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Missing?

thecozmo65

NAXJA Forum User
Location
Easton, Maryland
1990 4.0l idles fine but when I rev. the motor it seems like its missing. I just discovered this last night. I dont drive it on a regular basis but the last time I drove it, I think sunday, it seemed to be fine. I didnt have time to check much last night cuz it was raining but I did pull the cap and rotor and clean all the contacts though they werent really dirty. When I drove it it would accelerate but not w/much power and when I would floor it it would spit and sputter and backfire a little and try to stall. Just put in new injectors, IAC, TPS, has good Taylor wires and new (with in the last year or so) coil and I did put a tester on the #5 & 6 wires between the plug and thw wire and they were good. How can I check the injectors to see if one of them are bad? Besides checking the rest of the wires what else should I look at?
 
Check the coolant temp sensor, all the vacuum lines, fuel filter,and fuel pressure regulator for starters.
 
If it is idling rough you can pull one plug wire at a time to determine what cylinder is misfiring. That way you have narrowed you area down to at leastone or two cylinders. After that you may beable to determine if it is the injector or spark plug.

Good luck
chris
 
XJ Buzzard said:
If it is idling rough you can pull one plug wire at a time to determine what cylinder is misfiring. That way you have narrowed you area down to at leastone or two cylinders. After that you may beable to determine if it is the injector or spark plug.

Good luck
chris

Do the plug-pulling test first if it is idling badly. There's a good possibility of a bad plug or a bad wire.

Even if it is not idling rough, if it has a miss it might be an injector. You can pull one injector plug wire at a time to test this. If the injector is firing, you will hear the engine briefly slow down, then resume speed as the computer compensates. If the injector is not firing, there will be no effect at all. If you find one that is not firing, try swapping its lead with that of its nearest neighbor. Do the test again. If the bad injector symptom follows the wiring, it's the wiring, and if it remains at the same injector it's the injector.

Injector connectors come in several variants. Some are much easier to pull off than others. If yours are the type with a metal snapring on the plug, you can simplify the testing process by first removing all 6 snaprings so that you can pull them off without so much force. Just remember to replace the snaprings when you're done.
 
no it was idling fine. it was just when i would rev it there seemed to be a miss. I drove it today and it seems to have gone away. I think it may have been the fact that Im not driving it much at all and its just sitting alot, but I am still going to check all the plugs and injectors. I also think that the return line on the fuel rail has a bad o-ring so that may be causing problems too. Thanks for the help, its much appreciated.
 
thecozmo65 said:
no it was idling fine. it was just when i would rev it there seemed to be a miss. I drove it today and it seems to have gone away. I think it may have been the fact that Im not driving it much at all and its just sitting alot, but I am still going to check all the plugs and injectors. I also think that the return line on the fuel rail has a bad o-ring so that may be causing problems too. Thanks for the help, its much appreciated.

One of our family XJ's, a 93, had a wiring harness problem that only came up when it got hot. A bad splice had just enough resistance to heat up until it caused one injector to cut out. It wouldn't happen every time you drove. It happened especially after running fine and then parking it. Keep an eye out for that. If you go down to the store and it runs fine, then misses when you restart, it's time for the injector harness test.
 
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