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Thread: Tip-in stumble...

  1. #1
    turbo addict Tony Hanna's Avatar
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    Tip-in stumble...

    ...only does it when it's cold though. Once it's up to operating temp, it either goes away completely or it's so slight that I'm not noticing it. Whatever's causing it, it seems to be more related to throttle position than rpms. It stumbles right off idle, but also I can be cruising along at 2k off the gas, start to give it some pedal, and it will stumble, recover, and run fine. Initially I thought the tps might have had a bad spot, but I swapped it out with a spare last night and it acts the same. I'm going to swap the map sensor with a spare today, and check the plugs, wires, and rotor. Hopefully one of these will solve it. I'd appreciate any suggestions on what else to check.
    Thanks,

  2. #2
    boostaholic
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    Re: Tip-in stumble...

    Too much fuel.

  3. #3
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    Good call. I'll check fuel pressure and look for signs of gas in the vac line on the reg too. The engine (and computer) was swapped in complete out of a wrecked but otherwise untouched '89 Lebaron, so the fuel system is basically untouched atm. If it's getting too much fuel, something has to have failed. The only thing I've done to it was to swap in a 2.2 TII rail, injector harness, and injectors since the injector harness that was on the engine had a bad connector that was causing a constant misfire unless you held it in exactly the right spot. That shouldn't have anything to do with it though as the 2.2 TII and 2.5 TI injectors are rated the same.
    Thanks,

  4. #4

    Re: Tip-in stumble...

    I had the same problem with my '83 SC back when it was running the 2.5 turbo engine.. Never did nail down the problem.

  5. #5
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    It's not really a big deal, it doesn't cause any major drivibility issues or anything, it's just more of an annoyance. I know something isn't quite right and it bugs me. Plus little annoying stuff like that, exhaust rattles, interior squeaks and rattles add up to the point where a car just isn't fun to drive anymore. I like to try to stay on top of that crap and fix it as I notice it. Hopefully I'll be able to track it down. Gonna go through the ignition system tonight and try to rule that out as a possible culprit.
    Thanks,

  6. #6
    Hybrid booster
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    Re: Tip-in stumble...

    Possibly a sticking TB.

  7. #7
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    Quote Originally Posted by unluckyty
    Possibly a sticking TB.
    Shouldn't be. When I swapped tps sensors, I actually swapped the entire throttlebody because I couldn't get the tps screws loose on the old tb.
    I cleaned the replacement tb up good and it's pretty smooth.

    To recap, so far I've tried tps, hep, cap, wires, and rotor. The plugs are recent, and the one I pulled looked good. The ignition stuff seemed to help a little, but the problem is still there. If I can find my fuel pressure guage and timing light I'll check fuel pressure and ignition timing next and then try a different coil and map sensor. If none of that gets it, I'm out of ideas.
    Any thoughts?
    Thanks,

  8. #8
    Hybrid booster
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    Re: Tip-in stumble...

    Tony, my 88 Daytona Shelby does the exact same thing as well. I have never been able to fix it. I have thought it was because of too much fuel when it is cold. My fuel system is stock though other than a Walbro 255 and AFPR. If you solve your problem, please post your solution. I am very interested.

  9. #9
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    If I ever manage to figure it out, I'll definately post what I find.
    If I had an adjustable fuel pressure regulator, I could test your theory about being too rich when cold by turning the fuel pressure down to see if the stumble would clear up.
    Thinking about this from the fueling point of view makes me wonder if the coolant temperature sensor might not be the problem. I wonder if the resistance vs. temperature can change with an older sensor? If a sensor problem was causing the computer to think the engine is colder than it really is, then it stands to reason that it would be overfueling. Anybody have a chart that tells what resistance a cts should be for a particular temperature? I guess there's another thing to add to my list of parts to throw at it.
    I'm glad I'm a packrat. This would be getting expensive if I didn't have spares of everything.

  10. #10
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    Re: Tip-in stumble...

    Ever figure it out Tony?

  11. #11
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    Sure didn't.
    It's been pretty chilly lately, so I've been letting it warm up for a few minutes before driving. Since it only happens when cold, I haven't noticed it lately and sort of forgot about it.
    It's started making some really scary bottom end noises on a cold start that I need to look into before anything else, but once that's taken care of, I'll eventually get back around to trying to sort out the stumble.

  12. #12
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    Re: Tip-in stumble...

    thanks for the update Tony. Do you run a custom cal?

  13. #13
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    I'm still running the stock '89 2.5 TI auto computer that was in the Lebaron that the engine came out of. I'll probably go to a custom cal eventually, but I don't have enough done yet to justify it. Still running a non-intercooled mitsu at close to stock boost for now. Everything else is on hold until I get this bottom end noise sorted out.

  14. #14
    Supporting Member Turbo Mopar Contributor iTurbo's Avatar
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    Re: Tip-in stumble...

    My Spirit R/T does this as well. Still haven't found the problem and the OTC says everything is fine and TPS output is very smooth and consistent. It stumbles only at very light throttle input and cruise. If I accelerate suddenly and let off the gas to resume cruising, it will buck and/or surge. Very annoying.
    87 Shelby Lancer #127
    91 Dodge Spirit R/T
    08 Dodge Caliber SRT-4
    86 Dodge Omni GLH Turbo

  15. #15
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    Quote Originally Posted by iTurbo View Post
    My Spirit R/T does this as well. Still haven't found the problem and the OTC says everything is fine and TPS output is very smooth and consistent. It stumbles only at very light throttle input and cruise. If I accelerate suddenly and let off the gas to resume cruising, it will buck and/or surge. Very annoying.
    Does it only do it when cold or all the time? Mine straightens out after it starts to warm up.

  16. #16
    Supporting Member Turbo Mopar Contributor iTurbo's Avatar
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    Re: Tip-in stumble...

    Mine does it all the time, but not quite as bad when it's warmed up. I have another stock TB I'm going to swap on just to see if it makes a difference.
    87 Shelby Lancer #127
    91 Dodge Spirit R/T
    08 Dodge Caliber SRT-4
    86 Dodge Omni GLH Turbo

  17. #17
    turbo addict Tony Hanna's Avatar
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    Re: Tip-in stumble...

    Hey ssheen,
    you said you have an afpr right?
    Would you care to try cutting back your fuel pressure a little at a time to see if it makes the stumble go away? Obviously try to stay out of boost while you're testing. definately don't want any engine damage due to lean out under boost. If that stops it, then the permanent solution would be as simple as pulling some fuel in whatever table the cal uses for cold run. I'm sure the guys that do their own cals would know how to go about it.

  18. #18
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    Re: Tip-in stumble...

    Hi Tony,

    Yes, I do have an AFPR. I will try that experiment. Now if I can only remember which way to turn it to lower.

    Update: I change a few things this week-end. Just tested it out today when I came home from the gym. -10C, which is cold enough for the problem to show. However, today it did not. I changed the HEP to a spare. Changed the coil to cap wire to a new one. Put the cam timing back to 1 degree advanced from 6-7 degrees. Suppose to get colder yet. Will see how it does tomorrow.
    Last edited by ssheen; 02-06-2007 at 05:05 PM.

  19. #19
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    Re: Tip-in stumble...

    My issue seemed to come to a head yesterday. It was ok cold, but after I turned it off and restarted it, it was not running well at all. I pulled a 22 and 47.

  20. #20
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    Re: Tip-in stumble...

    if the accelerator pump values are off in the cal it will do this...i know you are running a stock computer, but you never know...

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