Dealer stumped: power loss, ticking noise, check engine light under heavy load

[jasonmeredith]

I could really use some technician help. Please take a look at the video below. I've shared this video with the dealer lead tech and he's stumped.

My truck is a 2003 Silverado 2500HD 8.1/Allison. This video was taken a few years ago when towing a 10,000 lb trailer up Snoqualmie Pass in Washington. I encountered this problem only a few times until this last weekend. I now have a 14,000 lb toy hauler and was towing on much longer and steeper grades on Hwy 97 thorugh Washington and Oregon.

The video is a shot of the instrument cluster with audio. When towing on an extended grade the tranny shifts down as usual but after a short while under load at full rpm a ticking noise develops and then the engine gradually loses power until the check engine light comes on. When I back off the gas and let the rpms come way down the ticking noise goes away, the check engine light goes off, and power returns to normal. The video shows this happening above 4,000 rpms. With my heaver trailer on steeper grades this weekend I experienced the exact same situation but at about 3,700 rpm. This was 100% consistent this last weekend. As long as I keep the rpm's way down the truck pulls the heavy load on the steep grade just fine but in the 30-40mph range.The truck has about 70k miles on it. I use it exclusively for towing and winter driving. It is serviced routinely per spec. Any help would be greatly appreciated.

http://www.flickr.com/photos/jmered/5908907485/

Thanks,
-jm

[DmaxMaverick]

Welcome aboard!

It could be a couple things:

Fuel delivery. Fuel filter, other restriction, or a failing fuel pump. Start with a fresh filter.

Fuel quality. Try using a higher octane and/or a lesser content of ethanol fuel. full premium should contain no ethanol. As you begin to really work the engine, the cylinder temps increase. A fuel of too low octane, or too much ethanol, will begin to detonate, causing a knock and power loss. You may have got a tank of bad fuel. If this problem spans several refills, from different stations/suppliers, your engine may just have a specific preference for fuel.

[Inspector]

I'm not sure about the 8.1 but as DMM brought up the detenation question, I recall that if a detenation sensor is part of the control package it very well maybe shuting you down to protect the engine. I agree that fuel quality and running to far advanced in timing is causing the knocking and the sensor circuit is backing you down. I know that the timing is ECM controlled and not adjustable so maybe a reflash or update is needed. I would also find another dealer. Second opinions can sometimes be valuable.
Denny