Hi All, just a quick question about the MAF sensor and the pin it uses on the ECU.

Looking at a diagram of the pin lay outs it lists B12 Dk Grn Maf Sensor Input 2.5v Key on 4.1v Run.

Well I went through all the points on the pins the other day and all come up what was listed bar this one! I could only get mv's out of it, and that's not to say that the meter was slightly jumping around when unplugged anyway.

So I went right up to the MAF and tested it there, and still nothing.

Funny thing is though, when I unplug the MAf it runs really bad, then smooths out when plugged back in again.

Is this normal? Or could this be a fault.

 

What year TPI? The '85s used a digital MAF, while '86-89 used an analog MAF. Using a voltmeter (even a true RMS) on a digital MAF is meaningless.

 

What was the original issue and code if any?

later
Jeremy

 

Hi, it's an 86, and there has always been a slight miss in the idle, along wiht if you let the car idel for awhile once hot it just stops.

 

"Just stop" as in the engine dies? I'd suspect a problem with the fuel delivery itself and not the MAF. The MAF measures air as an overall parameter for the entire engine, whereas rough idle or misfire is usually related to a problem in a single cylinder.

As for the MAF, pin B12 on the ECM should receive a 0-5VDC analog signal from the MAF (actually, 5-0V, but we don't want to get too confusing) while the MAF is connected and the engine is running. I've found through random testing that a 305 should present around a 750mV signal at a hot idle of about 900 RPM, and a 350 should present about a 800mV signal under the same conditions. That is with the MAF connected, engine running, and meter grounded at A11, D1, or any good chassis/ECM ground.

I have no idea what the whole "2.5V KOEO or 4.1V engine running" is about.

Backing up a step or two, are you even getting a MAF error code? If not, I think you need to move on and troubleshoot somewhere else.

 

Try ohming out the injectors. sounds like maybe one of them are shorting out causing the miss.