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PKRWUD · 09-02-2001, 02:43 PM

You don't have any shorts to ground, but this still doesn't make any sense. Now, this is where it get's confusing. Let me try to explain. The resistance tests I asked you to do have ruled out the wiring being shorted to ground as a problem, which leaves only the ECM and/or the MAF as the problem. You should not be receiving any voltage between the C & D pins when the MAF is disconnected because the voltage signal goes TO the ECM through the D pin (the C pin is nothing more than a ground that is controlled by the ECM rather than being constant like the B pin is). Since those wires come straight from the ECM, and the MAF is disconnected when you are getting voltage there, that pretty much leaves the ECM as the fault. HOWEVER, I also had you test for a short in the ECM at those wires, and there wasn't one. BUT, you said earlier that there was positive voltage present at the C pin even when the ECM was disconnected. Seeing as the ECM is what the C pin goes to, that doesn't make any sense. The C pin circuit must be shorted to positive voltage somewhere.

PLEASE confirm this for me: KEY OFF, MAF disconnected, ECM connected, NEGATIVE DMM LEAD to NEGATIVE BATTERY POST. DMM set to DC Volts on the 20 scale. TURN KEY ON. POSITIVE DMM TEST LEAD to C PIN (while the neg. lead is still attached to the battery). Do you have ANY voltage at all? If so, TURN KEY OFF, AND DISCONNECT ECM, and check for voltage between the battery and the C pin again. If there is still voltage present, then there is voltage leaking into the C wire from somewhere. If their is no longer voltage, but there was before, then the ECM must be replaced.

I'm not done yet. You said: "I tested pins C & D while running(idling) and got anywhere from 9.2-11.4VDC". The voltage at idle shouldn't be more than 1 volt, and should never exceed 5 volts at WOT. This could be consistant with a voltage leak into the C wire circuit, but also could be a damaged ECM or even a bad MAF.

After you confirm whether or not the C pin has positive voltage going to it, and under what conditions (by following the instructions above), I want you to put everything back together again, except the harness to the MAF. Leave it disconnected. Start the car, and let it idle for exactly one minute. Turn the key off, and perform the KOEO self test again (pull codes). If a code 66 comes up, the MAF needs to be replaced.

That's enough for now. print a copy of this and take it with you. make sure you test everything EXACTLY the way I said to, and post the results.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

[This message has been edited by PKRWUD (edited 09-02-2001).]

09-02-2001, 02:43 PM	#7
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	You don't have any shorts to ground, but this still doesn't make any sense. Now, this is where it get's confusing. Let me try to explain. The resistance tests I asked you to do have ruled out the wiring being shorted to ground as a problem, which leaves only the ECM and/or the MAF as the problem. You should not be receiving any voltage between the C & D pins when the MAF is disconnected because the voltage signal goes TO the ECM through the D pin (the C pin is nothing more than a ground that is controlled by the ECM rather than being constant like the B pin is). Since those wires come straight from the ECM, and the MAF is disconnected when you are getting voltage there, that pretty much leaves the ECM as the fault. HOWEVER, I also had you test for a short in the ECM at those wires, and there wasn't one. BUT, you said earlier that there was positive voltage present at the C pin even when the ECM was disconnected. Seeing as the ECM is what the C pin goes to, that doesn't make any sense. The C pin circuit must be shorted to positive voltage somewhere. PLEASE confirm this for me: KEY OFF, MAF disconnected, ECM connected, NEGATIVE DMM LEAD to NEGATIVE BATTERY POST. DMM set to DC Volts on the 20 scale. TURN KEY ON. POSITIVE DMM TEST LEAD to C PIN (while the neg. lead is still attached to the battery). Do you have ANY voltage at all? If so, TURN KEY OFF, AND DISCONNECT ECM, and check for voltage between the battery and the C pin again. If there is still voltage present, then there is voltage leaking into the C wire from somewhere. If their is no longer voltage, but there was before, then the ECM must be replaced. I'm not done yet. You said: "I tested pins C & D while running(idling) and got anywhere from 9.2-11.4VDC". The voltage at idle shouldn't be more than 1 volt, and should never exceed 5 volts at WOT. This could be consistant with a voltage leak into the C wire circuit, but also could be a damaged ECM or even a bad MAF. After you confirm whether or not the C pin has positive voltage going to it, and under what conditions (by following the instructions above), I want you to put everything back together again, except the harness to the MAF. Leave it disconnected. Start the car, and let it idle for exactly one minute. Turn the key off, and perform the KOEO self test again (pull codes). If a code 66 comes up, the MAF needs to be replaced. That's enough for now. print a copy of this and take it with you. make sure you test everything EXACTLY the way I said to, and post the results. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!! [This message has been edited by PKRWUD (edited 09-02-2001).]