ECU, MAF, or wiring

[SrKegler]

I've been battleing a AIT code. Went thru 4 different MAF and a different ECU. Original ECU had blown sensor grounds.

At present, I can drive about 15-20 minutes before the code will pop up. I've checked wiring and it "seems" to be good.

Help me narrow this down.

 

[400hp93talon]

Are you running the stock maf or a gm?

 

[steve]

It looks like the fault conditions are IAT < -49F or > 122F.
I suggest logging the IAT and see what's going on.

 

[400hp93talon]

IAT=Intake Air Temperature correct! If the air is to hot you should make sure your turbo is getting starved of oil/coolant.

 

[mschlanglv]

The IAT sensor is in the MAF, so turbo temp will not affect it.

Sounds like a wiring issue to me. How does the wiring "seem" to be good? Check for continuity through the wire, and also continuity to ground and positive. Unplug both the sensor and ecu and you should be able find any shorts.

 

[SrKegler]

The IAT sensor is in the MAF, so turbo temp will not affect it.

Sounds like a wiring issue to me. How does the wiring "seem" to be good? Check for continuity through the wire, and also continuity to ground and positive. Unplug both the sensor and ecu and you should be able find any shorts.

I jumpered around the wires ran it straitght from the MAF to the ECU. What really has me stumped is the code only comes on after driving 15-20 minutes. Sounds to me like it's heat connected.

I'm getting another ECU ready to ship out to Steve. Might as well have a spare unit since these are becoming hard to find. If the new one solves the problem I'll just have the old one rebuilt.

I'm getting ready to hook the logger back up and log the AIT just to see what is going on. Will post results tomorrow.

Update went for a drive and logged some items after the engine warmed up. No CEL on.

AIRT started off at 72 deg, 0-5V read 4.45, cool read 199, MAFS read 1098 at 4343 RPM, MAP read 4.51.

Then the other reading didn't change but my AIRT went to -75 deg and the CEL came on. Is this enough info for someone to figure out where the problem is.

 

[steve]

Sounds like you still have a wire broken or connector coming loose and opening the IAT circuit. Since you have changed MAFs and ECUs that's all that's left.

As it says in the FSM, the IAT resistance drops as the temp rises. -75F is likely the lowest temp recordable and equals an open connection (infinite resistance).

BTW unless you have a wideband connected to the EGRT pin the 0-5V is meaningless as is the MAP parameter. No need to log them or any of the parameters on page 4 of MMCd.

Logging baro would be more useful to see if it has any issues as well when the IAT drops out.