MontyPyFly

Jeep died the other day. Just quit. Classic Crankshaft Position Sensor symptoms.
Replaced CPS, still no start (most of the time)
Replaced the replacement CPS, still nothing.

My problem is similar to others here, but mine will start sometimes. Completely randomly.

I have good Fuel pressure
I have good spark
All good fuses inside and in Engine
All sensors show proper voltage/ohms
ECU has 12vt, 8vt, 5vt and Ground where it's supposed to
ASD relay swapped with Fuel relay
engine at TDC lines up Rotor to Plug one

Symptoms:
Cranks fine.
Usually doesn't start, but it has on a couple occasions, and when it does, it idles fine.
The other day, after sitting, it started up. After it ran for a couple minutes I shut it off and then tried to start it again. nothing.
Tried spraying Starter fluid in... not even a sputter.

Any one have any more ideas, I'm totally stumped now.
(Its the intermittent aspect that is killing me)

Thanks -Glenn-

jronald

If it will not run on Starter Fluid, you do not have spark. Sounds simple, but in reality its going to be a PITA to find it.

Ron

XJ5150

Have you checked the coil, cap, rotor button, spark plugs closely? blockage in the air intake tube?? If you spray starter fluid in there and it still does nothing then I would suspect spark... well, lack of spark for sure. But don't count out a blocked air intake tube... birds, mice, rats and other small animals like to build homes in these things. I know you said the timing marks line up but have you removed the valve cover to verify that both rockers/valves on 1 are in the up position when the timing mark and rotor button are pointing to 1? Other than that, ignition switch could be faulty or on its way out causing an interruption in power. That's all I can think of.

MontyPyFly

Air, fuel, spark.
It takes all three to run. It HAS all three, so I need to add another....... Computer!
It's all I can think of now, but the computer is NOT shutting off the fuel or spark.
When I sprayed the starter fluid, I left off the air intake, so that rules that out. (I will look inside for rats, tho :-) )
I have not removed the valve cover, since when it does start it seems to run ok. (just not for long enough to go anywhere :-( )

I found an ECM (PCM) on E-bay for $89 shipped. Same part number. Since it's a '93, I am assuming I don't need to reprogram it in any way. I figure $89 is a fine gamble to save my sanity :-P

There is no loss of power to the Starter. By "interruption of power" do you mean just the part sending the "on-start" signal to the ECM? That could be something I could look into.

XJ5150

Yes... Where the key goes and from there to all of the computer components that keep the engine running. The ignition switch does go out so it is also something to consider.

giwill

do you have an alarm or kill switch on it is so not a bad to check it out

retread

check for spark and put a noid on an injector plug or twofuel pressure is no good if the injector doesn't pulse

wildspear

To me it is sounding like a CPU issue, or maybe thesecurity system. If the CPU doesnt recieve the right signal it will shut everything else down. So if the ignition is going out the CPU will tell evrything after the ignition to not work. The CPU in our Grands run basicly everything. Also the security is also intergrated with everything. I had some security things pop up all of a sudden. Rig ran fine, then one day it would start and then shut off. This would continue even after mashing the gas. Found out it was the security, I unlocked the passenger door with the key and the rig runs fine.

1. CPU
2. Security

Let us know if you figure it out.

MontyPyFly

My "new" PCU should be here this afternoon! Hopefully that will just be a plug and go! (wouldn't that be nice)

I haven't actually tested the fuel out of the injectors, since Starter fluid doesn't work. But they have both fuel and power going TO them.

I went through the all the Security issues back when I installed this motor, so I know all about the start-stop issues associated with that. I made a little ground button next to my battery so I can make it think it has a key in the door :-) (This motor is in an 83CJ with no doors or tailgate now)

I'll let you all know who it works with the new PCU

MontyPyFly

There is no joy in Mudville.
The new PCM had no effect.
now I'm REALLY at a loss.

Bustedback

Try the cam sensor, it's easy and cheap to replace.

MontyPyFly

I tested the cam sensor for proper voltage and Ohm readings, so I ruled that out. Perhaps I should check it more carefully, or just replace it (it is almost 20 years old :-) )

Bustedback

It's cheap enough to replace without spending the time trying to confirm the old one is bad, part of the diagnostic trouble tree states "replace with known good sensor".

MontyPyFly

I just replaced the entire distributer, including the Cam sensor/pick-up coil.
No difference. At least I kept the new one clean enough to return ;-)

MontyPyFly

Replaced the coil today.... found a buddy with an extra one.
IT STARTED... IT RAN..... and it hasn't quit yet.

Theory.... It had enough spark to spark a plug when it was out in the open air, but not enough to spark when under pressure in the cylinder.
I don't know what else it could have been......