injector pump tuned for higher altitude??

[85-m1028]

I've read about injection pumps that are tuned for lower altitudes that over fuel and smoke at higher elevations, "lack of oxyen" does the opposite apply too only reverse?? I recently went up the mountain for some snowboarding and noticed that my engine idle was smooth no stumble or vibration and ran better than it has ever run since I put it in 10,000 miles ago "used take out". I did notice a little less pulling power. when I got back to lower elevation it ran almost the same but the next day went right back to missing and shaking badly, so I though maybe the pump likes elevation? I filled the tank on the way up and came back and ran the next day on the same fuel, Is it posible to adjust the pump for lower altitude? or does anyone know what is going on to cause this change, return line pressure? any leads as to what I should investigate first?? this is my 85 pickup with the hmmwv engine

[john8662]

Good point!

I've noticed a few things over the years about the DB2 pumps.

#1, the engine ALWAYS idles smoother when it's cold (after initial startup)

#2, the engien runs smoother the cooler it is outside..

In high altitude, you probably encountered colder temps, but not necessarily.

I'll talk to a pump builder I know in town and see what the fuss is, I do remember talking to him about pump settings, and he said he always used the high altitude setting on pumps he builds for here, which ain't really high altitude, but kinda is...

I'm with you though, I'd like that smooth running engine all the time.

Maybe this is why the newer 6.5 DS4 (electronic) pumps perform better here, because of the Baro sensor and computer adjustment on the fly.

I'll post what I find, I also need to do some reading in the 'ol manual too!