Crank but no start on my 99 TJ

Yes the tach should rise when cranking the engine and obviously anything in the crankshaft position sensor circuit including the sensor, connectors, wiring, etc. could cause a problem for it. So no, not just the sensor... anything in its circuit which includes the PCM. The CPS drives the PCM which derives the engine rpms from it and then drives the tach. Likely the sensor but....

Hmm, one of the first things I tried was swapping the cps out with a new one I got from Napa, which didn't help. I know the recommendation is to source Mopar sensors when possible, but I couldn't find any anywhere.

I'm suspicious of the PCM as well, but am trying to rule out other potential causes before I give Mark @Wranglerfix a call...
 
  • Like
Reactions: Wranglerfix
I'm always suspicious of wiring in that general area. There are places behind the valve cover that are prone to get worn on a particular bolt, but I've seen plenty of times where the harness look a-ok but there was cracked insulation inside the loom & tape (fixed one this week with that exact issue). I would dive into the harness before I did much beyond the crank & cam sensors....and if you have a distributor I might worry about the cam sensor later (because I don't [yet] know how to change that sensor w/o swapping out the whole dizzy).

If you have fuel & air, then it has to be spark. Lots of stuff can make the spark not happen, and there are a few of us here who have our pet causes that we always point to, biased by recency. And we are all right some of the time.

This reminds me that I REALLY want to identify a process to bench test various sensors.
 
To further clarify what myself and "Hear" posted above; the ECU harness is known to rub on the threaded head bolt in the right rear corner of the valve cover. I installed a red rubber spark plug boot to alleviate that from happening on my '01.

Split wire loom harness.jpg
 
Last edited:
There's wiring and connectors in the CPS circuit too and they could easily cause the CPS to not work.

Ok, so I haven't given up yet, and today I may have found a lead on my potential problem. Jerry I started tracing wires back from the crank position sensor and found two different wires coming from the connector where I could see worn thru insulation and exposed copper.

I'm a total noob at this, but what's the best way to fix worn thru wire insulation? Just wrap in electrical tape?

See pictures I've attached.

PXL_20230122_001558177.jpg


PXL_20230122_002137966.jpg
 
If it’s just 1 wire, and it’s in an awkward place, I’ll consider just using tape. My preferred way is to cut out the problem and splice in a new piece. But not everybody has the same splice skills. But also consider that if it is just 1 wire, unless it’s in contact with the block or other grounded thing, there’s nothing for it to short out to. There is probably another corresponding issue in a wire somewhere.
 
If it’s just 1 wire, and it’s in an awkward place, I’ll consider just using tape. My preferred way is to cut out the problem and splice in a new piece. But not everybody has the same splice skills. But also consider that if it is just 1 wire, unless it’s in contact with the block or other grounded thing, there’s nothing for it to short out to. There is probably another corresponding issue in a wire somewhere.

Yeah, that makes sense that the missing insulation alone isn't necessarily the problem and I don't see anything on the wires that looks burnt, which I'm assuming would be what I'm looking for?

I think I'm going to have to bite the bullet and tear apart the split loom and tape and trace everything in the circuit looking for something more obvious.
 
If it’s just 1 wire, and it’s in an awkward place, I’ll consider just using tape. My preferred way is to cut out the problem and splice in a new piece. But not everybody has the same splice skills. But also consider that if it is just 1 wire, unless it’s in contact with the block or other grounded thing, there’s nothing for it to short out to. There is probably another corresponding issue in a wire somewhere.

Ok so update. Today I wrapped 2 different exposed areas of wire coming from the crank position sensor connector. After doing this I was able to get the Jeep to start! But it promptly died after about a minute,I was able to restart it one more time, but again it died after less than a minute.

I can now hear a quiet vibrating sound which seems to be coming from the throttle body area, possibly the idle air control valve or maybe the throttle position sensor when the ignition is on.

Does anyone have any ideas on why the Jeep would start after wrapping those 2 wires in tape, but then quickly dies?

Should I be considering splicing new wire into the area where I found the worn thru wire?

I haven't been able to get the Jeep to start for almost 8 weeks, so it seems like I'm on to a potential cause here, just not sure what to try next...
 
Last edited:
Is that a big gob of dielectric grease on this connector? If so I’d spray contact cleaner on all three connectors and plugs.
BE2BFA7C-AF31-4664-B700-A50C929277DA.jpeg
 
Definitely. You can put it on the outside on the seals but never on the metal contacts. It does not conduct electricity.
 
Dielectric grease is an insulator which stops the flow of electrons. Read the part on which chemicals will remove the grease. You need to get all of it from the metal contacts.
https://www.electrical4u.com/dielectric-grease/

Well that gives me another thing to try, thank you!

I crimped a couple of butt end connectors on some frayed wires and used dialectric grease on the wires there as well, sounds like I need to pull those apart, clean then and see if that helps. All of the PCM connectors are coated in it.
 
  • Like
Reactions: TJ Jim
SOLVED!

maybe this will help some other poor soul dealing with a puzzling crank no start issue like I was. So a buddy came by today and we started working our way through the ignition system major components. We pulled the plug caps off first and inspected for any abnormal corrosion or charred components, all looked fine.

Next we inspected the distributor assembly, and saw nothing of note except for one thing. We noticed that the entire distributor assembly had a bit of upward/downward play in it. I don't think this was the cause of my no start issue, but I'm also not sure if it's normal to have that kind of play in the distributor when the engine is off? Once we got the motor running, I tried tugging on the distributor assembly and there was no play in it while the motor was running.

Next we inspected the ignition coil and stumbled upon the cause of my problem!

We first pulled and inspected the large supply wire that goes to the distributor, all looked fine.

Next we pulled apart the connector assembly that runs to the coil. To my eye it looked a little dirty but not obviously bad so we reconnected it. We did not try to start the Jeep yet.

We opened the PDC and swapped the ASD and horn relay. I then attempted to start the Jeep and it fired right up! I let it idle for about 5 minutes which it had not done once over the last 3 months.

So now we shut it down and started trying to figure out whether it was swapping the ASD relay or was it the connector for the ignition coil?

My suspicion was the ignition coil connector because I had previously already tried swapping the ASD relay with the horn relay and the engine didn't fire then. So first I swapped the relays back to where they were and tried to start it and it fired right up again. So in my mind that rules out the ASD relay and narrows it down to the ignition coil connection.

We assume the connection was corroded a bit and just by pulling it apart and reconnecting it must have been enough to restore a good connection?

We took it for a 5 minute drive through my neighborhood and it ran perfect. I pulled it back into the driveway and pulled the connector back apart and cleaned it with contact cleaner and a toothbrush, reconnected it and all seems well!

I drove it for probably 30 minutes around running errands this afternoon and she's running great! This was a frustrating ordeal but I learned a great deal from many posts on this forum, especially the factory service manual I downloaded from the sticky here.
 
  • Love
Reactions: hear