I've been having some problems with my Jeep for several months now. I have a 2004 LJ.
The problems started at the end of September. The jeep stalled at a stop sign and the check engine light came on. It stalled a few more times on the way home and when I checked it I got a P0122 -throttle position sensor voltage too low code. I’m used a Bluetooth OBD connector and the Torque App on my phone to read it. I bought a new TPS and replaced it only to still have the code. I rescanned for fault codes and a P0123 – throttle position sensor voltage too high code showed up as well. The battery was fairly old and I had to jump it last winter a couple of times so I installed a new battery the beginning of October with no changes.
I did some searching on this forum and downloaded the factory service manual. Per the FSM I checked the voltages at the TPS (both the new one and the original one) and the resistance in wiring from the TPS to the PCM and it all checked out good. I searced this forum some more and one possible cause mentioned was a bad clockspring, it can cause noise on the databus making the computer think the TPS is bad? so I unplugged the clockspring at the steering wheel but the same codes were still there.
I reached out to Mark @Wranglerfix and I rechecked everything I had done before and ordered a new PCM which arrived around Thanksgiving and installed it that weekend only to still have the same P0122 and P0123 codes. A week and a half later the battery was dead so I jumped it and let it run for probably an hour when before the jeep stalled. I restarted it and it was running rough so I rescanned for codes and got P0123 -TPS high, and P0351, P0352, and P0353 -ignition coil faults. I shut it down for another week. I went to work on it again and when I started it the check engine did not come on and it was running smooth. I took it to the end of the street for gas and the check gauges light came on. The gauges seemed fine and I scanned for codes while driving and I got a P0158 code -O2 sensor high voltage bank 2 sensor 2. When I got home I rescanned for faults and got the P0158, P0351, P0352, and P0353 codes. Also I turned the stereo volume up a little while I was looking through the FSM in the driveway and noticed when the engine was idling the stereo worked fine but as soon as I brought the rpms above 1000 the volume went off. I have an aftermarket radio with a separate amp and a sub under the rear seat. The headend stayed on and I could hear the sub so I assume the amp was cutting out. It is mounted below the steering column and grounded to the body by one of the steering column bolts which is also where my viper alarm and keyless entry is (yes I added power locks to all 3 doors). The headend connects to the factory wiring but the amp and sub both have power coming directly from the battery.
The weekend before Christmas I made room in the garage for it and the check gauges light was still on, scanned it got no fault codes and the gauges seemed to be working fine. I checked the grounds from the battery to the engine and the firewall which both seemed good but cleaned them and made sure they were secure but the light stayed on.
Just after the holidays I started it again there were no lights on and also there was no problem with the stereo. As I was checking for faults I noticed the voltage gauge looked high so I connected a meter to the battery and I was reading 18.0 volts. I shut it down and started reading up and looking for causes. Went back the next day and started it and the voltage was fine, 14.2, but as soon as the engine warmed up the voltage spiked to 18 again. Also that was when the stereo problem started again.
A couple of weeks ago I went back to checking grounds and checked the strap that goes from the back of the engine to the firewall to the hood. I wasn't too concerned about it as the hood doesn't really need a ground and the engine and firewall should be grounded from the 4ga and 6ga wire from the battery. Also as the strap is aluminum (I think anyway) which wouldn't be as good as the battery cables anyway. After cleaning the hood and firewall end I went to try to get to the engine end. I know need a valve cover gasket so I thought I'd do both at the same time. To get the wiring harness out of the way it looked as if I was going to have to disconnect almost the whole left side of the engines wiring harness and didn't really want to disturb that many connections right now so I just loosened the bolt for the ground wire a little sprayed some WD40 on it and tightened it back up.
It sat there until this morning and I went back out to start it and try to see what temp the voltage would spike. I let it run and no problems showed up. None. It got up to about 200 degrees and it ran there for a while with no problems. I'm think going make sure everything is buttoned up and drive it around the neighborhood a bit but I have no confidence that the issue could have been the ground strap at the back of the engine which was the last thing I touched.
So all of that rambling is just to ask, if the engine is grounded from the battery and the firewall is grounded from the battery what is that strap adding to the party?
I found a good post on removing the bridge for the wiring at the back of the valve cover so I might drive to the parts store and get a gasket to replace that so I can clean up the ground strap good if that really is the problem. If not the gasket will have to wait.
The problems started at the end of September. The jeep stalled at a stop sign and the check engine light came on. It stalled a few more times on the way home and when I checked it I got a P0122 -throttle position sensor voltage too low code. I’m used a Bluetooth OBD connector and the Torque App on my phone to read it. I bought a new TPS and replaced it only to still have the code. I rescanned for fault codes and a P0123 – throttle position sensor voltage too high code showed up as well. The battery was fairly old and I had to jump it last winter a couple of times so I installed a new battery the beginning of October with no changes.
I did some searching on this forum and downloaded the factory service manual. Per the FSM I checked the voltages at the TPS (both the new one and the original one) and the resistance in wiring from the TPS to the PCM and it all checked out good. I searced this forum some more and one possible cause mentioned was a bad clockspring, it can cause noise on the databus making the computer think the TPS is bad? so I unplugged the clockspring at the steering wheel but the same codes were still there.
I reached out to Mark @Wranglerfix and I rechecked everything I had done before and ordered a new PCM which arrived around Thanksgiving and installed it that weekend only to still have the same P0122 and P0123 codes. A week and a half later the battery was dead so I jumped it and let it run for probably an hour when before the jeep stalled. I restarted it and it was running rough so I rescanned for codes and got P0123 -TPS high, and P0351, P0352, and P0353 -ignition coil faults. I shut it down for another week. I went to work on it again and when I started it the check engine did not come on and it was running smooth. I took it to the end of the street for gas and the check gauges light came on. The gauges seemed fine and I scanned for codes while driving and I got a P0158 code -O2 sensor high voltage bank 2 sensor 2. When I got home I rescanned for faults and got the P0158, P0351, P0352, and P0353 codes. Also I turned the stereo volume up a little while I was looking through the FSM in the driveway and noticed when the engine was idling the stereo worked fine but as soon as I brought the rpms above 1000 the volume went off. I have an aftermarket radio with a separate amp and a sub under the rear seat. The headend stayed on and I could hear the sub so I assume the amp was cutting out. It is mounted below the steering column and grounded to the body by one of the steering column bolts which is also where my viper alarm and keyless entry is (yes I added power locks to all 3 doors). The headend connects to the factory wiring but the amp and sub both have power coming directly from the battery.
The weekend before Christmas I made room in the garage for it and the check gauges light was still on, scanned it got no fault codes and the gauges seemed to be working fine. I checked the grounds from the battery to the engine and the firewall which both seemed good but cleaned them and made sure they were secure but the light stayed on.
Just after the holidays I started it again there were no lights on and also there was no problem with the stereo. As I was checking for faults I noticed the voltage gauge looked high so I connected a meter to the battery and I was reading 18.0 volts. I shut it down and started reading up and looking for causes. Went back the next day and started it and the voltage was fine, 14.2, but as soon as the engine warmed up the voltage spiked to 18 again. Also that was when the stereo problem started again.
A couple of weeks ago I went back to checking grounds and checked the strap that goes from the back of the engine to the firewall to the hood. I wasn't too concerned about it as the hood doesn't really need a ground and the engine and firewall should be grounded from the 4ga and 6ga wire from the battery. Also as the strap is aluminum (I think anyway) which wouldn't be as good as the battery cables anyway. After cleaning the hood and firewall end I went to try to get to the engine end. I know need a valve cover gasket so I thought I'd do both at the same time. To get the wiring harness out of the way it looked as if I was going to have to disconnect almost the whole left side of the engines wiring harness and didn't really want to disturb that many connections right now so I just loosened the bolt for the ground wire a little sprayed some WD40 on it and tightened it back up.
It sat there until this morning and I went back out to start it and try to see what temp the voltage would spike. I let it run and no problems showed up. None. It got up to about 200 degrees and it ran there for a while with no problems. I'm think going make sure everything is buttoned up and drive it around the neighborhood a bit but I have no confidence that the issue could have been the ground strap at the back of the engine which was the last thing I touched.
So all of that rambling is just to ask, if the engine is grounded from the battery and the firewall is grounded from the battery what is that strap adding to the party?
I found a good post on removing the bridge for the wiring at the back of the valve cover so I might drive to the parts store and get a gasket to replace that so I can clean up the ground strap good if that really is the problem. If not the gasket will have to wait.
