Jeep YJ will not start - HELP! I've tried everything!


wowen727

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Apr 6, 2021
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4
Location
Tulsa, OK
my '93 yj with 4.0 and manual transmission will not start. i have recently acquired this jeep and before me, it had sat undriven for 3 years . my first thought was to run through the entire ignition system most of the ignition system components were testing within spec but, i still replaced them and will be keeping the "extra" parts in the vehicle for emergencies.

i replaced the timing chain as soon as i got it (284k miles) i was able to confirm that the timing did not jump a tooth. after putting the motor back together, i began chasing down what i perceived
jeep 3.jpg
jeep 2.jpg
to be an electrical gremlin (radio cutting in and out, windshield wipers, and a/c blower randomly coming on, short in courtesy lighting) after trying to run through the harness under the dash the best that i could, moved to the engine bay. i found some exposed wires on the cam sensor connector - this has been fixed. gave her a go and VROOOM!

fast forward a couple of weeks, i began stripping all of the trim, soft top components as well as the entire cab of the vehicle to get her painted and spray line the pan. the only wires i willingly touched were the speaker wires and dome light.

I hopped in the jeep the following morning to drop it off at the paint booth. she started up, cut out once but kept running and about 30 seconds later, died. now no start. she will crank all day long but will not fire.

so far, here are parts that have been replaced, tested and are known to be good:
- fuel pump
-fuel filter
- fuel regulator
- PCM has not been replaced but check engine light still comes on and i am getting appropriate reference signals at cam sensor, crank sensor, injectors and coil
- distributor and cam sensor
-crank sensor (literally went through 3 of these strait from the parts store- the brand new ones were not testing within spec)
- coil
-plugs (plug wires on the way but highly doubt this is the issue. seem to be testing fine)
- injectors (upgraded to 4 orifice injectors)
- all relays are known to be good
- 02 sensor tested good
- ignition lock cylinder
- i tested the ignition switch and i could have sworn i read a broken circuit for a split second. $20- new one is on the way
- new turn signal switch (left turn signal was broken)
- replaced the oil pump with a high output (oil pressure was getting dangerously low when motor was warmed up at idle)
- all grounds have been replaced with new connectors

seems to be an electrical issue. maybe some lose connection in the dash? i have recently found out that the inside of the windshield frame is toast- rusted plum out. so a new windshield frame is on the way. any ideas of common wiring issues within the dash would be appreciated. i believe the windshield has to be removed to open the entire dash, so if i need to do so while i have it removed, now is the time.
 

jeepjoe43

YJ Enthusiast
Joined
Dec 4, 2020
Messages
242
Location
Black Canyon City, AZ 85324
Had an electrical gremlin with mine, too.
It was cutting out on every bump in the road.
No codes.
Turned out to be a stressed supply wire for the coil.
Found it after I replaced the coil and broke it off at the plug that goes into it.
I didn't even know I had broken it.
Was able take the plug apart, solder a pigtail on, and crimp it back into the harness.
Been good since.
 
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wowen727

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Apr 6, 2021
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Tulsa, OK
Jeepjoe43, that’s a very good point that you made regarding the coil primary wires. However, given the fact I have looked those over very closely, I don’t think that is the issue. I’m pretty certain it is something in the dash. The Jeep ran fine before I pulled it into the garage to strip it for paint. I’m thinking I could have knocked something under the dash when I was removing the carpet- just not sure what it could be.
 

Flyer58

YJ Enthusiast
Joined
Apr 12, 2020
Messages
366
Location
Magnolia, Texas
1) Can you see the spark plugs sparking if you remove them and lean them against the block?
2) can you test the fuel pressure at the rail to see if it's priming and maintaining pressure?

Sounds like you've changes everything but I'm thinking about visual conformation they're working.

I would also remove and clean the tabs on every fuse and relay in the fuse box. Corrosion there is common and is the birthplace of many gremlins.
 
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wowen727

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Apr 6, 2021
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Tulsa, OK
1) yes, i have visually tested the plugs - I get a nice, strong bright blue spark on all 6 cylinders.
2)i have tested fuel pressure. or, lack there of. I have a known issue with fuel pressure. it is not holding pressure unless the vehicle is running. after leaving in the garage, I can smell gas fumes. this has been an issue since i got the Jeep. once I fixed the cam sensor and got it running, the leak in the system did not cause a no-start situation.

when i started it yestereday morning to take to the paint shop, it had a long start, as usual. i believe this long start is related to the fuel pressure building up. However, after the motor started, it shut off for a second or two then fired right back up (no stutter, shutter or acting like it was starving for fuel or air) after running for about 1 minute, it just died, as if i turned the ignition off. again, no stuttering at all.

as for the relays and fuses: i have sandblasted all of the contacts and even interchanged them with a known working components. i have even tested for resistance on each one.
 
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wowen727

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Tulsa, OK
has anyone heard of the ignition switch wearing out? I am not talking about the actual contacts because I have tested the functionality of the switch- it is operating as designed. however, I know that the steel rod pushes down on the switch to engage it. so, maybe the plastic has worn down to a point that the rod is not fully depressing the switch. Afterall, this rig does have nearly 300,000 miles on her!

when i get home today i will mic the switch position in relation to the rod and compare it to the new switch.

i have never felt so defeated before with regard to working on vehicles. i HAVE to find the solution and understand it.
 

jeepjoe43

YJ Enthusiast
Joined
Dec 4, 2020
Messages
242
Location
Black Canyon City, AZ 85324
Jeepjoe43, that’s a very good point that you made regarding the coil primary wires. However, given the fact I have looked those over very closely, I don’t think that is the issue. I’m pretty certain it is something in the dash. The Jeep ran fine before I pulled it into the garage to strip it for paint. I’m thinking I could have knocked something under the dash when I was removing the carpet- just not sure what it could be.
Just thought I would share what I found on mine.
I replaced every sensor I could find, the ignition switch, fuel press regulator, fuel pump and tank (mine was BROKEN) and finally the coil.
The ignition switch was pain in the arse, the tank & pump were an absolute war, 5th skirmish was the charm.
It also had a broken hose to the filter, but it ran, it just sprayed gas everywhere.

Ignition switches don't really wear-out, they fail when a contact overheats and kills the little coil springs under them.
They overheat because of contact wear or something shorting out down the line...
It could be wear at the key mechanism, but I doubt it, if it's cranking, it's throwing far enough.
Be sure to tape the rod to the column when you pull the switch, don't let it fall out!

As for fuel pressure, you should have 35-38psi, not holding pressure is the check valve in the pump.
Had the same slow start thing, too.
Sometimes the ground for the pump rusts off the sending unit.
 

Soto167

New Member
Joined
Apr 8, 2021
Messages
1
Location
Stroudsburg
my '93 yj with 4.0 and manual transmission will not start. i have recently acquired this jeep and before me, it had sat undriven for 3 years . my first thought was to run through the entire ignition system most of the ignition system components were testing within spec but, i still replaced them and will be keeping the "extra" parts in the vehicle for emergencies.

i replaced the timing chain as soon as i got it (284k miles) i was able to confirm that the timing did not jump a tooth. after putting the motor back together, i began chasing down what i perceivedView attachment 117360View attachment 117361 to be an electrical gremlin (radio cutting in and out, windshield wipers, and a/c blower randomly coming on, short in courtesy lighting) after trying to run through the harness under the dash the best that i could, moved to the engine bay. i found some exposed wires on the cam sensor connector - this has been fixed. gave her a go and VROOOM!

fast forward a couple of weeks, i began stripping all of the trim, soft top components as well as the entire cab of the vehicle to get her painted and spray line the pan. the only wires i willingly touched were the speaker wires and dome light.

I hopped in the jeep the following morning to drop it off at the paint booth. she started up, cut out once but kept running and about 30 seconds later, died. now no start. she will crank all day long but will not fire.

so far, here are parts that have been replaced, tested and are known to be good:
- fuel pump
-fuel filter
- fuel regulator
- PCM has not been replaced but check engine light still comes on and i am getting appropriate reference signals at cam sensor, crank sensor, injectors and coil
- distributor and cam sensor
-crank sensor (literally went through 3 of these strait from the parts store- the brand new ones were not testing within spec)
- coil
-plugs (plug wires on the way but highly doubt this is the issue. seem to be testing fine)
- injectors (upgraded to 4 orifice injectors)
- all relays are known to be good
- 02 sensor tested good
- ignition lock cylinder
- i tested the ignition switch and i could have sworn i read a broken circuit for a split second. $20- new one is on the way
- new turn signal switch (left turn signal was broken)
- replaced the oil pump with a high output (oil pressure was getting dangerously low when motor was warmed up at idle)
- all grounds have been replaced with new connectors

seems to be an electrical issue. maybe some lose connection in the dash? i have recently found out that the inside of the windshield frame is toast- rusted plum out. so a new windshield frame is on the way. any ideas of common wiring issues within the dash would be appreciated. i believe the windshield has to be removed to open the entire dash, so if i need to do so while i have it removed, now is the time.
Just thought I would share what I found on mine.
I replaced every sensor I could find, the ignition switch, fuel press regulator, fuel pump and tank (mine was BROKEN) and finally the coil.
The ignition switch was pain in the arse, the tank & pump were an absolute war, 5th skirmish was the charm.
It also had a broken hose to the filter, but it ran, it just sprayed gas everywhere.

Ignition switches don't really wear-out, they fail when a contact overheats and kills the little coil springs under them.
They overheat because of contact wear or something shorting out down the line...
It could be wear at the key mechanism, but I doubt it, if it's cranking, it's throwing far enough.
Be sure to tape the rod to the column when you pull the switch, don't let it fall out!

As for fuel pressure, you should have 35-38psi, not holding pressure is the check valve in the pump.
Had the same slow start thing, too.
Sometimes the ground for the pump rusts off the sending unit.
There is a ground wire under the dash that works the fuel pump and probably a few other things . That was my problem when I pulled my dash. Ran fine before then . Then would just crank . Had a friend who picked it up and then she started right up. Good luck
 
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JKP

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Feb 20, 2021
Messages
6
Location
Warner Robins GA
Your fuel pump has a bad check valve since it's not holding pressure.

Have you verified the spark since the no start? If you still have spark, dribble some gas or spray some starting fluid into the throttle body and see if it hits.
 
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