Put my scantool on my firebird today and I have these codes: 2.8v6 mpfi.

23, 32, 34.

23. My MAT is definitely bad. It reads -40C all the time. Where is this sensor located? It's in the airbox, correct?

32. EGR. I don't know anything about EGR. I don't have it on my 84 because I built the motor for it. So what do I do / look for?

34. MAP. Seems to be an intermittent problem. My scan tool can't tell me anything but that it fails a "HIGH" check. Where is THIS sensor?

Thanks! BTW, my symptoms are: VERY VERY rich at times.

Status of other sensors:

O2 -- checks out perfectly
TPS -- checks out perfectly
MAF -- checks out perfectly

IAC -- a little high. Should be about 25 at idle and I'm getting 40-45? No load of course.

I need a little guidance, please

 

C55, welcome to the v6 board!

Well, that MAT sensor will "say" -40 degrees when it's at an infinite (very high) resistance. The GM service manual says that happens at 100,700 ohms, but infinite's close enough.

So that would mean the sensor might just be disconnected (I've done that plenty of times!), or maybe a wire has cut through.

You haven't found the MAP sensor because you don't have one! Your '86 uses the Mass-Air-Flow technology for measuring the volume of incoming air. You should probably take care of code 22 first- the GM Service Manual for '86 says that the "MAT compensates the MAF." What that means, I don't know, but apparently the two are related somehow.

EGR? There's a few pieces to this system. You've got the actual EGR valve that lets exhaust gasses back into the motor; you've got an EGR solenoid that supplies the EGR valve with vacuum on the computer's request; AND you've got an EGR diagnostic switch.

The EGR diagnostic switch checks for a vacuum "after" the EGR solenoid. Say your computer doesn't want EGR- it won't turn on the solenoid. The EGR valve and EGR diag switch don't get any vacuum.

Say the computer wants EGR turned on. It will activate the EGR solenoid. Vacuum will flow to both the EGR valve and EGR diag switch. If the EGR diag switch does not see a vacuum signal, it won't close; and basically tells the computer that your EGR valve isn't activated.

This could be as simple as a cracked vacuum line in the EGR circuit. All the vacuum lines are easy to find. EGR will only activate when (A) the engine's warm, (B) the motor is at low RPM's, and (C) the car speed is high-- you're cruising down the highway. It makes EGR a bit more annoying to diagnose, since if the EGR system's bad, your computer won't tell you until you're cruising down the highway with light throttle.

If you need more, let me know! I typed up a code 34 chart a lonnnnnnng time ago, I'll put it up if you need it. It's not a hard chart at all; basically it has you check a bunch of points in the MAF wiring for correct voltages. It's meant to diagnose bad wiring, as opposed to a bad MAF.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
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