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Old September 3rd, 2009, 06:52 PM   #1
j_little3
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Default What now? Please help!

So i was having problems with my truck bogging and i figured out why. Its misfiring at the 7th cylinder. I changed the plugs, wires and cap and rotor. I have a 1996 silverado with the 5.7L 350. I dont see how my injectors would be plugged because i put seafoam in it and thats supposed to be the best. Its onlt the 7th cylinder? Before i found out it was only the 7th, i thought it might be a fuel problem but its only that one cylinder.... what now?
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Old September 3rd, 2009, 06:59 PM   #2
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Have you checked to see if you are getting spark on the dead cylinder? The way check it is just pull the boot off and touch it to the manifold. If you don't have spark then the problem is still in the ingition system.
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Old September 3rd, 2009, 07:01 PM   #3
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I would run a compression test on it on all cyls and see what #7 compares to. Possible burnt valve not letting that hole work like the rest. If it's the Vortec engine (can't remember when they started those) I've seen a bad injector in those once in a while.
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Old September 3rd, 2009, 07:04 PM   #4
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What injection system does this have? Only way the injector could be at fault is if you have multi-port fuel injection. Not real familur with all the options but if it does have mpfi then injector is a possibly if it's not a spark problem. Pull the plug and observe what you see. dry white ish brown = lean (no fuel) and black, wet and a fuel smell = rich (no spark)
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Old September 3rd, 2009, 07:21 PM   #5
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I have the vortec.
It only does it sometimes too. Like if it sits for a while, if i drive it for a while it will stop.
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Old September 3rd, 2009, 07:26 PM   #6
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All the plugs look the same.
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Old September 3rd, 2009, 07:28 PM   #7
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Stick a plug in the boot and look at the end of it while you crank it. The manifold trick may still work if you can pull the boot back and expose contact. Some boots allow this some don't.
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Old September 3rd, 2009, 07:28 PM   #8
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Yuck then a stuck or burned valve sounds likely if it's not fuel or spark.
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Old September 3rd, 2009, 07:33 PM   #9
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ugh damn. if it helps it started in the middle of my silver lake trip. I dont get why it gets better if i drive it for a little bit.
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Old September 3rd, 2009, 07:38 PM   #10
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yea the plugs got tons of spark.
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Old September 3rd, 2009, 07:38 PM   #11
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Assuming it is a valve that just sticking, it's probaly coated with carbon. They can do this randomly, with changes in heat, and speed. Is your check engine light on? If yes then get it to an autoparts store and have then run the code.
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Old September 3rd, 2009, 07:42 PM   #12
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ive checked the s.e.l. and all it says is misfire cylinder 7
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Old September 3rd, 2009, 07:58 PM   #13
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In the vortec engines I have seen the seals go bad on one cylinder causing the plugs to foul out real fast or makng it run like crap after sitting for a while if the leak is not bad....also seen them have leaky injectors and that does the same thing.
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Old September 4th, 2009, 09:09 AM   #14
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is there a way to check without taking the motor apart?
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Old September 4th, 2009, 09:10 AM   #15
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I beleive the compression check will tell you the story with the seals. The injector I have no idea.
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Old September 4th, 2009, 09:37 AM   #16
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last oil change i put some of that seal lube and pistion fixer stuff in with my oil and its went the whole 4000 miles and i changed my oil again. so my seals should be fine.
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Old September 4th, 2009, 11:37 AM   #17
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also check the intake gaskets, you can remove the pcv valve, plug the whole, plug the vent tube from the valve cover to the intake tube, remove the oil filler cap, and check for internal vacuum leak, if you have vacuum without a pcv valve in the engine, intake gasket is leaking from the bottom side, may seal at different times depending on temp of engine, intake, etc. also spray carb cleaner along the intake to head surface, see if rpm changes, good luck and just a try! david
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Old September 4th, 2009, 07:35 PM   #18
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Quote:
Originally Posted by j_little3 View Post
last oil change i put some of that seal lube and pistion fixer stuff in with my oil and its went the whole 4000 miles and i changed my oil again. so my seals should be fine.
Theres your problem.... that shit don't work!!! It prob. gummed something up it wasn't suppost too.
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Old September 4th, 2009, 08:25 PM   #19
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i really doubt it's your injectors, it's 97 vortec, and i'm pretty sure it's not the multi-port injection, it does sound like a burned/stuck valve, do the compression test, and take off the covers, crank the motor over (on and off a few times, warm/cold too) and make sure all the valves are working properly
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Old September 5th, 2009, 01:34 PM   #20
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Quote:
Theres your problem.... that shit don't work!!! It prob. gummed something up it wasn't suppost too.
Well how would i clean it out then?
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