myjeepisDEAD

IF IT HELPS, HERE'S A VIDEO OF WHAT'S HAPPENING:

YouTube - 99 Cherokee 4.0L - spark from ignition coil

Ok, so I have been having tons of trouble figuring this one out. I've got a 1999 Jeep Cherokee (4.0L manual) that is currently dead. To make a long story short, it was not getting spark, so I replaced the CPS. The old one was torn to bits. With the new one, there is now an intermittent spark from the ignition coil. Since then, I've replaced the ignition coil, distributor cap, rotor, pickup coil, and ECM. I've checked all relays, fuses and wiring. Everything seems to be okay.

From the coil, there is only a spark every 5 seconds or so. This is the first sign that something is wrong. It should be sparking much more rapidly - correct? I traced the spark through the distributor and found out that it is sending the spark to the 3rd cylinder (from the back of the engine) every single time I crank the Jeep. No other cylinder is getting a spark from the distributor.

Does this sound like it could be a timing issue? The Jeep died when we were doing some pretty heavy offroading, going through water, rocks, mud, etc.

Thanks!

Bustedback

Even if it were a timing issue, you would still have spark at the other cylinders, just not at the correct time. You may have to bite the bullet and take it to a shop. You threw a lot of parts at it and still have nothing. Did you check the PCM fuse?

myjeepisDEAD

Interesting.. No, I have not checked the PCM fuse. I'll check that one out.

The mechanic I took it to didn't seem to be the most knowledgeable guy in the world, but he thinks that it is possible that the electrical problem, whatever it happened to be, fired the first PCM and then fried the second PCM. I highly highly doubt this is it, but any chance?

I'm so so close to taking it to a shop...

myjeepisDEAD

Here's a video of the spark coming from the ignition coil:
and here's a video of the spark coming from the distributor to the only firing cylinder (4th from the front of the engine):
Any ideas?

myjeepisDEAD

I had a friend manually turn the crank pulley while I inspected the flywheel from the CPS gap in the bell housing. As far as I could tell, everything looked normal except for one thing - there is some sort of hard object wedged in one of the 12 gaps. I believe these gaps are what the CPS senses for timing, but it doesn't seem like one small imperfection would throw off the entire system.... But I could be totally wrong!

Here's a photo of a 99 cherokee manual flywheel:


Notice the 12 square notches around the outside edge (3 sets of 4 notches). One of these notches is blocked.

I took a video of the flywheel + obstruction and I can upload it if that helps.

Bustedback

Have you even checked the fuel pressure?

myjeepisDEAD

Yes, fuel pressure is fine... and that wouldn't cause a no spark condition, would it?

Bustedback

Did you replace the CPS with a new one, or a used boneyard sensor?

myjeepisDEAD

The CPS was replaced with a brand new one from Auto Zone. I've tried new different brand new sensors, so I don't think that's the issue... Though I have heard that aftermarket sensors can sometimes act up.

96tudor

I know that we all want to be self-reliant renaissance persons; however, sometimes it costs less to take it to an automotive technician who has an OBD II scanner and an oscilloscope and, from that information, knows how to diagnose the problem. Parts swapping without diagnostic work can be expensive, time consuming, and just fill landfills or our garages with good auto parts. I hate taking my cars to mechanics, and I used to be one in a past life. Get references from friends, coworkers, and neighbors. And always trust but verify.

fantic238

The gaps are for the ignition timing and the injectors timing. Remove the rail with the injectors attached and observe if there is a spray sequence or just the third one (fourth cylinder), like for the spark. Clean the flywheel teeth and be sure the CPS gap isn't too big. Check the CPS wires, connector, coil module connector, especially the +12 feed.

Bustedback

[QUOTE=96tudor;522427]I know that we all want to be self-reliant renaissance persons; however, sometimes it costs less to take it to an automotive technician who has an OBD II scanner and an oscilloscope and, from that information, knows how to diagnose the problem. Parts swapping without diagnostic work can be expensive, time consuming, and just fill landfills or our garages with good auto parts. I hate taking my cars to mechanics, and I used to be one in a past life. Get references from friends, coworkers, and neighbors. And always trust but verify.[/QUOT
Well said, and I agree.