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Engine misfire after changing exhaust manifold
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jyank
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Jul 25, 2016, 3:08 PM
Post #1 of 14
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Engine misfire after changing exhaust manifold
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I have a 77 Pontiac Trans Am 400/6.6 engine with about 59,000 miles on it. The right exhaust manifold cracked and had to be replaced. A week before the exhaust manifold was replaced all spark plugs were changed and new fuel filter. Old plugs all looked good and the same. Also earlier this summer the pick up coil was replaced due to engine cutting out. Last year all plug wires were replaced due to mice chewing off the wires while in storage. Also new cap, rotor, ignition module and coil. Car ran good with no misfire until the manifold was changed. Drove car the day after the change. Ran fine. Drove it 2 days later. Started to miss and low power. Drove it the next day was fine no issues. Drove it the day after that which was the 20th of this month same issues. Haven't driven it since. Starts great. Rev up engine . Misfires. Goes in the shop tomorrow. Any ideas what going on here.
One more thing. Of course it was a hell of a job changing the exhaust manifold. It had to be heated with a torch to get the bolts out. Two bolts broke off in the head. They were gotten out and rethreaded.
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Double J
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/ Moderator
Jul 25, 2016, 7:36 PM
Post #2 of 14
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Re: Engine misfire after changing exhaust manifold
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I'd be looking at the Spark plug wires and/ or plugs first.
If it was fine until manifold change ,maybe they got damaged when removed or from the heat.
Breaking up/misfiring under a load is a symptom of faulty plug wires.
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jyank
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Jul 25, 2016, 7:53 PM
Post #3 of 14
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Re: Engine misfire after changing exhaust manifold
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Thanks for the reply. My shop mechanic said the same thing as you. Hope that's all it is. My baby goes in the shop tomorrow. Will let you know the outcome. Thanks again!!!
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Double J
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Jul 25, 2016, 7:59 PM
Post #4 of 14
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Re: Engine misfire after changing exhaust manifold
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Cool
Curious, where did you end up getting the manifold from?
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jyank
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Jul 25, 2016, 8:56 PM
Post #5 of 14
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Re: Engine misfire after changing exhaust manifold
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Got the right and left side on Ebay. Used of course. But were in excellent condition. Still had some of the original paint on them.
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Double J
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Jul 25, 2016, 9:19 PM
Post #6 of 14
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Re: Engine misfire after changing exhaust manifold
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Every once in a while when i can't find something local I'll find it on Ebay
Had a need for an OEM used alloy wheel, everything around here for miles was all crap and high priced.
Found a salvage yard down in Florida on Ebay that had one like new for a quarter of the cost , Had it in 2 days.
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jyank
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Jul 25, 2016, 10:18 PM
Post #7 of 14
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Re: Engine misfire after changing exhaust manifold
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Got the manifolds in 2 days. Got the left side just in case. Came out of Illinois. The 400 engine in my TA was in use from 1975 to 1978 or 79. Why can't you get new parts. You can for a Chevy 350. Do I have the only 400 Pontiac engine left? Ha Ha.
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Double J
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Jul 25, 2016, 10:46 PM
Post #8 of 14
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Re: Engine misfire after changing exhaust manifold
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I'm in Illinois, I may know the guy that sold them to you...LOL
He has a couple of the Bandit T/A's-one has a 6.6L 403 Olds engine
The other I think had a 400 which he yanked anyway, its getting a big block...He can't leave well enough alone.
Chevy 350's are like crap in a barnyard, there all over...
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jyank
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Jul 25, 2016, 11:01 PM
Post #9 of 14
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Re: Engine misfire after changing exhaust manifold
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I'm in the UP of Michigan. If its him tell thanks and fair price.
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jyank
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Jul 26, 2016, 5:51 PM
Post #10 of 14
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Re: Engine misfire after changing exhaust manifold
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Changed plugs on right side. Checked out wires still the same issue. Plugs appeared wet when taken out looked like they where never in the engine. Checked plugs on the left. Appeared wet when taken out. Choke not staying open. Very loose. Ran engine with choke held open still the same issue. My tech thinks it got to be the carb. Had car since 1978. Carb never rebuilt. Got rebuilt carb going to try that next. Any other ideas on what could be going on. Like I said in my original post this all started after the exhaust manifold was changed. I don't believe in coincidents.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jul 26, 2016, 6:22 PM
Post #11 of 14
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Re: Engine misfire after changing exhaust manifold
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What exactly does "checked out wires" mean?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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jyank
User
Jul 26, 2016, 6:27 PM
Post #12 of 14
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Re: Engine misfire after changing exhaust manifold
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Tech said wires were good. they had a new set in case they needed them.
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Hammer Time
Ultimate Carjunky
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Jul 26, 2016, 6:32 PM
Post #13 of 14
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Re: Engine misfire after changing exhaust manifold
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That doesn't answer the question but I guess there isn't one.
Have you tested for spark using an adjustable spark tester?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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jyank
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Jul 26, 2016, 6:46 PM
Post #14 of 14
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Re: Engine misfire after changing exhaust manifold
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I don't think so.
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