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[Abbott]

Hey everyone,

She wont start....

Its a TJ 4.0L, the battery is good, it turns over, I think the fuel pump is good (I don't really know how to check it except to listen for strange sounds). I am assuming it is some sort of spark issue then and I dont know how to remove the spark plugs. There is some sort of clip that has to be taken off, but from there I dont really see how to unscrew them.

-Thanks, Cody

[Axle]

If you are not sure, don't mess with it. but, check fuses?

[Twisty]

You should hear your fuel pump buzz when you put the key in the "run" position.  If you have no spark, id check the cps on the top drivers side of the bell housing.

[Ian]

The fuel pump can sound fine and not be working.  Do you have an engine code?

[Posimoto]

Buy a multimeter if you don't have one (you can buy them for less then $5) and check the battery voltage should be 12.6 (fully charged). After verifying the battery is fully charged check for spark.   

Do you know someone with a timing light? If you do put the red clamp on the positive side of the battery and the black to ground. Then one at a time put the big clip on each spark plug wire. Turn the engine over and if there is spark the timing light will flash.

It's a very easy and quick way of checking for spark without removing wires and plugs.

Let us know how you make out.

[Twisty]

He might not have spark plug wires.  The coil packs go right on the spark plugs.  No dizzy and no wires


I did not know that technique for checking spark.  Thanks for the tip Chuck.

[Posimoto]

Wow, no wires......the engineers are taking all the fun out of it.

[Ian]

He might not have spark plug wires.  The coil packs go right on the spark plugs.  No dizzy and no wires

really?

[Bluerocket]

Lots of new cars are that way, which is nice and not nice.
Takes away the distributor part, and a bad coil only effects 1 cyl so it wouldnt be the issue.  This helps with reliability.

It does leave you open to an issue I experienced in my 04 chevy.  The computer assumes timing based off crankshaft sensor, and as the timing chain stretched over time the timing became off (causing random misfires logged on all cyls).  The computer felt the timing was different than it actually was.   This baffled the dealer for a while, and caused CEL's.  Eventually they ended up having GM corporate fix it, which was simply to trigger a "re-learn" cycle on the computer I'm told.  This resets what the computer thinks is TDC, so its timing is right again. 

Not that this is the issue with this jeep, just an observation on modern ignition systems.  My vote is CPS or fuel for this jeep.  Is there a schrader valve you can check fuel  pressure with on the fuel rail?

[Abbott]

Battery voltage 12.6. All fuses good. No engine code.

[Posimoto]

Has the engine run since we had the heavy rain Monday?

You could also spray starter fluid in the throttle body and crank it. If it stumbles and doesn't run its a fuel condition.

[Ian]

what year is your 4.0 tj? 

[j-dawg]

did you do anything to it prior to the no start problem...
ie: install a radio, or something else?? wondering if you accidentally
messed something up...if not...i'm going with CPS

[Abbott]

Yeah it ran good all yesterday and then just decided to die last night. I thought that it might have something to do with the automatic starter that the person before me had installed, but I pulled that out and still nothing.

I just said screw it and had it towed to the local shop, hopefully it is nothing major.

[Posimoto]

We were just starting to have fun with this repair and you go and have it towed away.....

J/K, but it would have been fun to follow it through until we found the fix.