'90 Renix Occasional NO-START after running

Hey all,
So here it is:My '90 Cherokee 4.0 auto will occasionally not start right after I shut it down.For example I'll drive to the store,run in get my stuff(like 5min.) then when I go to start it nothing but crank crank crank.Like shes gettin no spark.Push in the little shrader valve and plenty of fuel squirts.heres the funny part:all i gotta do is wait like ten minutes and she fires right up like nothing ever happened!There are NO other problems with this thing she runs perfectly otherwise.What im thinkin is something is heat-soaking while its shut down,something that has a coil in it like a CPS or the IGNITION coil and opening the circuit.Then it cools down circuit closes,everthing is fine.And whatever part it is just doesnt get hot enough to do this same thing while running down the road.DONT KNOW?Anybody had this before?!

Thanks all !

Well, you're on the right track. You can test the components easily enough. Just drive around until it gets hot, then pull into your driveway or other parking spot, and shut down. If it won't restart, then start testing.

Test everything cold first, so you have baseline, and know where to find everything. Naturally, you may need to use gloves since the engine will be hot.

OK, having said that, the CPS is a common problem. I have not heard it behave quite like the symptom you're having but close enough.

Thanks for the reply!
Yeah I keep meaning to throw a meter in the Jeep to be prepared for the next time,but it happens so rarely that i forget all the time!Its very random and only happens like maybe once a month on average and i cant recreate the condition at will.I know the CPS is an issue on these but like you said they dont seem to act quite like this.They either seem to work or not.not just randomly like this,which made me think the ignition coil could also be a suspect.Had a chrysler that would just randomly stall,would do the same thing,start back up after about ten minutes like nothing happened.Drove me insane tryin to figure it out,ended up just being a bad coil.Anyway thanks for the reply,if you get any more ideas please share em!

Bob

Next time it won't start, pour some water on the CranK Position sensor to rapidly cool it. If it restarts, replace it.

x2, with Winterbeater on this.

I meant that I've not heard of the CPS failing due to heat soak. My own failed only when hot and would die after about 30 minutes of driving from a cold start. I had to wait 10-15 min for it to cool until I could restart. Then, since everything is still pretty warm, it only took 5 min or so until it failed again.

Saudade said:

I meant that I've not heard of the CPS failing due to heat soak. My own failed only when hot and would die after about 30 minutes of driving from a cold start. I had to wait 10-15 min for it to cool until I could restart. Then, since everything is still pretty warm, it only took 5 min or so until it failed again.

Click to expand...

I don't think anyone is disagreeing with you.

Generally, the famous "heat soak" problem presents as starts with rough running until enough throttle is applied to clear the excess fuel from the system. The late model XJ exhaust manifold change is what some believe caused the problem, along with the change to the fuel system return. Heat soak OEM fix is to wrap the number 3 injector in insulation. Better fix is to put a timer in the efan circuit to run the efan for a few minutes after the ignition is turned off to cool the engine compartment.

No disagreement taken.

Heat soak can affect many parts. I had a problem for a while where my coolant bottle would overflow but only after I shut down. As long as the engine was running, it didn't matter if it idled all day, if was stuck in traffic, or it was 100 deg out. I finally figured out I had a bad cap on the bottle and wouldn't hold the full pressure. With the engine running, the system ran cool enough to keep the coolant below whatever boiling point it had due to the pressure it could hold. Once I shut off, the coolant in the block got hot enough to boil and it all blew out past the cap. Once I changed the cap, the increased pressure raised the boiling point high enough to stop it.

So I suppose that *could* be what's happening to his CPS (or coil or whatever). When running, there's enough airflow and coolant flow to keep it cool enough. Once he stops the local temps climb enough to open/short it out.

Anyway, we're all in agreement that he can do a few things to determine what's wrong rather than suggest he throw parts at it.

Agreed. Test first.

Here is what I would do because I am guessing it is has nothing to do with any CPS problems. Pull out the air filter and throw it in the trash. Bet it will start when hot, cold or luke warm. The normal age of the 19 year old engine has developed the dreaded oil blowby situation and the oil soaked filter is acting like a fawking choke on a carburetor and won't allow it any air. Once the oil drains off the filter into the bottom of the airbox that will allow it to flow enough air to start.

Hey all,
Thanks for all the ideas.The confusing thing about this is the Jeep has NO other quirks.Does not EVER stall or run rough or idle funny or ANYTHING.The engine only has like 30k miles on it,rebuilt it a couple years ago so its pretty well mannered.Maybe it is the CPS and it just hasnt gotten to the point where it WILL start acting like Saudade's example!? Didnt replace any sensors but the O2 when i did the rebuild,didnt need to.What do you guys think?Is that plausible?

Thanks all,
Bob

I'm with Joe on this, i have fixed a few "hot -slow/no starts" by insulating #3 injector.