05/03/2026
Had me questioning life. Cummins ISL G.
Didn't originally diagnose this, but was told it was long overdue for plugs and coils. Performed tune up, cleared codes and ran it. Still surged, flashed stop engine and 2457 Multiple Cylinder Misfires. In between surging it would rev and run perfectly, but kept surging and "missing" only at idle.
Already had new ICM and ICM harness, valves adjusted recently. Monitored Datastream and verified that all coil voltages were within spec. Even when "misfiring" they were normal. So I eliminated the Ignition system from diagnosis.
Cleaned the Fuel Mixer, Throttle Body and MAF. Much needed. Reassembled and retested. Still missing, but sounded better.
I saw that the fuel pressures at idle were a tad low, but nothing that should cause an issue. Replaced the high side and low side fuel filters, reset the fuel tables, and retested. Still surging but a definite improvement.
One trend I started to notice when monitoring the Datastream was that the issue was only happening during Closed Loop. So during Open Loop at Cold Startup it ran great, until the system went into Closed Loop.
I performed a visual of the O2 sensors, and found the upstream sensor had been rubbing on the turbo, causing damage to the shielding and wire. Replaced the sensor only to find the same thing happening.
I was scratching my head, but figured I'd check the downstream O2 Sensor. It looked fine, until I disconnected it and found the corrosion on one of the pins inside the connector.
Replaced it, cleared faults. Done.
Genuinely was scratching my head, questioning life decisions, and getting the parts gun ready.