slightly inconsistant fuel pressure reading at idle?
10-18-2002, 10:35 PM
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slightly inconsistant fuel pressure reading at idle?
A minor problem, but one I'm curious about. My fuel pressure at idle will stay at 16-17psi most of the time, but every now and again will slip down to 14-15psi for a while, and then climb back up again. Cranky lift-pump, or normal variations due to things like fuel temperature, line connection expansion, etc.? <br><br>Thanks!<br><br>GP
10-19-2002, 08:45 AM
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Re:slightly inconsistant fuel pressure reading at idle?
I noticed this on the last lift pump I had in my '01. It did it for 20K (it started when the pump had about 30K on it), and never seemed to get any worse or any better. I'm not sure if it was a tight/sticky internal bypass, or if the pump was starting to go out. I don't think I'd worry too much, just keep an eye on it. How are your WOT numbers?<br><br>Rod
10-19-2002, 10:52 AM
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Re:slightly inconsistant fuel pressure reading at idle?
I agree, when the outside temp is colder I lose 1-2 psi of pressure at idle, never seen below 11psi at WOT. I personally think that Cummins has some Jamaican guy put a voodoo hex on all lift pumps made. 
10-19-2002, 12:48 PM
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Re:slightly inconsistant fuel pressure reading at idle?
Mine bounces between 13.0-13.4 @ Idle. The pump actually seems to be getting better the more it gets worked. Maybe the internals just need to be broken in or something.
10-19-2002, 10:52 PM
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Re:slightly inconsistant fuel pressure reading at idle?
Outside temp -- thought it might be that. Yesterday it was 45*F here -- 15 psi at idle. Today it got up to 73*F -- 17 psi at idle. Wonder what it might be at -10 or -20*F? Any of you cowboys up in the Great White North have insight? An additive might have an effect in that situation, yes? <br><br>Rod, my WOT is 10-11 psi. <br><br>GP
10-20-2002, 08:46 AM
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Re:slightly inconsistant fuel pressure reading at idle?
Up here, our fuel pressures don't vary alot in the cold, as our fuel is constantly blended from the pumps for cold weather operation. We may see a 1 PSI hit in the winter.
Another thing I thought was interesting about my lift pump is that it would show 13PSI when I first fired the truck up, and then after running for awhile, it would increase to 15 PSI idle pressure.
First fuel pump I ever had that required warm-up ;D
Anyway, GP, it sounds to me like you're just fine. The WOT throttle numbers are good, so just keep an eye on it...
Rod
Another thing I thought was interesting about my lift pump is that it would show 13PSI when I first fired the truck up, and then after running for awhile, it would increase to 15 PSI idle pressure.
First fuel pump I ever had that required warm-up ;D
Anyway, GP, it sounds to me like you're just fine. The WOT throttle numbers are good, so just keep an eye on it...
Rod
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10-20-2002, 09:19 AM
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Re:slightly inconsistant fuel pressure reading at idle?
Mine acts the same as rods about 15psi normally but sometimes stays at 13 psi then increases slowly to 15 psi. However my WOT is only around 4 psi with comp on 5x5! :'(
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