mediccody

My 98 4.0L has been not starting occasionally. It sounds like it is cranking hard, but must not be getting spark, fuel, or air. Sometimes running down through reverse, neutral, and drive and then back to neutral allows it to start. Other times it seems to have no effect.

It has also stalled once recently while travelling at 70 MPH and once while idling.

This has all happened within about two weeks. It normally runs fairly smoothly and quietly.

I've gotten code P0306 (Misfire on cylinder 6) a couple times, but I got P1391 (intermittent crank shaft sensor) and P0120 (throttle position sensor, weird...) when my Jeep stalled on the highway.

Research suggests that it's probably a bad crank position sensor, as our Jeeps have that problem frequently. I'm going to clean the contacts and check the wires for damage first, too. The symptoms of a bad neutral safety switch would explain the starting problems too, though.

Any suggestions?

jeepbrattt

Seems to be a common issue with these things. My daughters 2000 did the same thing. Changed Crank position sensor( do yourself a favor, buy the OEM sensor......aftermarkets are junk), started back up but then pulled misfire code. Swapped in a buddies spare coil pack and also replaced spark plugs, ran a bit better but still pulled yet another code. Camshaft sensor and also neutral position code. After doing quite a bit of reading on several Jeep sites my best guess is a bad wire somewhere that is causing the issue...be it ground or whatnot. I HATE wiring so I sent it off to another buddies shop. Waiting for results......
I have a thread on here as well about same issue. Will update that one and maybe it will help you out as well. One I read was as simple as a bad ground by the oil dipstick......how po'd am I gonna be after spending $$$$$ on sensors just to find a loose wire....ugh. Good luck

Stabsthedrama

Read Cruiser's tips (his very first one) on ground refreshing. Takes all of an hour to refresh the main grounds, and refresh all plugs/harnesses a bit, and finish off a few beers.

Reading his tip you will see just how many important things are all grounded on the dipstick...it's pretty stupid honestly.

Might cost you like $10 for 2 beefier pre-made ground straps, and ~$6 for a 6 pack.

mediccody

I'll be sure to at least clean up and check all the connectors for the wires on the dip stick bolt and check the block to chassis ground before buying a bunch of parts.

Stabsthedrama

Be sure to also unhook the connectors and spray them out with contact cleaner and sand/scrape off any corrosion as well, which would be the first thing I would do in your situation (he also has a tip about this as well, and it's very easy to do)

It's very possible it's a legit TPS, CPS, or NSS issue, or even all 3, who knows - but start with connectors and grounds, reset the battery/touch the cables together, which will clear the codes (or clear the codes with a scanner if you have one, which I recommend anyway, for $20 you can get a good OBDII bluetooth scanner for android on amazon), then drive safely (backroads) for a bit, even for a day or two (IIRC it seemed like roughly 15-20 miles of driving in a normal commute to reset the codes on my 96) and see if your codes re-appear.

I wouldn't risk getting back on the highway until you figure this stuff out.

A complete die-out does tend to be CPS usually - if you do this - again, GET OEM.

syncview

I would also suggest you check and fix / clean the grounds first.

mediccody

Yep, starting on this project today.

1. Clean grounds on engine block just for the hell of it
2. Use multimeter to test CPS
3. Probably remove the CPS and clean the contacts anyway since the bellhousing end looks really oily and dirty when I look down on it.
4. ???
5. Profit

Stabsthedrama

Let us know how it goes. I would be very surprised if it was tps related, as it seems to just be a fault that got thrown because of something else - but they are pretty easy to test (its easy to find a tps writeup)