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Old 08-02-2010, 09:36 AM
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An old stand-by troubleshooting test developed here in The Diesel Page more than ten years ago, for the 6.2/6.5, to help determine whether a stalling/low power/hard start problem might be due to worn fuel injection system parts is to:

Once the fuel level in the tank is down to about 5 gallons, create a mix of 4.5-gallons of diesel fuel and 2 quarts of 30W motor oil in a separate fuel container, and pour it into the tank. This will result in a 5% oil mix in the fuel tank. If the added fuel viscosity temporarily solves the problem or lessens the symptoms, you've learned something. Worn parts are the likely problem. Once the troubleshooting is complete, fill the tank with straight diesel.

The oil won't hurt the engine or fuel injection system, but I'd not do this in a 2007+ truck equipped with a diesel particulate filter in the exhaust system.

If increasing fuel viscosity helps, you have a choice of either replacing the high pressure pump or injectors. I'm not sure whether the FPR would be helped by added fuel viscosity.

Jim
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