Why a fuel pressure gauge

[RStamand]

I apologize in advance if this is a stupid question, but other than the obvious (fuel pressure) what does the gauge alert me to. Let the verbal beating commence.

 

[fox]

No one will flame this question.



A fuel pressure guage will let you see what the pressure is before the injection pump.

On the ISB motors, 98. 5 thru 02 Dodges have a poor design fuel system and it takes out- destroys- the lift pump, then this will over heat and not lube the injection pump. Then the truck dies and it is expensive to get fixed.

The electric lift pump cannot draw fuel from the tank very well. The injection pump will run with a bad lift pump because the injection pump can draw fuel. BUT it doen't cool and lube it.

I think a similar issue happens with the newer trucks. Older, it isn't an issue.

What year truck do you have?

 

[RStamand]

05 2500 auto 3. 73 4X4

 

[TSpecht]

If it's a 2005 it should have the in tank fuel pump which should in theory solve the problem, at least for a while, since a pump pushes better than it pulls. Of course time will tell on that. The other downside I see to the in the tank pump is it's more difficult to swap in an aftermarket tank or an aftermarket pump.

 

[nps]

On the HPCR trucks (03 and higher), the value of a fuel pressure gauge is limited because if the lift pump goes, the truck doesn't run, but nothing gets damaged. So the gauge is really a no-start diagnostic tool and if you go for one, doesn't really need to be inside the cabin. The fact that you have an 05 with an in-the-tank lift pump means you will probably never see a failure, although time will tell if the pump in the tank works better.



On the 24V trucks, like fox says, no lift pump=no VP44 sometime thereafter. And neither event (LP or VP failure) is on or off - rather a slow, erratic and expensive death. Both parts are covered on the 10/100 engine warranty.



Dodge is rumored to be making a 24V kit to put lift pump in the tank. Must be getting tired of all the residual warranty work given they are addressing a design that is 3 years out of production.

 

[TRAMPLINEMAN]

nps, I work with guys who have already had fuel pump problems with their 03-05's. I would have to say the problem isn't fixed.

 

[SKargo]

Can't a FP gauge also alert you to a clogged fuel filter, or one that's in the process of clogging?

 

[nps]

nps, I work with guys who have already had fuel pump problems with their 03-05's. I would have to say the problem isn't fixed.

I'm not saying the LP doesn't have problems. The difference is that when the LP does have a problem, it doesn't break other parts on the HPCR. Therefore on the HPCR the guage doesn't prevent any damage, just helps diagnose other problems, like a clogged filter, bad LP, etc. So the question becomes the value of a diagnostic tool. Issue 48 had a good writeup on this point, but the option is always there to put the guage on.



On the 24V, a bad lift pump takes out the VP44 even though the truck still runs normally (until the damage is already done). Thus a FP guage on a 24V keeps things from breaking and other bad things from happening. On a 24V the guage should be mandatory,



Please elaborate on the pump problems the guys you work with are seeing.

 

[TRAMPLINEMAN]

Dead pumps

 

[rbattelle]

The difference is that when the LP does have a problem, it doesn't break other parts on the HPCR.

This is not actually true. The CP-3 injection pump is fuel lubricated just like the VP-44. Although it does seem to live longer with a bad lift pump than a VP-44 will, it will eventually go bad.



When the '03s came out everyone thought the new lift pump design would be "the one". Nope. People are still having LP failures that destroy the injection pump. Now everyone thinks the in-tank pumps are the answer. I hope so, but as was mentioned the in-tank pump is now a big tradeoff. Maybe it will be reliable forever, but for bombers who need to increase fuel delivery rate it's likely to be a giant expensive headache installing an aftermarket pump. Already the question has come up - how do you install a supplemental fuel filter on an '05 with the in-tank pump? Is the in-tank pump powerful enough to push through a 2-micron final filter? These are unknowns that the pioneer '05 owners will need to discover.



-Ryan

 

[Cattletrkr]

Doesn't GM use the CP3? I thought I've read that here numerous times. And they do it without a liftpump. Or have I ben reading bunk posts??

 

[rbattelle]

Doesn't GM use the CP3? I thought I've read that here numerous times. And they do it without a liftpump. Or have I ben reading bunk posts??

I believe that's true, but they don't have any lift pump restricting flow, so the CP-3 is able to suck just fine. Of course, I think they have to add a pusher pump if they add supplemental filters (which many of them do). And their system is not self-priming like ours is.



-Ryan

 

[nps]

Seems contradictory - CP3 can work just fine without a LP, but the LP causes a restriction if it goes bad (hence no fuel and no start) and causes the CP3 to fail?

 

[rbattelle]

Seems contradictory - CP3 can work just fine without a LP, but the LP causes a restriction if it goes bad (hence no fuel and no start) and causes the CP3 to fail?

That's exactly as I understand it. When the LP is not spinning it acts like a big flow blocker and the CP-3 can't suck enough fuel through it. So it starves.



-Ryan

 

[Signal73]

If a 12 V still has a LP, which it does according to the diagram in the stickies up top, Why is it more reliable then the 24V version, Thanks, Jim... .

 

[Joe G.]

The 24 valve and later lift pumps are electrical. The 12 valve lift pump is a very simple mechanical push rod pump.