Jerry E

Hello Everyone,

I tend to be long winded so Im going to do my best to shorten this up.

I have a 2001 XJ 4.0 auto, 190k miles. Have had a evap large leak code for a few months but has been running fine enough for this procrastinator. Three months ago I was getting ready to leave work and the jeep wouldnt start. That ended up being the crank position sensor.
Three days ago on my commute home as soon as the engine reached full warmup the once steady engine light started blinking and the engine started missing a little. Got a little worse on my 40 minute ride home. Checked codes when i got home and I had cyl 6 misfire/multiple cyl misfire.
Borrowed gf's truck next day, later that night I had an event to attend. I assumed it was the coil pack so i bought one and threw it on, no change, so i put old one back on. At this point jeep seemed to run ok until it warmed up and then the misfiring would start, now misfiring was getting worse. Went to the event, on my way home the real fun began. No warmup required. Misfiring badly, engine barely running, gauges were acting a little goofy, died multiple times on way home. I was only 15 minutes from home and I didn't want to have to pay for a tow if i could limp home. Checked codes when I got home and still says cyl 6 misfire but now also P1391 "Intermittent loss of Cam Position Sensor or Crank Position Sensor".
Is it possible the cheaper crank sensor i threw on already went bad? I always though when a crank sensor went bad the motor would not just run badly it would not run at all.

Anyway, thanks for any help or pointing in the right direction on what I should check next.

Jerry E

Probably should also be noted that a month or two ago I changed the coolant, flushed it out with cooling system cleaner since the heater core was blocked. Changed the thermostat at that time as well.

Turbo X_J

Are you sure it's not the circuit itself?

Jerry E

You mean wiring or the ecu? Haven't started checking wiring yet. Trying to clear a spot in the garage as I type this to put the jeep in and really start getting in to it.

Jerry E

I'm seeing a LOT of warnings about replacing the crank sensor with OEM mopar, the one I put in was not a mopar.

BlueRidgeMark

Absolutely YES. Replace it wth OEM. You can get the NTK/NGK part at NAPA for less, usually, and it's the same part.

Turbo X_J

If the wiring or connector is defective that can lead to an intermittent signal condition.
ETA
You can if you want. When mine died the only one I could source locally was a BWD brand I couldn't/wouldn't wait like three days for the dealer to order one. When I offed my ride it was still running easily more than five years on that CPS. But then again the wiring wasn't all screwed up either.

Jerry E

Checked for spark at the coil, everything's getting spark. Checked compression, all cylinders check good. Swapped #s 1 and 6 injector, still get #6 misfire. Checked wiring with multimeter at the fuse box (green/orange wire) and at the ecm connector (green/black wire) and wiggled connectors, no change. Insulation near connector of fuel injector was half stripped off so I replaced the connector. No change. I'm really running out of ideas here. I have noticed that since this started happening the engine sounds like it ticks/clatters a little more than usual. All I can think of to look at next is the ecm, but I've never had a vehicle that needed that or known anyone that has done it so to me it seems extremely unlikely.

XJRed96

your driving a car that hasn't been made in 16 years... anything is possible at this point. with that being said though. Improper correlation between the cam and crank can cause bad misfires, this can be caused by either a bad cam sensor or a defective crank sensor.

With that being said I've come across one jeep that would intermitently Crank but not start, and we had a ***** of a time tracking down the problem. The fault was the same that you are throwing out. we ended up tracing it to a slightly broken wire at the forward most ECM connector about 2 inches back from the connector itself under the wire sheathing. It was right in the area where the harness would bend.

Jerry E

Thanks, I'll get into the wiring more tonight after work. The harnesses under there are easier to get at than I was expecting so I'll just pull the convoluted tubing and tape off everything and look it all over. I did that with the injector harness to an extent but there are lots of places a short or open could be hiding. Thanks for the heads up!

Jerry E

So quick update, tried and tested everything spark and fuel related, yes everything. Finally pulled valve cover and saw intake rocker on #6 wasn't moving as much as the others. Pulled the head and found a wasted lifter. So I'm now getting ready to swap the cam and lifters. Anyone have experience/good luck with Melling OS replacement cams and lifters? Seem to be the best priced without buying a cheaper brand I've never heard of. I know I'm on borrowed time now that cam lobe and lifter material might have made its way to bearings, but I figure I'll run it until I rebuild a used motor completely.