Q: In my shop in Texas, we're currently working on a 2002 Chevy Silverado 2500 with the 6.6-liter Duramax diesel. The truck's owner put gasoline into the tank and drove it 12 miles before it died. We replaced the injection pump, tank module, and fuel filter and cleaned out all the lines. We went the whole nine yards, and there's fuel from the pump to the engine, but it won't start. It'll crank but it won't turn over.
A: I once worked on a car where diesel fuel was accidentally pumped into its gas-burning engine. In that instance, the biggest problem was an inability to shut down the engine; it just kept banging away with the ignition off. But there was no residual damage once the diesel was drained from the entire system and replaced with gas. In gas-into-a-diesel situations, two factors that determine damage incurred are the ratio of gas to diesel in the tank, and the amount of time the engine ran on the mixture. My understanding is that a diesel engine running on a high content of gasoline will have limited power and get nowhere fast.
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The longer it runs, the worse off you'll be. One issue is that gasoline has minimal lubrication properties, compared with diesel fuel, and the excess friction can damage the inner workings of the injection pump. Damage also can occur due to the higher combustion-chamber temperatures from gasoline. Prior to replacing any parts, I would've drained and flushed the entire fuel system, filled it up with fresh diesel fuel, and thoroughly bled the system of air, then started the engine hoping damage would be minimal or nonexistent. Air in the system may be the problem you're dealing with right now. Be sure you're following GM's recommended air-bleed procedure.
Once the possibility of air in the system is eliminated and fuel delivery checks out, injectors are the next area to inspect, because they may have developed a coking at the tips. In other words, they're getting clogged by carbon residue from the burning of improper fuel. (Never mind that some Duramax injectors normally tend to develop problems running on diesel.) Next would be a compression test to evaluate any internal engine damage.