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Discussion Starter · #1 ·
I am having an odd problem with my 89 XJ, it was running fine but got very bad gas mileage (roughly 250k a tank) but about a year later it started doing weird things, such as bogging down to the point where you cant even accelerate and would just backfire out the intake (restart was a temp fix but replacing the ignition control module seemed to fix it) then a few weeks later, I started it up, and it ran like crap, less power then if it was running on 4 cylinders, and was really rough, and shook the whole vehicle quite a bit, but it still ran...
it was a few weeks later that it stalled after it shook more then usual, went to restart it, but it wouldn't start, it really was trying to, as it sputtered/sorta ran, but it would not actually start. The day after is when I bought a second XJ (1990) for parts, I suspected that it had something to do with the timing, so I swapped the whole distributor over and set the engine to TDC and made it so the distributor rested at 5 o'clock, (Ok yes, I messed it up and didn't put it in on the compression cycle (180 off I guess), which blew my muffler to bits after excessive cranking, fixed it and it ran) I swapped over a few other sensors afterwards (just because I knew they worked and mine were questionable, cps, iac, ait, tps, fuel sending unit) however there was so little power that I had to floor it to get it to move out of the driveway, took it around the block and it stalled 3 or 4 times, the last time is when it died, I have been unable to get it to start since, its getting 150-175 compression on all cylinders, its getting spark, good fuel pressure, injectors are pulsing properly, its getting air, the valves are moving properly and the seals looked good, the timing chain is strong and is lined up properly, yet it will not start. the wire harness seems OK, I couldn't find any broken wires, and I refreshed the grounds, so its not that, it really makes no sense whatsoever.

If anyone could shed some light on this, that would be amazing, replacing parts will not be a problem as I have the parts jeep, hell I even plan on replacing the engine and harness after I rebuild it, but that wont be till the fall, so I need this to work till then.
Thanks.
 

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I had a major loss in power problem caused some issues similar to your bogging down issues, mine ended up being the feul pump. have you checked your fuel pressure?
 

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Discussion Starter · #4 ·
I have replaced the fuel sending unit, with a good one from the parts jeep (it ran perfectly and the pump seems to be fairly new I think it was walbro or something like that) I have a new ICM and swapped over the coil from the working jeep (tested with both ICM and coil) - nothing. I got a orange/blue spark when I tested it from the #4 cylinder (#3 gave me nothing) so its possible that its a problem with spark, but even if 1 cylinder is getting spark, then the engine should at least try and do SOMETHING, but there's just nothing. I was talking to the P/O a few days ago, he said that in 95 the transmission and TCM were replaced due to some kind of problem (he didn't go into detail as time was limited), I remember that when I got the thing on the road there was alot of rust in the place that the tcm mounts, if there is a problem with the tcm, is it possible that it could prevent the PCM from allowing the engine to start? (just a hunch, as I have checked just about everything else at this point)
 

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Time to replace that O2 sensor. That era XJs will not run without them. Replace ECM? As soon as it stopped going on previous presets and running on data it went back to what you had. Had you replaced it you could have saved yourself a lot of headaches
 

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Discussion Starter · #10 ·
TCM swap didn't seem to do anything, however I had the cps unplugged and reattached a few times (when testing voltage) from searching online, I believe that .2 volts is too low to generate spark (should be closer to .5) I will post if it changes anything, however it seems odd that it was working fine on one xj and registered too low voltage when reinstalled.
 

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Discussion Starter · #11 ·
I think I may have narrowed down the problem, I am getting spark from the coil to the distributor, but it does not seem to be going from the cap to the plug wires, it may be caused by improperly indexing the distributor, however I don't know why it would have ran for a few hours then died, I will try and re-index it properly and see what happens
 

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Discussion Starter · #12 ·
I found the problem! turns out, the coolant temp sensor wire had a bare section and was grounding to the intake manifold, I guess the computer got a weird reading from it and decided to prevent the engine from starting.

for some reason it pops out the intake a few times when I floor it, nothing major though.
 

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Glad you found the short. A true short will drain all the power from an ECM. Had that happen on a TJ
 

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Discussion Starter · #14 ·
Yeah, I was just backtracking wires, and found the short.

However, an old problem that I forgot about (had hoped tearing things apart and resembling might fix) resurfaced. Every time I start it cold, it will idle fine (sometimes a bit erratic, but that's because the brake booster is shot and causes a vacuum leak) but if I try and give it some throttle, it will bog down severely, and backfire (enough to blow the muffler to bits) if I do it too long. it just bogs down and won't go, also since I got it running again, if I floor it from a dead stop, it will pop out the intake 4-5 times (only when floored from a dead stop, and a few seconds afterwards) Not too sure whats causing this, but until I find a fix, I cant drive it.
 

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So at this point, you age getting a rough idle when cold, with a known intake leak? Hate to say this, but fix that known issue first. Then look at your throttle position sensor. The Renix TPS can need recalibration. Not sure if there is a thread on here on that or not
 

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Discussion Starter · #16 ·
It it possible that its caused by the TPS I suppose, I replaced mine cause it failed, but I just stuck it on there, I didn't adjust it or anything, so its possible that that is the cause. I tried running it with the brake booster vacuum line plugged, and it made no difference in the bogging down, I have a replacement that I intend to put in when I swap the engine, but right now I am just looking for cheap and temporary "band-aid" fixes till I get that done. I will adjust the tps and see what happens.
 

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No, not under half throttle or better. It is the idling issues I was thinking about
 

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Discussion Starter · #19 ·
I replaced the brake booster today. Its going to take some time getting used to assisted braking XD

I was able to adjust the tps according to cruisers guide and got it spot on, it certainly runs better and accelerates smoother.
however it still misses under 2k rpm and shakes the whole vehicle, I determined this to be a problem with the #2 cylinder, as unplugging the injector their does not change the pitch of the engine, and the spark plug always comes out wet and fouled (regardless of swapping the wire and plug), I've known about this for a while, and is not that important, but what really needs to be fixed is the bogging down when trying to accelerate from a cold start. It honestly feels like its just dumping so much gas when it does anything other then idle that it almost kills it. I will swap out the CTS and see what happens (it was the cause of the previous problem, and I have a spare, so why not) I also swapped the O2 sensor, and will swap the MAP, but I just what to know what your thoughts are.
 
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