Is the fuel system SUPPOSED to hold pressure?
 

Hey all!

Probably a pretty dumb Edit question. However, is the fuel system supposed to maintain pressure, for example, overnight or does it naturally bleed down when left sitting for a number of hours.

The reason that I ask is that now that I have my Edge Juice w/attitude installed it tells me, every morning, that I have 0 fuel pressure. That, of course, fires off the alarm for, say, 5 seconds or so until the pressure gets past 3.5lbs. This brings me to my second related question. It seems to take an inordinate amount of time, like about 2 minutes, before the pressure gets up to 11 or 12 lbs.

I am also VERY confused about how much pressure, in stock trim, the fuel system/lift pump is supposed to be supplying. I have purchased an OEM Cummins fuel pump, made by Carter, for immediate install if the consensus here is that my LP is shot. Right now the pump will put out 11 to 13 lbs at idle and 11 to 12 lbs at cruising speed. When I get on the pedal a bit the fuel pressure will drop to 7 to 9 lbs and then quickly climb back up to 13 when I get off the gas. When I floor it the pressure caves to 0 or less and takes FOREVER to build back up to 12 or 13 lbs. Is any of this normal? Am I heading for disaster in the very near future? Please note that I am only running my Edge at level 1 with no intent of ever pushing it to the dark side.

I really need some input here gang -

Thanks for listening!

Mike

If you see 5lbs or less at wide open throttle the lift pump is not supplying fuel like it should.

Definitely time to replace that lift pump. You shouldn't see it dropping that low, even with your foot on the floor. Plus, it shouldn't take that long to bring pressure back up. The return to normal pressure should be almost instant.

May want to consider some larger lines as well to help supply a little additional volume up to the pump so that you don't pull pressure down so easily.

I am using a mechanical guages so it may act differently than your edge. When I turn the key to the on posistion, my fuel pressure jumps to 10 psi and quickly falls back to zero. I assume this is the lift pump priming itself so to speak. Once the truck has started, the fuel pressure climbs to 17 psi in under a second. Never does my pressure go below 9 psi. (I replaced my original lp with an airtex pump about a month ago.) Since you already have the pump, I would go ahead and replace it.

You are taxing your VP44 heavily! I feel so strong about this that I'd say it would even possibly be wise to stop driving your truck until you replace that fuel pump. You can choose OEM again but your only pressing your luck if its not already to late. The VP may already be hurt because of your obviously lacking fuel pump. The OEM fuel system is just terrible and should be abandoned at the soonest convenience. ESPECIALLY if you have any power enhancing add ons. There is many many reasons that the OEM fuel system is garbage but I wont go into that right now.

Yes the fuel system holds a "prime" but not full pressure. Meaning that when you turn the key to start, the LP should be able to instantaneously bring the pressure to the maximum amount that pump is set for, then drop to zero, but only to instantly regain maximum idle pressure in seconds after the engine starts. If this is not happening and your pressure is below 10 psi at any time then you're only destroying your VP. My recommendation to you and all VP owners is no less than 15 psi fuel pressure EVER so as to allow excess fuel to pass through the VP's overflow valve all the time and help keep the VP cooler.

Mike, since you didn't mention I'll ask, Did you check or replace your fuel filter? If it's new, then I'd say it's your LP going out. Other possibility might be trash in your tank or clogged pickup screen if you still have original module in there. Just some things to check.

There is no pressure anywhere in the system the moment the truck is shut off. But it's not supposed to "bleed down" whatever that means, either. That would imply a leak. Liquid (fuel) is not compessible, and maintains pressure to the pump(s) and injectors only through the force of a running pump.

If everything is functioning normal, yes. And like Kreynolds described as well. But I actually had a pump that had a stuck checkvalve that would hold line pressure after the key was turned off. It stayed at 15psi and took almost five minutes for it to "bleed down" on its own, or I could go under the hood and flip the water drain and watch it shoot out under pressure till it reached zero in only a second or two.

This is excellent information you guys and I thank you so much for helping me learn and understand about the diesel side of trucking! I am installing the new OEM pump today as I have it in my hand and ready to go. I will upgrade this to an after-market system (FASS, AIRDOG, something similar) as soon as I can reasonably afford to do so. Based on what I now understand I am really grateful that I installed the Edge since otherwise I would have had no idea that the OEM pump was hurting. The parts guy at Cummins sounded pretty incredulous that I still had the OEM pump at 158,000kms. I hope that I have not already done damage to the VP44 - that would really suck and I would have to park the truck for several weeks as I simply doesn't have the $$$ to replace a VP44 right now. Being a semi retired older phart has resulted in a somewhat restricted inflow of cash right now.

Cheers everyone and thanks again!

Mike

Hi folks!

Just a quick update to those following this thread. I installed the new fuel pump without too much drama - actually it went quite well if I may say so [director] I now have fairly decent FP, although I'm sure nothing compared to the aftermarket products. At WOT the pump holds 7 pounds of pressure so I feel much better about the whole situation. As soon as I can afford it I plan on upgrading the LP system and I will keep the current pump in the truck as an emergency spare. Thank you for your help everyone.

Cheers!

Mike

Mike, I dont want to burst your bubble but given what you just said, you better be a really light footed driver until you can change that fuel pump. 7 psi is just tooooo low. Especially since that probably means your driving FP is around 11-12 psi, right? Still, tooooo low. You can get away with it for awhile as long as you stay light on the throttle.

And the arguement of how much the VP needs goes on. Most people with AirDogs run 12# & higher always. Blue chip says those systems are overkill & you need 5# or better. http://www.bluechipdiesel.com/vp44diagnostichelp.html

My VP died with 13-15# solid. Truck may be for sale while the VP is new.

Very true..... bluechipdiesel.com is still down for maintenance so I cant check if Chip has fully changed his website to his new thought on fuel pressure. Chip used to say 5 psi at WOT was acceptable because he and his crew had tested the VP on a dyno while monitoring the VP's temps. During that testing, they determined that there was no significant increase in temperature when going from 5 to 10 psi. BUT, with that said, years later, he admits that he may have been wrong since the VP failure rate was still high and now thinks that the VP needs a minimum of 15 psi. WHY? Because of exactly what I've been saying. The VP has an overflow valve that doesn't let fuel pass by the VP until 14-16 psi sooooo how can ANY fuel do its job of passing over and cooling the VP if its not allowed to pass by at all????? It cant unless you set your WOT fuel pressure above 15 psi.

Even though I feel Chip is one of the most intelligent guys dealing with the VP, I'm not defending him either. I always thought that 5 psi was to low and when I lost my VP and changed out my LP to the Raptor, I set my fuel pressure to 19 idle and 16 WOT.....not because I think I'm smarter than anyone but simply because it just makes sense.