I am at my wits end here, so hope someone can help. I have a 2002 Grand Cherokee Overland I picked up at auction. 4.7 automatic. Insurance claim was for "engine fire", but I found nothing to substantiate that claim. No sign of fire any where, no burnt wires, NOTHING. Got it home and charged the new battery that was in it. Everything came on line, except the starter spun and wouldn't engage. Cool man, or so I thought. Put the new starter in and it started, but was running on maybe three cylinders. Strong odor of raw fuel out of the pipe. NO CODES! Changed all 8 coil packs and plugs, runs much better but still rough. At this point I am at least getting codes. Defective airbag clockspring. When I open it up I found the column had been hammered by some half wit, so I installed a used column and new clockspring. I reinstalled the original skim and key cylinder as well. Now I am running on 7 cylinders! Whoo Hoo! Now we are seeing codes, The main code being PO204 ~ECM loose, broken or burnt wire/ Injector 4 circuit open. Changed # 4 injector, I removed the ECM and found frayed wire under ECM Bracket. Taped them up and stuffed a rag between harness and bracket and clean and inspected all connections. Reassembled and started it. Runs better but after three or four cycles it throws codes PO141, and PO161~ O2 censors down stream. Changed both downstream sensors with new ones. Restart vehicle and for the first time drive it! Stupid man... It runs fine under power but stalls as soon as you slow rpm below 1500 or so. Get back home and scan codes again. Throws codes PO442, 445, and 161 AGAIN! I found the evap vacuum problem was a hose off, fixed that as well as checked and confirmed gas cap seal is good. Cleared the codes and restarted. After three start and run cycles code PO204 is back and for the first time I now have PO500 ~ Vehicle speed sensor! I stopped wrenching 20 years ago, so I am having to learn all this new stuff. What am I missing here? I have so far resisted changing the ECM, but I am at the point of surrender. The wires to the number 4 injector appear to be ok, when I unplug them it makes no difference the engine has the same miss, so I believe the code PO204 is correct. Any thoughts or suggestions would be greatly appreciated!

 

Welcome to CF! I am also an old mechanic.

Test the #4 injector circuit for input power and it's continuity in the coil circuit or short to case. If everything shows good, then swap it for a different one from the engine. If the code moves to the other cylinder, the injector is bad.

I believe the injector cycles by the PCM (ECM) grounding it's circuit when fuel is needed so 12V is supplied to the injectors at all times. Your smell of fuel in the exhaust makes me think this injector is on steadily, either by being stuck open or the wire to the PCM being grounded somewhere. Wait a minute, it made no difference when you disconnected it, right? It's probably burnt out in the coil circuit.

Try installing a junkyard injector in #4.

Your declared "engine fire" may have been the starter shorting out and causing a lot of smoke, but no damage.

 

Thanks Dave, I already replaced #4 with a new injector, so I don't think it's bad, but what do I know? LOL

Love the Pyle quote!

 

NO...WAIT!! If you connect the harness to a different injector, your fuel pulses will be out of synch. Test the connector's pins to ground with the engine off. You shouldn't get any reading from either pin. You shouldn't get 12V until the engine is running either.

The way this system functions is when you turn on the key, the system energizes and the fuel pump runs just long enough to pressurize the fuel rail. When the crankshaft starts turning, the CPS signals the PCM to pull in the ASD relay thus energizing the fuel pump, injector circuit, and the ignition. If the PCM doesn't receive this signal, nothing turns on and the engine won't start. That's why a failing or failed crankshaft position sensor is so critical to keeping the engine running or not starting. The CPS is just a hall-effect switch that senses that the starter teeth on the flywheel are moving.

 

OK , so I tested the injector harness connection and confirmed pulsing on one probe, and 12 volt solid on the other...So I'm wondering if the new injector I installed is defective? I guess I need to pull it out again and move it and see if the problem jumps to the new cylinder location.

 

Changed the suspect injector to number two cylinder, code came back PO204. So I believe it is the ECM

 

Ok new ECM installed and runs like it did, no improvement. Codes are PO204,500, and 161. I'm ready to sell the thing for parts.

 

Hi wolfman96771, in my little experience let me tell you that my GC, used to have many electrical issues, i thought it was the ECM, crank position sensor, IAC valve, injectors, Hall sensor, ignition coil, spark plugs and wires....it was driving me crazy, and finally found that the real culprit was a bounch of wires making contact each other. This happened in the fuse box behind the kick panel on the passenger side, one wire overheated and three wires plastic cover melt. I hope this exprerience could help you good luck and cheers!

 

Thanks for the tip Maxxtreme! I will have a look and let you know what I find.