Fuel Pressure, Rail Pressure Gauges

why not do both. install a srt apillar trim and mount your piro there, thats where mine is, and then your tranny and fuel pressure gauges up on the dash.. or you could do the steering column mount, this mount comes in both dual and single gauge. i've got a dual on mine but still only the boost gauge (i have yet to buy the fuel pressure gauge) i'll email ya a pic of my setup if ya want.

i personally still want to monitor the lift pump (but i have yet to install the capability lol)

First, while it's true the 3rd gen trucks' lift pumps were more reliable than previous years, and the CP3 pump is much more tolerant of lower fuel pressures, DC felt that the lift pump was still enough of an issue that they re-designed the low-pressure side of the fuel system, and re-located the fuel pump inside the tank.

There have still been reports of lift pumps failing, even on the 3rd gen trucks. While this doesn't automatically trash the injection pump like it used to in the VP44 days, it's still not a good thing for the CP3. Yes, the CP3 has it's own small gerotor lift pump built in, which in other applications draws straight from a fuel source (no aux. lift pump), but that's just it - it's not trying to suck fuel through a locked-up electric lift pump in those applications.

IMO, a fuel pressure gauge is still useful. I use mine all the time to judge when it's time to change fuel filters (I notice the drop-off in pressure, meaning the filter's getting more loaded up with gunk).

A rail pressure gauge is really just a "gee-whiz" kind of gauge, unless you're planning on playing around with your fuel pressure to get more power out of the engine. That's a whole 'nother story, then - and in that case, yes, a rail pressure gauge could be useful. I, personally, am against cranking up fuel pressure much beyond stock (the pictures I've seen of worn injectors sold me on that one). I currently have an Edge EZ box hooked up, that I run on level 1 (mildest setting), just to give a little more fuel way down low.

As for the boost gauge, again - not all that useful if you're running a stock truck. It can be helpful in diagnosing problems (for instance, a blown, or even leaking, intercooler boot is going to be easily noticable on your boost gauge).

For reference, I currently run 7 gauges - pre-and-post-turbo EGT's (pre-turbo being read by my TST box), boost, fuel pressure, tranny temp, oil pressure, and water temp (needed to fill the last hole, and I never trust the factory idiot lights in the shape of gauges).

I considered the steering mount, but it blocks part of the dash. I'm a no-clutter kinda guy.

Yes, please.

Remember, I am not a mechanic, so what I'm about to say might be worded incorrectly ... or worse yet, just downright wrong. :-)

My understanding is that the issue on the older Rams was that they had two pumps. When the fuel pump in the tank failed it caused the lift pump to work harder and eventually fail. Which is why the fuel pressure gauge was necessary (to detect the failure of the cheap pump in the tank and get it fixed before the expensive lift pump failed). In my Ram, there is now just a single, more powerful lift pump. Therefore, the fuel pressure gauge really serves no purpose. However, the rail pressure gauge can be useful in detecting a faulty FCA.

Does this sound correct?

If I ever decide to add a boost gauge, I'll probably put it on the a-pillar with the SRT mount.

Thanks! Craig C.

This is the justification from the mechanic I have been dealing with after asking him why a rail pressure gauge is preferred over the fuel pressure:

"On the rail pressure, low or fluctuating rail pressure don't necessarily equate to a dead CP3 (injection pump). It's use is to give the operator a base line of rail operating pressures at given load and engine rpm's. Out of the norm for same driving conditions could help diagnose the concern with the high pressure side of the fuel system. Ie. the fuel control acuator (fca) sticking or cycling improperly (low to no rail pressure) or a bad rail pressure sensor or fuel valve. both would cause performance concerns and could asst. Dodge or other diesel techs in more accurate diagnosis of the concern. For example the CP3 could be failing causing a low rail pressure, if the tech, did troubleshooting and found the FCA, rail sensors and low pressure side volume's to be up to par, the ECM (engine control module) or CP3 would be the obvious culprit."

Note, I am not trying to pit anyone against anyone. I trust this guy, he's a great mechanic. What I am trying to overcome is my own personal ignorance on the matter. I'd like to understand better why one is better than the other. Or ... if I'd be better served with scrapping the fuel gauges altogether and just put in two gauges (tranny temp and pyro).

This is what I am trying to avoid. Having a gauge for the sake of having a gauge doesn't excite me at all.

I highly doubt that my truck will ever be anything but stock. I like it just the way it is.

Okay ... you *might* need to calm down a little. :-)

Craig C.

Well.... no :)

Back in ye olden days, when there were only two valves per cylinder, there was a mechanical lift pump mounted on the back of the engine that sucked fuel from the tank, and fed it up to the P7100 injection pump. The P7100 was lubricated by engine oil, and if for some strange reason the mechanical lift pump failed and stopped feeding fuel to the P7100, the extent of the damage done was probably a sore toe from you kicking the truck because it stopped running (not to mention all the fun of re-priming the fuel system and getting it running again... but still, no permanent damage done).

With the introduction of the 24V ISB engine, came electronics. With that, the mechanical lift pump was replaced with an electric pump, still mounted on the left-rear of the engine, still sucking fuel from the fuel tank, but now delivering it to a VP44 injection pump. The VP44 no longer used engine oil to lubricate itself as the P7100 did... it relied on diesel fuel for lubrication. You can see where this is going.... when (not if, but when) the electric lift pump failed, it starved the VP44 of fuel, which in very short order would gawl itself all up, and you were then the proud owner of TWO broken pumps.... one relatively cheap (the electric lift pump), and one really expensive (the VP44).

The 3rd gen trucks, with their new ISBe (also called the HPCR, High-Pressure Common Rail engine), use a different version of the same electric lift pump, and a newer, higher-pressure, yet still fuel-lubricated CP3 pump. The CP3 is cheaper to produce than the VP44, as there are no electronics (the VP44 contained electronics to control injection timing) - all the injection timing is now done at the injectors themselves. However, the CP3 is still an expensive unit, and not something you want to fail (and believe me, starve anything that spins around and around of lubrication, and that's exactly what will happen).

Starting in model year '05, DC decided that pulling fuel 12 or so feet through a tiny little tube probably wasn't the best use of a pump designed to push, rather than pull - and re-re-re-designed the fuel system with an in-tank "pusher" pump, that would now feed fuel directly to the CP3 (still going through the stock fuel filter canister, however). Guess what? Sometimes, those pumps fail, too. Of course, now you have the added fun of dropping the tank, and removing the fuel module to replace the pump - something that old 24V guys could do by feel on the side of the road on a moonless night inside of 10 minutes.

Thanks for the lesson. As usual, your explanation is easy to understand, even for those of us that have the random retard gene floating about.

:-) Craig C.

All of what he says is correct - however, all that information is available to any tech diagnosing the truck by simply hooking up the DRB3 will operating the truck. So having a rail pressure gauge is only going to be of use to you to indicate that, "yep, there's a problem - better take it to the dealer". However, the truck having little to no power is going to be an even bigger indicator of the same problem.

Okay - then that narrows things down a bit. In your case, then, I'd say the most important gauge is the tranny temp gauge, followed by the pyro, followed by fuel pressure, and here's the reasoning:

In stock form, it's much more likely to kill your tranny from overheating it (pulling heavy at slow speeds, no torque converter lock-up, building lots of heat in the transmission) than it is to burn up your engine. When towing with my truck (and with the power dialed down to more sane levels), I could see 230°F+ on my tranny temp, before I would hit 1300°F on the pyro.

Now, that doesn't mean that the engine is immune from melting itself... the

3rd gens do run hotter than the previous 24V's, and with the right combination of power and load, it's possible to see 1350°F+ on your pyro - and that's not something you want to do for an extended period of time. At that point, it's time to slow down, downshift, get the engine RPMs (and thereby boost) up to help cool those EGT's a bit.

And lastly, from our previous discussions, a failed/failing lift pump can still cause damage to your injection pump... not nearly as quickly as the older 24V's, but the possibility is still there.

Other gauges - rail pressure, boost, and others, are simply informational.... you're not going to kill your engine if you loose boost (but you're going to know it right away, because power will be down, and EGT's will be up). You're also not going to damage anything if your FCA breaks and you lose rail pressure. Again, you're sure going to know it, because power will be low-to-non-existant - but again, no damage can come of it.

Thanks. Just what I needed (and wanted) to hear.

Craig C.

Hummmph!! Only 7 gauges!!?? I have eight!! The seven you mentioned plus the heated seat temp gauge!!

Pantywaist!!

;^)

Mike

I'm not even going to venture a guess where ya plug that one in.

Roy

Craig zip me an email so i can send you those pics.

snipped-for-privacy@windstream.net