jasonb751

I just picked up a 96 xj here in Florida for a measley $600. It runs perfectly except for one thing... When i go WOT the thing falls on its face. I can hear all the air rushing through the airbox, but it doesn't accelerate at all, if I let up on the throttle a little bit, it goes like a raped ape. If i go from idle to WOT really fast, it may backfire through the intake maybe 25% of the time. I hooked up the obdII scanner and when driving down the interstate the short term fuel trim is from -0.7 - 3.5% and the long term is at 32.08%. As soon as I go WOT the long and short term fuel trim go to 0%. This thing has me stumped, being that it only acts up at WOT.

Anyone have any pointers for me, I have a pretty robust scan tool, and can go out and check anything else if you guys may need it to help me. Also there is no CEL and no stored, active, or pending codes in the ECU.

Also, in case this is needed for help, 96, 4.0, AW4, 8.25, and np231 all with 138K miles.

Bcs_customs

Mine does this as well, its an 89 with the 4.0, hope you figure it out, might help me with mine as well

Bustedback

Hook your scan tool back up and do a sweep test on the TPS, it should be less than a volt when the throttle is closed, and about 4.5 volts at WOT. You may also want to check the fuel pressure.

jasonb751

My scan tool only does percentages for the tps. It shows about 15% when the throttle closed and sweeps fine up to 78% and that's when it falls on its face. I started it and in neutral when floored it only revs to about 1700 rpm. When I let up on the throttle to about 65% it goes like hell. I don't have a fuel pressure tester, but can run to the store tomorrow and pick one up and test the fuel pressure. What should the fuel pressure be on my 96?