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flat spot or hesitation

jkmhb

NAXJA Forum User
I have a '99 4.0 5-speed that has a flat spot or hesitation from 1200 or so RPM. One I get it to 2000 RPM it is fine. Very occasionally I also get a backfire at this RPM when I nail the throttle. I've already changed plugs, wires, cap rotor, air filter, and voltage tested the TPS.

No OBDII trouble codes or pending codes are present in the computer.

Any ideas????
 
Check the TPS. You check it with a volt meter. hook it up and slowly open the throttle. You should get a smooth reading 0 to 5 volts. you can do this test the with engine off and key on.

Hope this helps
 
I had the same problem and found that my map sensor vacuum line was broke. Fixed the line and solved the problem...possibly could be your problem...Just take a peek at it
 
How's your exhaust? Still have the cat or modified? I don't have the cat and low rpm's suffer a little. HTH.
 
I do not know if this is normal but my XJ did the same thing minus the backfire. I attribute it to larger tires and complete exhaust system. However, it wasa only noticable when trying to excelerate quickly from a stop. Then again my XJ has an AW4 and the torque converter locked up at low RPM's which means the XJ had to reach enough MPH to get the 4.0L to reach it's peak torque band.
My $0.02
 
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