Same problem, no start when hot
 

So here I am still with a no start when hot problem. Yes I do have a CEL but I haven't been able take it anywhere to have it read because once I get there I won't be leaving for a while. See other thread here for prior story: https://www.cherokeeforum.com/f2/doe...142383/index3/



I have ordered a new Mopar CPS that should be here tomorrow, but today I feel certain that is not my problem. Lets talk about the cam positioning sensor. Today I did a little diagnosing and this is what I found.
Started the Jeep up and took it for a little ride, got it good and warmed up. The electric fan cycled on once. Turned off the Jeep and left it sit about 10 minutes. Tried to start the Jeep, just cranks - no start. I then left it sit for about an hour. Engine was very cooled down by now, I could even touch the exhaust manifold (briefly). Still no start. This time I poured a little gas in the TB... it started right up. I did this a while back too and had the same outcome- no start before, start right up after.

So I really feel it's a fuel injector or cam sensor problem, Fuel pressure is fine- hot or cold, running or cranking it's alway 45+psi. So today when I put a little fuel in the TB and got it running, and it stays running fine once it starts, I decided to unplug the Cam sensor... it stayed running. Hmmmm....
Shut the jeep off, plugged the sensor back in, made sure it started back up fine- it did. Unplugged the cam sensor, tried to start- no start. Plugged it back in, tried to start it, stumbled a little at first but started and then ran fine. Unplugged cam sensor and it stayed running. I get the impression that it's running on a "default" fuel mapping once it gets running- but it is still obvious the cam sensor is doing something. When it's cold and has been setting for a while, 3+hours, it will always start right up.

So you might say it's a bad cam sensor. I have two used ones and they both do the same thing. Exactly the same. Is there a chance I have two bad sensor... of course. But something about not being able to start it with the sensor unplugged and then immediately being able to start it once I plug it back in tells me that it's got to be doing something.

Your thoughts?

I'm waiting for a good answer also, I'll be watching as I said sounds just like my issue.
Thanks for posting again.

drive it there see if they can read it with it running maybe

Get the code scanned... could be in the coolant temp sensor?

So exactly how would a coolant temp sensor cause it to not start? I'm not exactly sure how that works. I'm pretty sure the coolant temp sensor is new, as is nearly everything else on the engine.

The code is absolutely INVALUABLE in resolving your issue.

You can buy a code reader for around $40 on Amazon. Money well spent; you'll use it again sometime in the future.

So I didn't have quite the "luck" I hoped I would. I hooked up the scan tool and read the codes- no crank signal, no cam signal, downstream O2 voltage high.
The previous day I had disconnected the cam sensor just to see if it stayed running (which is did), so I assume that is why I had the 'no cam signal' code... but as well as I can remember I didn't disconnect the crank sensor- so that's still suspect. Downstream O2 shouldn't cause the engine to not start when hot.. would it?

I cleared the codes and took it for a drive to warm it up. All readings from the scan tool seems to be fine. Got back to the house and sat in the driveway with it idling to get it good and hot. After about 5 minutes I heard the engine sort of miss once... then twice. Before I could get the scan tool set to graph the Crank Sensor the Jeep stalled. It's never done that, at least not in the past several months and only once before. Jeep would not restart. The graph for the crank sensor never budged- flat line. There were 'counters' for each the crank sensor and cam sensor. Cam sensor counter was counting, crank sensor counter remained at 0. Hopefully the new cranks sensor will be here today. Coolant temp was at 221*.

Stange thing this time. Even after the engine cooled down the Jeep would not restart, even when I poured a little gas in the TB. We'll see what tomorrow will bring... story to continue.

moving parts around and then pluging them in after awhile, just sort of resets the brain. thats why after 3 hours or longer it seems fine because its trying to read system all over again and once it figures out its screwed up it wont work untill its brain is reset again, i have suggested this to a couple other people this sort of thing happened to me, take it or leave it its probably cheapest thing you could do. regap the pig tail connectors on your coolant temp sensor also check idle air sensor as well. then let me know what happens. also my connectors looked fine, but were worn out i had to splice new ones in. now its nice and tight and works great.

Had a YJ with the same issue, turned out to be the ecu...once switched she ran like new...Sounds like your problem, see if you can find a used one.

Well I'm thinking I may have solved my problem. When I pulled the motor I had ripped the end of the ground strap from the block to fire wall. I had cleaned and fixed it but I feel it was not getting good contact. Pulled it yesterday and redid it and she runs great and no problem with restarting. No more engine codes setting off the check engine light. I will be replacing it with a new ground strap. Keeping my fingers crossed that this solved the problem. I don't drive this on the road because this is a project vehicle for my son so I have not put any miles on it to get a long term test, just driving it around my property and leaving it running until it's good and hot.

I have replaced the Crank Sensor but I have not tested under hot conditions yet as I discovered something else...

Attachment 359406

The harness for the Fuel Injectors, TB, and Crank sensors is... melting.

Attachment 359407

I found the wires were all fused to each other. I was able to seperate them and checked to make sure none were shorted together, but everything looked okay. With a pic request in the Cherokee Chat forum I was given a picture that proves to me that my harness was run in the correct position... but it sure is damn close to the exhaust manifold. I think I'm going to fab up some sort of heat shield to help protect these wires better. For now I cut a hole in the side of the harness retainer:
Attachment 359408
And I'm going to loop the harness over top of the Fuel rail instead of under it.

Keep up the work! Make sure those wires are still good wrap them up good with wire shield and tape them up! Keep checking all connections! Engine looks clean

It's NEW! lol- see avatar

So far so good... seem the new cranks sensor has fixed the problem.