Stumbling 4.o

So heres the story. I have a 2001 4.0L swapped into my 84 cj-8.

Started a while ago just stuttering once in a while going down the highway (slightly annoying but not critical)

Starting about last Memorial day at Rubicon it started loading up at low rpm's, If I revved it up it would clear out and run normal. (this is where I first noticed the loss of power) Also, in neutral it revs up fine all the way to red line (crisply) and even pulls hard at idle......but when going down the road it is slow, and won't rev past three grand.....and won't kick the trans down.

Over the summer it started not wanting to start when hot (almost like it was flooding, again I revved it up and it would clear out), I noticed a large drop in power and started sucking down gas around town. It threw a code for multiple cylinder misfire which told me injectors or 02 sensors...replaced injectors and o2 sensors with no improvement.

I took it to a shop where they tested sensors (seemed to be operating within tolerances) they also noted the sluggishness but couldn't reproduce the hard starting or stumbling. They seemed to think the only option left was the computer. But couldn't figure it out for sure.

Any Ideas??? I am lost!
~Robert

P.S. I am stuck in a borrowed minivan until I get my jeep running right, HELP!

If we assume that you swapped the ECU along with the engine, a sluggish or failed Coolant Temperature Sensor will cause those symptoms. A failed Throttle Position Sensor may have similar symptoms.

Tim_MN said:

If we assume that you swapped the ECU along with the engine, a sluggish or failed Coolant Temperature Sensor will cause those symptoms. A failed Throttle Position Sensor may have similar symptoms.

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Would the coolant temp sensor show an odd reading on the dash? or ....is there a way to test it? my needle reads 210 constantly .....once its warmed up

jeeperman19 said:

Would the coolant temp sensor show an odd reading on the dash? or ....is there a way to test it? my needle reads 210 constantly .....once its warmed up

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I had a 97 with similar symptoms, the dash gauge looked OK and it didn't have any CEL trouble codes, for several weeks while I tuned, cleaned and changed all the other possibilities. There is a test procedure in the Factory Service Manual for both the CTS and the TPS.

Cool I'll try testing them, I have the manual.

Thanks for the help amigos, Turns out it was the fuel pump.........the old one sucked up some shit from the tank, from a shitty gas station ( ie metal shavings and formagasket) dropped the fuel pressure to 20-30 psi