Dealer says I have some open circuits under the valve covers, probably bad harness. Obviously a change in fuel didn't cause that. Just a coincidence that it went flaky the day after a bio fillup. Thanks for all the information.

 

Please keep us posted as to what the dealer fixes for you!

 

Dealer replaced UVC harness. According to service order, test readout showed hard faults cyl #2&4 high to low side open. Found UVC harness disconnected. replaced both sides with revised harness.

Not sure exactly what that means. I don't know whether it was just a couple of wires in the harness that were disconnected. It's hard to believe the whole harness could have been unplugged and the truck was still running. I assume "revised harness" means that sometime after the truck was built, they changed the harness design, maybe to make it less likely to come loose.

Total cost about $550. $175 for harness, 332.50 for labor, 25 shop supplies. The labor charge was 3.5 hours, so my calculator says $95/hour. Not sure how reasonable the rate is. Looking at all that "stuff" on the engine, I can see how it would take 3.5 hours to get the valve covers off and back on.

 

Probably one of the connectors on the harness coming unplugged. They did change the connector at some point to prevent this. If you hang around here long enough you will be able to figure out what these things are and feel confident enough to fix most of them yourself.

Glad your up and running, and don't be afraid to ask questions along the way.