I’ve been fighting misfire codes 0300,0303,0304 and occasionally 0301 and 0306 for weeks now. Engine is a freshly installed reman 4.0 in a 2000 Jeep Cherokee XJ. A Mopar mechanic and another local mechanic don’t seem to be able to tell me what’s going on without part swapping and charging me for all of it. Compression tested good twice, new fuel pump/good fuel pressure, new injectors, coil pack replaced with k suspension coil mod…when connected to scanners and it throws misfire codes the scanner says it isn’t misfiring. I don’t have any coolant loss and my oil looks like I just poured it out of the bottle still.

After talking with the Mopar tech I tried changing my Amazon CPS with a Napa Echlin brand one and for some reason the Echlin one seemed to be contacting the flex plate and was immediately damaged. Not sure if that part was out of spec or what. I can’t find an OEM Mopar CPS. I think it’s possible my flex plate has a deformity that’s causing the sensor to read a misfire, but if that were the case wouldn’t the misfire codes be consistent and not totally random? Sometimes I can drive around all day and not see the CEL flash at all. If I put the Jeep in park and hold a 2-3k rev for a few seconds it’ll make the CEL flash damn near every time. I’m at a loss and can’t afford to keep taking it to the dealer to have them tell me they’ll happily take my money to replace something else they’re not sure is gonna fix it or not. I’m thinking it’s a flex plate issue of some kind, another sensor, or an electrical issue of some kind with all the disturbance of the wiring with the removal/install any thoughts?

 

What year?

 

Sorry, it’s a 2000

 

Where did the flexplate come from?

 

It’s the original flex plate, I’m guessing I possibly damaged it during install and didn’t notice

 

Did you do the engine install? The flexplate is pretty tough. It seems like you would know of an instance that the flexplate might have been damaged. A member just had a flexplate issue that caused engine stumbling problems associated with similar RPMs, but there was no pedigree on that flexplate, so it is possible, but I wouldn't start there.

 

I did the install. I’m not really starting with the flex plate, all the ignition and fuel delivery stuff has been replaced. I only thought of the flex plate because I thought it was a little concerning it chewed up a CPS 😂. I’m sorta spitballing because I have no idea and the actual mechanics haven’t been overly helpful

 

It seems you thought you had a crappy CPS, so you got a better CPS and it was damaged, so you went back to the suspect CPS. If you have an inspection mirror, you can look into the window where the CPS is installed and rotate the engine a few degrees at a time to validate there is no defect on the flexplate. You could also remove the starter and rotate the engine and validate the CPS tone ring won't chew up another CPS.

 

I’ll try that out tomorrow thanks

 

0301 and 0306 together, and 0304 and 0303 together are very suspicious. Cylinders 1/6, 2/5, and 3/4 are called companion cylinders. That means they're at the same height, but on different strokes. This means they can share ignition coils (2000 and 01 only) because while one cylinder will fire on the top of the compression stroke, the companion cylinder will also fire at the top of the exhaust stroke.

You replaced the coils with the Ksuspension coils. The quality of KSuspension's products (despite their vehement protests) have been considered questionable for a while. Lots of people have had problems with their 4 hole injector "upgrade", which usually ends up upgrading your engine to less power and stumbling.

I hope you have your old stuff still.

 

I know way back when the coil that Ksuspension sold was a Spectra.
00xjfreedom bought the set and that is what they sent him.
Also bought the Mopar Coil that you would use in that set up.
Mentioned how much "heavier" the Mopar coil was compared to the Spectra.
I followed his lead and used the Mopar coil when I did mine.
agreen brings up a good point about the wasted spark and it would not be the first time
that a part was defective out of the box so......

 

I had the same exact codes with the original coil rail, I still have it. It is definitely interesting it’s always companion cylinders but I can’t figure out the significance beyond the coil 😂 electrical stuff is completely over my head. The flex plate/tone ring looks okay to me.

 

I reinstalled the original coil pack today just to see if it made a difference, it still threw the same codes in the exact manner. I can drive it for long periods of time if I’m careful with the throttle, go a little more than half pedal for too long and it’ll throw the codes. I hillbilly smoke tested it for a vacuum leak and checked all the lines pretty carefully and I don’t think it’s leaking. I throttle it from the bay and can’t tell when the lights come on, there’s no hesitation or jerking or anything at all. I’m still completely stumped.

I was wondering about the cam sensor, I carefully followed the manuals directions when I put it in. Found top dead center on compression, zeroed the timing mark, put the pin through the holes in the cam sensor ring and then installed it into it’s hole in the direction I remember it facing before. I have seen that they may need adjustment with a scan tool and was wondering if it was off enough that it’s causing my issue

 

Put a piece of black electrical tape over the CEL.

 

You can get an entry level oscilloscope for about 200 bucks and be able to check your signals. You'll still have the tool, so it's money not totally wasted.