OxfordCherokee2

My xj as 190k and has run great for a long time.

In March it died on the road and it wouldn't start again. It was idling rough and the idle dropped off then came back the nearly stalled then finally did. After waiting 20 minutes however it started right up. Of course the check engine light came on so I read it and it said short circuit in the coil pack circuit so I replaced to coil pack. I usually would have just left it but I was leaving on a 530 mile drive to school the next day so I changed it.

Today.
The same thing happened again nearly stalled and then finally did stall. Wouldn't start. So I waited 20 minutes and it started again. But no check engine light. It would crank and crank both times but not start. The fuel pressure is good on the rail and everything is plugged in, nothing rattled loose.

So I'm wondering what could cause it this. I'm thinking that the coil pack is just a side effect of the actual problem.

skife

Sounds like a good time, check the coil harness for any signs of damage.

Turbo X_J

Trouble code indicates a problem in a circuit, not necessarily a component.

OxfordCherokee2

I thought that too and after looking over the wiring as best I could there were no worn spots or anything seeming cut. And with my up coming drive I thought it would be safe just to change it.

Turbo X_J

What's the fuel pressure in psi, have you confirmed no spark? If there is a failure a code is logged whether or not the CEL is "ON". When you cleared the original code did it later return after you replaced the coil pack?

OxfordCherokee2

No the CEL did not come back on after replacing the coil pack and when I say it good I mean that when I take the cap off and press the pin it sprays out I don't have a gauge on it.

I'm kind of thinking it could be the crank sensor.

RTorrez1

The only thing that tells you is that there is fuel in the rail. The only way to check the fuel is with a mechanical pressure gauge and you need to know that you have the correct pressure. For your 01 you should have 49psi plus or minus 5psi. Next time it doesn't want to start you need to check to see if you have a good blue spark and you have the correct fuel pressure.

OxfordCherokee2

The spark is the first thing I usually check when anything won't start but with the coil pack that's not really possible at least that I know of. I guess I could take the coil pack off and put the plug in the pack and turn it over.

Rollincoal420

Sounds like the perfect example of a bad crank sensor.


Just an fyi, the crank sensor is where the ecm gets signal for spark timing so it is possible for it to throw a code relating to spark

OxfordCherokee2

Is there anyway to check the crank sensor before changing it?

Turbo X_J

My recommendation is don't replace anything until after you have checked the coil (video below), fuel pressure with a gauge, and scanned the codes.

OxfordCherokee2

Aright I will check those first. The hard part about this is that it has only happened twice and had no side effects in between so I don't think it will show it self while testing things.

biskitjeep

You can do an ohm test to the CPS I believe there's a how to in your Haynes or chiltons
I had a problem like this on my mj and after checking the fuel and replacing the whole ignition I noticed my CPS wasn't connected all the way and was just hanging by the slot in the bell housing so it falsely looked to be hooked up

Turbo X_J

CPS can ohm test good, and still be bad. If it is bad there will be a code (at least I pulled one when mine died in the driveway)

Rollincoal420

The only time the cps will ohm bad is when the jeep stalls and wont start... for tho 20 min.

If say if u can push the valve in for the fuel test port, and it always out with force for over a second, not spray hard instantly then turn into a trickle but instead, stay a strong spray, your fuel pressure is fine. A fuel pump either pumps or it dont.