Ok guys, here I go with a couple questions that have been bothering me. My first one is this - is it really necessary to have a fuel pressure gauge on the low side if you have a way to monitor the rail pressures? Seems to me if your rail pressures never drop to low levels then you aren't having any fuel supply issues. Secondly, monitoring rail pressure. I know of a couple ways you can do this. You can buy a diprocol (sp?) gauge (which in my opinion are way too much $$, but I know some of you don't like digital gauges). You can buy a quadzilla commander that taps a wire for it's signal (so I'm told). Lastly you can buy something that uses the OBDII port for it's readings like a bully dog outlook or diablosport predator. I have read, however, that some do not like the idea of using the OBDII port to monitor system parameters real-time. I'm sure there is a good reason for this, but I can't get my head around it. It might not be as fast acquisition wise as a wire tap, but I was under the impression that OBDII sampling rates are in milliseconds.... so that's pretty quick! Any input?

 

I like the idea of monitoring both pressures because you can see a problem coming and react before its too late. I think if you starve the CP3 of fuel, rail pressures are going to drop too quickly to respond by lifting your foot, and possible CP3 damage can occur. If you're watching low pressure also, you'll be able to see impending doom as lift pump pressures drop, and lift your right foot before rail pressures plummet. I think I'd rather watch lift pump pressures over rail pressures for this reason.

If I'm wrong (believe it or not I have been wrong before), someone please correct me before I blow up my truck!

 

ptgarcia-
I agree with you on the basis of what you're saying. The only issue I see there is that if you had (sudden) pump failure you would be aware of it with or without a gauge due to the power loss. An eventual decline in low pressure side supply could be observed with a gauge, so you're right on there. But what about the sudden loss of pressure due to stabbing the throttle with an aggressive downloader/box/stack? You would have to be paying some really close attention to your gauges to catch it before it drained you empty with a stock LP. I don't know if I've heard of anyone with an aftermarket bypass pump or auxilary pump ever losing pressures to the point of danger due to throttle change (but then I haven't asked everyone out there either).

 

What about having fine lift pump pressure, but your not monitering it... and all of the sudden your CP3 pressures start dropping. Now you may think it's your lift pump crapping out but instead it could be the CP3 or injectors dumping fuel. What it comes down to is how much do you really care about your Cummins? I have 7 guages currently, one waiting to install. Of course I'm far from stock... I have used my Diablo to read rail pressure. I now use Quads rail pressure guage which can be bought right here on DTR for very little $ in my opinion. You didn't mention that guage so I thought I'd throw it out there...

 

You should monitor both lift pump and rail pressures.
1. Install an under-hood lift low pressure gauge. ~$30 from Glacier Diesel.
this will help you diagnose any problems in the future and also help you decide when your filter(s) are in need of replacement. I don't know that there has been any evidence of CP3 failures due to low inlet pressure, although this was the VP44's primary cause of failure.

2. Install the Quadzilla rail pressure gauge (has a low pressure fuel pressure option for a few bucks more) and monitor both pressures with one gauge. The quad gauge is super easy to install, and looks great above the steering column, and doesn't require any additonal components for installation (pods etc.)

Technically speaking, a rail pressure gauge alone would indicate any fuel related problems, but wouldn't help at all in diagnosing the problem. For 30-40 bucks more, you won't chase your tail trying to figure out whats wrong in the event of a fuel related problem.