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Thread: runs good at idle but not while driving

  1. #1
    Join Date
    Feb 2008
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    Default runs good at idle but not while driving

    I have a 1978 dodge magnum with a 400ci engine that runs good while at idle but if you go to drive it act like it has no power and only gets worse the faster you try to go. I've done the timing just like the Manuel said to and still i can not fix the problem. I thank you very much.

  2. #2
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    Jan 2007
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    Matthew27 - Not much to go on. Here the best guess, that early spark control system causes all sorts of problems including what you described and next would be the fuel system.
    Good luck.

  3. #3
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    Feb 2008
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    Sorry just kind of new at this whole thing. i know enough about engines to do the more simpler things, not things involving the inner workings. a guess your talking about the spark control computer. some one tried to tell me that it may not be advancing. i didn't know if maybe the computer was bad. i can try to explain it little bit better. at an idle the engine sounds fine but when you go to give it some gas it acts like it is missing. it almost felles as if the engine is going to fall apart. there is a rattling noise but not like a rod or any thing like that. i didn't know if there is a manual that is more for just my car or for the motor that i have. the Haynes manual is a great help and all but the one i have seams to be for for Plymouth and Chrysler then for mine, the manual is 30050. the car did sit for over a year and a half. the other thing is that you can tell that whoever had the car last know less then i do. the spark plugs where not even gaped. just straigh out or the box. just would like to do myself to learn more. afread to take to any one else because i think they will try to replace things that don't need to be. i don't have a whole lot of money to play with.

  4. #4
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    Mathew27 - Hook up a timing light to your engine. See what it does at idle the reading should be steady. Raise the rpm slowly and look for the timing to advance the smoothly and not bounce around. Try a few quick hits on the accelerator pedal. Timing should respond quickly and smoothly if not it may be the spark control computer.
    If it has sat for over a year you may want to replace the fuel in the tank and the filter.

  5. #5
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    Feb 2008
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    thanks. is there a certain type of timing light i should use or is there one just for what you are talking about. once again thanks for the help.

  6. #6
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    Jan 2007
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    No you just need to see the timing mark. There are all types just pick one that you can get into a good position to see.

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