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Discussion Starter · #1 ·
Just bought a new rig that has a 98 4.3 that only has no more than 25k miles on it. Motor runs strong and clean when motor is cold and warming up. After motor is running for about 10mins, engine temps come up to normal running temps, it starts to run really rough especially on load. Almost like a plug wire is loose and it is firing on 5. All wires are tight. As soon as I put it in nutural and rev it a couple times to clean it out, it will run good again for a few seconds then start running rough again? I know it is something basic but new to this motor and knew some one here would know.

Thanks
 

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Discussion Starter · #4 ·
jeepruler said:
try the coolant temp sensor for the computer. It sounds like it thinks it's cold all the time.
Well replaced that with no luck. Back to the drawling board
 

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Im not sure about running good when cold then worse when hot but whenever mine has a problem with running badly under load i icheck the fuel pressure. This has twice caused me problems. My 99 4.3 always runs better when its cold and i have any sort of problem, I think it is because the computers rely on less outputs when cold. Did you pull the codes? Another quick thing to check that i remember causing me problems is low voltage. good luck-
 

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Discussion Starter · #6 ·
I have not checked fuel pressure or voltage issues. When you had the fuel pressure issues did you just buy a new fuel pump?
 

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One was only about 7 PSI too low but it was about 20 years old. You dont need to immediately go out and buy a new pump, just check the pressure at the schrader valve on the fuel line on the drivers side near manifold. quick and easy
 

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If you had a way to pull the codes, that could make things alot easier. Do you?
 

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Discussion Starter · #9 ·
Turtle Bite said:
If you had a way to pull the codes, that could make things alot easier. Do you?
I have a friend who lives about an hour away that can pull codes. I may just have to take a road trip to figure this thing out. Thanks for the ideas!
 

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Well if your going to own it and work on it you might as well just buy the tool you need? I think that's an OBD II and those readers are about $100 or so.

If it's really running that rich it might not be that good to drive a lot. Change the oil filter when your done...
 

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You should try checking the O2 sensor to make sure it is reading correctly also. This could keep it in a rich condition too.
 

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Discussion Starter · #12 ·
You think? How do you change an oil filter? Is that the thingy that has something to do with the oil stick reader thing? :flipoff2:

Eagle-Mark said:
Well if your going to own it and work on it you might as well just buy the tool you need? I think that's an OBD II and those readers are about $100 or so.

If it's really running that rich it might not be that good to drive a lot. Change the oil filter when your done...
 

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Discussion Starter · #13 ·
Yeah, I thought about that one also and am holding off going out and buying 02 sensors. I just drove it for an hour at TonyK's house on his comp rock pile and it drove perfectly. I am going to drive it some more this weekend and decide if I need to hook up with my buddy who is a GM tech to roll down there and hook it up to his code reader. Seems to be intermitant at this point.

rockcrawler304 said:
You should try checking the O2 sensor to make sure it is reading correctly also. This could keep it in a rich condition too.
 

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Roc Dog said:
You think? How do you change an oil filter? Is that the thingy that has something to do with the oil stick reader thing? :flipoff2:
Close! Don't forget to put the oil back in the 710.
 

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