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timing or sensors or flexplate

D

dodge90wood

NAXJA Forum User
Location
Evanston, Wy.
O.k here we go. I have a 1990 jeep cherokee limited with the 4.0l six cylinder. I just put a brand new engine in the jeep yesterday and it fired up fine. The only issue of many is that when i go to give it throttle it spits, sputters and backfires. I have checked I swear alomost everything.

crank sensor
tps
map sensor
distributor cap/ rotor
plugs / wires
dampner hasn't spun on the rubber my tdc is perfect this engine was rebuilt by the manufacturer

I just barely pulled the tranny back out and pulled the flex plate thinking that I bent it or something putting the engine in. We did a run out on the flex plate the chilton manual say to not be in excess of .016 the one I pulled off had three spots on it that was low or out of round by .020 so I assumed that was the problem. The used one that I had laying around only had one spot that was kind of flat or out of round by .017 which is pretty close to .016 I think it might work.

Can anyone give me more ideas about what to check.

I have also pulled the keeper off of the dist. and stared the engine and when I retard it or turn counter clockwise it will pick up and run descent. The alignment hole on the dist. is covered up about half way with the tab

on the dist. :paperwork
 
Good call 89xj....
I had the same problem when I dropped in my new motor....even though I thought the dist was installed properly it was off.I re-indexed the dist and it runs fine.
I'm willing to bet the dist is off because those are classic symptoms....
 
x3 distibutor cap. Mine sputtered like crazy after putting the engine back together when I got it. Searched here and was told advance one tooth, sure enough has run fine ever since. Try that first cause it's so easy to do.
 
ok I have tried retarding the dist one tooth and advancing it one and in those positions it won't start at all. WE decided to pull the timing cover back off and it appears to be correct. I was curious what would it do if the engine was the high output and I put the intake of mine onto it; with the original computer would this be a chance. I got the motor from autozone but it actually came out of spokane washington. the paper work says it is the correct one but how do I tell the difference between the h.o and the regular?
 
another idea:make sure your map sensor is good and the vac line that runs to the tb is intact...oh and you are installing the dist with the motor on #1 cylinder at tdc on the compression stroke correct?I ask this because I know how easy it is to get it 180* out
 
I have double checked for it being 180 out and I wasn't. I even pulled the timong cover back off to see if the builder of the new engine didn't get the timing gears set right and they were correct. I was reading some where else that the knock sensor could cause the backfiring and not send the right signal to the ecm/ecu is this true?
 
:huh: Alright I am losing my mind I started to work on this again last night and come up with nothing. I went to moab over the weekend with the family and was wishing my jeep was running, but no the dang thing wants to argue with me:badpc: . SO this is what I tried I tried another ecm out of another jeep, yes knowing that it was the right one, and the same symptoms appear. I also double checked the
*map sensor
*cps
*icm
*tried a brand new tps
*messed with the high idle doomaflotchi on the throttle body


Now answer me this why is it possible that the engine can run when I unplug the coil wire from the coil? Do I have a bad ground, electrical problem, bad distributor, could there be something to do with the tranny wiring:looney: ? I feel like I have tried everything, I was just hoping that when I left for a week the thing would self mend and I could come home and it would vrooooom start up. Nope didn't happen, if any one can help it is all of you guys with xj's and there significant problems.
 
The plug on the MAP sensor can be installed into the throttle body two ways. Make sure it it correct. It looks fine but won't run for crap.
 
89CherokeePioneer said:
The knock sensor would only retard timing. Disconnect it if you want to rule it out, it simply won't retard if spark knock ever occurs.

Did you check fuel pressure?
Click to expand...

Wrong. Have you noticed that the wire to the knock sensor is shielded. If you leave it disconnected it will pick up even more noise and retard the spark all the time. The sensor is nothing more than a piezo microphone tuned to approximately 18kHz.
 
Thanks I tried unplugging the knock sensor and noticed no change, and as far as the map sensor goes mine just has a green pluggin that looks as if it can go only one way but I will double check tonight.:wierd:
 
As a last ditch resort, you could try disconnecting the Manifold air temp sensor. It screws into the intake, two wires coming out of it. The CPS harness is next to it up atop. I've heard of that causing problems, but I haven't seen it or had it occur to me.

I might try to get a used ECM to see what that does, but more likely if I were you I'd quit and see what a trusted shop had to say.
 
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