Electrical How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs


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Mar 10, 2000
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@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it...

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.



If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.[/B]

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.


The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader 3145.
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
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Adding some useful info. Copied/pasted from another forum. Credit to Joel5.0

These are the following codes which will display a check engine light on the 86-93 Mustang. They will display the CEL if the condition is present, but will turn off the CEL if the condition is cleared

ACT54, 64
ECT51, 61
MAF26, 56, 66
TPS23, 53, 63
EVP31, 32, 34, 35
HEGO(1)41, 91, 42, 92
(1) Based on a "lean-rich" switching counter timer function.

Also, key to know is that when a key sensor is found to be in fault, the ECU will default to a Failure Stratgy to compensate

The Failure Mode (FMEM) strategy protects vehicle function from adverse effects of an EEC component failure. The strategy recognizes open or short circuit failure for six sensors: MAF, TP, ECT, ACT EVP/EPT, and BP. In general, if the continuous Self-Test strategy recognizes a failure the FMEM strategy will execute an alternative vehicle strategy. The alternative strategy disables logic which relies on realistic sensor values. Some sensor FMEM strategies also substitute a "safe" value for the bad sensor

What does that mean? Well this chart shows what changes if a disabled sensor is detected


NOTE: decel fuel cutoff is only enabled on 1993 cobra ECU. All other 86-93 mustang ECUs lack this programming.
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