1999 TJ intermittent no start

Jody Ray

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Original poster
Joined
Jan 4, 2026
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5
Location
Oklahoma
my wife has a 99 TJ 4.0L automatic trans. it began turning over but not starting a while back after being driven and warmed up good. let it set a while and it will eventually start up and she can drive away and no issue. I researched a bit and determined the CPS was going bad so I bought the best one i could from napa. problem seemed to go away but started doing it again. finally did it to me at O'Reillys one day so I just bought another CPS and changed it. fired up and I drove off. continued to have same issue and today she started it and as she was pulling out of driveway it died and wouldn't start. I took air breather off and sprayed starter fluid in it. still wouldn't start. pulled a plug wire and stuck a new plug in it to check for spark and it has spark. also I've put a fuel pump in it just because. im at a loss.
 
Is it throwing codes? If so, what are they?

I'd be inspecting the wiring harness for damage personally. All it takes is tiny little break in the wiring.
 
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my wife has a 99 TJ 4.0L automatic trans. it began turning over but not starting a while back after being driven and warmed up good. let it set a while and it will eventually start up and she can drive away and no issue. I researched a bit and determined the CPS was going bad so I bought the best one i could from napa. problem seemed to go away but started doing it again. finally did it to me at O'Reillys one day so I just bought another CPS and changed it. fired up and I drove off. continued to have same issue and today she started it and as she was pulling out of driveway it died and wouldn't start. I took air breather off and sprayed starter fluid in it. still wouldn't start. pulled a plug wire and stuck a new plug in it to check for spark and it has spark. also I've put a fuel pump in it just because. im at a loss.

You say you spray starter fluid into the intake manifold and it doesn't start, yet you have spark when you test the spark plugs? That doesn't make sense.
 
Is it throwing codes? If so, what are they?

I'd be inspecting the wiring harness for damage personally. All it takes is tiny little break in the wiring.

I roughly ran thru wiring. I didn't see anything glaring. have not put a meter to it though.
 
Well if you have spark, and you have fuel...and it's not starting...then it's either compression or timing.

I'd be testing fuel pressure. Verifying spark. Then a compression test. Inspecting the cap, rotor and plug wires. Checking the battery voltage at rest and while cranking.

-Mac
 
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Well if you have spark, and you have fuel...and it's not starting...then it's either compression or timing.

I'd be testing fuel pressure. Verifying spark. Then a compression test. Inspecting the cap, rotor and plug wires. Checking the battery voltage at rest and while cranking.

-Mac
it runs fine when it does run. I don't believe it's either issue.