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cranks but doesn't start

So I got this '96 Jeep Cherokee XJ that cranks but doesn't start. It's got around 180k on her but I keep everything in good shape. Batt seemed strong.

I used to drive it everyday but this past year I've driven it only about twice a week. It's been just slightly slower to start in the last couple of months, but just barely slower. Was guessing it had something to do with aging plugs or something.

Drove it yesterday and everything was normal like always, sat overnight and today it cranked but didn't catch.

Any ideas on where to start?
 

dustybumpers

don't play well w others
First thing would be to check codes.

Not sure which motor you have, but the 4.1 six is known for bad crank shaft sensor.
 
So far I've been able to run a couple tests..

Hooked up a fuel pressure gauge and first key turn got it up to only 20psi. Second turn got it up to 45. And third and subsequent turns got it up to 48. It only fell to 43 after 2 minutes so I think that means the fuel pressure is good.

Hooked up a spark tester between a plug and wire and it didn't light at all when cranked so I'm guessing I've got a spark problem. I'll start by doing a tune up with new rotor, cap, wires and plugs then see what happens. After that it I'll go after the crank position sensor and spark sensor.
 

dustybumpers

don't play well w others
Order a crankshaft sensor. Honestly, you will find your problem. The computer shut down the tfi because it thinks the crank isn't turning

Sent from my SM-N960U using Tapatalk
 

Fellro

Moderator
Staff member
You are correct in that it has a spark problem. Trick is, tuneup or trigger trouble? Unless it has been running poorly or you got water under the cap, it is more likely a control sytem failure, which a crank sensor is part of. If the crank sensor is bad, the computer doesn't recognize that the motor is even turning.

Another quick check on the crank sensor is to listen to the fuel pump. It should run at first when you turn the key on, then stop after a short bit. Then it should come back on when you crank it. If it doesn't, crank sensor is definitely suspect.
 

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