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Thread: Signs of a bad intake manifold gasket?

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    Banned? CMC Boss460 mark95turbo's Avatar
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    Default Signs of a bad intake manifold gasket?

    What are the signs of a bad intake manifold gasket? When I start my car it jumps straight to 4k rpm and backfires. It just has the startup tune so I know it's gonna run like crap but I noticed my boost gauge is not reading any boost/vac either. Ive checked the tps and iac valve for the high idle and both are brand new and seem to be functioning just fine. I've also checked all of the vacuum lines by blowing. Compressed air in to the system and everything is tight and leak free. What do you guys think? Did I mess the intake mani gasket up when I installed the blower? Thanks!

    2000 Mustang GT
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    Renegade 2V CMC Boss429 Mustang Matt21's Avatar
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    could very well be the gasket. try unplugging the mass air and see if it changed anything? i know sometimes they get dirty or go bad

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    Makin' Waves and Catchin' Rays CMC Event Coordinator 03RedFireGT's Avatar
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    Did you use new intake manifold gaskets? Were you careful not to drag the lower intake across the gaskets during installation? Torque down the intake in the proper order?



    Tried the trick of using carb cleaner and spraying around the mounting surfaces? If you have a leak it will drop the idle once the carb cleaner hits it as it temporarily seals the leak.


    Dang'ole CMC Mang.

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    UPS Whore Extraordinaire CMC SuperCobraJet jimmysfords's Avatar
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    tim@MPH is tuning your car right? i assume you talked to him, also try what redman said.
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    Warning: The above post may contain large amounts of sarcasm!


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    Banned? CMC Boss460 mark95turbo's Avatar
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    I reused the gaskets as they were just fine. I'm pretty sure I didnt drag the lower intake and I'm positive it's torqued down positively. I can't call tim as he is on vacation until the 23rd. I'll probably order new gaskets and reinstall the assembly. I just can't figure out why im not getting any boost/vac.

    2000 Mustang GT
    Stroked and Blown
    302 Stroker, Ported heads, Blower Cams, Ported Eaton, Etc.
    Almost as cool as a 3V

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    Cobra Brigade Mad Scientist CMC Boss429 01bluesnake's Avatar
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    Did you use a gasket between the blower to manifold? You more than likely have a big intake leak somewhere to be having no vacuum. When you ground down the Knock sensor bosses on the block, did you test fit the manifold with the gaskets in place or just manifold to heads to check for flush and level?
    Last edited by 01bluesnake; 01-19-2012 at 06:37 PM.
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    Banned? CMC Boss460 mark95turbo's Avatar
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    Quote Originally Posted by 01bluesnake View Post
    Did you use a gasket between the blower to manifold? You more than likely have a big intake leak somewhere to be having no vacuum. When you ground down the Knock sensor bosses on the block, did you test fit the manifold with the gaskets in place or just manifold to heads to check for flush and level?
    Yeah. Used the factory blower to intake gasket along with gasket RTV and I test fit the whole assembly after grinding down the knock sensors. After I was sure it would clear I ground down even more to be sure I had plenty of clearance. I did lift the entire assembly on to the heads by myself and Ide say it weighs ~60 lbs. I'm guessing even though I was careful not to drag the manifold onto the gaskets I probably messed them up anyways as that is alot of weight to be lifting and placing precisely in place by yourself. I'll get a buddy to help me this next time and also buy some studs to help guide the assembly in to place. I'm also gonna buy a cheap boost gauge from autozone just to be sure mine is working, even though im pretty sure it is.

    2000 Mustang GT
    Stroked and Blown
    302 Stroker, Ported heads, Blower Cams, Ported Eaton, Etc.
    Almost as cool as a 3V

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    Cobra Brigade Mad Scientist CMC Boss429 01bluesnake's Avatar
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    Ya, pulled off more than i want to count, and it is a PIA to lift while in a extended position. I always bolt the manifolds down first, easier to allow the lower gaskets to align properly. Good, glad you did the RTV and gasket method, helps with any possible pin hole leaks.
    '12 Race red Raptor
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    Banned? CMC Boss460 mark95turbo's Avatar
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    Quote Originally Posted by 01bluesnake View Post
    Ya, pulled off more than i want to count, and it is a PIA to lift while in a extended position. I always bolt the manifolds down first, easier to allow the lower gaskets to align properly. Good, glad you did the RTV and gasket method, helps with any possible pin hole leaks.
    Yeah. I'm pretty sure I got the blower bolted to the manifold without any leaks. I'm not sure why but the instructions said to install the whole intake manifold\blower assembly before mounting it to the heads. After I got it all lifted on there I remember thinking. That would have been a whole lot easier to mount the intake to the manifold first and then the blower to the manifold while it was on the car.

    2000 Mustang GT
    Stroked and Blown
    302 Stroker, Ported heads, Blower Cams, Ported Eaton, Etc.
    Almost as cool as a 3V

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    Makin' Waves and Catchin' Rays CMC Event Coordinator 03RedFireGT's Avatar
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    Their main reason for doing so is I believe the intercooler coolant elbows would be a PITA to get pushed through and secured to the lower manifold.


    Dang'ole CMC Mang.

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