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PKRWUD · 09-02-2001, 10:02 PM

I really don't know what to tell you then. The D pin is the wire that the MAF uses to send it's info to the ECM. The A pin is battery voltage that the ECM applies to the MAF when the ignition is turned on. This same wire is also spliced into the IAB Solenoid, the EGR Vacuum Regulator, the Canister purge Solenoid, both Air Management Solenoids, the WAC relay, the EEC relay, the Fuel Pump relay, and each of your injectors. This gives the ECM control over applying voltage to all of them only when the ignition is on. The B pin is goes directly to a junction between the negative battery post and the ground supply wire for the ECM. The C & D pins are used to send a specific signal to the ECM. basically, one is positive and one is negative, WHEN IN USE. The D pin sends the MAF signal, a positive voltage signal, to the ECM. The amount of volts sent are proportional to the amount of air entering the engine and the load the engine has on it. However, in order for any electrical signal to be sent, there has to be a complete circuit, which means there has to be a ground wire for the for the signal to return to the MAF on (a ground wire). While the MAF and ECM could function using the ground wire supplied with the MAF power wire, the engineers at Ford felt that that ground signal was too subject to fluctuation based on other possible loads (ie: turning your headlights on or playing the stereo. So they designed the ECM to regulate a ground wire that would always be at a constant, and used it to return the signal to the MAF (complete the circuit by grounding it). The C & D pins are not supposed to ever see much more than 5 volts at any time, while the A & B pins recieve battery voltage. That is why I am concerned that you read battery voltage at the C & D pins at idle.

When you reinstall the MAF, clear all codes and see what happens. If it sets any new codes, we can go from there. For future reference, next time you get a code 56, do what I said before: unplug the MAF, idle it for 1 minute, and then check for KOEO codes. If the MAF is bad, you'll get a code 66.

You should unplug the MAF connector on your friends car and see if he has voltage to the C pin.

Try this for me. Hook up everything but the MAF. attach the alligator clip end of a 12 volt test light to the C pin (use a paper clip if necessary). Turn the key on. Now touch the other end of the test lamp to the engine block. Does the lamp light up at all?

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, 10:02 PM	#9
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	I really don't know what to tell you then. The D pin is the wire that the MAF uses to send it's info to the ECM. The A pin is battery voltage that the ECM applies to the MAF when the ignition is turned on. This same wire is also spliced into the IAB Solenoid, the EGR Vacuum Regulator, the Canister purge Solenoid, both Air Management Solenoids, the WAC relay, the EEC relay, the Fuel Pump relay, and each of your injectors. This gives the ECM control over applying voltage to all of them only when the ignition is on. The B pin is goes directly to a junction between the negative battery post and the ground supply wire for the ECM. The C & D pins are used to send a specific signal to the ECM. basically, one is positive and one is negative, WHEN IN USE. The D pin sends the MAF signal, a positive voltage signal, to the ECM. The amount of volts sent are proportional to the amount of air entering the engine and the load the engine has on it. However, in order for any electrical signal to be sent, there has to be a complete circuit, which means there has to be a ground wire for the for the signal to return to the MAF on (a ground wire). While the MAF and ECM could function using the ground wire supplied with the MAF power wire, the engineers at Ford felt that that ground signal was too subject to fluctuation based on other possible loads (ie: turning your headlights on or playing the stereo. So they designed the ECM to regulate a ground wire that would always be at a constant, and used it to return the signal to the MAF (complete the circuit by grounding it). The C & D pins are not supposed to ever see much more than 5 volts at any time, while the A & B pins recieve battery voltage. That is why I am concerned that you read battery voltage at the C & D pins at idle. When you reinstall the MAF, clear all codes and see what happens. If it sets any new codes, we can go from there. For future reference, next time you get a code 56, do what I said before: unplug the MAF, idle it for 1 minute, and then check for KOEO codes. If the MAF is bad, you'll get a code 66. You should unplug the MAF connector on your friends car and see if he has voltage to the C pin. Try this for me. Hook up everything but the MAF. attach the alligator clip end of a 12 volt test light to the C pin (use a paper clip if necessary). Turn the key on. Now touch the other end of the test lamp to the engine block. Does the lamp light up at all? 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).]