The muffler shop used an OBD1 scanner (it showed codes for both O2 sensors, nothing else)
Hi John, I wanted to thank you for your help so far. Looking at the thread I can see why you were frustrated trying to get the message to me that I was looking at the "module" connection and had missed the "fuse" location. I don't know why my computer didn't show your posts, maybe I needed to refresh it, but I didn't see any of them until I responded with a confirmation that I "got it". Once your message got through I realized that the fuse location was there and I acted accordingly. Now, after the 15 minute trick, and driving the truck about 10 minutes, things seem to be smoothing out with less roughness at idle, which I'm very happy about. The CEL is still lit and I'm hoping that somehow it will just go out but that's probably not realistic. I guess I'll have to try to figure out if something happened to the O2 sensors during the switchover or something else. I wonder if it's possible that now that the truck is running smoother that another pulling of the EFI fuse will reset the CEL?Typically, the idle will be higher than normal until the ECU relearns the sensors. If the ECU is giving you O2 codes and it's running poorly, then there's your answer.
You also stated that as soon as the exhaust shop was done, it threw codes and ran poorly.
Thanks for the guidance, I'll try to trace the wiring and look at the sensors tomorrow. Bob.First check that the plugs going into the O2 sensors are connected, and the wiring is not damaged. Then follow that wire from the O2 sensors all the way up as far as you can to the main harness branch. Ensure the wiring at least looks good and no shorts or burnt segments.
You should be concentrated on the O2 sensors and associated wiring.
(FYI .. jonheld is our resident 3FE guru...I'd do whatever he told me to...)
Well I've got a problem and hope someone here has experience in this area. My 1991 80 series LC needed a new exhaust, ? ...........The muffler shop used an OBD1 scanner (it showed codes for both O2 sensors, nothing else) and couldn't clear the CEL,
Thanks for the additional info. The CEL does come on immediately on start so I will inspect the wiring and test the O2 sensors. From my research I've found that I can test them without removing by reading Ohms while not running and reading fluctuating voltage while running. Bob.If I've flowed correctly you stated the CEL comes on immediately after the 15 minute reset. You need to read what the exact trouble code that is being generated and use the factory service manual to determine the possible causes and any additional components the need to be further tested. If your not doing that everything you are doing is all just guessing and hoping.
That said with the CEL immediately coming on, with the work you have had done there it very well could be the oxygen sensors. If the sensors were still connected/attached when the welding was done could have damaged the sensors depending on the type of welding process. Two thing can fail in an O2 sensor. The O2 heater circuit failure would generate a code immediately. The second is the sensor output is not within specification. That normally requires the engine up to temp and a series of driving conditions before a CEL is triggered. I the wiring harness has been damaged the sensors might be OK but the damaged wiring would generate the same codes.
That's good to know, I suspect they just kept lying once they couldn't get the CEL reset or the rough idle fixed. I know how to find the codes by using a jumper wire and I'll try to find out what the codes are today. Bob.I dont know how the shop used OBD1 scanner since your rig is not OBD1, 1991 is pre OBD1 and your ECU dosnot have OBD1 data stream