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Old 09-18-2010, 12:43 PM   #1 (permalink)
Tourque
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8.1L Fuel pressure specs

I know it's been posted before but could not find during a search...... If I remember correctly on the 2001 8.1's, to test, you disconnect the vacuum line from the regulator and you should see 70+ish PSI and then I think like 55ish under normal conditions? Is this right? I may have a clogged filter as I'm only seeing 55 no matter what and it's fluctuating a lot while sitting at idle. I'll mess with the regulator but wanted to verify what I'm aiming for again.

Thanks!
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Old 09-18-2010, 05:45 PM   #2 (permalink)
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The spec should be 58psi with the vac ref removed from the pressure reg. Pluging it back on should drop the fuel pressure from there.
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Old 09-19-2010, 12:00 PM   #3 (permalink)
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Cool, thanks. That's pretty much in line with what I was remembering. I'll adjust and go from there. I'm still concerned about the surging but I'm thinking it may have something to do with some of the other issues I'm having. I have an exhaust leak that's making the truck run really rich. On the list to fix here shortly.
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Old 09-29-2010, 10:35 AM   #4 (permalink)
wftruthseeker
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Idle Pressure

My 2001 8.1L GMC 2500HD started dying out on the way home and I barely made it to my driveway before it died. It acts like it is not getting enough fuel. It will run fine and start to die, and run fine again and die. Sometimes I can start it for a sec, and sometimes not. My first thought was the fuel filter, but that made no difference. In fact, the more I try to start it, the worse it seems to get. I just hooked up a pressure gauge and primed the system (by turning the key on) and I'm getting about 29psi. Does this sound low. I know it should be much higher while running, but I'm having trouble getting to that point. If that is low, what should I check next?

Please help, I've gotta get this running!
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Old 09-29-2010, 12:03 PM   #5 (permalink)
Tourque
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Sounds pretty much like a classic fuel pump failure. You should scan of other codes in case something else is acting up and providing the same symptoms just in case. However, pumps usually go immediately and the symptoms are as you described. That is exactly the way that mine behaved when it went. 29 is not what you want for pressure, you want to disconnect the vacuum line from the pressure regulator and that will give you what your pump is capable of producing for pressure. Spec is around 58psi. Not sure technically at what low level you'll produce the symptoms you described but 29 does not seem adequate to me and if you've replaced the filter with no improvement you're in for a pump.

They're pretty easy to replace. Drain the tank (can be done by disconnecting the feed either at the fuel filter or at the main feed on the fuel rail) give the fuel pump power (can be done by completing the circuit where the pump relay plugs in in your electrical box) and let it pump itself out. Drop the tank (4 bolts I think and a couple fill hoses) and then you'll need fuel line disconnect tool to undo the pressurized lines. I was able to do all this without having to jack up my truck and I'm running relatively stock suspension. The tank does clear under the truck.

Hardest part for me was disconnecting the pressure lines. I have several different disconnect tools and found that the lines are bundled so close together it proved to be a significant challenge to get the tool in there to get the lines to release. I had to grind down my tool to get the right clearance to make it work.

Hope this helps, good luck!
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Old 09-29-2010, 02:15 PM   #6 (permalink)
wftruthseeker
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Thanks for the reply. I got it to start a few times and the pressure was anywhere from 34 to 18. The MOST I saw it peak at was 40psi. When I saw that, I decided to drop the tank. You're right, the hardest part was the lines, and the filler tube. I dropped mine with just over a quarter of a tank of gas. I don't recommend that, but it wasn't too bad. I was looking the pump over for anything obvious, and am about to pour the remaining gas out of the tank (into containers for my lawn mowers). Anything else I should do while I'm waiting on a new pump?
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Old 09-29-2010, 05:26 PM   #7 (permalink)
Tourque
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Nothing I can think of. The pump should come pretty much assembled with the exception of the float for the fuel gauge. All parts are pretty much there so all I'd do is try to keep the tank from getting junk in it while it's sitting open and then slap the new pump in.

When you ordered the pump, did they ask you which one you wanted? There are actually 2. One in the main tank and one in the reserve tank. You should make sure they've ordered the correct one for you. The one in the reserve/extra tank simply pumps it out into the main tank.
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