Engine Maf Wires Touched

Deleted member 215073 · Apr 2, 2017

What happens when the red and black MAF wires touch with power on? Like an idiot, I got in a hurry tried to start the car with the wires exposed. I was going to drive it to my work to fix the butchered wiring, and didn't make sure the wires were insulated enough for the short drive. I saw smoke come out from under the hood, and the engine won't idle or rev now without stumbling badly. No codes yet, just wondering if I smoked my computer, MAF, or anything else? I know I damaged some wiring near the MAF, but what else should I check?

jrichker · Apr 2, 2017

No code 11 (two flashes when the computer dumps the codes)? A perfectly functioning system will always get a code 11, it is the everything is OK code. The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.

Use the following Code 66 test path to troubleshoot MAF problems.

Code 66 or 157 MAF below minimum test voltage.

Revised 10-Feb-2014 to add 95-95 Mustang code 157 and 94-95 ECC diagram

Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

Computer connector for 88-93 5.0 Mustangs

Diagrams courtesy of Tmoss and Stang&2Birds

ECC Diagram for 88-90 5.0 Mustangs

ECC Diagram for 91-93 5.0 Mustangs

94-95 Diagram for 94-95 5.0 Mustangs

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables. Changes in RPM causes the airflow to increase or decrease, changing the voltage output.. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

89-90 Model cars: Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

91-95 Model cars: Measure the MAF output at pins C & D on the MAF connector light blue/red and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and pins A or B. Make your measurement with the MAF disconnected from the wiring harness.

Actually MAF pins C & D float with reference to ground. The signal output of the MAF is a differential amplifier setup. Pins C & D both carry the output signal, but one pin's output is inverted from the other. The difference in signal between C & D is what the computer's input circuit is looking for. The difference in the two outputs helps cancel out electrical noise generated by the ignition system and other components. Since the noise will be of the same polarity, wave shape and magnitude, the differential input of the computer electronically subtracts it from the signal. Then it passes the signal on to an Analog to Digital converter section inside the computer's CPU chip.

The following are diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs

Fuel, alternator, A/C and ignition wiring

Deleted member 215073 · Apr 2, 2017

My code scanner is at work, so are my multimeter and test light. I'll scan codes ASAP, and do the pin, component, wiring tests per the post above as well. I did pull the MAF, it's filthy. I also found a used MAF connector in good shape to replace and repair the wiring.

Deleted member 215073 · Apr 9, 2017

Replaced the melted hack job wiring at the MAF with a used in good condition MAF connector. Soldered the wires and used adhesive lined heat shrink (I hope that's the correct way to repair wiring). Car starts up, runs, and drives like it should. Let the engine warm up, no MAF codes. Only codes were for missing thermactor stuff and missing carbon canister vent valve (code 85). Carbon canister replacement is on the list, gas fumes are horrible. I did both KOEO and KOER tests with my Snap-On Solus scanner.

I did a resistance test on the MAF as outlined with the connector unplugged and key off.

jrichker said:
There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and pins A or B. Make your measurement with the MAF disconnected from the wiring harness.

Here are my results:

Red to Tan/Light Blue wire 6.68 megohms

Red to Dark Blue/Orange wire 6.68 megohms

Black to Dark Blue/Orange wire 3.87 kilo ohms

Black to Tan/Light Blue .7 ohms

I have 12 volts at the red wire when the key is on. Is the MAF sensor bad? The sensor was filthy, and I cleaned it with QD electronic parts cleaner.

jrichker · Apr 9, 2017

JMGlasgow said:
Replaced the melted hack job wiring at the MAF with a used in good condition MAF connector. Soldered the wires and used adhesive lined heat shrink (I hope that's the correct way to repair wiring). Car starts up, runs, and drives like it should. Let the engine warm up, no MAF codes. Only codes were for missing thermactor stuff and missing carbon canister vent valve (code 85). Carbon canister replacement is on the list, gas fumes are horrible. I did both KOEO and KOER tests with my Snap-On Solus scanner.

I did a resistance test on the MAF as outlined with the connector unplugged and key off.

Here are my results:

Red to Tan/Light Blue wire 6.68 megohms

Red to Dark Blue/Orange wire 6.68 megohms

Black to Dark Blue/Orange wire 3.87 kilo ohms

Black to Tan/Light Blue .7 ohms

I have 12 volts at the red wire when the key is on. Is the MAF sensor bad? The sensor was filthy, and I cleaned it with QD electronic parts cleaner.

Looks good, have a happy Mustang Spring

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