Intermittent Issues With 85 Gt

Discussion in 'Fox 5.0 Mustang Tech' started by Mike1970, Jul 2, 2013.

  1. Hello 5.0 guys and gals. I'm new to the forum and new to the mustang. I bought a 1985 GT with 94,000 on it. it's all stock exept for the rear gears (373) and a B&M shifter for the AOD trans.
    I bought the car from a 65 yr old man who had the car for 21 years. Great car and my favorite car as a teenage kid growing up.

    The problem the car has is. periodically the car stumbles and runs rough at part throttle. When this happens it feels as if the car is flooding it's self. I can floor the car and it kicks the trans down a gear and runs like normal. It will also idle normal. Then as soon as i take off again it stumbles at part throttle.

    The fix is to switch the ign key off, then back on (while driving) and problem solved. It might do it again the next time i drive it, or not again the next 5 times i drive it.

    No check eng light comes on. The car has a new tune up with car,rotor,wires. Has new fuel pump,pick up and sock, has new ign key. All done right before i bought it.

    Any suggestion would be greatly appreciated.

  2. Last tune up? Is it running rich?
  3. from the reciepts i have the last tune up was 3,000 miles ago. The car runs great until this happens. Just so happened on my way home again. It again idled fine, ran terrible at part throttle, floor the car ant it goes like normal. I can stop and the car idles normal. As soon as i take off (light throttle) all was good till 1000 rpm's. Runs bad as in it seems either out of fuel or way too much fuel. Floor the car and it's fine. The only way to fix the car is to shut the ign key off and back on. Fixes the problem everytime. I don't stop , just a quick off/on of the key and it's good to go.

    thanks for the help..
    I just got a manual and see there's a fuel regulator on the top of the efi ? i'm wondering if it's getting stuck and making the car rich at part throttle ? Just a guess though
  4. Is it still the cfi stuff or has it been swapped out for a proper carb? Because the cfi unit used on the 85 aod cars is problematic. Not hard to swap out though.
  5. still the stock cfi. I would gladly swap it out if i could keep my cruise control and the trans would still operate properly.
    would you have a link to the swap by chance ?

    thank you for helping.
  6. I don't have a link, but I did one once and needed a intake, carb, distributor , and regulator . I did a one wire hei dizzy. This was years ago.
  7. And a kick down table for the tranny and new throttle cable.

    Instant increase in power and it just drove better
  8. thanks for the info. i will start looking into it.

  9. Check your EGR valve for carbon build up. Clean it / replace if bad. I have an 1988 GT that had a stumble and after a full tune up did not fix the problem, I found my 60K EGR valve was caked with carbon. Problem solved with a good cleaning with carb cleaner.
  10. thanks roger. I found and fixed the problem. The pre cat o2 sensor was unplugged. I replaced it with a new one (after the connector melted on the exhaust) and no more rough part throttle issues and gas mileage has increased.
    thanks for all the help and suggestions