Nor_Cal_Angler

general question is this....

is it possible to have a ZERO psi reading and still have the truck running?

had a disscusion with a friend and we both feel the same.

so hypotheticaly here is the secenero:

installed a pressure guage. at the IP fuel in line...primed the system...truck fires up after only 1 bump of the starter and a 5-7 second crank of the engine...idles smooth...runs up the block....then out on the main street @35-45 mph..then up and over a hill @55 mph...then back and at the last stop sign a WOT is applied..returns to the house and throughout the whole test the guage reads ZERO psi...

now i say NO way...first my understanding is if the LP is bad and not sending pressure the truck would not even prime....second even if the IP is doing ALL the work...it still would have read some sort of PSI...maybe say 2 psi or something...third how in the world would a truck with ZERO fuel pressure do a 25 minute test run and then as he says be able to DRIVE for the last 3 days and have NO cels come on or the truck die out....

please tell me my thinking is right......please say that the truck can NOT run with out some sort of fuel pressure.

NCA

chuxtruk

I was wondering the same thing but upon thinking a bit about it, it reminds me of something I read the other day about Dodge not mentioning psi again in reference to lift pumps. Now they say that as long as there's "POSITIVE PRESSURE" through the lift pump the VP will be O.K. or something real close to that. My friend says they won't run, I'm saying it will run tho maybe not at top performance and maybe not for long either.
I checked the pressure in my pump in the tank setup and got 9 psi on an idle and 7 psi @ 2000 rpm's and while not spectacular, I guess there's plenty of "POSITIVE PRESSURE" at least till I get the Holley Blue and the gauges installed this weekend.


first my understanding is if the LP is bad and not sending pressure the truck would not even prime...

Maybe, maybe not. Seems there are cases in both circumstances. Personally, I think that if the LP was dead or dying and the VP isn't damaged yet, I'm betting the truck would start, hence the importance of that FP gauge.


second even if the IP is doing ALL the work...it still would have read some sort of PSI...maybe say 2 psi or something...

I doubt it beings you're reading the fuel pressure at the banjo bolt from the lift pump feeding fuel to the fuel pump which is prior to entering the pump, if I'm not mistaken. Someone help me out here....


third how in the world would a truck with ZERO fuel pressure do a 25 minute test run and then as he says be able to DRIVE for the last 3 days and have NO cels come on or the truck die out....

Now you know the importance of having at least one (test) gauge that YOU KNOW is working and is accurate. Positive pressure and some luck are what's going on here. Especially if you don't have the FP gauge on this truck. Stock truck doesn't need as much fuel as a high performance truck so maybe the VP is taking the deficit in this case....but I still say you're pushing your luck without at least trying another gauge.

You still running the stock lift pump??

coachgrowl

I installed an idiot light on top of the fuel filter canister. It would come on "at times" sometimes at start up, sometimes when running, anyway this bothered me as I know how important fuel pressure is to these trucks. The idiot light is supposed to come on when it drops below 5 psi. I decided to install the vulcan big line with a new stock lp. Did this and the idiot light never came on again. I also installed a gauge, about 2 weeks later, and it now reads 14 psi at idle and I cannot pull it below 10 at WOT. just my experience.

bziggy

Hello I to have had problems with my truck and then my friends truck. I have a friend at cummins who told me you should never go below 6-8psi at wot. At idle it should be 14-15 psi. What happens if you run it on low psi you make the injection pump pull the fuel. Also you will damage the injection pump over time beacuse the low fuel burns up the pump cause it is not getting the proper lubercation. I got rid of my factory set up and went to an air dog and am running 26 pis at idle and 23 at wot. Also made the truck idle better and perform much better.
My friends truck 02 would run like it was missing on cilinders after wot. With a gauge on it idle had 6 psi then would go to 0-1 at wot and never come back unless you shut the truck off. Went through two pump befor we found the problem. Now has the upgrade with the pump in the tank and never goes below 10 psi at wot and about 14 at idle. I would change the pickup pump it is much less expensive then an injection pump befor you burn out the pump.

Nor_Cal_Angler

ok...but here is the catch....if you have a bad lift pump...the system would not prime....

i just dont see how a truck can run for 3 days with zero fuel psi.

NCA

chuxtruk

Maybe positive pressure is enough or positive pressure is immeasurable to convert to psi, I dunno.

It must prime, otherwise it wouldn't run and if it didn't run the VP wouldn't be damaged when the lift pump was out. But the VP's a frequent victim, so they must die a slow death from lack of a lift pump, not all at once....usually. I'm saying most of these trucks run after the lift pump is gone, damaging the VP.
Put a gauge or a low pressure light on that rig, quit changing the subject and just get a replacement lift pump!! (Like I WISH I could do....but that's another story.) That's the cheapest, easiest fix you can do. If you have more $$, some time and know which upgrade you want (FASS, Walbro, Holley Blue, etc) you can do that anytime after you ditch that weak pump....if it is weak. Which you won't really know till you can compare that gauge with a known working gauge.
My dad had the low pressure light put on his 99 dually a couple of weeks ago. He was worried that he may not see it right off the bat should it light up but no need to worry about that. He describes it as like a laser in intensity even tho it's a very small idiot type light. Well, wait a minute. If that thing has zero pressure that light would be blazing away in your rig....better get that gauge!!! The tester gauge that you know is good. Vulcan Performance has a good one for about $50. I found one on Ebay for $30 but they're accurate and you could even run that one out under the hood for awhile to check the interior gauge against tho you'd of course have to secure it well while it was riding.
Those lift pumps can go at anytime. My dad suggested to the Cummins mechanic that his truck now has 100k miles so why not R & R the lift pump while the truck's here and put a new one in?? He recommended NOT replacing that lift pump till it goes out as "you may have one that lasts forever or the new one could last a couple of weeks. This light is your insurance policy and if it comes on steady, first change the fuel filter. And if it stays on after that, the lift pump is probably toast. Change it then...." That's what my dad decided on....listening to him.