Powerstrokes and altitude.
 

I just got back from a 1000 mile trip with the family. We went into the Sierra Nevada mountains to do some fishing and get some rest and relaxation ... by the way, the fishing was phenominal!

Something I noticed was the truck took a while to prime. The light would stay on for a good 4-5 seconds, maybe longer at times. We were doing most of our driving between 8000 and 10000 feet. Is this normal for this engine at high altitudes?

The glow plug's are only based off of temps, I think it reads intake air temp and oil temp to determine what to do. It would/should have nothing to do with elevation.

Also the GP's stay on for a full 2 minutes after the light even goes out.

Did the truck start like normal and run ok?

Yes, the truck ran fine, no problems whatsoever. The weather was pretty mild up there ... 40s at night and high 60s/low 70s during the day.

Well if it was colder there than it was at home, then yes they will stay on longer....

Good stuff ... thanks!

The GPs are activated by the PCM based on BARO, ECT and EOT to determine GP on-time. The command to the GPCM is over a datalink.

Altitude (baro) will affect the operation somewhat.

Thanks for the info.