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  1. #1

    Default Part-throttle surging, slight backfire, ticking

    Any ideas where I should start? I'm thinking I'm getting a backfire every now and then when I let off the throttle in gear. Slight surge at part throttle and some ticking at idle/low rpm. Some hesitation when I hit the gas.
    This is a mostly stock 85 GT.

  2. #2
    FEP Super Member erratic50's Avatar
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    Fuel pump. Check your fuel pressure or if it's old as hell get a new one.

    Plugged fuel filter sometimes show these symptoms too but then it will seem to run out of gas when you get on it.

  3. #3

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    Quote Originally Posted by HurricaneJesus View Post
    Any ideas where I should start? I'm thinking I'm getting a backfire every now and then when I let off the throttle in gear. Slight surge at part throttle and some ticking at idle/low rpm. Some hesitation when I hit the gas.
    This is a mostly stock 85 GT.
    Funny that you bring this up. My 85 M code GT has been doing pretty much the same thing for years.
    A bad low speed surge in 1st & 2nd, it would also fall flat on its face if you tried to pull away from a stop too quickly and had a slight miss at idle and it would idle better with a slight load on it such as using the AC. A few days ago I was cleaning out some old parts from the shelves and discovered the OEM vacuum advance canister and remember that it had been changed out about 10 years ago and it got me to thinking that's also about when these symptoms showed up. Started to do some research on distributer vacuum units and found out that replacement units are adjustable so I checked mine and found that the screw was turned all the way (clockwise) against the stop. After taking a few test drives after each counter clockwise turn of the screw I was able to eliminate just about of my problems.
    So if your distributer vacuum unit was changed you should try adjusting it. All it took was a 3/32" allen wrench, super simple. Good luck.

  4. #4
    FEP Super Member erratic50's Avatar
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    Wow!

    Btw - are the 86 and up advance setups adjustable on the dizzy also? seems to me I lost some power seat of the pants when I had to swap mine out even though the base timing is exactly the same. Replacement went in back when it was a daily so it came from a Mcparts joint and was dropped in on a windy night outside when it was about -20 F outside.
    Last edited by erratic50; 06-03-2017 at 08:01 PM.

  5. #5

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    no the advance on an 86 is controlled by the computer...just curious you did remember to put the spout connector back in correct? Otherwise you'd be stuck at whatever your base timing is set at.

  6. #6

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    I'll give the fuel filter a shot after work today and see if that helps. Maybe run some fuel system cleaner through it. Any suggestions on that front?

  7. #7

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    Float levels? Idle mixture settings? Accelerator pump arm adjustment?...
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  8. #8
    FEP Super Member erratic50's Avatar
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    Sorry to hijack the thread on the 86 dizzy side conversation. That's what I thought but I was curious so I asked.

  9. #9

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    Quote Originally Posted by erratic50 View Post
    Sorry to hijack the thread on the 86 dizzy side conversation. That's what I thought but I was curious so I asked.
    No worries, man. Hijack away.
    I swapped out the fuel filter and it seems to be idling/revving better. Couldn't take it for a drive because the rain was pretty gnarly and my weatherstripping is not so great...

  10. #10

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    So I think it was a vacuum leak. The PO seems to have plugged a few cut hoses with screws. One must have popped out the other day when she was running hot because that's when the problem started. I put a bigger screw in there and drove up the road and the surging/backfiring is gone. Gonna find a more elegant solution tomorrow.
    Thanks for the help, fellas. I'm in way over my head but I make up for it with creative use of curse words.

  11. #11

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    Quote Originally Posted by JacksAO View Post
    Funny that you bring this up. My 85 M code GT has been doing pretty much the same thing for years.
    A bad low speed surge in 1st & 2nd, it would also fall flat on its face if you tried to pull away from a stop too quickly and had a slight miss at idle and it would idle better with a slight load on it such as using the AC. A few days ago I was cleaning out some old parts from the shelves and discovered the OEM vacuum advance canister and remember that it had been changed out about 10 years ago and it got me to thinking that's also about when these symptoms showed up. Started to do some research on distributer vacuum units and found out that replacement units are adjustable so I checked mine and found that the screw was turned all the way (clockwise) against the stop. After taking a few test drives after each counter clockwise turn of the screw I was able to eliminate just about of my problems.
    So if your distributer vacuum unit was changed you should try adjusting it. All it took was a 3/32" allen wrench, super simple. Good luck.
    So the problem came back recently minus the backfiring and histrionics. Just a stumble at 2k RPMs. I just backed out that screw one turn. Will report back shortly.

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