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GMC Jimmy Misfiring, Backfiring, Spark Plugs

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    rickwbrickwb Member Posts: 6
    Grose67 - Thanks for the input. This has been a stumper. Maybe we can get headed the the right direction now....
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    jlflemmonsjlflemmons Member Posts: 2,242
    I have seen a similar symptom from a bad temp sensor. The sensor reads the engine as cold (even in the summer after running for a couple of hours) and richens the mixture, causing the idle to gain speed. Ended up having to use an ohm meter and compare the readings from the sensor to the temp and found it was off by 2X.
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    rickwbrickwb Member Posts: 6
    Thanks. I did get lucky enough to catch this thing in the act yestewrday and got it attached to some diagnostic equipment. Engine temp sensor seems to be reading and registering the correct engine temp. The Idle Air Controller does however seem to be malfunctioning. We'll see what shakes out.
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    rickwbrickwb Member Posts: 6
    JUST AN UPDATE - Seems it was the Throttle Position Sensor that was the culprit. We determined the problem by observing that it acted differently when cold and after the engine heated up. When hot the sensor indicated a 4 or 5% throttle even when no throttle was applied.
    Anyway the Jimmy runs great after replacing that sensor.
    Thanks for the input.
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    rickwbrickwb Member Posts: 6
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    tidestertidester Member Posts: 10,059
    Thanks, Rick! That's good to know.

    tidester, host
    SUVs and Smart Shopper
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    hdguy72hdguy72 Member Posts: 1
    i have a 97 jimmy 4x4 auto
    it has had a problem since i got it in the warm wheather it starts fine. but when i drive it i have to go 1/8 th of a mile before it will run ok it spits and sputters then just clears up but i still cant floor it if i do it sounds like a popping sound comeing from the exaust and it does this every time i start the car even after a 20 mile drive. then in the cold wheather it is worse i had to drive 10miles before it cleared up yeaterday then on the way home it just out of no where lost power. here's the kicker if i turn the car off then back on and drive a little further it will clear up both in warm and cold wheather but in the cold it will do this constantly for about 10 miles. PLEASE SOME ONE HELP !!!!
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    rhicksonrhickson Member Posts: 7
    I have a 96 jimmy (4.3) with a 2000 engine. My sensors were used on this engine. It has a problem with random misfire. I have changed two distributer caps as well as the plugs and wires. I also had the O2 sensor (upper passenger side) replaced. The misfire always returns and now it has started backfiring. Should I also change the O2 sensor before the Catylic converter as well or am I looking at something else?
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    nljewellnljewell Member Posts: 21
    I have a 99 Jimmy and I was going to ask the same question. Thanks for the ideas.
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    Dkiser22Dkiser22 Member Posts: 1
    I've got a 97 gmc jimmy with the 4.3, the car starts and idles fine,but is extremely choppy from idle to mid throtle,and runs smooth when wide open. I have replaced the plugs wires, rotor, cap, the mass airflow sensor and the tps, any ideas???
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    rhicksonrhickson Member Posts: 7
    I did all that with mine (three caps & rotors). I ended up having the intake manifold gasket replaced and the intakes cleaned. I also found out that I had a weak gaspump so I replaced that as well. It works pretty well now. The intake cleaning was under $60 and may be worth your while to check into it
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    saxmandonsaxmandon Member Posts: 3
    I have a 2000 Jimmy, 118000 miles. I keep getting a misfire code. Especially occurs if Jimmy sits for a day or longer. Bad misfire for first 5 minutes, check eng light goes on. Engine smoothes out after 10 min and next day light goes off. I have replaced plugs, wires, cap & rot, cleaned fuel injectors. Don't know source of problem, need suggestions.
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    rhicksonrhickson Member Posts: 7
    I did all that plus replaced the manifold gasket. What are you getting for a code. Mine was P0300 (random misfire). It's also possible that your oxygen sensors are causing your problem. I had to replace 2 of mine, both on the passenger side. After all was said and done I had to replace another rotor button. It runs like new now.
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    saxmandonsaxmandon Member Posts: 3
    Thanks for help, yes my code is P0300 misfire, I'll check my records on my O2 sensors I may have replaced. Is rotor button the rotor (as in cap & rotor)? Was your problem after ideal a day or two?
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    rhicksonrhickson Member Posts: 7
    Yes rotor button is the same as cap & rotor...I'm showing my age. I did all the work I mentioned and 6 months later it was still acting up. I don't know about your situation, but my Jimmy didn't take too well to after market distributors. In March I put another rotor and cap on that I got at a dealership. It has been fine ever since. Make sure your gas cap is good. A friend of mine couldn't resolve an issue and it turned out to be that cap. I wish you luck. The problem eluded me for 2 years.
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    gymshoe1gymshoe1 Member Posts: 1
    l had the intake gasket replaced. The mechanic reported a "bad miss". He played with the distributer until the truck backfired. "it sounded like a shotgun !" since the "boom" there is no action. You turn the key ,the dash lights up,but that's it. No fuel pump winding,motor turning,ect. The mechanic thinks the security system. I say the "boom" shot the computer. Could anyone please offer a solution !!! p.s. the machanic works under a shade tree.
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    saxmandonsaxmandon Member Posts: 3
    Replaced my after mkt cap & rotor w/GM on Sat and let car sit until Monday. Typically I got bad missfire for 10 minutes. Purred like a kitten, thanks for your help.
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    rhicksonrhickson Member Posts: 7
    You're very welcome....it was a pleasure....I wish you the best
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    twarner1twarner1 Member Posts: 1
    I have a 2000 Jimmy 4WD with only 90,000 miles on it, just had a new motor put in it .drove it for two days and it was just fine then the check engine light came on and it started cutting out and backfiring at around 1500 RPM's took it to the auto shop and they said it was the cam sensor replaced it and it is still doing the same thing but the check engine is not on.
    ANY IDEAS? PLEASE HELP!!
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    jayrob0311jayrob0311 Member Posts: 1
    I just replaced the head and intake manifold gaskets on my 2000 jimmy 4.3 vortec I have everything put back together and engine for the most part will idle pretty well with an occasional backfire, but once it goes into gear that is when it really happens I'm just about to my wits end, and I really need to get this thing going. I haven't changed the rotor cap or wires yet, I'm doing the work for a friend and am trying to save him a little money. Please any suggestions will help at this point.
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    rhicksonrhickson Member Posts: 7
    edited February 2011
    I replaced a motor and transmission (1996) with a 2000 engine. I had to eventually replace the manifold gasket as well as fuel pump as it was giving a low reading. It still acted up so I had the intakes cleaned. None of this helped. The long and short of it was that I needed a better distributor cap, better wires and a rotor. Its been fine since then.
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    rhicksonrhickson Member Posts: 7
    My problems were resolved after I changed the fuel pump, changed the manifold gasket, had the intakes cleaned then replaced the wires, distributor and rotor with good replacements.
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    crazydad66crazydad66 Member Posts: 1
    mine will back fire for a few seconds then runs fine what did you do to fix problem
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    michael79michael79 Member Posts: 21
    i was driving down the road about 35 mph and all of a sudden the motor started running very rough, any suugestions'? i got it going to put it in the garage and now i tried to start it again to move it back but seemed to kick backwards and didn't start. any idea's would be great. i am looking towards electrical, changed the fuel filter as i haven't done this in awhile but nothing else.

    thank you much.
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    ctbrownctbrown Member Posts: 1
    need some info, i've reset the timeing on my Jimmy 3 times already and it keeps jumping out of time. would the Camshaft Positioning Sensor or the Crankshaft Positioning Sensor be the cause of it jumping time? Any other information anyone has with this issue would be really appreciated. Thanks
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