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1991 Chevy K1500 jerking at low speed
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robertcarter
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Nov 13, 2015, 1:36 PM
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1991 Chevy K1500 jerking at low speed
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My 1991 Chevy k1500 runs good when pressing down on the gas, but when you go thru town at slower speeds or coasting the truck jerks and seems like it will stall, but it doesn't. Why is this doing that?
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Tom Greenleaf
Ultimate Carjunky
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Nov 14, 2015, 12:31 AM
Post #2 of 10
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Re: 1991 Chevy K1500 jerking at low speed
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It probably is on the verge of stalling to feel like that.
Of many possible things let it idle and look for and fix any vacuum leaks. Not sure of anything just yet if transmission or engine running so start somewhere,
T
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robertcarter
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Nov 14, 2015, 6:47 AM
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Re: 1991 Chevy K1500 jerking at low speed
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All new plugs, wires, vacuum lines, sensors, could changing the transmission and not changing the ECM be an issue? Idles fine and drives fine as long as you give it gas.
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Tom Greenleaf
Ultimate Carjunky
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Nov 14, 2015, 7:09 AM
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Re: 1991 Chevy K1500 jerking at low speed
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If trans was the issue it would be with staying locked up at torque converter too long at low speeds perhaps. Site has a trans specialist but don't think a 91 has a lot going on with any "Engine Control Module" but plenty of opportunity for other things named already - vacuum leaks. Not just hoses - base of throttle body and integrity of air intake parts right along the way.
What engine do you have? I think choice of 4.3V6, 5.0V8 and a 5.7V8 for a 1500 would be about it.
Try this if you still think a transmission issue. Use non overdrive at those low speeds. I don't think you have a switch just first selection of "D" and maybe another plain D or 3,2,1 showing. "3" on those is high gear just shouldn't allow torque converter lock up at all.
More: Assorted ways to find vacuum leaks. Smoke machine, carb cleaner sprayed at suspect spots - all intake items that control intake manifold vacuum gaskets and all. Maybe even plug off brake booster but know you don't have power brakes if testing only in a controlled place for a test or vacuum check it as well. Don't forget PCV also - it and line to it.
Most engines available probably would idle OK and since you said asking for power or driving along it goes away suggests leaks more than other things FIRST.
Could also do well to plain clean up throttle body real well up to the "toothbrush" down it and clear any ports in there as well.
I'd have to look and lazy right now not know which engine what it uses for an IAC or "Idle Control" but if in fact near stalling it's out of it's range to self adjust or doesn't work.
Recheck the mentioned above. If nothing found for a '91 model a simple vacuum gauge could be helpful info can tell of valve timing, cylinder balance or other problems quite well. You can get codes off of this also but find most for those years aren't much help,
T
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Discretesignals
Ultimate Carjunky
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Nov 14, 2015, 8:11 AM
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Re: 1991 Chevy K1500 jerking at low speed
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Which engine does this have?
If you remove the vacuum line from the EGR valve and plug the end of the line, does your issue go away?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 14, 2015, 8:14 AM)
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robertcarter
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Nov 14, 2015, 9:42 AM
Post #6 of 10
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Re: 1991 Chevy K1500 jerking at low speed
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tried that, still have the same issue
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robertcarter
New User
Nov 14, 2015, 9:45 AM
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Re: 1991 Chevy K1500 jerking at low speed
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I'll try a complete carb clean, and the motor is the 5.7 v8 by the way, thanks
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Discretesignals
Ultimate Carjunky
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Nov 14, 2015, 9:55 AM
Post #8 of 10
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Re: 1991 Chevy K1500 jerking at low speed
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Should be fuel injected (TBI), not carbed. Is the check engine light on? If so, jumper A to B in the diagnostic connector and count the flashes of the check engine light when you turn the ignition on. The codes are two digit.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Tom Greenleaf
Ultimate Carjunky
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Nov 14, 2015, 10:12 AM
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Re: 1991 Chevy K1500 jerking at low speed
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Just FYI OP: No carbs but looks kinda like one in this year or several before. EGR can still be a vacuum leak - spray at it's base.
EGR shouldn't have any vacuum at low speed or idle. If it does hoses are wrong or a another item wrong allowing it vacuum.
Get your codes as DS suggested. EGR can still be the problem if pintle inside undersde can't seal tight would run rougher and almost stall or really stall. You'll wreck the gasket most likely to try to clean it up which only works sometimes.
Maybe, maybe if you idle engine and pull up on diaphragm with your fingers, it should stall right away. Just full motion might clear it up if the problem at all,
T
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gsferraro
Veteran
Nov 14, 2015, 2:53 PM
Post #10 of 10
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Re: 1991 Chevy K1500 jerking at low speed
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When you feel the problem, put the car into neutral and see what happens, does it go away or still there. Not sure how fast your going but if the converter is not releasing you would feel it when coming to a stop. Gary
(This post was edited by gsferraro on Nov 14, 2015, 3:04 PM)
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