The flat spot you speak of sound to me like the throttle position sensor. It is on the back of the throttle body and will give many of the symptoms you talk about and is heat sensitive as well. If you go that route call around and get a good one from the DEALER. DO NOT go to a local auto parts store. They suck. Same for the CPS if thats where you got that.

Do you have any shifting problems? High rpms before shifting, hard shifts, weird down shifting, jumping between gears. These can all be other side effects of a bad TPS that kind of get knocked off as a different problem.

 

It runs perfect 99.9% of the time. But yesterday. The wife drove it to her moms, then took the kid to tutoring, then stopped by the dollar general, when she came out it would barely start, it spit and sputtered, popped and cracked and made all kinds of noise. She was able to barely get it moving and it started clearing up and by the time she was 1/4 mile down the road it was running fine. It was 95 deg yesterday. ?? I'm starting to think the fuel pump is allowing fuel to leak back into the tank when sitting and what little fuel is left in the fuel rail is "heat soak" whatever you want to call it and because there is no fuel in rail but just little it is causing it to do that this problem. I'm going to replace the fuel pump my next day off and see if that helps.


What is up with the "Knock off stores" sensors?? I did replace the CPS with one from Advance Auto?? Could that be my problem?

Thanks for help.

 

Could be your problem. For whatever reason sensors from parts stores just don't do the job. Always go to the dealer for sensors. If you decide to change the TPS go armed with your VIN number. There are two different TPSs that went on the '96. One is still really available the other isn't and you may have to call around to different dealers to find one and have it shipped. On mine I called 4 stores. Finally found one and it was stocked at the dealer back on 94 to give you an idea of the scarcity of them. I believe the CPS is readily available from most places. If you have to go to a parts store get NAPA and get the best they have.

My XJ did the exact thing yours is doing. Got a little better with each change of sensor. TPS first, CPS second, then this last week I changed my cracked exhaust manifold and up stream 02 and then was all good. I drove around Tuesday all day in 105 degree temps without a single hiccup. Before the manifold change every time I would start in that type of weather I would drive around the lot to get the sputters out. Not anymore though.

I know I keep adding to the pile but often problems come from a combination of things not being just right.

 

Great info. You're right about the sensors. I just replaced the CPS about 2 years ago from Advance. How did you know the manifold was cracked and where did it crack? Thanks.

 

Did you try the "poor man's prime" suggested by RTorrez1 in post #5? This is a useful diagnostic tool, not just something he dreamed up.

 

It cracked right at the collector. Where most XJs crack at. It's down right before the flange that goes in the down tube. Right after I bought it I took it to my dad's and thats the first thing he said. He could hear it. It's kind of a ticking sound. It got way worse about 6 weeks ago, along with more power loss and sputtering as you described. When I got it off the inside tube was completely cracked all the way around.

 

Get a fuel pressure gauge and see if the fuel rail holds pressure after running the engine for awhile. Shutoff the engine and watch the pressure. My guess is it drops like a rock, causing what little fuel is left in the rail to atomize due to the heat.

RTorrez is on to something, take his advice. It's the cheaper way to do what I'm saying....