Did you check and clean the IAS? How bout checking the TPS and the CPS? Be sure all your vacuum lines are all still connected.

 

I checked the TPS voltage in, and it was right on, I dont know how to check voltage out. What is the other one? I took the CPS out, but did not test? how do you test the CPS and other one you named? where is it at?

88 xj, 2 door, black, 4.0L, 5 speed, NP231, rear sway bar off, air box opened up. 30x9.5 BFG AT's

 

The Idle Stepper Motor should be screwed into the side of the throttle body. I haven't looked at a pre HO engine in a while but it's gotta be on there somewhere. I am unsure of how to test the CPS. But you did mention that you were backfiring and that leads me to believe that the computer is firing the plugs at the wrong time. I think a faulty CPS will do just that. The test procedure should be in a manual. Get a Haynes or Chiltons. Better yet get the factory manual(I have all 3).

 

Could this possibly be timing related? I know the newer models timing is controlled by the computer, what about the old? Sounds like it might be out of whack.

Why do they call it tourist season if you can't shoot em'!??
http://www.skyboom.com/Robison

 

I could be wrong but this sounds fuel related!
Hows the fuel preasure do you got good fuel preasure?
is fuel pump relay working properly?

91 jeep cherokee 270000 kms deceased
93 jeep grand cherokee living 213000 kms With
92 cherokee T case drop in!

 

piaa_nissan, that's one of the prime functions of the CPS -- to tell what time to inject and fire. I'm guessing too, that this is the problem. But you could do Fred's fuel pressure check before spending any money.

Just because I don't care doesn't mean I don't understand!
'88 MJ SporTruck shortbed
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K

 

Thank you all, that is pretty much what I was thinking. But i couldn't decide if it was fuel or timing, and since timing was CPU controlled, i was out of luck on that one. I have a chilton manual (garbage). I will look at the CPS and TPS today and let you know. It has fuel pressure, not sure how much thoughm I dont have a gage, and I will look at the relay today too. Thanks you all very much.

88 xj, 2 door, black, 4.0L, 5 speed, NP231, rear sway bar off, air box opened up. 30x9.5 BFG AT's

 

Re: UPDATE!!!!

Ok, I just done done running the tests, the TPS is getting 5 volts, it reads .9 at idle, then proceds smoothly too 1.4 at WOT. The CPS has .160 ohms, spec is 125-275. So im good with both of those. The fuel pressure is 38 with the key on, and engine off. It then turns off pump, and slowy decreases, turn key on again, back to 38. Every thing seems good right? What now? HELP!!!! ps. i'll let you know what the fuel pressure is with engine running as soon as the alternators back on. Adam

88 xj, 2 door, black, 4.0L, 5 speed, NP231, rear sway bar off, air box opened up. 30x9.5 BFG AT's

 

what do the factory manuals cost?

1990 XJ Laredo 4.0 5spd 180kms

 

Just because it has voltage doesn't mean that the CPS is functioning correctly, but it does make the chances of it a lot less.

Did you check all your vacuum lines for leaks? Pull each one, one at a time, and plug one end with your thumb and blow through to see if you got leaks. This has caused many a Jeep to stumble, die, and backfire.

Just because I don't care doesn't mean I don't understand!
'88 MJ SporTruck shortbed
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K

 

Oh yeah, FSMs are best obtained on Ebay if they are around. Otherwise you have to pay like $69 or something. I remember finding a site that wanted $99. I got my MJ manual for $20 on Ebay and I'm guessing XJ ones go for about 40 bucks.

Just because I don't care doesn't mean I don't understand!
'88 MJ SporTruck shortbed
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K

 

I got my 1995 XJ/YJ manual from the publisher for 80 bucks to my door. Another thing you might want to think of is weather or no your timing chain slipped a few teeth. I had a 258 engine in an 83 AMC that used to do it all the time. Unfortuneatly you dont have adjustable timing so you can't play with the timing and see what happens. The only way to really know is to pull the timing cover and have a look. Even if the parts are good you may want to just replace em while your in there. If you choose to do it that is.

 

Yeah, that's possible -- how many miles are on your truck, Adam? It'd be a strange coincidence with the clutch going out, but those things happen.

I was lucky that my engine finally lost oil pressure b/c the tensioners for the chain were just about to let her slip away. I say I was lucky to "lose" my old engine the way I did. I drove her 45 more miles to the spot I pulled it out at. With the timing chain deal, you don't get that.

Just because I don't care doesn't mean I don't understand!
'88 MJ SporTruck shortbed
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K

 

My audi has a timing belt, if the belt breaks all the valves will hit the head and bend, this happend to my friends audi V8, he had to replace all 32 valves, not cheap. If the timing chain were to break on my jeep would there be any damage?

1990 XJ Laredo 4.0 5spd 180kms
re-wired and relayed high wattage lights, flowmaster

 

it's got 160,000 miles on it

88 xj, 2 door, black, 4.0L, 5 speed, NP231, rear sway bar off, air box opened up. 30x9.5 BFG AT's

 

If the timing chain is the origional it would be a prime suspect.

 

It depends on how far out of whack the timing chain gets. The timing chain regulates the position of the camshaft versus the crankshaft. If you get out of synchronization, you can have a valve opening (which moves the valve stem and head into the cylinder) when the piston is returning to it's top position -- aka BANG!!!

Lucky people have their timing chain either explode or totally derail. Although these two occurences can lead to worse problems alone, it usually prevents the collisions because the cam is no longer driven. If the chain is just stretched and continues to operate after a quick slip, well, that's what your friend had.

Just because I don't care doesn't mean I don't understand!
'88 MJ SporTruck shortbed
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K