Bullstang360

So update I checked out your wiring diagram and double checked the wires and pins with a continuity test and they rung out to match the diagram. So next I pulled the harness side of the ECM off and rung out pin 24 which is the CPS return wire just to make sure I had the right pin on both the ECM side and the CPS side. Next I left one of my leads in the CPS return wire socket on the CPS side of the harness then I checked continuity with every pin on the ECM side and I only had continuity with pin 24 (which is what I should have). So I guess that determines that my short is not in the harness but the ECM. I also bought a OBD1 reader today (the INNOVA 3120) and it was unable to communicate with the ECM. So fingers crossed that is my issue, a bad ECM. So I called the local junk yard and they have 2 91 Cherokees with automatic transmission I'm going to go tomorrow and check them out. They only want 30 bucks for an ECM so thats not bad. My question is now if I pull an ECM from another 91 cherokee with an automatic transmission thats the same as mine it should work right as long as I do the reset procedure on it?

BillyBoy

I had a similar issue... cleaned all grounds, the starter turns over, no spark past coil...

I went "old school" and it worked. Try having someone turn the key to crank it, put on some rubber or leather gloves, and start jiggling wires/plugs. I know it's not as scientific as checking wires and pins for specific voltage, but as soon as I jiggled the coil connection/wires, the jeep started. Might be worth a shot... just MAKE SURE to keep your hands away from anything that MOVES when the engine starts up. It'll scare th heck outta ya if it does.

Bullstang360

Ill give that a try I cant get help till Sunday so i have been trying to do the best testing I can by myself.

DFlintstone

All I can say is I suppose I'd go about it about the same way. I might check for voltage on that line with it unplugged from the PCM (Poewertrain Control Module).

I might also check that pin on the PCM and see if indeed, that 9V is coming from there.

Hey! Supper that file went through. That one FSM there had it all chopped up into individual files. No index, took some hunting. Not sure I could do that with some others.

It's over my head, but geez, if the PCM has 9 volts there I cant see how it's gonna make sense out of what comes back from the 5v feed. I could be dead wrong there though! I hope that 9v didn't mess up your CPS

Bullstang360

So I got to the junck yard and they said it showed in their computer that they had 4 91 jeep Cherokee ecms that would work for me. When to go pull them and every ecm out of every jeep was gone except a 94 ecm. Some one must have gone in and ripped them all off. Just my luck. So I got the 94 I know it won't work to drive it but it might work to at least test my systems.

Bullstang360

Ok so here is an update. I put in the ecm out of the 94 and instantly everything came back to life. I could hear my fuel pump kick back on and when it turned over it tried to fire off. So I have spark back! So it seems like I threw my timing off changing my distributor. I know its not 180 off but just a bit. Can I loosen the clamp on the distributor and just do the old school twist it one way of the other till timeing seems right? Or will that just make it worse?

DFlintstone

Supper! Well done! Don't really see allot of bad computers.

One tooth off will wreck your day, and NO, she doesn't move. Just one spot and the Puter' does the rest. The book might be wrong, #1 is at 5:00.

You gotta find compression stroke in #1 and set it on TDC. Then drop it in with the rotor "above" (counter clockwise) of 5, so as it rotates clockwise sinking in it ends up at 5. Here is one deal> there are more, it can be tricky. This link suggests removing the VC to find compression. You can do that with a finger in #1 hole, or with your rotor it it's even close.
http://www.angelfire.com/my/fan/dist_index.html

Bullstang360

I have read alot of the write ups on timing but was just curious is the old school way would work. Good to know it wont. What I dont understand it if I was off by one tooth how would I have been able to seat the distributor all the way down?

DFlintstone

If there were 16 teeth on the dist drive gear, there would be 16 different directions the Rotor could end up pointed, Depending on where you were holding the rotor as you seat it.

You could "go commando" and cut the pin that holds the dizzy with #1 at 5, but you won't advance the timing by turning it.

DFlintstone

My 90 Renix is very different than your 91 there on the dizzy. Renix is fine with the cam sensor unplugged all-together. It might only tell the ECU if #1 or #6 is coming up, which the ECU will figure out in a second anyway.

The cam sensor aside, the rotor does not always fire right dead aligned with the electrode on the cap. The blade is a cirtian width, like the electrode. I believe it is set up to hit just on the trailing corner, so when the computer advances the spark it can still make the jump to the electrode during max advance.

Writing this helped ME wrap my head around the thing!

Bullstang360

Ok having a hell of a time figuring out if Im on the compression or exhaust stroke but getting there. Tried it a few times and thing I had it set on the exhaust stoke instead of the compression. So just a word of warning I too a corer of a rag to put over the spark plug hole because I couldn't fit my had in to cover the hole and had my buddy turn it over. Well sucked the rag into the chamber.....funny to think about now. So an hour later we fished it out so use a big rag not a small one. Lesson learned.

freegdr

Put finger over hole and turn motor over with nut in center of harmonic balancer.....

Bullstang360

Did that got it right now. So now its turning over and sounds good. Doesn't sound like the timing is off. But still no start. Since I replaced my ECM my check engine light is working again so I did the key trick. Its throwing code 12 (Means the computer was recently replaced) and 14 for a MAP sensor. I looked it up on the forum and checked the harness and I have the 5 volts from the ECM and a good ground. So im going to chock that up to maybe going bad from the ECM going bad. Also it shows 4v on the middle terminal at the MAP on the harness side. Is that right?

DFlintstone

I found this in a thing on Renix sensor diagnostics. I haven't seen anything (in years) to say yours is different for the MAP.


MAP Sensor. (Btw, it moved to the TB, maybe in 97)
Located on firewall behind valve cover. To test, using a voltmeter with the ignition on/engine off, voltage at terminal B should be 4 - 5 volts. The voltage should drop to 1.5 - 2.1 volts with a HOT, neutral idle engine. Supply voltage can be checked at terminal C with the ignition on. Voltage there should be 5 volts + or - 0.5 volts (Terminal A is the ground wire).

DFlintstone

[QUOTE=Bullstang360;2664077] when it turned over it tried to fire off. So I have spark back! /QUOTE]

I'll read through again, but I hope someone more familiar with your OBD-I chimes in. What is it doing now?

I might see it a plug is wet, even try unplugging the rear wire off the ballast resistor, (to kill the fuel pump), then see if it fires with starting fluid.

Got a crisp, blue spark?