Need Help With Code 66 Test Results

jraap82

Active User
Aug 29, 2016
50
5
18
I finally cleared code 67 on my 89 Mustang GT and was able to progress to the KOER test and got codes 66 and 98. After some research on here I found the following testing procedures posted by another member. I put my results of the tests next to them, and I think it's clear what the problem is. Now I'm wondering what this means and what my next step should be? Is it a bad MAF sensor? bad wiring? bad computer? Also, in case it makes a difference, I used a sensor from a 1994 mustang to go with a 70mm MAF from a thunderbird. Any information is much appreciated.

Results:

Code 66 MAF below minimum test voltage.
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. 12.16 volts

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). Just cleaned a couple weeks ago prior to install and re-cleaned today to be safe.

Changes in RPM causes the airflow to increase or decease, 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. 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.

At idle = approximately .6 volt .010-.012 volt measured at pins C & D on the MAF connector (FAIL)
20 MPH = approximately 1.10 volt can't measure these at the moment, car is on jack stands
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. D & 50 = .1 ohms / C & 9 = .2 ohms

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and ground. Make your measurement with the MAF disconnected from the wiring harness. C & ground = 29K / D & ground = 100K
 
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FYI: The text you posted is from one of my test paths.

The resistance readings are OK. The voltage ids low, and that's why you got the 66 code.

If you want to check the voltage while you are actually driving the car, use pin 50 on the computer (dark blue/orange wire) and pin 9 on the computer (tan/light blue wire)


a9x-series-computer-connector-wire-side-view-gif.71316.gif


eec-iv-computer-connector-for-5-0-mustang-gif.88243.gif



Here's a replacement suggestion if you are using the stock MAF and housing.;

Swapping the MAF sensors between different MAFs is a big no no. The MAF body and sensor are designed to match each other. Therefore you can't swap sensors between different part number MAF bodies and maintain proper calibration. The assembly is designed to match the computer’s internal program, and swapping a different MAF can upset the computer's calibration.

The OEM Ford MAFs are not calibrated to injector size. The injector sizing is done in the computer’s internal programming. Aftermarket MAF’s “lie” to the computer in an attempt to fool the computer into changing the injector pulse on timing to match the increased airflow.

The exception to the above statements is if you have an aftermarket tuner system such as Moates Quarterhorse, Tweecer, or similar device. Then you can alter the computer's MAF transfer function table to match whatever MAF housing and sensor you have. The tuner device works in conjunction with a high quality Air/Fuel ratio meter so that you can tell what sort of air/fuel mixture you have a any given time.

The only other MAF that is a one for one swap for a 93 and earlier 5.0 Mustang is the 94-95 Mustang MAF.

94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

Once your replacement 70MM MAF is in place, disconnect the battery for about 10 minutes. When you reconnect the battery and start the engine, the computer will relearn the settings for the new MAF.

*1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.
 
FYI: The text you posted is from one of my test paths.

The resistance readings are OK. The voltage ids low, and that's why you got the 66 code.

If you want to check the voltage while you are actually driving the car, use pin 50 on the computer (dark blue/orange wire) and pin 9 on the computer (tan/light blue wire)


a9x-series-computer-connector-wire-side-view-gif.71316.gif


eec-iv-computer-connector-for-5-0-mustang-gif.88243.gif



Here's a replacement suggestion if you are using the stock MAF and housing.;

Swapping the MAF sensors between different MAFs is a big no no. The MAF body and sensor are designed to match each other. Therefore you can't swap sensors between different part number MAF bodies and maintain proper calibration. The assembly is designed to match the computer’s internal program, and swapping a different MAF can upset the computer's calibration.

The OEM Ford MAFs are not calibrated to injector size. The injector sizing is done in the computer’s internal programming. Aftermarket MAF’s “lie” to the computer in an attempt to fool the computer into changing the injector pulse on timing to match the increased airflow.

The exception to the above statements is if you have an aftermarket tuner system such as Moates Quarterhorse, Tweecer, or similar device. Then you can alter the computer's MAF transfer function table to match whatever MAF housing and sensor you have. The tuner device works in conjunction with a high quality Air/Fuel ratio meter so that you can tell what sort of air/fuel mixture you have a any given time.

The only other MAF that is a one for one swap for a 93 and earlier 5.0 Mustang is the 94-95 Mustang MAF.

94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

Once your replacement 70MM MAF is in place, disconnect the battery for about 10 minutes. When you reconnect the battery and start the engine, the computer will relearn the settings for the new MAF.

*1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

Thank you for the great info! Also, I seen the test path in a few different posts so I wasn't sure who it originated from or I would've gave you a shout out for it. Everything you're saying makes sense to me now about the sensor being calibrated for the type of housing it was designed for. I had seen on the 4 eye forum that a 90's thunderbird/cougar housing was a 70mm like the 93 cobra and would work with the sensor from a 94 95 mustang so that's what I went with. Now, to make sure I'm tracking correctly, if I use the 70mm housing like the 93 cobra I need a 93 cobra sensor? And if I use the 94 sensor, I need the 94 housing with flange? Then, in theory, everything should work correctly and code 66 should go away....key word should lol. Also, I seen a few different threads where reclocking the MAF does the trick to fix this issue, do you have any input on that? Thanks again for the info, this is me and my son's first engine rebuild so it is helping out a ton!

-Joe
 
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Use the MAF body & MAF sensor from the list that I posted.. I will not promise you that anything else made by Ford will work.
 
Use the MAF body & MAF sensor from the list that I posted.. I will not promise you that anything else made by Ford will work.

Ok, will do. I have the sensor already so I'll go ahead and get the body for it. I'll post back on here if it helps with the issue once we get it installed. Thanks for your time and information.

-Joe
 
Use the MAF body & MAF sensor from the list that I posted.. I will not promise you that anything else made by Ford will work.

Finally got the MAF body and adapter in the mail the other day and got it installed today....runs like a champ now! It took care of the codes and the minor hunting for idle it had going on. Was finally able to let the car run for a while for the first time since the engine rebuild and found a small coolant leak at the front where the covers meet the block and another one inside by the heater core area. Those should be easy enough to take care of though. I greatly appreciate the help on this issue!

-Joe
 
Finally got the MAF body and adapter in the mail the other day and got it installed today....runs like a champ now! It took care of the codes and the minor hunting for idle it had going on. Was finally able to let the car run for a while for the first time since the engine rebuild and found a small coolant leak at the front where the covers meet the block and another one inside by the heater core area. Those should be easy enough to take care of though. I greatly appreciate the help on this issue!

-Joe
Glad to hear that you got it fixed. Spring is coming, enjoy your ride!