Engine misfire and stubmble

MrShaft696 · May 31, 2006

I have a 96 XJ 4.0, and recently on cold startup only after sitting for a day, it will misfire and stumble a little bit until it warms up or runs for 30 seconds or so. Just over the weekend I changed the spark plugs, wires, cap & rotor, and the fuel filter thinking that would help but nothing. Still stumbles on the cold start up, where should I look next? thanks in advance
Chris

RichP · May 31, 2006

FIrst thing I would do is run a couple of LARGE [20oz] cans of Chevron Techron fuel SYSTEM cleaner thru the next two tanks of gas. Then I would pull the throttle body and clean it on a workbench, careful with the cleaners around the sensors [tps.map, etc] they can damage the plastic parts but getting all the carbon out is step one. Might want to run a can of top engine cleaner thru to clean the valves and such, seafoam can be used for this.

Phager · May 31, 2006

I'll second the recommendation of cleaning the TB. I'm having the same problem, and bench cleaing the TB is on the list. Prior to me cleaning it on the truck, my MJ would absolutely refuse to accelerate for 5-6 mins after starting it up. Now it just takes 30 sec or so.

Pat

TsizeXJ · May 31, 2006

same problem here.... atleast i know what to add to the list

MrShaft696 · May 31, 2006

RichP said:
FIrst thing I would do is run a couple of LARGE [20oz] cans of Chevron Techron fuel SYSTEM cleaner thru the next two tanks of gas. Then I would pull the throttle body and clean it on a workbench, careful with the cleaners around the sensors [tps.map, etc] they can damage the plastic parts but getting all the carbon out is step one. Might want to run a can of top engine cleaner thru to clean the valves and such, seafoam can be used for this.

Thanks for the advice, my jeep is my second vehicle, after it stopped being a DD it started this so i can understnad the carbon buildup. What should I clean the TB with? brake cleaner or something like that?

RichP · May 31, 2006

MrShaft696 said:
Thanks for the advice, my jeep is my second vehicle, after it stopped being a DD it started this so i can understnad the carbon buildup. What should I clean the TB with? brake cleaner or something like that?

Any good decarbonizing cleaner, use a paint/parts brush.

MrShaft696 · Jun 5, 2006

Well i cleaned the tb and ran some fuel system cleaner through which made it a little better, but it still runs rough for like a min or two after starting it up after it sits over night, but otherwise runs great.

Dr. Dyno · Jun 5, 2006

Re: Engine misfire and stumble

MrShaft696 said:
I have a 96 XJ 4.0, and recently on cold startup only after sitting for a day, it will misfire and stumble a little bit until it warms up or runs for 30 seconds or so. Just over the weekend I changed the spark plugs, wires, cap & rotor, and the fuel filter thinking that would help but nothing. Still stumbles on the cold start up, where should I look next? thanks in advance
Chris

Check the resistance across the coolant temp. sensor (t'stat housing) when the engine's cold (you'll need a thermometer to read the coolant temp.) and check it against the readings on this page.

Engine misfire and stubmble

MrShaft696

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RichP

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Phager

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TsizeXJ

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MrShaft696

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RichP

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MrShaft696

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Dr. Dyno

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