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Fuel pressures...interesting find.

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Now, this has nothing to do with my FASS's operation, but I found it quite intriguing...



On my trip to UT a couple weeks ago, I was running around 15psi idle on the flat lands during the trip out. I got into the mountains, and I was holding 9 to 10psi at idle for whatever reason. When I got back out onto the flat lands for the trip home, I was back to 15psi at idle.



Now during this oddness, my low pressure light (set at 7psi) never illuminated (it is working BTW)... so I wasn't pulling the pressure down much when pulling the hills... I worked 5th gear hard a couple times just to see if it would pop the light on... never came on. The truck ran fine, pump ran fine, no weirdness other than the lower than normal psi.



So, what is the explanation for the low pressure at higher elevations??? Was it the fuel?? Was it the higher altitude (that should have made no difference in this application)??? Was it the guage???



Ideas??



Again, it isn't a problem, but I would like to know what others think the cause of the drop was...



steved
 
I live at 6200 ft and my pressure is good. When I go up to say 10k I dont notice any drop in pressure. Could it have to do with the gauge and not having had time to adjust to the new atmospheric pressure - wait that should have made the pressure reading go up. So no help here.



By the way how was the trip, where did you end up going (I remember your trip suggestion thread)?
 
I live at 6200 ft and my pressure is good. When I go up to say 10k I dont notice any drop in pressure. Could it have to do with the gauge and not having had time to adjust to the new atmospheric pressure - wait that should have made the pressure reading go up. So no help here.



By the way how was the trip, where did you end up going (I remember your trip suggestion thread)?





I'm leaning towards the guage being wacky... it is a sealed liquid-filled guage...



We ended up going a bunch of places... they wouldn't leave us up Pike's Peak, so that didn't happen. Hit Garden of the Gods in Colo Springs, Moab (Arches, Dead Horse Point, and Canyonlands), Natural Bridges, Glen Canyon Rec Area, Capital Reef, Bryce Canyon, North Rim of the Grand Canyon, Hovenweep, and Mesa Verde... it was a busy nine days... 5500 miles in 9. 5 days!!! It was definitely a good time!



steved
 
The gauge. If its sealed, the pressure inside the gauge stays the same even though atmospheric pressure at the higher elevations is less. Did the needle go below zero when you shut the truck off at the higher elevations?
 
Are you using an isolator? They can get unstable at different elevations or different temperatures, especially if they are mounted on a surface that gets hot.
 
The gauge. If its sealed, the pressure inside the gauge stays the same even though atmospheric pressure at the higher elevations is less. Did the needle go below zero when you shut the truck off at the higher elevations?





Never looked at it when it was shut down...



But I am also guessing the guage was the culprit...



steved
 
Heat will cause the pressure to drop. 24 valve trucks with the VP44 recirculates a high volume of fuel. The fuel in these trucks can get very hot as you drive them long distances and more so in the summer months. I suggest to stop more offen and fill up with cold fuel at a half empty mark. This will cool off the fuel in the tank and help with the VP44 longevity. In winter when the ambient temperature is colder this will not be nec. Thanks
 
Heat will cause the pressure to drop. 24 valve trucks with the VP44 recirculates a high volume of fuel. The fuel in these trucks can get very hot as you drive them long distances and more so in the summer months. I suggest to stop more offen and fill up with cold fuel at a half empty mark. This will cool off the fuel in the tank and help with the VP44 longevity. In winter when the ambient temperature is colder this will not be nec. Thanks





Being this is a 3rd gen, we are dealing with a CP3... but the same principles apply. My fuel tank gets plenty warm, but it never caused a issue before this...



steved
 
It sounds like TDR member rweis had a good point when he recommended adding a fuel cooler in the fuel return line.
 
Since i have the FASS, and it recirculates the fuel at such a high rate... I have often considered adding a oil cooler on the FASS'a return to the tank.



The fuel int the tank will get quite warm, no doubt.



steved
 
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