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  1. #1
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    Default Heat Soak Misfire

    Ive been trying to tackle this issue for a while and cant seem to get anywhere. Im chasing my own tail here and have dumped too much money into it. My 96 xj sport 4.0 runs great...until it sits and idles (drive thru, traffic, etc). It idles fine for a while but when it gets hot in the engine bay the idle gets rougher as time goes on. I checked the codes and i have random misfires and a misfire on cylinder 2 (p0302). Its definitely due to heat in the engine bay. Earlier my lower hose decided to crack and leak and i got my temperature light but it idle fine. It rides like a champ without coolant so its definitely to do with heat gathering in he engine bay. I was recommended to heat sheilding the fuel line, but that did nothing. Please please please help! Im about to give up and sell this thing


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  2. #2
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    Default Re: Heat Soak Misfire

    How did you heat shield it. You can also vent the hood
    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
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    30 gal gas tank
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    And a bunch of other stuff

  3. #3
    Join Date
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    Default Re: Heat Soak Misfire

    I know the 99+ have a heat shield from the factory on the IM, under the fuel rail, to help with heat soak... might be an option to look at, if it is due to fuel system heating up too much... I actually got a misfire code for cyl#1.. I think it was due to a loose wire/connection though, because it was right after I got done spraying down the engine bay to get rid of excess mud (wish I had done this before the oil change)... but yeah... another thing you could do is take a look around the injectors, and make sure doesn't look like any leakage.. as 1 it's a fire hazard, and 2 might allow the fuel to heat up easier.. especially as things start to expand at different rates due to the added heat of sitting still.. Another possible way to try and block heat from the intake/fuel rail area.. is to run a sheet of heat guard on the bottom of the intake manifold, to create an insulate barrier above the exhaust manifold..
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  4. #4
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    Default Re: Heat Soak Misfire

    Quote Originally Posted by bluedragon436 View Post
    I know the 99+ have a heat shield from the factory on the IM, under the fuel rail, to help with heat soak... might be an option to look at, if it is due to fuel system heating up too much... I actually got a misfire code for cyl#1.. I think it was due to a loose wire/connection though, because it was right after I got done spraying down the engine bay to get rid of excess mud (wish I had done this before the oil change)... but yeah... another thing you could do is take a look around the injectors, and make sure doesn't look like any leakage.. as 1 it's a fire hazard, and 2 might allow the fuel to heat up easier.. especially as things start to expand at different rates due to the added heat of sitting still.. Another possible way to try and block heat from the intake/fuel rail area.. is to run a sheet of heat guard on the bottom of the intake manifold, to create an insulate barrier above the exhaust manifold..


    I heat shielded it very inadequately looking back at it. I bought heat wrap and thinly wrapped the actual rail. I saw a kit online that has everything for 50 bucks that takes 20 minutes. Ill post how it ends up working. Im like 99% sure its vapor lock due to the heat. But then again right when i think i find out what it is, its not. We'll see. Ill add updates


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  5. #5
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    Default Re: Heat Soak Misfire

    Quote Originally Posted by 4.3LXJ View Post
    How did you heat shield it. You can also vent the hood


    Just a thin layer of heat wrap. Not very thorough. I do have the hood propped up. I used polymer blocks to prop the hood up. And i did install a hefty radiator. Tri core with 3 efans hooked up to the thermostat. But i think that fuel line gets too hot. I saw a complete kit online for 50 bucks


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  6. #6
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    Default Re: Heat Soak Misfire

    Bought the heat sheilding kit that came with a shield for the manifold, the fuel rail, and each injector. Seems to be working. But i live in Phoenix and its only in the 90's right now. Well see once it hits 110+. Thanks to all


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