I finally got my engine back in after an 8 month suspension and engine rebuild and it started right up. Yeah!

Unfortunately the check engine light indicated a code 33. Idle is fine, but it's in limp home mode. I have the FSM and looked it up and started troubleshooting. I don't know much about electrical stuff so any advice is appreciated.

With the MAF sensor unplugged and ignition on, engine off, I am getting 5 volts on the green wire which means good ECU signal I think.

With the engine on, and the MAF unplugged, I am not getting 12 volts on the purple wire, more like a tiny amount of stray voltage. This means my burnoff module is not powering the MAF correct?

I am trying to find out why the burnoff module is not sending power. The code 33 instructions say to check the sensor harness terminal wire E(black wire). Where is that? What is that? Is that an intermediate junction between the MAF and the burnoff module? It says to check using a test light, I don't have one. Am I checking for a voltage or a continuity?

The burnoff module is behind the instrument cluster??? WTF?? Do I need to get in there? I swapped some LED bulbs into my gauges and and that was a total PITA to get all that apart and back together again.

Online, there is a lot of info on code 33, it's frightening all the things that can trigger it. Am I going in the right direction? Thanks

 

That is correct.

Terminal E is in the MAF connector. It's the signal from the MAF to the ECM. You check it with a voltmeter or some other way of measuring voltage.

Yes. The MAF burnoff module is also the power source (12 volts) for the MAF sensor.

Error code 33 means that the MAF is not communicating with the ECM. That could be a dirty connector pin or a broken wire.

The ECM sends 5 volts to the MAF and the MAF "loads" it down to the correct voltage that corresponds with the air flow rate through the MAF. Zero volts means no air flow and 5 volts means maximum air flow.

 

Thanks for the reply. I re-examined the vague burnoff module location pic in the FSM, and I think my freakout was unfounded. It appears to be in the right side of the dash, in front of the passenger. I was thinking I was going to have to completely disassemble the dash again.

The descriptions can be tricky so I have included what I am looking at from my 1985 FSM.

In the wiring diagram the top left MODULE CONNECTOR (pins ABCDEF) is the burn off module connector. This corresponds to the BURN OFF MODULE (pins ABCDEF) center left.

The left bottom is marked AIR METER CONNECTOR (pins ABCDF) and bottom center is marked AIR FLOW METER (pins ABCDE). These are essentially the same thing, correct?

They are just calling circuit 993, pin F at the BURN OFF MODULE, pin E at the MAF, and pin F at the AIR METER CONNECTOR right?

This is confusing me. Do you mean circuit 998? AIR METER CONNECTOR F and AIR FLOW METER E are the same thing right? A 12v power source. How is this the signal from the MAF to the ECM?

In my original post I was doing #2 on the diagnostic. "probe sensor harness terminal E with a test light." In #2 the AIR FLOW SENSOR is disconnected, ignition on, engine stopped. Do they really mean the the AIR METER CONNECTOR F purple wire? If so I should see 12v on this with the above conditions?

I assume that no power here means in #3 I check the BURN OFF MODULE pin F to see if circuit 993 is broken.

 

I diagnosed my burnoff module as bad and opened it up. I could easily see where it had shorted on the board. I soldered a bridge over the burn spot and it tested good. So back in it went, and my car started with no codes.

 

So, 3 1/2 years later, is your Burn off Module still working? Mine just failed(I went through he FSM charts) and I am not able to find a replacement.
I haven't got it apart it yet, but I am hoping I can repair it.

 

Have you checked with All American Classics on 4th Plain? About the only place in town that has wrecked Vettes.

 

The solder trick is quite the fix around a costly problem. I’ve seen burn off modules at $1,000. Not that sellers get what they want but you get the idea: sellers realize they have a one year only item and want a premium for them. May be best to attempt the solder operation like the OP. Spend some time saving hundreds.

 

Search the forums, tons of info on code 33 and MAF burn off.
Be advised, many MAFs produced now that are considered compatible, no longer include (or need actually) a burn circuit.
Instead of spending a ton on an ancient model, I had my MEMCAL modified to turn off the code 33 check. MAF replacment about $100.

You should check the relays first, may get lucky that one of those went bad.

Key item on code 33, this is ONLY checked after engine has reached closed loop (warmed up fully), stopped for a couple of minutes and started. Disheartening to see no code on first trip and then pop up on next drive if this is not known.

 

Hi, glad to help out. My fault in that module was an over voltage condition and I found the spot on the board to bypass, as you can see. It is still working. If your fault is not so obvious, you would probably need some electronics repair experience to diagnose.

 

Glad to hear your repair has worked for this long BlueTwoTone. When I get mine out this weekend, I will assess the module and see if I can repair as you and 1985 Corvette suggest.

I did find a used one at a local salvage yard "All American Classics".. (Thanks for the suggestion Jazfe!), and it looks good,so I am hoping I can repair mine and then have a spare.
I will work on it this weekend and report out the resolution.

Thanks for all the help guys!

 

Thanks for the idea, I may go that route if I can't resolve it with the stock setup
I ran into the same issue on MAF compatibility. O'Reilly sells a "Spectra" and Autozone sells a "Duralast" that they claim works for 1985-1989 Corvettes. I would not trust either as the 1985 MAF is one year only part.
I did find a "Blue Streak Electronics" Rebuilt MAF that I bought. The BSE unit is listed as a 1985 only part. It is a rebuilt Bosch unit. I have traced my problem to the Burnoff unit, so I may not even have to use the BSE MAF, but I bought it just in case.
I also see "Delphi" makes a new 1985 only MAF. Anybody have any experience with the Delphi MAF?.

 

Report out on my issue (Code 33,34 traced to MAF Burn-off Module Failure).

I installed a used MAF Burn-off Module from a local salvage yard (I don't know the miles on it). I reran the MAF Burn-off Module test in the FSM and it passed. Codes 33 and 34 did not come back and the vehicle runs good now (driven for about a week). I also installed a rebuilt MAF (Blue Streak Electronics). The BSE unit is a rebuilt OEM Bosch unit and it works great. I cleaned my stock MAF unit with Mass Air Flow cleaner and will keep as a spare..

Incidentally, I bought a NEW Delphi MAF Sensor and I returned it. The Delphi unit looked different inside from OEM and I was not convinced it would work. If you need a MAF for your 85-89, I recommend a rebuilt BOSCH unit from Blue Streak Electronics.

Regarding the MAF Burn-Off Module: These have not been made for probably 15 years. Seems like an uncommon failure but it is a one year only part. (85 Camaros and Firebirds with the 305 TPI have this module as well). My nephew (who is an electrical engineer) is going to attempt to repair my old one, but I have not found anyone who rebuilds these, so hopefully my salvage yard one will last.





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