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FixItMan, Master Technician
Category: Australia Car
Satisfied Customers: 17088
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I'm in Australia and there isn't much tech help here for

Customer Question

Hi. I'm in Australia and there isn't much tech help here for these imported trucks.
I have a 2005 GMC 2500 HD 6.6 litre diesel/auto.
When driving without towing.... no problem.
When driving with a 4 tonne boat on the back and after travelling for half an hour or so it will go into "limp" mode.... no power, engine still running but no throttle response. NO engine warning lights. I pull over and switch off. After a minute, I can fire it up and travel again for about an hour or more before it happens again. Generally only happens when running up-hill and under heavy load. No smoke out the back, no warning, just drops power. Runs great otherwise. Temperatures all remain within normal. No fault codes showing.
Have replaced EGR valve assembly. Have had an extra fuel pump fitted at the tank. replaced fuel filters. It's like a sensor is telling the ECU that something's not quite right (under heavy load), and after stopping and switching it off, it "resets" itself?
What should I look for?
Submitted: 12 days ago.
Category: Australia Car
Expert:  FixItMan replied 12 days ago.

Hello, my name is***** you tell me if you get any other warnings beside the limp mode warning. Do you get any transmission or shifting messages?

Customer: replied 12 days ago.
Hi Bobby, there are no warnings coming up. There is no "limp" warning coming up. There are no transmission warnings coming up. I had the transmission serviced just in case, by a very reputable company. The vehicle just loses power and I pull over, switch off, wait a minute, and then fire up again and off I go, with full power. This may happen once every 1 or 2 hours BUT only when towing and only when under load going up hill. Transmission temp and engine temp are in the normal to warm range, but certainly not hot.
Expert:  FixItMan replied 11 days ago.

Thank you. The most common causes I have seen is either a fuel pressure drop or an issue with the ignition switch. Check the fuel filter housing for any signs of leakage. Even a small amount of wetness can be enough of a leak that it causes a fuel pressure issue. I also see ignition switches cause this all of the time. One other part, and actually one of the most common is the fuel relief valve located in the fuel rail. These become warped and some times do not seal which will cause this to occur.

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