burn-Off, this didn’t fix it
• Finally bit the bullet and bought another (New) MAF thinking maybe we just were unlucky, paid for a new one, came in and had the same issue, interestingly in my excitement to test I had forgotten to plug the relays back in after my previous test and the car did the same thing, plugs the relays back in and no change

I checked for 12V on all the hot wires, which it had, checked grounds again
Back probed signal coming in from burn off relay to MAF, with car running (with MAF plugged in) it showed ~37mV, which I assume is normal
Back probed signal coming from MAF to ECM with car running (MAF plugged in), car off I got 1.43V, car running pulsing throttle with somewhat high revs, I got 2.2-2.3V, I think that seems right, probed at both the ECM and MAf side, readings matched
Replaced temp sensor (passenger side) and O2 sensor on the off chance these were causing faulty readings (O2 sensor wire got toasted on header, this was fixed)
Checked TPS, got .556V with throttle closed and 4.46V with throttle full open and seems to trend linearly with throttle position, that seems like it is working to me
Nothing seemed to fix this issue, with the MAF plugged in, the car is not throwing any diagnostic codes, I’m not sure what else to do other than replace the ECM, what else to look at or test??

Thanks for your help!

 

Any scanner datalog data to see if the ecm is reading maf ? Should throw a 33 or 34 unplugged.

 

If you do find you need an ECU, I have one for sale. I swapped my 1989 L98 to an EBL ECU, So I have the ECU, PROM, adapter board, hypertech chip, and a MAF available in chicago.

 

Just de-winterized and tried an obd2 scanner and realized it's obd1 . Any suggestions for a good tool to pick up?

 

Paperclip will get you the codes. Moates.net or 1320electronics.com for datalog equipment.

 

Wasn't sure if it was something else, using paperclips last year didn't show any codes. was all clear. I'll try again this weekend to see if it's different

 

Got a code 22, fixed the TPS voltage (didn't install it right i guess) cleared the codes and now nothing is showing whether the MAF is plugged in or not

 

Might take some runtime to generate more I suppose. Is it acting different?

 

nope same issue as before, running it for any length of time i think is not going to be a good idea. The cat gets red hot because the only way to sustain running is to unplug the MAF and it runs really rich

 

First thing I'd do is look for an air leak after the MAF sensor. Rubber boot or around the throttle body.

 

moates xtreme aldl but kinda a crap shoot on connection mt2500 might work better

 

I have an old scan tool for OBD1 like yours, but I'm in NJ.
If you unplug the MAF and it runs better it has to set a code as was mentioned above.
When my MAF went bad on my 1988 Formula 350 I bought a Accel Power Processor and learned how to tune aftermarket EFI, that was in 1989 or so believe it or not!
I run Holley EFI on both of my 3rd gens, got tired of the GM stuff giving me headaches plus they aren't on the street anymore, but they could be since they are more than 25 years old now. No emissions to worry about so any EFI is legit.

Check for leaks after the MAF. If you can gain access to a smoke machine do it. You may find leaks you didn't know were there. Can drive you nuts.

You really need to find a scan tool that can show the MAF sensor output with the car running or you will be chasing your tail.

 

Got the datalogging and i'm still trying to figure out what it all means. If anyone has some insights from this please let me know

 

What’s idle gps cl ?

 

What is idle gps cl and how do i get that? If i need to idle the car, i can't or it stalls

 

The snapshots are confusing don’t really tell the story. Driving in 10k mode I’m guessing since tcc is locked. The gps fluctuation looks like possibly a vacuum leak but not comparing and live data it’s hard to say circumstances of data you posted. Cl is closed loop btw

 

Got it to run in CL after the engine warmed up. Good news is that there's readings from the MAF, so it looks like another problem. A vacuum leak is probably a culprit. Old lines and all

Raw data file:
https://file.io/PqapIFLY3POB