I have a 93 jeep cherokee sport. 4.0 with less than 150,000 Its been my daily driver for over a year and has always ran great.
We decided to take it on vacation this past weekend and on the interstate it died on me. (At first it acted like it wasnt getting fuel. The more throttle i gave it the more it bogged down until it died completely and i coasted to the side of the road.
I checked my fuel pump and fuel filter. Both were good and getting fuel to my injectors. So i started checking for fire. I have no spark whatsoever. So, i Started doing some back probing and have no power to the distributor at all. From what i read on other forums, when u turn the key on u should see power to the crankshaft sensor and injectors for just one second and then that power should return when cranking and if it does not then its one of the sensors bad. I tried that and have no power to any of them even for the one second when the key is tuned on. Does that mean i need a new conputer? The only code i found was a code 12 which is battery disconnect (i think from where i kept trying different things and then cranking until finally the battery died.) (But did that erase any other codes)
From what i read on other forums, when u turn the key on u should see power to the crankshaft sensor and injectors for just one second and then that power should return when cranking and if it does not then its one of the sensors bad.
Can you post the link to that? I don't believe that's correct but want to see the context.
Quote: From what i read on other forums, when u turn the key on u should see power to the crankshaft sensor and injectors for just one second and then that power should return when cranking and if it does not then its one of the sensors bad. I tried that and have no power to any of them even for the one second when the key is tuned on.
This from 1995 but I think it's been the same forever:
Quote: IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following actions occur:
• The powertrain control module (PCM) pre-positions the idle air control (IAC) motor.
• The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
• The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
• Intake manifold air temperature sensor input is monitored. • Throttle position sensor (TPS) is monitored.
• The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
• The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged.
• The O2S sensor heater element is energized via the ASD relay. The O2S sensor input is not used by the PCM to calibrate air-fuel ratio during this mode of operation.
The only code i found was a code 12 which is battery disconnect (i think from where i kept trying different things and then cranking until finally the battery died.) (But did that erase any other codes)
I think you can fry the coil and not generate codes in OBD I.
Similar to several somethings I had in my 1996 XJ 4.0
Check connections before replacing parts.
When it died and would not restart, that was the coil wire falling out of coil, but appeared to be seated. Was also a bad coil and needed new wires.
For years it has been dropping out to no power, tach drops to zero even when engine was turning. Pulled the harness that goes to the coil, cleaned and dielectric greased contacts, cleaned and silicone sprayed the gasket, reassembled (gasket is swelled hard to jam back together) and zip-tie across the short axes across the clip (heard clip crack on removal).
Cutting out reduced, but did not go away. Repeated the process with the CPS plug to harness. All cutting out issues went away. BTW, the CPS was replaced several years ago, probably prematurely because of not checking connection to harness.
In 1996 when I bought this XJ new, I went through all of the connectors I could see/reach under the hood and did this. Back then the gaskets fit snug, not over tight like now. But I had better manual dexterity then too. One of the O2 sensor connections, in the engine bay, passenger side, the plug could not be reconnected with round gray gasket in the plug, Had to leave it out and seal it with Permatex gray #2 (doesn't harden).
Years ago while changing plugs and ignition wires, a gaggle of wires on passenger side of engine cam out of their connectors just by moving the harness nest out of the way a little. Ended up crimp splicing them back together. Forgot about them for a decade or so and the cutting out issue had come back again. Finally remembered those wires and all the connections looked sketchy. They all ground to the block. This time I cut all the connectors off, crimped on eyelets, bolted them all together with a stainless nut/bolt/washer, and attached to a NAPA brass grounding strap and grounded to grounding lug on passenger side of engine. Until I refreshed CPS and Coil harness connectors, I still had a problem with engine cutting out if I hit a minor bump with driver's side wheels.
Will be spending a day soon going through every connection I can see top and bottom with this method.
Not sure if that is what you got, but it took me years to get to this.
All of my connections are good all wires are still in good shape inside wiring harness. (Nothing frayed or out of place).
(Jeeps in really good shape for 93. It was owned by an older couple and then sat for about four years before i bought it and used it for daily driver since feb. 2018)
I tried changing my ignition coil. And swapping relays around Didnt help. And in order to change the pick up coil (cam sensor) i have to pull the whole distrubutor out. Dont really want to do that unless last resort, and bc theres no power to it or the cps when u turn the key on i didnt figure either was the problem. I should still have power going to them at first even if they are bad
From what i read on other forums, when u turn the key on u should see power to the crankshaft sensor and injectors for just one second and then that power should return when cranking and if it does not then its one of the sensors bad.
Quote: The Engine Computer grounds the coil in the automatic shutdown, (ASD) relay for one second when you turn on the ignition switch. That sends 12 volts to the ignition coil(s), injectors, alternator field, oxygen sensor heaters, and fuel pump, or it grounds a separate fuel pump relay when one is used.
CPS is not included on the list (and since it's not a 12 volt sensor, should it expected to be).
Despite how the wiring looks I would refresh every ground in there.
Having NO power to the CPS at any time is a bad sign tho. See if you have power for the CPS and CKS at the PCM (I'm looking at the 95 schematic, and it's 8V at #7). Including cranking.
Despite how the wiring looks I would refresh every ground in there.
Having NO power to the CPS at any time is a bad sign tho. See if you have power for the CPS and CKS at the PCM (I'm looking at the 95 schematic, and it's 8V at #7). Including cranking.
How do you feel about taking the ECU apart?
Only mechanic work i know is from working on my own vehicles and learning as i go. Ive never incountered anything like this and tbh I'm not sure what i would be looking for if i took it apart. I did however unbolt it and layed it up on my airbox just to get to the wires a little easier and when i did i magically got continuous power to my cps when key is on and when cranking. But still no start. I feel like putting the jeep in the lake down the road at this point.
What is cks?
Get the 1994 too, the 93 wiring diagrams aren't very complete. and I believe the 1994 is pretty close.
When you checked the ASD socket, did you have power at 30 and 86 with key on engine off, and cranking? If those never had power then doesn't matter what the PCM commands, nothing will get juice.
In re: PCM there are 2 things you can DIY fix: broken solder connections and faulty capacitors. The soldered connections from the harness plug to the PCB break, and are easily repaired by resoldering. That you connected to the CPS after jiggling the box strongly suggests this is what's happening (at least there).
Actually, the nomenclature is CPS = camshaft position sensor and CKS = crankshaft position sensor, but everybody calls the CKS CPS.
Only mechanic work i know is from working on my own vehicles and learning as i go. Ive never incountered anything like this and tbh I'm not sure what i would be looking for if i took it apart. I did however unbolt it and layed it up on my airbox just to get to the wires a little easier and when i did i magically got continuous power to my cps when key is on and when cranking. But still no start. I feel like putting the jeep in the lake down the road at this point.
What is cks?
Unfortunately, on a 26 yr old Jeep (or other vehicle), its not unknown for a problem to develop problems with either wiring, connector or PCM itself.
These problems can be quite difficult to diagnose, but the systematic fault finding knowledge to do so is available on these forums, and will be forthcoming to you if you persist
while have someone wiggle the PCM harness & connector, see if it will start.
If not, while dong the same thing, you will need to backprobe the crank sensor CKS and cam sensor CPS for appropriate voltage, then the PCM conectors
I personally own 2 known good correct used PCM, so I can plug them straight in the event I suspect a faulty PCM
