Finding the Real Cause of This HMMWV’s Hot-Stall

This 1992 HMMWV 6.2L diesel ran great cold but would begin sputtering and eventually shut off once it warmed up. After replacing a faulty fuel shutoff solenoid, finding and replacing a battery with a dead cell, verifying proper 24V system voltage, repairing several fuel-system air leaks, and confirming good fuel flow from the tank, the problem still remained. Further inspection revealed rust, contamination, and black debris inside the injection pump. Fuel samples from the tank and pump also confirmed significant fuel contamination.

We had the opportunity to diagnose this beautiful 1992 Hummer HMMWV equipped with the 6.2L diesel.

The truck would start, run, and idle extremely well while cold. Once it reached operating temperature, however, it would begin to hesitate, sputter, lose RPM, and eventually shut off. After cooling down, it would start and run normally again.

Our initial testing led us toward the fuel shutoff solenoid. We were seeing an abnormal voltage drop around the time the engine would stall, so the solenoid was replaced. Unfortunately, the hot-stalling issue remained.

From there, we moved into the electrical system. Battery testing revealed one of the batteries had a failed cell, so it was replaced. We then verified approximately 26 volts at the fuel shutoff solenoid with the key in the RUN position and approximately 28 volts with the engine running. Even with proper voltage supplied to the solenoid, the engine continued to stall once warm.

That allowed us to move away from the electrical side and focus more heavily on the fuel system.

We performed a smoke test and found several areas where the fuel system could potentially pull air. Those leaks were resealed and repaired, but the hot-stalling condition was still present.

We then inspected the fuel supply and injection pump more closely. The pickup tube showed good fuel flow with no indication of a restriction. However, when we opened the injection pump, we found rust and contamination inside. Fuel samples were taken directly from both the tank and injection pump and sent out for testing, which confirmed significant water contamination in the diesel.

We also found additional contamination and black material inside the pump, further supporting internal deterioration from contaminated fuel.

At that point, the diagnosis started coming together. The HMMWV had proper electrical supply, good fuel flow from the tank, the air leaks had been corrected, but the problem continued specifically as the injection pump became heat-soaked.

The evidence pointed toward contamination-related internal failure of the DB2 injection pump rather than simply a bad shutoff solenoid or electrical problem.

This one was definitely a process of elimination, but that’s why proper diagnostics matter — test it, verify it, and keep following the evidence instead of throwing parts at it.