Bigsky-xj

I've looked through a couple threads but haven't found one describing the problem I'm having. I have an 88 xj with a 4.0 and aw4 trans. I was having an issue where if I floored it oil would shoot out of my valve cover and the engine would sputter and lose all power. I did a compression check and it scored horribly so I assumed my engine was just wore out and had too much blowby. I bought an 89 xj with a good motor, swapped it in and replaced plugs wires cap rotor exhaust manifold new exhaust and a new o2 sensor. I drove it around for a day and it was good, but today I gave it some gas and it fell on its face again. As soon as it hits high rpms it will start sputtering and backfiring and losing rpms until I let off the gas. The more I do it the lower rpms it takes to make it sputter until its to the point I can barely give it any gas. But when I put it in park or neutral it has no problem revving. I'm stumped as to what would cause this especially because the engine wasn't doing this before it was pulled. Any advice would be helpful
edit: I have also checked timing and fuel pressure and both checked out

Roler

Especially the normal operation when in neutral, makes me think CPS...
not sure about the oil spouting out though, does it still do that?

Bad TPS and even CAM sensor can do this too, btw

Bigsky-xj

it doesn't spout oil anymore that was definently caused by blowby so the engine had to be replaced anyways but I was just stumped that both engines had the same problem even though I didn't reuse any sensors off the old engine

JeepXJ96stroker

I would start by cleaning the IAC valve then move into your TPC Clean the inside of your intake also. Check all connections and inspect vacuum lines. You can do all this with one can of censor cleaner.

Bigsky-xj

I would also like to mention, I havent tested it on this engine yet but if it acts the same as the last one, if I let the jeep sit for a while the problem will go away the next time I drive it until I hit a high enough rpm then it will start again and keep getting worse until I let it sit again

Roler

This is quite important info to mention!
Were the sensors that you put in, working correctly?

Bigsky-xj

I would assume they were working correctly
As the jeep they were pulled out of didn't have any problems, but i didn't thoroughly test it. I just drove it to the shop but it drove fine

Roler

it seems to be somewhat heat related because you say if you let the jeep sit for a while and start again, the issue is gone (untill it occurs again when driving)

Assuming the old sensors were functioning, there is two ways you could go about this

1) either look into what was NOT changed out, since that would still be there and cause the issue, new motor or not
2) start checking for possible causes (and there is many)

Still I'd like that CPS checked as one of the first things: besides doing the continuity tests on it, next time the issue plays up, one quick easy non-scientific test is poring cold water on the CPS and see if the issue disappears right after.
PS: do NOT do this with your TPS.

Bigsky-xj

I'll take a look at the cps after work today thanks for the info