91 c1500 5.7 timing problems - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-23-2012, 12:53 PM
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Originally Posted by alabamasho View Post
searched most threads, still can't determine how to seat distributor completely. I'm at TDC with no alignement marks on distr. shaft.. reason I pulled, had missfire, no acceleration. and I've installed new tank, filters and TBI. still have same problems. detected no vacuum leaks spraying around TBI, no CEL on. removed distr. cap and rotor is pointing straight ahead down center of intake, instead of pointing toward no. 1 cylinder. do I ccw oil pump shaft, so rotor, when seated is pointed toward cyl #1? thanks, ya'll are the best!!
Given this is a 1991 it probably has a lot of miles on it, the signs of miss fire, and lack of power are also indicators that the timing chain and gears are wearing out. Typically the cam falls retarded when this happens this results in the distributor falling behind which makes for a common sign that the timing set is wearing out as the ignition timeing needs to be reset, essentially advancing the timing just to keep it the standard marks. Since the distributor is gear driven off the cam this is a common situation as the engine ages.

The only really good test for this is piston positive stop and a degree wheel. The testing is almost as much effort as simply replacing the timing set. A rough indicator that can be seen if the engine runs is to hook up a timing light, accelerate the engine a few thousand RPM then slam the throttle shut while observing the timing marks with the thiming light. If the timing mark moves all over the place it is one possible sign that that the timing set is worn out allowing the timing to run in and out at the chain rattles through the clearances between its links and their pins and its links between the gear teeth.

Bogie

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Old 07-23-2012, 01:31 PM
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thanks Bogie. truck just has 138k on it, that's practically brand new down here in Bamer,, had 2 or 3 350's before with around 300k, and ran great. This one set up with an ole man few years, tank was rather nasty was reason I changed it. I've put 20k on it and had the slight miss. Gonna go ahead change the dizzy, which I think will fix. If not, compression test and vacuum, then make yard ornament cause I put a goodlooking stamped billet grill in it
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Old 07-23-2012, 05:44 PM
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I don't know why I didn't think of it before but is the EGR valve sticking open a little? That can also cause a rough idle. With it cold and off, put a few fingers in the back of it and actuate the valve a little bit. Then start it and see if it changed at all. EGR is essentially a variable vacuum leak to the exhaust. Not sure how else to check it other than that.
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Old 07-23-2012, 07:17 PM
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I'll double check in couple days, post results. i believe you can use vacuum pump on it it too. biggest problem is the stall out when I punch the gas a little. Thanks everyone for all the input!!
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Old 07-23-2012, 09:48 PM
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I think the vacuum pump will tell you if it has a hole in the diaphragm but not if it's not closing all the way. I think you can remove it and clean out the carbon though.
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