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'91 Chevy Truck wont idle anymore!!
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Guest
Anonymous Poster
tallpaulcop@hotmail.com
Dec 23, 2008, 1:23 PM
Post #1 of 7
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'91 Chevy Truck wont idle anymore!!
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I have had this 1991 Chevy C1500 for about ten years now. The chassis has around 210K miles on it. For the last few months it would die at red lights but start right back up and be fine for a while. I gave the truck to my son who wanted to rebuild the engine. The engine now has less than 100 miles on it. Once it starts heating up the idle drops (cold start @ 1100RPM) and finally dies at around 180 degrees. Oh yeah, it is a 5.7 L with TBI. No codes showing at all even after we drive it around and make sure it has gotten to operating temp.
Other than the rebuilt engine it has a new ECM, O2 sensor, Throttle Position Sensor, Coolant Temperature Sensor, Electronic Spark Control, Idle Air Control Valve, cap, rotor button, and plugs. I have also put in a new fuel pump, fuel filter, and fuel pressure regulator in the throttle body. No vacuum leaks have been located and the timing is set to 0 per the specs (with the ECM disconnected).
We have noticed that as we drive down the road it does seem to lack power and "hick-ups" occasionally back through the throttle body. This is usually as we start to pull a hill or exert some pull on the motor. This would normally make me think of timing but the only things in the timing circuit we haven't replaced are the pick-up and control module, which I've been told have no affect on the timing curve.
At this point my son and I are very frustrated. Any advise will be greatly appreciated.
Happy Holidays!!
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Loren Champlain Sr
Veteran
/ Moderator
Dec 23, 2008, 2:40 PM
Post #2 of 7
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Re: '91 Chevy Truck wont idle anymore!!
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Could be that it is running too lean. Fuel delivery when cold will be rich, then leans out as engine temp increases, thereby masking the lean condition. Could he have over tightened the valves? You should check; If memory serves, it would be zero lash + 1 turn with engine warm, but check those specs, just to be sure. A tight valve can cause the symptoms you are experiencing, including the popping back through the intake. (I'm assuming that the firing order is correct and no carbon tracks on the inside of the dist. cap).
Loren
SW Washington
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Guest
Anonymous Poster
Dec 24, 2008, 2:53 PM
Post #3 of 7
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Re: '91 Chevy Truck wont idle anymore!!
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You are correct..no carbon tracks in the cap. The valves could be the problem. On the stand I adjusted each cylinder on TDC to zero lash plus 1/2 turn prior to putting it back in the truck. It could be that as it warms up the clearances tighten up too much. I will give that a try.
Thanks!!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 24, 2008, 3:12 PM
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Re: '91 Chevy Truck wont idle anymore!!
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Hmmm? Just some thoughts on the valves and Loren may know better/more about it.
If valves were "ground" in the rebuild (been too long for this mind ) the 1 degree interface angle difference would set in to match better when warm and not be the "cold" setting. A Chev typical small block if like older than even this would run ok with valve covers off and you could play with them then without being sprayed to death with oil.
As a valve breaks in it would sink some into the seat if anything thus reducing the clearance first measured. The warmer valve and push rod would/should be longer also. The whole idea of hydraulic lifters was to have a range to take that for ages but if in fact it's too tight it would show more when warm than cold and poping back thru thottle body would be a clue with a burned up valve soon to follow if that's the trouble.
Being rebuilt my guess is there's some more room for deviance in protocol and probably best to go back and recheck those again - all of them.......Erring to the too loose side would/should just cause a harmless tick.......
T
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Loren Champlain Sr
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Dec 24, 2008, 3:12 PM
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Re: '91 Chevy Truck wont idle anymore!!
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New camshaft and lifters? The lifters will take a while to 'pump' up, especially if not primed, first. It's messy, but they really need to be adjusted with the engine at temperature and idling. There are clips made that can be put on the rocker arms to divert the oil so it doesn't go all over the exhaust manifold. You'll notice that you will only be able to go about 1/4 turn at a time so that it doesn't kill the engine. Back off the rocker until you can hear it clicking. Then tighten in 1/4 turn increments and let the engine 'recover' after each 1/4 turn.
Loren
SW Washington
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Tom Greenleaf
Ultimate Carjunky
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Dec 24, 2008, 3:17 PM
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Re: '91 Chevy Truck wont idle anymore!!
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WOW - Loren - we hit at the same nano second! I like your idea of creeping up on adjustment after loosened to ticking for a rebuild. May have to go back and do or check yet again later depending as first post said just 100 miles so far on this??
T
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Loren Champlain Sr
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Dec 24, 2008, 4:23 PM
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Re: '91 Chevy Truck wont idle anymore!!
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LOL! Great minds think alike? Do you know of a pair?
Loren
SW Washington
(This post was edited by Loren Champlain Sr on Dec 24, 2008, 4:24 PM)
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