The tach not budging is generally a sign of a failing crank sensor, but, the mopar fellers are not inexpensive for a "guess".... The aftermarket fellers tend to introduce more issues than they solve.... Might check the connections at both ends for the crank sensor, make sure they are clean, and tight.

 

I have replaced the crank sensor with a brand new one - though not a MOPAR part, just one that I could get my hands on. I technically have another one I could put in as well - though it isn't MOPAR either.

I'll check the connection for sure. It's not too bad to change out, so since I have another on hand, maybe I'll throw the other in to see if I get lucky. This part also has a lifetime warranty so I can always trade it in for another - the main reason I bought it.

 

Checked/cleaned connections for the Crank sensor. Thought I was on to something - the weatherpack doesn't quite let the connector seat fully - so took that out and got it nice and tight and even installed my other new crank sensor last night and the truck continued to do the same. The truck will always start - eventually. Haha!

Looked for a bit for a MOPAR or NOS crank sensor and getting a little paranoid about what to trust - I've seen some people listing "NOS" (and charging more for it too) and upon inspection it's just a "Walker" brand sensor like what I've got in there now.

On the up side - got new taillights installed and they look alright. Fitment is a little off but from a distance you couldn't tell. New bulbs where necessary all around the truck.

 

I'm sorry, I've lost track -- do you have a quality MAP sensor now? I may have already said this but my buddy with a '98 XJ 4.0 was having intermittent extended crank and a new MAP sensor corrected it. I was sure it wouldn't work but he did a ton of research and he was right.

Also, your ECT reading is reasonable? I think we already discussed that. Incorrect coolant temp readings will cause a hard start, but it will usually run oddly for the first few minutes once started.

 

"Quality" might not be the right way to describe it but it is the only one of 4 I've tried that's actually changed voltage readings when tested. Haha!

It took the MAP and modifying and adjusting the TPS to get her to run again. Also new plugs at the same time as the TPS....

The ECT seems to be accurate in its readings...? When looking at live data at least... it runs well but it does idle really high when started cold - about 1.5k RPM. It'll hold there for a few minutes and then slowly climb down... then it idles really low when warm - about 600RPM.

I keep trying to remember to look up if I can adjust that at all... the past few days have been chaotic. 😂

 

Nope. Idle speed isn't adjustable. At least, not without a programmer.

Mine will flare to 1200-1300 RPM at startup cold, but, it immediately starts slowing, and settles around 650-700 even when cold. When hot, idles just above 600.

 

Well, dang...
Yeah - mine shoots straight up to 1500 for a least a minute - maybe I should time it.... But then it'll slowly go down about 100 RPM every 10-20 seconds after that until it gets to 900-1k and then just drops to 600.

When it's warm it behaves more like yours does cold.

 

Wonder which one is wrong.

Of late, on a hot restart, drive into work, stop at McD's for a couple burritos to go, come back out, and it'll stall on start, gotta hold the gas, drive with two feet till I get out of the parking lot, then it's fine again. No problems on cold start.

 

For fun I actually timed it when I got home.
My numbers I gave earlier might have been a little exaggerated - though it was a really warm day today compared to what it's been like..

Cold:
Took 4 key cycles to fire.
1500 RPM - 36 seconds when started to fall
Dropped about 100 RPM every 2-3 seconds down to about 900RPM
Then dropped to to about 650 and settled at 600 - never sounds like its going to die or anything - idle seems strong and pedal is immediately responsive.

Hot:
Jumps to about 1200RPM and then settles down pretty quickly back to about 700 for a few seconds and then down to 600
Seems fairly consistent... Though this is just driving around the property and then up and down the road for a few laps - drive about a mile down one way, turn around and go a mile past the property the other way and turn a round ect... Then coming back to the shop - checking on things and then taking off again or just starting because I'm betting myself drinks on how many key turns it'll take to fine "this time"

 

Put some gas in the truck and drove it. Was going to take it to town to fill it up and the truck with gas and it wouldn't shift into 4th gear... was at maybe 2.6k RPM at 55 MPH (or so) and was making terrible rattling/clattering sounds. Turned around and got home and checked fluid levels and seemed fine...

Was driving perfectly fine yesterday. In fact - when the Wife was riding with me were were talking about how nice the truck rode and drove. Other than the major "climb into the truck" for her - she said she liked it more than my K1500 and when we got back home asked me: "are you going to just get rid of the other truck then?"

Drove the truck around the property and everything seemed fine - took it out on the road again and still wont shift into 4th and the same noises. Went to turn around and the truck died. After many key turns it fired up but it was "soft"..? Not sure how to describe it better. It's like the truck didn't "fire up" it was like it was cranking and then suddenly was running...? Anyway... It was idling at like 400RPM... Put it in gear and kept heading home. I didn't have to mess with the throttle or anything to keep it running.- in gear kept idling at the same RPM and then would start moving after I got the RPMs up above maybe 800RPM and then the truck would start moving... Drove the same except for when coming down a hill just before my property I was light on the throttle and suddenly it shifted into 4th . When I hit the bottom of the hill and touched the throttle more it down shifted and rattled. I just let off the throttle and momentum got me more than far enough to get back in the driveway.

Parked in the shop and shut it down and started again 2 more times and each time it started the same way - not a fire but more like the engine just kept firing at the same RPM that the starter was spinning it...? It'd sit and idle like that fine - wasnt really any shaking/missing going on that I could tell - just a really slow idle.. The second start I noticed oil pressure was down to 5PSI so I just shut it down and left it for now.

Probably should've just taken off the oil pump when I had the oil pan off... I don't mind getting back in there again though because then I can re-check the pickup tube bolts as well. Somethings gotta be up with the pump... As for the transmission.. We know I need toadjust the bands.. But otherwise - Im about to start looking up information...

Sadly, I did not think to get my scan tool to check any data but the PCM didnt throw any codes.