ghack

I originally posted this in the oem tech forum by mistake. It should have gone to this forum. Since this post, I had two helpful responses, the reply to which I tried to include here after the original post.

I have a 2000 Jeep Grand Cherokee. It had been running fine. My daughter parked it, and about 6 hours later went to start it, it cranked but wouldn't start. I read a little about the cps, so tried unplugging that, but no joy. I verified fuel pressure at the rail, which rebuilds if I bleed it off. I took off the spark bar, and checked the first wire attachment for spark, but nothing. The gas gauge doesn't move, the fuel empty lamp is lit, and when I turn the key on, the rad fan starts going. The odometer does show the mileage. At one point, the battery terminal was a little loose, as I had taken it on and off a few times, when I turned the key at that point, I got a clicking, and the gas gauge started reading. After i tightened the battery cable though, the gas gauge stopped working again with key on. Also,when the key was off, i took the battery cable off then put it back on again, and the rad fan started running for a few seconds. Is that normal? I'm thinking I should check all my ground wires, but I'm thinking I might have a bad ecm. Any ideas of what I should check next?
I have tried using my code scanner, but it just comes up "no link". For testing my fuel pressure, I only bled off the fuel rail, though each time i reieved the pressure significantly, when I tried again after turning the key on, the pressure was built back up. I assumed by that, the fuel system was working properly. I may still put a pressure gauge on. I'm thinking my pcm is bad. On the cps, I measured resistance between ground and the 5volt power line while unhooked, and it showed about 5 ohms. I tried to get voltage with the key on, connector in place, between the 5volt power line and the ground, and it only showed 45 milivolts. I'm referring to the wire on the right with the connection clip on top as you face into the connector from the cps as the 5volt power line. I should also add, some people trying to help my daughter did try using jumper cables. My daughter said that it only clicked when she tried it initially. It's possible when they used the cables, they were reversed, and fried the ecm?

PeterB

I'm no tech so I'm in for the education-

I'm sure you have done this already but thought to mention it in case you have not.
One thing I have learned about these cars in the last decade and was recently reminded again is that the terminal definitely need to be cleaned & that the battery needs to be fresh. I'm sure you have tested it or at least tried putting the charger on it right overnight? Just my 0.02 and at the very least ttt she goes.

Good luck GHack, I'm sure someone will chime in with knowledge & experience and help you soon. Stay well sir.

PeterB.

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ghack

I have a 99 grand cherokee with 8 cylinder engine for parts. Can i use the CPS and ECM from that for my 4.0?

Thexjfiles

ECM, no.....cps....maybe.

ghack

Thanks Peter, I did put on charger and cleaned terminal as it did need it.

SHELBYGT NSM

I would be looking for loose grounds.

ghack

I did get a fuel pump pressure of 27psi. I did some more testing on the cps. i'm getting 4.8 volts to it, I used the "turn the crank with a ratchet" test till the voltage goes up to 5v(4.8) on the signaling wire, then down again till next spark time. That seemed to work.
Cleaned up the three grounds I found, two on the block near each other, and one on the firewall outside the battery. It still seems funny that the rad fan starts momentarily when I hook the battery up, and will run continuously when cold with the key on. That didn't happen before.
I read that the check engine light should come on immediately when the key is turned on then stay on for 3 seconds. I don't see the cel come on when the key is on until about 20-30 seconds, then it stays on. That's anytime, with cps plugged in or not. I Is there any other good test for the ecm? Maybe I have a bad ground for the rad fan? I guess next I will clean the alternator connections.

Bustedback

Your fuel pressure is low. Hint hint.

ghack

OK, so I don't know the proper way to test fuel pressure. Now it's just a shade under 50psi, so that should be ok. I'm still not getting any spark.

ghack

So I used a brazing rod clamped to ground next to the COP for my spark test. Absolutely nothing. I'm pretty sure the cps is getting enough voltage(steady 4.78v on the feed to the cps). It's signalling also with that same voltage when I turn the crank with a ratchet. On the signal wire, it's like 48mv normally, then goes up to 4.78 volts or so when actuated. I'm really thinking it's the ecm since the gas gauge is still wacky and unplugging the cam pos sensor and crank pos sensor both at the same time have no effect on the gauges. Also the no link on my code reader.

fletchFL

Before you condemn the ECM, get yourself a set of noidlights, and check to see if the injectors are getting a pulse signal. You can probably rent them, but I bought a cheap set at the local parts store for about $20, use em at work, good stuff.

And, even though I can't give you any specifics on this, I would try to verify you're getting the proper signals to the coilpack as well. If no signal at the injectors or spark, check fuses. I didn't notice if you mentioned you checked fuses, but that's a must. Get out a test light and check em all.

As far as your scanner not communicating, you should check your fuse box inside the vehicle, there is a fuse for the datalink, I can't remember if it's on the same line as the cigarette lighter or if it's separate, labeled something like 'OBD' or 'ALDL'. But, again, might as well probe em all.

If the jumper cables were hooked up backwards, you will most certainly find atleast the ALT fuse blown in the underhood fuse box. I've never personally seen that fry an ECM, but that doesn't mean it can't happen. Usually just pops a couple fuses, so long as it was a very short time it was hooked up wrong.

I will also throw this in for good measure; find the ASD relay in the underhood fuse box, and do what you can to verify it's working. I would suggest swapping it with another, but I think the only other relay identical to it is also critical to running the engine.

ghack

Thanks FletchFL. Those are very helpful suggestions. I will check them out tonight.

airnutt

I have been having same issue with my 97 grand cherokee. I had # 17 fuse blow in motor bay, replaced fuse and now cranks fine but not starting. Also the dash gauges are not coming on. Checked all the fuses and can not find what the issue is. Any help would be great.

ghack

Last night I prayed for help fixing my jeep. This morning, I still thought it was the ecm, but hadn't heard from the company that i ordreded one from. I did a little research, and found they had poor ratings from the Better Business Bureau, so I called and cancelled the order. I still thought it was the ecm, but wanted to do more testing. After work, I started checking fuses as fletchFL suggested. Sure enough, the fuse for the pcm was blown, probably from a jump start gone amok. I took one from my old jeep, put it in, the gauges started working, I hooked the cop back up and she fired right up. Thanks everyone, and a special thanks to fletchFL. I would have given you a hug if you were here when it started. The whole pcm fuse is a bit of a mystery to me, some functions of the pcm still worked and some didn't. It all works now anyway, and I'm happy.