I'm out of ideas

OK, my buddy just picked up an '89 limited with a rebuilt motor. It's been driven one block and in that time the exhaust got red hot, and it did not run well at all. The guy who put the new engine in work is suspect . The sparkplugs were out of order and it barely ran, and wouldn't run if they were right. So we dedided the timing must be off. The distributor and timing chain were suspect so we pulled them and set them to specs. There is spark at the coil and the plugs. The engine just cranks with an occasional small backfire through the intake. I know it's not the cps because that kills the spark and I swaped the MAP and coil in from mine to see if they were defective. I'm out of ideas on this one.

well if the exhuast was getting red hot how about the cat being clogged causing to much backpressure. the only other thing i could think is along the lines you are.not enough spark and to much gas the unburned gas is making it the exhuast and burning the rest of the way off down there.

check the O2 sensor as well

Red hot exhaust can also be a sign of drastically retarded timing, and if now it backfires through the intake but doesn't start, I wonder if it's too advanced. Have you tried reindexing the distributor one tooth further back?

I am assuming that after redoing the timing chain, etc. you were careful to check that the distributor is not 180 degrees off, as might occur if you set the crank to TDC on the wrong cycle. If not, you might want to double check that. Don't assume that the previous mechanic got it right, because that might be why he reordered the plugs. Make sure that when the rotor is at #1, cylinder #1 is at compression TDC not exhaust TDC. When that is done, make sure the plugs are indeed in the right order.

This sounds almost exactly like what happened to my friend's cavalier. He had a bad timing chain. The thing was, the chain was OK, but it went out of timing because the tensioner went. He replaced the timing chain and tensioner and that fixed it. It sounds almost identical to your problem though, it was back fireing through the intake and we were getting spark to All plugs. maybe you reset the timing, but the tensioner on the chain is bad, so it just goes out again. Now this was a GM 2.2 OHV I worked on and it has nothing in common with the 4.0 other than being OHV I guss, so this might not be the problem, but it sounds really simular.

the_bandit87 said:

This sounds almost exactly like what happened to my friend's cavalier. He had a bad timing chain. The thing was, the chain was OK, but it went out of timing because the tensioner went. He replaced the timing chain and tensioner and that fixed it. It sounds almost identical to your problem though, it was back fireing through the intake and we were getting spark to All plugs. maybe you reset the timing, but the tensioner on the chain is bad, so it just goes out again. Now this was a GM 2.2 OHV I worked on and it has nothing in common with the 4.0 other than being OHV I guss, so this might not be the problem, but it sounds really simular.

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A tooth off on the cam timing could very easily cause these problems, I think, but there's no tensioner on the XJ timing chain, and CW says he checked the chain and set it to specs. If he did it right, the problem must lie elsewhere.

There are timing marks, closer to the 1-2 Oclock position when looking at the front of the motor. There is a "0" cast into the timing marks.
The timing index mark on the balancer pully, is hard to see, I usually mark the pulley with a cold chisel across the face and move the mark to the front.
The easy test is, with a compression gauge run Number 1 up the compression stroke by hand (near the top but a bit before), with a piece of welding rod (slightly curved) make sure number one comes all the way to the top, if you go past, back up and make the last motion to your right on the crank (to take the tension up on the chain). Timing marks should line up, usually the second tick on the timing marks (close enough). Rotor should be pointed at or actually slightly after number one on the cap. Cap is almost always marked with a 1.
If everything is good to this point, remove the valve cover and look at the number 1 rockers, they should be close to level with each other and you should be able to wiggle the rockers a little, maybe even spin the push rods by hand.
A compression test will tell you quick if the valve timing is out. A vacuum gauge reading with the motor running, will tell you quick if the valve timing is out or there is a faulty valve, the needle will swing wildly across the face.