No spark from harness to coil

Hi folks,

I have a 1998 JGC. 4.0L motor. Driving it around town the motor would just shut off. Used to do it once in a while....then started happening more and more. I replaced the spark plugs, wires, cap and rotor....thinking maybe it needed a tuneup. Sometimes it restarted right away (right after it quit). Sometimes it wouldn't start until the next day.

So two days ago, daughter was driving it home from work and the motor just quit again. This time it will not restart. Motor cranks over fine. I read on this forum that this is a sign of a bad CPS....although a bad CPS will usually allow you to drive home eventually. So I replaced the CPS. Cranked it over....no change. Now, to check for spark and fuel. I turn on the ignition...I hear the fuel pump in the tank going. Then I pull the coil wire (brand new since I replaced all wires)...and put a spark plug on it....crank the motor....and NO spark. I then pull the wire harness that feeds the coil. It's a 2-prong plug. I turn on the key and nothing showing on the voltmeter. I then put the volt meter on the battery and it reads fine. So I follow the coil harness connector back...and it just goes into the main engine harness. I then put the OBDII reader to the port in the Jeep and turned on the ignition. I get "Link Error".....so it's not getting a read, but the cigarette light is working...so the port is fine. So no spark to the coil harness and the Link Error does this mean a bad ECM (computer)? I'd hate to spend $300+ and find out that was not it. Thanks in advance! Also note that the fuel gauge (and maybe other gauges) are not registering when the ignition is turned on. The check engine light is not on. Maybe security system? I thought a security system failure would turn off spark AND fuel....but I hear the fuel pump running.

I ordered a used ECM from eBay for $150. We will see. If that's not it...then I have an extra ECM for later use. Update to follow...

UPDATE:

The used parts store I ordered from on eBay cancelled the order, and apologized, as they said the description was not correct....and gave more details. I called the guy directly and he said my ECM needs to be programmed to a BCM (Body Control Module). HUH?? I checked autozone, OReilly's, etc and there is no such thing as a BCM. What the heck is going on? I don't get it. There is no "BCM" that I can see...and not even orderable. Here is the official explanation from the parts guy:
***START***
PCM Programming Advisory for:
96- 98 Jeep Grand Cherokee
98-00 Dodge Durango

VIN PROGRAMMING: This PCM does not require VIN programming to work in your vehicle.

SECURITY FEATURES: The security on this vehicle is controlled by the Body Control Module (BCM), and not the PCM. It is recommended that your Body Control Module be programmed to the new PCM.

IMPORTANT: This process requires the use of the original key fob, which may not be present your vehicle. We highly recommend you or your repair facility has the necessary items to complete the programming before making any attempt to install.
***END***

Remote keyless entry works....so it seems the BCM has power if it's the BCM that controls the keyless entry. I will look for the BCM next.

For the benefit of others with this problem...I have found out a few things. For a quick review of the symptoms:
1) Car was dying while on the road. Sometimes it wouldn't restart at all.
2) Replaced the CPS (Crankshaft Position Sensor). There is also a Camshaft Position Sensor....I have not touched this. Replacing the CPS made no difference.
3) Noticed that when the ignition is on...the dash lights all come on correctly...like it's ready to start...BUT two things are happening that are NOT normal:
3a) The fuel gauge is not registering at all.
3b) You can hear the fuel pump stay on. When the ignition is turned on, the fuel pump should only come on for about 3-5 seconds....then stop.
4) Checked the OBDII reader with the ignition on...got a "Link Error"....so not reading the ECM (main computer)
5) Checked fuses and made sure the cigarette lighter worked...as some have said that the OBDII port feeds from the cigarette lighter. NOTE: I have no battaries in my reader, and I got power to the reader....so it's not a power issue to the port.

PROGRESS....what I found today:
1) I "thought" I checked the only fuse that goes to the ECM and the ASR (automatic shutdown relay) as the underside of the fusebox cover shows where those fuses are....those are the large 20-40AMP fuses in that fusebox. There is a cluster of 6 small fuses in that main fusebox (at the engine compartment)....but they are unmarked....so I ignored them! DUH....:nono:
2) I opened the owner's manual for this 98 JGC and on p.206 it explains what each fuse goes to in that fusebox. Then I found Port#5 (20AMP) with the following explanation: "Automatic Shutdown Relay, Powertrain Control Module"....also known as the ASR and ECM. Derrrrrrr. I pulled the fuse and it was blown! Fuses don't blow for no reason. So next test....
3) I replaced the fuse. Turned on the ignition....but did not crank the motor. Now the fuel pump stopped in about 3 seconds, and the fuel gauge went up to 1/2 full. BINGO! I then cranked the motor to start it...nothing. Then the fuel gauge was back below 'E' and fuel pump going. I turned it off. Checked the fuse...blown.

CONCLUSION:
1) I have a short someplace within the ignition system.....affecting the ASR, ECM fuse. Looking for it.
2) The fuse popped initially when cranking over the engine....now it pops when I just turn on the ignition, but do not crank the engine yet.
3) The ECM controls the fuel gauge and fuel pump...as when the fuse was initially replaced, both these items worked correctly. There was probably also spark from the harness to the coil...as the ECM had power after the fuse was replaced....but I didn't check it. I am sure the spark was there. The easy symptom check is to watch the fuel gauge.
4) Checked for loose or frayed wires all round the engine. Nothing found....everything is tight and wrapped. Also checked the 3 ECM harness plugs. Some have reported that a loose harness connector can cause engine failure...so check those. They are tight on mine. Next up...I might just replace the ignition switch itself and see if that's the cause.

Well you are not going to believe this. I didn't believe it when I saw it. I replaced the key cylinder.....same short issue. I replaced the key lock itself (that goes into the cylinder)....same short....fuse pops when the ignition was turned on. Therefore I returned the key lock to Autozone. Damn thing was $66 just for a key lock...ripoff!!

I then tested turning on the key (all the way to ON position) with just one out of three harnesses plugged in....no fuse pop! I then plugged in the other....no fuse pop. I then plugged in the 3rd one (black one on the right)...and fuse popped.

I thought it was a short in the PCM. I then read to check O2 sensor for loose connection (back towards the middle of the tailpipe). Mind you I already checked for loose ground all around the engine bay. THERE IT WAS....staring me straight in the face. The O2 sensor harness broke off it's plastic tie-downs to the under carriage and the harness wires were laying directly on top of the rear driveshaft!! Are you kidding me? Months of driveshaft spin...wore a hole through the harness and bare wires were touching the driveshaft. THIS was the reason for engine cut off earlier.....but only after it got this bad...the fuse blew. I taped up the wires, and zip-tied the harness away from the driveshaft (with multiple zip ties)....Turned on the ignition....NO fuse blew. The fuel gauge went up to 1/2 full. Cranked up the motor...it started on first crank....

It runs PERFECTLY now. Glad I cancelled the PCM order. Here is the morale to this story....the simplest answer is usually the answer....until it isn't. ALWAYS check for loose wires or frayed wires first....and check everywhere. Seeing the PCM blow the fuse when connecting the 3rd harness...would make one think the issue is with the PCM....not so! I would say, never order another PCM(ECM) or BCM until ALL other options are exhausted first. I saved a BOATLOAD of money by not taking this to the dealer....and yes....I got lucky also! Make your own LUCK! I hope this entire post helps you out. If not, keep reading other posts....that's how I found out to look for the O2 sensor connector. Oh, and an amp meter is a MUST! GOOD LUCK!

followup info for the "Link Error" from earlier in this post....Now that the PCM has power...the code reader reads "No Codes"...so 'Link Error' issue is fixed. Therefore, 'Link Error' usually means the PCM has no power.