1990 jeep xj 4.0 bucking and poor mpg. - Pirate4x4.Com : 4x4 and Off-Road Forum

TKD_MIKE · 02-16-2007, 08:55 AM

I have a 1990 jeep xj with a 4.0 and automatic aw4. I had it parked for a while apx. a year or so. It ran fine before I parked it. When I restarted it it was running kinda rough and started bucking like it has a major miss while driving 65mph or so. I changed the fuel filter, cap, rotor, wires, plugs, a/f, o2, changed the oil, checked all the vac lines and routing. I even changed out the ecu thinking maybe it been running in limp mode. after doing any work noticed it runs a little better but still have not fixed the bucking issue while driving 65 or so. and I still am not getting very good mileage apx. 10mpg. This thing is driving me crazy. If you guys have any info for me I would greatly appreciate it. Oh and before anyone says did you search for it. I did and I think I have been reading for days, google, pirates, nxj.

90xjDave · 02-16-2007, 09:09 AM

just a thought, but did you change the fuel after letting it sit for a year?? Could be bad gas. Whatever it is, it sounds like a fuel problem though.

TKD_MIKE · 02-16-2007, 11:15 PM

I have put a couple tanks through it. one with lucas fuel aditive. no change. Some told me that there was an issue with the cps. I always thought that if a crankshaft position sensor when bad it wouldnt run.

02-16-2007, 08:55 AM	#1 (permalink)
TKD_MIKE Registered User Join Date: Oct 2005 Member # 56449 Location: PHX (HELL) Posts: 111	1990 jeep xj 4.0 bucking and poor mpg. I have a 1990 jeep xj with a 4.0 and automatic aw4. I had it parked for a while apx. a year or so. It ran fine before I parked it. When I restarted it it was running kinda rough and started bucking like it has a major miss while driving 65mph or so. I changed the fuel filter, cap, rotor, wires, plugs, a/f, o2, changed the oil, checked all the vac lines and routing. I even changed out the ecu thinking maybe it been running in limp mode. after doing any work noticed it runs a little better but still have not fixed the bucking issue while driving 65 or so. and I still am not getting very good mileage apx. 10mpg. This thing is driving me crazy. If you guys have any info for me I would greatly appreciate it. Oh and before anyone says did you search for it. I did and I think I have been reading for days, google, pirates, nxj.

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02-16-2007, 09:09 AM	#2 (permalink)
90xjDave Registered User Join Date: Apr 2005 Member # 46447 Location: Auburn, Ca Posts: 107	just a thought, but did you change the fuel after letting it sit for a year?? Could be bad gas. Whatever it is, it sounds like a fuel problem though.

02-16-2007, 11:15 PM	#3 (permalink)
TKD_MIKE Registered User Join Date: Oct 2005 Member # 56449 Location: PHX (HELL) Posts: 111	I have put a couple tanks through it. one with lucas fuel aditive. no change. Some told me that there was an issue with the cps. I always thought that if a crankshaft position sensor when bad it wouldnt run.