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Unable to accelerate while at more than half throttle

xjrick94

xjrick94

NAXJA Forum User
Location
Lynwood
I have a 94 xj 4.0 auto and it had ran great up until this weekend. I went to drive it this saturday after it had been sitting for 3 weeks and when i drove it to the store it ran great. I didn't notice an issue since i didn't really try to accelerate hard. Later in the day I went to enter the freeway and I accelerated a little more than half throttle, my jeep downshifted, started accelerating then it would just go up about 500 rpm then back down and would just keep bouncing around like that until i let off of the throttle and just accelerated slower. I was able to cruise to around 80 and it did great until there was an incline and i accelerated to try and maintain speed.

I uploaded a short video to see if it makes diagnosing a bit easier.

https://www.youtube.com/watch?v=QnzP9nB8NCc
 
No CEL?

I hate to guess, but if it feels like the engine (not the trans) then I'd guess tps or cps
 
No cel. Previously i have had issues with the tps. It would begine bucking as i'm driging, then a check engine light and when i would restart it would go back to normal. I suspect some sort of wiring issue with the tps since i went through around 4 autozone tps' then moved to a factory one. I'm not the greatest with wiring.

I forgot to mention taht when i rev it in neutral there are no issues accelerating.

Yeah i don't feel that it's the trans either.
 
Also I did notice that the CPS connector was a bit loose. I connected it all of the way in and the issue persists.
 
Could be too little fuel during acceleration. That can be caused by fuel issues (pump) or computer control-sensor issues.... The sensors to check are the TPS (use a multmeter and see if the WOT area is too low, like under 3.8 Volts, power on engine off), the Air Intake Temp sensor (cleaning them can help, check the resistance, but I doubt it is the issue), and the MAP sensor and its vacuum line (could be a hidden crack in the hose under the sensor). Map can also be tested with a multi meter and a vacuum pump or back probe the wire leads with the engine running.

Could be a Cat clogging up too, check for rattles when you tap it cold with a rubber hammer.

Too little fuel from issues with the TPS, MAP, fuel pump ... or a bad CAT are my top picks. Might be a spark coil going bad (overheating) too, but hard to test or verify, and not a high probability.
 
Ecomike said:
Could be too little fuel during acceleration. That can be caused by fuel issues (pump) or computer control-sensor issues.... The sensors to check are the TPS (use a multmeter and see if the WOT area is too low, like under 3.8 Volts, power on engine off), the Air Intake Temp sensor (cleaning them can help, check the resistance, but I doubt it is the issue), and the MAP sensor and its vacuum line (could be a hidden crack in the hose under the sensor). Map can also be tested with a multi meter and a vacuum pump or back probe the wire leads with the engine running.

Could be a Cat clogging up too, check for rattles when you tap it cold with a rubber hammer.

Too little fuel from issues with the TPS, MAP, fuel pump ... or a bad CAT are my top picks. Might be a spark coil going bad (overheating) too, but hard to test or verify, and not a high probability.
Click to expand...

I did run it low on fuel before i parked it. It didn't shut off on me but instead of driving it to the gas station the next time that i wanted to drive it I grabbed a jerry can that i just bought, filled it with 5 gallons of fuel and poured it into my jeep. Not sure if it's relevant but just something that I remembered when I read that you mentioned fuel.
 
I'd stop right there and put in some good fuel...no sense diagnosing anything if you already know a possible cause....and old gas is a possible cause.
 
IT COULD BE
the rubber fuel line on the pump to the sending unit in the tank. they get old,swell up and tear and leak. when it does that you lose pressure going to the engine. let me be clear, this hose is inside the tank on the sending unit. it comes out the top of your fuel pump. my 1989 MJ did this to me and my current 1988 did till yesterday when i fixed it.
 
Gunter said:
IT COULD BE
the rubber fuel line on the pump to the sending unit in the tank. they get old,swell up and tear and leak. when it does that you lose pressure going to the engine. let me be clear, this hose is inside the tank on the sending unit. it comes out the top of your fuel pump. my 1989 MJ did this to me and my current 1988 did till yesterday when i fixed it.
Click to expand...

I heard years ago that the new fuel formulas, ethanol were causing the problem, not sure...and I think a fuel pressure leak down test, engine off, gauge already installed before ignition switched to run 2 times. to prime the lines, then off anf watch for 10-30 minutes to see if it holds pressure? Would detect that sort of leak?
 
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