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  1. #1

    Default Check engine light - EEC codes

    Bone stock 1992 Mustang, check engine light intermittent, mainly on with foot on the gas, light accel or cruise, off when coasting with foot off the gas. Three codes came up, 31, 91, and 95. Replaced O2 sensors, code 91 went away. Just 31 and 95 left. The scanner book and different online sources have conflicting information about the 95, with either a Fuel pump circuit problem or thermactor air diverter circuit problem, while 31 says canister or EGR valve control system. Neither gives much insight as to what might be the bad part. The car does have a fuel pump cutoff switch for an anti-theft measure, but the fuel pump runs fine and the car operates normally.

    So far, I've replaced the EGR valve, EGR position sensor, and EGR vacuum solenoid with known good, low mile takeoff parts from my stash - no changes in that 31 code.

    Thanks for any ideas!

  2. #2

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    In getting your codes, depending whether KOEO/KOER/CM, code 31 means:
    KOEO or KOER - EVP (EGR valve position sensor) or PFE (pressure feedback EGR sensor) circuit out of range. Known good... test it/them
    CM (continuous memory) - EVP or PFE circuit below minimum voltage or intermittent... test it/them

    Depending whether KOEO/KOER/CM, code 95 means:
    KOEO - Fuel pump secondary circuit failure
    KOER - Secondary air not diverting
    CM - Fuel pump ground bad or circuit failure (fuel pump monitor signal)

    (Info from Probst book)
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  3. #3

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    The fuel pump code doesn't effect the way the car runs, just a fyi. The cougarbirds dont have this wire ran in the factory setup and it causes no issues with a h.o. Computer installed, other then the code popping up.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  4. #4

    Default

    Fixed. I'll give a complete rundown here, since this code 31 on a Fox Mustang seems to be a popular Google search, as well as in the F-150/Bronco community, so maybe this will help others in the future.

    The Sunpro scanner book says Code 31 - EGR valve position (EVP) sensor or pressure feedback EGR (PFE) sensor - signal voltage is below minimum specification or EGR vacuum regulator (EVR) solenoid circuit problems.

    I took a suggestion from another board and pulled the 10 pin connectors apart, (salt and pepper plugs on the back center of the intake) cleaned them up with electronic cleaner spray, and applied dielectric grease to all pins before plugging them back in. Test drive: No changes. Next, check the resistance range of the EPS. Removed it from the EGR valve and probed the connections. Around 0-4 ohms throughout the pin travel, linear action. Tested another one I have, identical readings, no problem there. Next, check EVP voltage, key on: 4.5 volts - in range. Next, check EGR vacuum from the vacuum regulator solenoid, engine running. You are not supposed to feel any vacuum at idle, but I did - a little. I learned of a foam filter in these units from a Bronco site, they get dirty and plugged. I pried the cap off the top and pulled the filter out. It was packed with dirt and just about solid, so I soaked it in water and dish soap, cleaned it up, rinsed and dried it. I also blew the dust out of the unit with compressed air, and hit it with a shop vac for good measure.

    I also had to replace three plastic vacuum hoses on the tree, because they get brittle with age and all split when I unplugged the tree including two right at the rubber. Had to drill them out. Fortunately, I have a pile of these hoses from boneyard Tauruses and such, so I was able to get it all back together and looking decent - albeit with a few different color hoses.

    Test drive with the cleaned vacuum solenoid filter - no CEL. None. I now have two days and four errand cycles on it, no CEL. Seems it's fixed. The plugged filter didn't allow the diaphragm to move enough to supply vacuum to the EGR valve, and the EVP reported insufficient movement to the EEC and lit the CEL. It would also explain the foot on/foot off gas CEL on/off. So while the code didn't tell exactly what to look for, it did provide an area to look in.

  5. #5
    FEP Senior Member
    Join Date
    May 2011
    Location
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    Thanks a lot for the detailed explanation, I have the exact same problem on my "new" 89 Mustang 5.0, whenever I accelerate the check engine light turns on, when iddle it turns off. IŽll do exactly what you describe and clean up everything

  6. #6
    FEP Senior Member
    Join Date
    May 2011
    Location
    Mexico City
    Posts
    582

    Default

    Quote Originally Posted by Maindrian Pace View Post
    Fixed. I'll give a complete rundown here, since this code 31 on a Fox Mustang seems to be a popular Google search, as well as in the F-150/Bronco community, so maybe this will help others in the future.

    The Sunpro scanner book says Code 31 - EGR valve position (EVP) sensor or pressure feedback EGR (PFE) sensor - signal voltage is below minimum specification or EGR vacuum regulator (EVR) solenoid circuit problems.

    I took a suggestion from another board and pulled the 10 pin connectors apart, (salt and pepper plugs on the back center of the intake) cleaned them up with electronic cleaner spray, and applied dielectric grease to all pins before plugging them back in. Test drive: No changes. Next, check the resistance range of the EPS. Removed it from the EGR valve and probed the connections. Around 0-4 ohms throughout the pin travel, linear action. Tested another one I have, identical readings, no problem there. Next, check EVP voltage, key on: 4.5 volts - in range. Next, check EGR vacuum from the vacuum regulator solenoid, engine running. You are not supposed to feel any vacuum at idle, but I did - a little. I learned of a foam filter in these units from a Bronco site, they get dirty and plugged. I pried the cap off the top and pulled the filter out. It was packed with dirt and just about solid, so I soaked it in water and dish soap, cleaned it up, rinsed and dried it. I also blew the dust out of the unit with compressed air, and hit it with a shop vac for good measure.

    I also had to replace three plastic vacuum hoses on the tree, because they get brittle with age and all split when I unplugged the tree including two right at the rubber. Had to drill them out. Fortunately, I have a pile of these hoses from boneyard Tauruses and such, so I was able to get it all back together and looking decent - albeit with a few different color hoses.

    Test drive with the cleaned vacuum solenoid filter - no CEL. None. I now have two days and four errand cycles on it, no CEL. Seems it's fixed. The plugged filter didn't allow the diaphragm to move enough to supply vacuum to the EGR valve, and the EVP reported insufficient movement to the EEC and lit the CEL. It would also explain the foot on/foot off gas CEL on/off. So while the code didn't tell exactly what to look for, it did provide an area to look in.
    I got a new EGR (original motorcraft), as well as the EGR control module, but now I need the vacuum hoses because they were so brittle they broke. They have a hard plastic line inside. Any idea where I can buy a replacement hose?

  7. #7

    Default

    I usually just get small vacuum line from the parts store and replace it, using the old connectors with the brittle line inside.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

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