Security light on and won't start after I blew fuses
Hi. I have an 01 Grand Cherokee 4.0 I just got. Once it gets up to temp, it starts to miss bad. When it's cold, it's runs pretty smooth. I thought it was the coil pack so I put a new one on. Same deal. It also had no oil pressure and had a top end noise. I changed the oil pump, but I didn't prime it by opening it up before installing and filling it with petroleum jelly. However, i pulled the electronic ignition sensor on the block and spun the pump with a drill and got the oil pressure up, and reinstalled the ignition gear unit. It ran quiet and smooth til it warmed up and then started missing again. After additional research, I think it may be the upstream O2 sensor causing the rough running when it warms up. Also, the fan wasn't turning on when it does warm up. Soooo, I decided to temporarily hard wire the fan to run whenever the key is on. The trouble is, I was having a hard time finding switched power under the hood. I unplugged lots of sensors and connectors, INCLUDING 2 OF THE THREE CONNECTORS ON THE COMPUTER ON THE PASSENGER FIREWALL, and used the red fan wire as a tester, and popped several fuses in the process, but eventually, I found switched power feeding the wiper motor.
After I was all done, I replaced blown fuses that I could find, and proceeded to start the vehicle, which was driven into the garage running pretty good before I started clowning around with the wiring. Now it cranks but won't start, and the yellow security key light comes on, goes out momentarily, and then comes back on steady. That's where I'm at with this thing. I figured on possibly changing the O2 sensor once I saw it staying cool, but I want to see it running again first.
You may have fried the pcm. Sounds like you went all willy nilly trying to fix it and now its worse than it was. Check simple things first like plugs, oil pressure sensor, frayed wire harness, check engine codes.
Maybe I fried the PCM, but I wasn't messing with it. When I pulled the 2 connectors from it, I was pushing the fan wire into the each of the pin holes in the wires and the PCM only had one of the connectors still attached to it because I couldn't manage to unplug it from the PCM. I forgot to mention that, before I changed the oil pump, I did replace the oil pressure sending unit, because the top with the plug on it was snapped right off. But, with the new sending unit installed, it still read no pressure. I believed it too, because of the lifter noise and the 200,000 miles on the vehicle. I do think the engine was replaced because it has the yellow crayon writing from a parts yard on it. The transmission definitely was because there's a Jasper sticker under the hood and paperwork in the glove box. Oh yea. Before I changed the coil pack, I did replace the spark plugs. And the engine light has never come on, and I still checked for codes but there hasn't been any. I had a bear of a time rei-installing that timing module that goes where the distributor would go, cuz of the spiral gear rotating the blade on the end that engages in the oil pump. I had to pull it and turn the pump drive a hair, then re-insert it until the 2 engaged and it dropped all the way down in place. Then when I got it, I had it a tooth off from where it was originally so the timing was off. Then I pulled it, did the same things over and over and over and over again and again, inserting it, bolting it in, walking around to get in and try to start the vehicle up, only to find that i was still out of time, until I finally got it back in the the proper tooth of the gear and the pump lined up and all. I was black with grease and had spent several hours just doing that! But, by the time i'd finally gotten it, I knew it, cuz the engine had completely cooled off and when I got it right, it started up smooth and steady, but once again, when it started to warm up, it got that bad miss back again. Nightmares!!!!
Anyway, I burned about 8 fuses screwing around trying to find a power source to tap into for the cooling fan to run constant until I get this driveable. Most of them were 10 amp ones under the dash including the ones for the SKIM. They are replaced, and they didn't blow again, but it hasn't done anything but crank and not start ever since. And the security key light comes on steady.
Well I'm sure the sentry key light coming on means its not gonna let u start it. I really hate that sentry key immobilizer btw. Try and disconnect battery for half hour or so if you haven't yet, or you may have to take it to dealer see if they can reprogram it. Also did you check compression? And when you dropped oil pan for oil pump was everything looking ok in the bottom end?
Thanks! I keep forgetting important details. Yes, I did disconnect the battery, overnight. When I hooked it up, it did exactly the same things. No, I didn't check the compression, but before I messed with the cooling fan, the engine started up cold immediately, and ran smooth until the temp needle got up about 1/8", probably 110 degrees, then it would start to miss. Again, from what others have said on forums I've read, a faulty downstream 02 sensor can cause these symptoms. I will definitely look for the cooling fan relay where you said. As far as the bottom end with the oil pan down, everything looked good and had no slack. And, once I got the pump done and had it running the lifter noise went away, even though the gauge still isn't working.
I guess the question I still have is if there might be a fuse or 2 somewhere by itself like on the PCM or something. I had a Mercedes that had a row of fuses in one of the computer modules in a box under the hood on the other side of the car from the actual fuse box. Or possibly a fuseable link somewhere. I did remove and clean a ground on the passenger side of the engine block that was caked with grease hoping that possibly that ground was faulty and causing the new oil pressure sensor not to work.
What one of the stupid things I did could have caused the security system to need reprogramming? If it has some sort of ROM memory, that doesn't need power to store information. Kind of like a USB flash or camera memory card.
Well hopefully someone will chime in because as far as that sentry key thing goes that is beyond my knowledge. At least the internals you checked are in good shape and no piston pieces in your oil pan. Hope you can track it down. If you can get someone with the right scanner (drbIII I think) you can probably get some good info on whats wrong with it. I know dealer has it, just dont know how much they would rape you for. Good luck! Keep updated.