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HELP! first startup not so good

Old 06-03-2010, 11:57 PM
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Default HELP! first startup not so good

ok so, finished my 4,0 head today in school. Had to replace the head because the original cracked, but the one I just did, I gave it a 3angle valve job and backcuts ont he intake valves, got all my stuff(gaskets) and got the head back on the jeep tonight while dodgeing the rain. First startup, started up and was rough, wouldnt idle on its own, and after running for about 3 or 4 seconds started to pop really loud, got my buddy to start it with me out in the engine bay, and determined it seems that its backfireing through the throttle body, the backfires sound like a loud pop, not like a rod knock or anything like that. PLEASE someone help, im to flustered right now to think straight, more or less pissed off that my jeep is still on crack, also since its a 97 i did the obd test with the key, no codes so it shouldnt be anything electrical

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Old 06-04-2010, 01:29 AM
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Popping through the manifold is an obvious, and classic symptom of timing being off. since the ignition timing is fixed and non-adjustable on these, it means that your camshaft timing is incorrect. Even being off by one tooth on either the crank or cam sprocket would cause the problem that you are describing, since your distributor is driven off the camshaft at 1/2 crank speed. You will also experience problems due to the valve timing being off as well. Just bring it up to top dead center using a piston stop and a degree wheel, and check the marks on the timing set and you will see your problem. Good luck,

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Old 06-04-2010, 01:30 AM
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just did a compression test, they are all good 160-170. Tryed messing with a few things, no change, and it might not be a backfire, about every second or 2 it makes a pop, like if u put your tounge on the roof of your mouth and slap it down quick, only thing i can think of to describe the noise so bear with me.
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Old 06-04-2010, 01:32 AM
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how would I have jumped a tooth on my timing though? As i said, aside from the head cracking it ran fine before I took the head off, and the second the jeep turned over it started doing this, just good timing on being a PITA?
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Old 06-04-2010, 01:41 AM
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Well, I don't know how far you tore your engine down to replace the head. I wasn't implying that it necessarily jumped timing, those pops through the throttlebody are backfires, and that means the ignition is too far retarted, so I assumed you had the timing chain off. If you didn't, it is entirely possible for it to have jumped time considering that you had all of the valve train tension off of it, the lifters could have been collapsed, and if the chain is old and stretched then it may have jumped right when it fired for the first time. If it were my truck, the first thing I would do is verify the timing marks, like I said, what you are describing are textbook symptoms of off timing.
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Old 06-04-2010, 10:09 AM
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crossed plug wire, or incorect valve adjustment.
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Old 06-04-2010, 11:14 AM
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Originally Posted by fonman25 View Post
Well, I don't know how far you tore your engine down to replace the head. I wasn't implying that it necessarily jumped timing, those pops through the throttlebody are backfires, and that means the ignition is too far retarted, so I assumed you had the timing chain off. If you didn't, it is entirely possible for it to have jumped time considering that you had all of the valve train tension off of it, the lifters could have been collapsed, and if the chain is old and stretched then it may have jumped right when it fired for the first time. If it were my truck, the first thing I would do is verify the timing marks, like I said, what you are describing are textbook symptoms of off timing.
I agree, I would start here and make sure this is not it, once you do this it cuts out most of the what if's. I know you did not have to but did you pull the distributor?
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Old 06-06-2010, 04:04 AM
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well figured it out friday after school, started pulling injector plugs, narrowed it down to cyl 2, when i pulled the injector it stopped poping but there was no difference in roughness in idle, that told me it was igniting but it was an issue of a valve sticking closed, took the valve cover off and sure enough, working on my jeep at 3am got the best off me, cyl 2 exhaust rocker was loose, tightend it up put the cover back on and fired it right up smooth as could be, then drove it around and realized the crack in my radiator came back
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Old 06-06-2010, 04:00 PM
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Cool, glad to see you got it fixed up.
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