The Wiring Problem, Part 2

[dvmotorsports]

So some of you remember the 3rd cylinder misfire I had about two weeks ago on a buddies car. Well I rewired the engine with another harness. Bingo. Misfire gone. But now I have a AFM fault. I swapped out with two other units with no luck.

So again, here we are with another wiring issue.

Your thoughts? Recommended testing procedures?

[jscribble]

ACK! This is no good. I have no helpful info on this order, but DesktopDave is going to be here soon to save the day.

[zmannz803]

JUst run yourself a new set of wires from the afm to the computer. You can pull the one from the bad harness.

[DesktopDave]

I'd just run the usual continuity test and a resistance test.  I'll bet that AFM runs some odd low-level 5VDC signal at very low wattage or something like that.

I had an AFM issue on mine too, removing the resistor pack fixed that problem.  There was water in the connector as well.  Enough wrong to throw a 1215 code.  No CEL though, I had to do a stomp test.

[dvmotorsports]

Do you know where I can find the target values?

[dvmotorsports]

Okay, so I measured everything out and compared them to an operable vehicle.

The results

Pin 1 - 5v Ref
Pin 2 - AFM Signal
Pin 3 - Not in use for vehicles with cat conv.
Pin 4 - Intake Air Temp Signal (Resistance Varies with Temp)
Pin 5 - Sensor Ground 0.1 MAX

The Bad Car
Vehicle Voltage On/Off (AFM Connector to Ground)
P1 5.01/5.00
P2 0.26/0.26 (4.62 WOT)
P3 2.50/2.50 (Not Used)
P4 2.88/2.85 (Irrelevant)
P5 0.01/0.01

The Good Car
P1 5.03/5.34
P2 1.2-1.3/0.20 (4.69 WOT)
P3 2.50/0.01 (Not Used)
P4 3.11/5.02 (Irrelevant)
P5 0.02/0.01

So, the issue is obvious. The values on pin #2 are .06 different with the car on and not running and 0.07 at WOT. The problem lies at idle (which is when the bad car cuts out). Clearly the variation is 0.94-1.04 and thus we have found the problem.

Now here is my question...WHY? I have swapped DME's and no luck. Could it be a broken wire or arcing somewhere?

[jscribble]

Broken wire is unlikely. That low of a voltage discrepancy is likely due to added resistance somewhere. Corrosion, or possibly a bad ground? How does the inside of the dme look? cold solder joints, corrosion, or a poorly seated chip might play some wierd havoc. One of my favorite tools is my fiberglass pen, mcmelectronics.com has them for cleaning contacts and boards. My guess is that .06 volts is within spec, but I don't know enough about the afm or dme to be more helpful.

[dvmotorsports]

I'm sure the variance of 0.06 and 0.07 volts are fine. I just can't figure out why the vehicle is not at or over 1.00 volts at idle. I don't want to blame the DME as I have changed it out. And if corrosion is the issue, I would think there would be a voltage discrepancy throughout the voltage range not just at idle. Although I could be wrong about that. I have the same feeling I just mentioned about the ground. Why would it only be a problem at idle. I'm lost. I'm going to be a damn expert by the time all of these wiring issues are worked out though. LOL.

[dvmotorsports]

BTW can a mod move this to electrical? I just realized I started the thread in the wrong section.

[DesktopDave]

Wish granted.  I'm baffled as to the rest.  0.1 VDC doesn't seem like enough to cause the behavior.

[longtallsally]

This is kinda cool.

I'm kinda with DJ scribble that it could be resistance oriented.

However- and perhaps I'm being a bit rudimentary- but I guess I'm going back to big picture.  It is the A FM.  In other words, it is measuring air.  In other words, perhaps it is not getting a signal from the meter itself.  That tells me that the meter may not be bad, but just dirty.

You sparked me to do some searching.  Give me a few minutes here and I'll post some pics from one of the electronic manuals I've got that may give you some guidance...

EDIT:  Here you go.  I think if you read this, it could help.  So where I'm going with that is check #2 on the right- the resistance for the AFM sensor- and see if you are good there.

[dvmotorsports]

Wish granted.  I'm baffled as to the rest.  0.1 VDC doesn't seem like enough to cause the behavior.

I think you are looking at the wrong vehicle specs. The variance of 0.1 is found in my car at idle (which is fine). His is 0.26 with ignition on, car off. And at idle.

This is kinda cool.

EDIT:  Here you go.  I think if you read this, it could help.  So where I'm going with that is check #2 on the right- the resistance for the AFM sensor- and see if you are good there.

I ran that test on several AFM units and I think it is some sort of error. All the units had the same resistance values when the door was moved. The number stayed solid, no variation in resistance at all. It seems odd to me, but they can't all be bad AFM units.

[longtallsally]

Are you doing it correctly?  Not being a smart alec, just wondering.  Did you do the test on your correctly functioning car?

[dvmotorsports]

I did it right. And I know you aren't being a jerk. I questioned myself too.

I think there might be a massive vac leak at the ICV that I was unable to see.

[DesktopDave]

I think you are looking at the wrong vehicle specs. The variance of 0.1 is found in my car at idle (which is fine). His is 0.26 with ignition on, car off. And at idle.



I ran that test on several AFM units and I think it is some sort of error. All the units had the same resistance values when the door was moved. The number stayed solid, no variation in resistance at all. It seems odd to me, but they can't all be bad AFM units.

You're right...they can't all be bad, and I'm sure that number should change.  I'll have to dig out the old manual & take a look.

Just tested mine.  Pins 1 & 2 range from ~500 ohms with the door closed to ~800 ohms with the door mostly open (I couldn't open it all the way out of the car like that).   Pop the lid and check the arm, brush or resistor circuit for malfunction.  These two sensors (AFM and IAT) have a floating ground.