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XJ help

xjshorty21

xjshorty21

Buckle Up And Shut Up
Location
Sandy
so i put in a motor about a month ago ran fine .... then thursday
(a coarse during the huge snow storm ) it started jolting and like cutting out like the fuel filter was plugged then died.... got it towed home.... replaced the fuel pump , fuel filter, changed the crank sensor to a old one that i had. tryed a different coil played with the timing but still no start .... we tried another computer and nothing and tighted all the wires nothing i need some help or ideas why it wont start please help me its a 91 xj, 4.0 , aw4
 
UNSTUCK

UNSTUCK

But stuck more often.
First thing to do is stop throwing parts at it. It costs a lot to do that. Back to basics: an engine wont run for only a few reasons.

Fuel
Spark/timing
Compression

Fuel pressure is pretty easy to check, if its there, move on. It's also easy to see if you have spark coming out of a wire. If its there, move on. Now, you can pull all the plugs and then put your thumb over each hole, one at a time to check for compression, but you should use a guage.

Try these tests and let us know what happens.
 
K

kowe69

wannabe
Location
West Valley, Utah
If you have fuel and spark, then you have either lost timing or compression, or both. Could be the timing chain jumped. Another possible cause is a plugged catalytic converter. Remove an oxygen sensor (if equipped) to vent excess pressure and see if it starts. If none of these suggestions work, stop wasting time and money and take it to get diagnosed by a competent mechanic. Usually spending the $70 or so to get it diagnosed will save you hundreds in parts you didn't need. Good luck.:)
 
Last edited:
K

kowe69

wannabe
Location
West Valley, Utah
xjshorty21 said:
to time it dont you find tdc and turn the crank twice and reline the distrubor back up correct ?
Click to expand...

? Never heard that before. You need to find TDC of the compression stroke in cylinder 1. Once you do that, remove the distributer cap, the rotor should point to the number 1 plug wire on the cap, if it is off, something moved. Maybe the distributer, cam etc.
 
UNSTUCK

UNSTUCK

But stuck more often.
If it was running then all of a sudden it wasn't running, I dought it's your timing. Was your distibutor lose? Before messing with it, try to start it with either. Then you will know for sure if it's fuel or spark.
 
UNSTUCK

UNSTUCK

But stuck more often.
xjshorty21 said:
to time it dont you find tdc and turn the crank twice and reline the distrubor back up correct ?
Click to expand...

All that would do is put you right back where you started from. Don't forget, each cylinder has 2 TDC's. If you're going to check timing, but a light on it first. If your light is off the lines then you know you have timing issues.
 
UNSTUCK

UNSTUCK

But stuck more often.
kowe69 said:
? Never heard that before. You need to find TDC of the compression stroke in cylinder 1. Once you do that, remove the distributer cap, the rotor should point to the number 1 plug wire on the cap, if it is off, something moved. Maybe the distributer, cam etc.
Click to expand...

If you're on TDC #1 compression then remove the cap, the rotor should be just past #1 plug wire. Big difference in a few degrees.


I am assuming it isn't even trying to start, right? Just cranks over all day long? Any funny noises?
 
K

kowe69

wannabe
Location
West Valley, Utah
UNSTUCK said:
..... Big difference in a few degrees.
Click to expand...

A few degrees only makes a difference when talking about engine performance. If the rotor was pointing at the right wire, it is close enough to start the engine and determine that timing is NOT the problem. If it was the problem it is likely it would be off by much more then just a few degrees. Remember, we are trying to help him rule out potential problems, not tell him to skip them.
 
dungbeetle

dungbeetle

Registered User
Location
Provo
I have a 94 Grand Cherokee with a 4.0 liter engine. I think it's probably the same engine as you have. When I got it, it was wrecked, and by the time I had it fixed, it had sat a round for over a year at my house. No telling how long it was at the auction. But, it started and ran just fine after I changed the plugs. After that, it fouled the plugs completely in about three different running sessions. Then it would just sit and crank without a hint of ignition. I changed the plugs about 3 times in all before I figured out that the #3 injector was hanging open. Once I replaced it, it ran perfect. Haven't had a problem since.

My advice is to change the plugs or at least check them before you worry about anything else. I used NGK.

Richard
 
DaveB

DaveB

Long Jeep Fan
Location
Holladay, Utah
My brother bought a TJ from the auction block and it ran fine when they did a test run before the auction. It died just before the auction with the same symptoms as yours. He got it for less than the minimum bid and we found that it was the plugs. There must be something about sitting for a while that does them in.
 
dungbeetle

dungbeetle

Registered User
Location
Provo
Basically, old gas turns to varnish. Varnish fouls the injectors, and keeps them from turning off cleanly. That puts too much gas in the engine which fouls the plugs. Interestingly, if you can get the engine going on a few cylinders, revving it up to a high rpm and then shutting the throttle can create a high vacuum in the intake manifold which can suck the crap out of the injectors, and start them working again. I was listening to my injectors with a stethoscope one day when I heard one clean itself out and start working as I revved the piss out of the engine. Unfortunate, I have not seen that work on a fouled plug. Once it fouls, the only thing that worked was to pull it and either replace it or clean it. BTW, I used Denso plugs instead of NGK as I previously posted.
 
phatfoto

phatfoto

Giver of bad advice
Location
Tooele
Something I haven't seen anyone ask for yet... There is a simple diagnostic test available without tools. It just gives an idea of where to start, not always specific items. DO NOT START the vehicle. Key on-key off, key on-key off, key on and watch the check engine light. After it goes off it will pause, then it will flash codes. these are simple to read, a series of flashes with a short pause and another set of flashes. Longer pause and more. Example... flash, pause, flash, flash, longer pause, flash, flash, flash, flash, flash, pause, flash, flash, flash, flash, flash. No more. THese were 12 and 55. 12 shows the battery might have been low or disconnected sometime in the last 100 key cycles, the 55 is an end of test. This works on the OBD1 Chryslers. So this SHOLD work on your 91 as long as the CEL isn't burnt out.

Same key sequence on my 03 Neon shows P codes which are far more specific.
 
xjshorty21

xjshorty21

Buckle Up And Shut Up
Location
Sandy
phatfoto said:
Something I haven't seen anyone ask for yet... There is a simple diagnostic test available without tools. It just gives an idea of where to start, not always specific items. DO NOT START the vehicle. Key on-key off, key on-key off, key on and watch the check engine light. After it goes off it will pause, then it will flash codes. these are simple to read, a series of flashes with a short pause and another set of flashes. Longer pause and more. Example... flash, pause, flash, flash, longer pause, flash, flash, flash, flash, flash, pause, flash, flash, flash, flash, flash. No more. THese were 12 and 55. 12 shows the battery might have been low or disconnected sometime in the last 100 key cycles, the 55 is an end of test. This works on the OBD1 Chryslers. So this SHOLD work on your 91 as long as the CEL isn't burnt out.

Same key sequence on my 03 Neon shows P codes which are far more specific.
Click to expand...


i did this and all i got was 12 and 55 ... but i will check the plugs but i changed them about a month ago plug one cindler is alittle black but i will check the others and look at the fuel injectors
 
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