I just searched "fuel pressure" and hunted through four pages of results, and I'm not crazy about overlaying what I found with my situation, so before I do any more homework I thought I'd throw this out there and see what happens.
I recently installed pillar gauges (Thanks Ken!), one of which is an electric FP gauge. It's been a bit of a project, and I've been working with one of the engineers at Isspro as his guinea pig to sort out their problems with the erratic delivery of the 12V mechanical lift pump. Initially, I popped the gauge in and hooked it up through a tapped banjo bolt in the stock filter housing, on the filtered (to the P7100) side, and it was unreadable. Just constantly bouncing all over from end to end and everything in between with no pattern or reasoning.

Stage 2: I called Isspro, and started talking to this guy. He had me send it back to reprogram it for a mechanical lift pump, because it was set for an electric one. That helped a lot. It still moved around, but I was able to at least pick up an average. It seemed to idle around 15psi (and by around I mean swinging back and forth by 2-3psi, so like 12-17) and cruise around 20psi (same deal).

Stage 3: He thought we could smooth it out more by simulating the long capillary on mechanical gauges which apparently don't have this issue so much, so we remote mounted the sensor with a grease gun whip, essentially an 18" hose screwed into the tapped banjo, and the sensor into a coupler on the other end. This made minimal difference.

Stage 4: We added a needle valve at the banjo, and an orifice on the sensor end. This seems to have finally worked, it only ticks by about 1/2 a psi. Here's where my issue comes in, which has me wondering when it was more accurate. The "averages" aren't even close to the same. Now it idles around 11psi, give or take 1psi, and even cruising around low speed (below say, 40mph) it really doesn't go up over 12psi. Faster speeds, like 55-70mph, it sits right around 14psi. If I've been cruising at 70 and let off a little it will go up to 15psi or so, then settle down to 12psi if I don't load it again. These numbers are considerably different than the averages I thought I was discerning before the needle valve and orifice.
Furthermore, if I'm stopped at a light idling at 11psi and get on it a bit to take off, it will actually drop to about 9psi, and in a few seconds climb back up to whatever was typical for the speed I settle at. It wasn't doing that in stage 2-3. If I'm already rolling and go to WOT, it doesn't do that. Doesn't do anything in fact, it stays right wherever the pressure was while cruising. I find this unusual, but what do I know? If this behavior is accurate, I worry about my lift pump. If it was telling me the truth in stage 2-3, my research here tells me that I'm probably ok, but that would mean that the gauge, while not so unstable, isn't accurate now.

What I'm asking is, the guy at Isspro wanted me to let him know if these last parts fixed it, and I'm not sure if I should tell him they did or not. As far as I know it's the original lift pump, filter was changed a couple thousand miles ago, and the pre-screener is clean. Does it sound like I have an issue that needs addressing?

 

You may want to try this.....http://www.torkteknology.com/product...ER-CBS010.html...in place of the needle valve.

 

Thanks, I'll definitely look into it. I must say, I'm not crazy about the needle valve, although the relocation of the sensor is sort of nice.

 

Lets us know if it helps or if something else works for you.

 

The engineer was nice enough to send me a free gauge programmer for helping him with this, so I'd like to be able to feel like we accomplished something. If I try the snubber it will either confirm one set of averages or the other, or give me something completely different to think about. I suppose it's all progress

 

So the Tork Tek snubber showed up yesterday. It's not the same size as the tapped banjo from Isspro that went in the top of the filter housing, the directions said to put it right in the injector pump. I put it in, and my pressure is reading even lower now. It idled around 8-9psi, and stayed the same cruising at low boost. Put a little load on it, say 10psi of boost, and fuel pressure dropped down to 5-6psi, sometimes as low as 4psi- and stayed there until I let off.

Out of curiosity, I took the Tork Tek out and switched back to the needle valve from Isspro. The idle pressure went back up around 10psi, but it's still cruising around 6-8psi under any load and never goes over 10psi while cruising.

I think I may have installed this gauge just in time to witness the slow death of my original (nearly 260,ooo mile) lift pump. Everything I've done has changed the reading, but now I'm getting a lower reading with the same parts I'd been using for awhile.

I've also noticed a new sound coming from that side of the engine bay that I'm having trouble pinpointing, but I suspect it's coming from the lift pump if a failing one makes this sort of noise. It's a ticking sound, but it's erratic. Not steady like a metronome, more like morse code. It's loud enough to hear inside the truck, but only when it's stopped and idling. I can hear it under the hood if I rev it up just a little bit, and the beat changes and speeds up with the engine, but only a little. Rev it too high and it seems to go away. This new noise (as of this past week) combined with the dropping fuel pressures I've been seeing the last couple weeks, does it sound like the lift pump is about to go?

 

It sure sounds like it is going out. But I honestly don't know.

Do you know what pressures you should be seeing?

 

From what I've read on here, a lot higher than that. I've also been told that the lift pump was a major Achilles heel on these trucks, so much so that I've found out Chrysler doesn't even sell the lift pumps anymore and hasn't for years. If it goes, they sell you a whole conversion kit instead that puts a pump in the tank. That's about $200, I'm not sure if it's worth or not in my case to spend the extra and just get something like a Raptor or something.

 

IMO I would not purchase an intank LP, I know the 24v 2nd gen ones are horrible, as I'm sure these will be. I would spend a little extra and get an Airdog or FASS.

 

Well, it's a little more than just a little more.