Ruman25

I have a 2001 Jeep Cherokee that is having engine problems. When it warms up the check engine light flashes when pushing down in the accelerator. It misfires and has no acceleration. When I stop in idles rough. The repair shop has replaced the ignition coils, and put in new fuel injectors. It worked for a week but the problems have come back. What else could it be beside the coils and fuel injectors?

tjwalker

A flashing check engine light indicates a SERIOUS misfire. Unless resolved quickly, this condition will trash your catalytic converter.

I would recommend not driving this XJ until this is resolved. As you have a check engine light, the code(s) must be retrieved for guidance and clues on where to look for your misfire.

For a 2001, you will need either a code reader or a scan tool. You gotta get those codes and when you do, post the exact codes (not just a description) here for comment.

Ruman25

It coded P0302 - a misfire on cylinder #2.

We've had the fuel injectors, spark plugs, and coils replaced. Its been happening intermittently. I was told to have it checked for a possible PCM problem.

tjwalker

If this were my XJ, this is how I would proceed. And in this order.

1. Test compression on all cylinders and see where cylinder #2 is in the mix. Can't rule out some sort of internal engine issue. They can happen really at anytime. The compression spec for the 4.0 is 120-150 psi with no more than a 30 psi variation between cylinders. Testing compression is something you can easily do yourself and if you don't have a gauge, one can be rented inexpensively from most any parts store. Call around for availability.

2. You need to see if the #2 injector is firing. Use of "noid lights" inline with the fuel injectors can be very helpful here. You can get these at most parts stores and they aren't expensive. I know you replaced the fuel injectors, but gotta make sure that the computer is pulsing the #2 injector to fire properly. If it isn't, then it is a possibility that the driver inside of the computer for that injector is failing.

Good luck and keep us updated!

Ruman25

When I started to check the injectors I discovered that at some point #1 and #2 had been miswired. I corrected that and drove it for about 30 minutes when misfire returned. The pressures all check so I'm scratching my head.

It only happens when its been driven for 30-40 minutes so I'm wondering if the heat is causing the misfire. The cylinder head was replaced four years ago and I'm wondering if there is a leak somewhere.

extrashaky

It's essentially free at Auto Zone. What happens is you "buy" the tool from them with a credit card, then they credit it back when you return it. If you never return it, the charge just stays on the card. They usually have the noid lights for loan also.

Drive it long enough to get it hot, then do a leak down test.

What does the #2 plug look like?

Have you pulled the valve cover off and looked to see if you have any rocker or spring damage?

extrashaky

Never mind. I missed that you already have new injectors.

Ruman25

It turns out in was the #1 injector. There was a hairline crack on the side of it. I replaced it and its running smoothly so far.

nujeepguy

a new one? great fix..

extrashaky

So did the repair shop actually replace that injector with a cracked one, or did they charge you to replace the injectors without actually doing it?

EEVEE

That is my question. Shouldnt be cracked already....

Ruman25

The injector in the photo is the #1 injector that I changed out. The repair shop kept changing the #2 injector. I don't think they ever checked the others. I checked the others to make sure there were no other cracks.

The repair shop was good about not charging me to keep replacing the injector, but I can't believe that they didn't catch the crack.

extrashaky

Ya know, if one cracked, and the rest are the same age, I think I'd just go right ahead and replace them all.