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cowboy71584
User
Mar 30, 2009, 4:34 PM
Post #1 of 12
(1854 views)
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Engine idle and rpms
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Hey there
I have a 1994 K1500 Z71 5.7 350 275000 miles on the truck I have never done any big repair jobs the 4 years I have had it and never had a problem tell now I replaced the wireing harness thinkn it would fix a trans problem I am haveing it did not fix that but now I have a engine problem with the old harness the engine would start and idle fine with the new harness I have to give the truck a little gas for it to start and then it idles very very low and sometime dies but after it warms up the engine idles realy realy high has never done this tell I put the new harness on I have check to make sure all plugs are pluged in and everything is fine there I do know the guy I got the truck from took alot of short cuts to fix a problem instend if doing it rigth what can this be a bad sensor maybe and with the old harness was not pluged in and me puting a new harness and pluging it in is the problem???? any ideas or maybe the computer behind the cove box
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Loren Champlain Sr
Veteran
/ Moderator
Mar 30, 2009, 4:46 PM
Post #2 of 12
(1852 views)
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Re: Engine idle and rpms
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If you are having to open the throttle to get it to start, that is telling me that it is over fueling. With fuel injected engines, pressing the throttle allows more air, not fuel. Yes, check all of your connections.
Loren
SW Washington
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cowboy71584
User
Mar 30, 2009, 4:48 PM
Post #3 of 12
(1851 views)
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Re: Engine idle and rpms
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Hey there
I have check all plugs they are all pluged in and are fine like i said befor never had this problem tell replaceing wireharness
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 30, 2009, 7:12 PM
Post #4 of 12
(1846 views)
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Re: Engine idle and rpms
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Hey,
275,000 miles is enough for anything at any time. Whatever "harness" you replaced (??) seems to have caused the problem so go back and check what you did. What more can anyone say on this possibly "short cutted" work history on this?
T
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cowboy71584
User
Mar 31, 2009, 5:37 AM
Post #5 of 12
(1838 views)
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Re: Engine idle and rpms
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I have check everything and it seems to be fine the guy I got the truck from would rig things to make them work did not know this tell just recent I was hopeing he rig something back when i gotthe truck and me puting in this new harness undid what he done just dont know were to look
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 31, 2009, 8:58 AM
Post #6 of 12
(1831 views)
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1994 K1500 Z71 5.7 350 275000 idle problems
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Whatever was hacked to cover something is now showing itself if wiring is now correct and well connected. Just maybe he was able to by pass something so it ran ok with bad info from something and now the info is making wrong adjustment choices. I can't second guess how hacked up this is.
Try a code reading to lead to a source but don't just take any reading for aiming directly at a bad sensor. Sensor may be the result of a problem NOT the cause,
T
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cowboy71584
User
Mar 31, 2009, 2:58 PM
Post #7 of 12
(1827 views)
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Re: 1994 K1500 Z71 5.7 350 275000 idle problems
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So I need to have the computer read for codes and go from there????
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 31, 2009, 4:31 PM
Post #8 of 12
(1823 views)
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Re: 1994 K1500 Z71 5.7 350 275000 idle problems
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Yes!
This engine has so many miles it's an open book of things that "could be" the trouble. Codes may lead to the major problem.
What history other than abuse does this engine have? Has it had an intake gasket job YET, Timing chain replaced YET and so on. Those things rarely last that many miles without doing something.
Compression check - there's 10 zillion things and any one could cause a rough idle. If in fact wiring is all where it belongs then perhaps a sensor is sending wrong info and wrong adjustments are being made.
Vacuum leaks are an open book for troubles too. It may be just coincidence that this starter when you changed some wires. What the heck was this so called "harness" anyway?
T
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cowboy71584
User
Mar 31, 2009, 5:14 PM
Post #9 of 12
(1815 views)
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Re: 1994 K1500 Z71 5.7 350 275000 idle problems
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ok I will have it read and I have done nothing to the engine the truck had 198000 when i got it and its has 275000 now and it was great tell I replaced the wires so i am not sure what has been done to it befor I got it
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 31, 2009, 6:10 PM
Post #10 of 12
(1810 views)
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Re: 1994 K1500 Z71 5.7 350 275000 idle problems
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Would you kindly expound on WHAT WIRES you replaced? You call it a harness. Some vehicles have 10 miles of wire in them - which so called "harness" did you replace that seemed to trigger this? Did you mean spark plug wires?
T
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cowboy71584
User
Apr 1, 2009, 5:25 AM
Post #11 of 12
(1800 views)
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Re: 1994 K1500 Z71 5.7 350 275000 idle problems
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Hey there the complet harness comeing from the computer behind the clove box to all the engines items down to the starter then to the trans the complet truck besides inside stuff and lites and Also the plugs and wires
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Apr 1, 2009, 6:19 AM
Post #12 of 12
(1798 views)
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Re: 1994 K1500 Z71 5.7 350 275000 idle problems
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Ok - Here's what I'd do asap for this:
Code reading. There are sensors for engine temp, engine rpms, (air temp possible) throttle position and MORE that if wrong info is sent or NO info is sent may show that as an area to look. If running lousy for any length of time now you about certainly with get an oxygen sensor code but not so fast to replace anything yet.
Double check plug wires are in proper order.
Either a compression check on a few OR a manifold vacuum check with as smooth a low idle as you can AND read it at just over 2,000 rpms also - don't overdo rpms with no load especially - report the Hg#s you find as that's good info.
Look at the old harness plug ends to see if any were corroded and make sure that connection new is now good to any old plug ins.
All this stuff will or could affect the trans shifting simply by engine running poorly or shared bad info.
Spray water or carb like cleaner around suspect gaskets and places for vacuum leaks. Idle should remain the same unless you hit a leak and it would improve or get worse when one is found.
Timing chain: They don't last that long IMO and can run perfect till one nanosecond and jump a tooth or more and still run. Compression and or vacuum readings would show if valve timing is off.
I think you can look at distributor rotor with cap off on this engine (not certain) and turn engine by crank bolt one way then the other watching how far the lower damper pulley turns before the rotor for distributor turns. If in excess of 5-6 degrees there's a chance for it to run lousy or plain jump. This will cause low compression evenly and low vacuum readings.
Again - it's enough miles for lots of things. Lot's of things may already have been done and some more than once. Cat converters will not be happy with an engine that doesn't run well and will choke up on unburned fuel and croak on you if you allow it to run lousy too long so it is important to straighten this out as soon as possible,
T
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