'89 xj new modified motor, won't start.

[Troy's xj]

Hello. I'm a new member but I've been to this site before. I grew up a die hard Ford guy via my father & grandfather. I bought my first Jeep almost six years ago after my daughter was born and I needed a more family friendly vehicle. It is an '86 Cherokee. Aside from the underpowered 2.8L v6, it has been the most reliable, dependable rig I've owned. A couple of friends who have owned Jeeps gave me a lot of grief for buying the 2.8. Lesson learned. After listening to them praise the 4.0 for having decent power and saying it was a "bullet proof" motor, I recently bought an '89 Cherokee Limited w/o the motor in it. I had the 4.0 sent to a local machine shop. It has been bored, zero decked, balanced, comp cam, Clifford performance headers, and magnaflow exhaust. Now, the bonehead who pulled the engine before I bought the rig cut through all the vacuum lines and didn't label anything. I have never worked on vehicle that was newer than '75, so I was left to try to piece everything back together. The electrical connections all seemed self explanatory & the vacuum diagram was fairly easy to follow. So I got the engine in place & couldn't wait to start it up to break it in & see how it sounded! Therein lays my problem, IT WON'T START!!! It's getting fuel, has spark, timing ok, dist. & rotor ok, new plugs, new battery. It turns over strong, just won't fire up! I'm baffled. I know I'm a new member but I hope you guys can help. When I get this thing going I will be doing a lot more mods & would like to post pics & info. I appreciate any info you guys might have and look forward to continued correspondence from here on out.
Thanks so much,
Troy

 

[crawlingxj]

did you check the camshaft position sensor

 

[Troy's xj]

I was told that if the positioning sensor was bad, then I wouldn't have spark; I have spark. That's why I'm kinda lost as to what to do now.

 

[crawlingxj]

i cant remember if i had spark or not when mine went bad. but it doesnt hurt to check i know they are known to go bad.only thing remember is it was a pain in the butt get to.

 

[dingus]

something with the injectors? you have fuel at the rail???

 

[crawlingxj]

something with the injectors? you have fuel at the rail???

i had that problem also my injectors where cloged but it ran for a few secs then die. i ended up replacing all my injectors and ran great ever since

 

[Troy's xj]

I have fuel @ the rail, pressure is good, everything checks out good. I recently had a friend of mine come over,(he owns a mechanic shop), He siad it has to be a timing issue. I had already checked the dist. @ TDC on #1 cylinder, that was ok. I also put a timing light on it. That was ok too. Now here's the thing, I had two motors that came with the jeep, & two flex plates. That's right, the sensing rings on the flex plates are slightly different. My friend said that would create a timing issue if the crank shaft positioning sensor is telling the injectors to fire @ different time than the plugs. Next step: drop the transmission & put the other flex plate in. Why are they different? Nobody seems to be able to answer that question. The local Jeep dealer service tech said that maybe it came out of a grand cherokee or it could be from a different year & the manufacturer sometimes, for whatever reason, has different components in same models of the same year. Who knew?? Thanks for the replies & I'll let you guys know what the outcome is after I switch the flexplates. I would like to hear any comments you might have on this subject also. thanks again.

Troy