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I have a 1964 C10 with a 5.3 LS. The truck idles rough and sounds like it has a miss.
Stock 5.3 with long tube headers, 34# fuel injectors, GM ECM.
The O2 sensor on Bank 1 is not as smooth as the other side and ECM is adding a lot of fuel in the Fuel Trim (short and long).
I have tried switching injectors from side to side, as well as coil packs, and the problem stays wilth the Drivers side. Disconnected coil packs one at a time and get noticable difference each time. Plugs are relatively new and look ok. Tried a new O2 sensor. I didn't have a noid light that fit the connector, but using a long screwdriver as a stethoscope, I can hear the injectors cycling. Did a compression check and leak down test and everything looked good. While the rockers were off for the leak down test, inspected pushrods, rockers, and springs. Tested the wires from the O2 sensor back the ECM and they check fine. Occasionaly get code the P135 (O2 sensor heater circuit malfunction), but senor is getting 12V at the connector, and have had three different sensors on that bank. Verified the ECM had a good ground to the back of the head. I have probably tested more, but can't think of it at the moment.
Seems like the signal is legit based off of the rough idle. Not getting any misfire codes and seems like it is likely mechanical, but compression and leak down tests performed well. About ready to start pulling my hair out!
Thanks in advance for any advice!
Last edited by Southside R and C; Oct 19, 2022 at 03:00 PM.
Mostly thinking out loud so smarter people can check my logic, but if you have an actual misfire on bank 1 then that O2 sensor will see more air on that side (even if injector worked) and calculate lean and throw more fuel at that side, which would explain your trim being high that side. Make sure your trims on other side are good. If it were me with just this data I'd swap plug/wire from #7 with something on the opposite bank and see if the problem follows. But having a better scanner watch live misfires/counts would be helpful to know to chase one cylinder or not.
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Rough Running Engine HELP 
