Anybody know what the low side pressure should be!? "Supply to CP-3" My monitor is reading 5psi to 1 psi at full throttle but my Hi side is still at 25000 give or take a few thousand! Aftermarket lift pumps are set at 25+ psi to the CP-3 so am I starving my CP-3??

 

I read a minimum of 15 psi and I can't find jack in the service manual. But the CP3 will draw fuel on it's own, and most D-Maxes don't even run a fuel pump.

 

Minimum 3 psi for stock fueling, needs to go up if you are throwing more fuel at it. As longs as your rail pressure doesn't start taking major bounces your adequate on the supply.

What are you suing to read the low side FP?

 

Here's part of the project on how I plussed up the fuel supply on my '07 5.9:

http://stuff.is-a-geek.net/PhotoAlbu...ics/CRD_27.JPG

It's a Walbro FRB autopulse marine internally regulated to 10psi. Before, the engine would pull the stock supply to 5psi under WOT load running a Smarty Jr. at default SW1. Not bad, actually. Probably not even necessary, but... I wanted a backup pump just in case, because I don't trust electric pumps. It will run the truck all by itself pulling through a dead in-tank pump, albeit not as well as the stocker alone. It's only a 40gph pump, still plenty for a stock or near stock 5.9 Cummins.

Here's the good part. When I throw this switch at WOT:

http://stuff.is-a-geek.net/PhotoAlbu...ics/CRD_29.JPG

...Low side FP jumps right back to 10psi. One of these days I'll get around to running some higher tunes to find out just how much this helper pump really helps.

I think the answer to your question is: as long as you have any pressure at all going into the CP3 it's OK. But (big but) when it starts to drop from previous readings, you either have filters clogging or a pump dying. Good idea to monitor that situation.

 

I have a quadzilla monitor and bought the extra low side sender so I could see what was going on.

 

Typically, not as accurate as it could be. You probably have more pressure than it is reading.

 

True the duramax dosent use a supply/lift pump and all CP3s have a small one built in but the dmax pump pulls more fuel than ours so 5psi is ok at load wouldnt want any lower than that IMO see if you can get your hands on a analog gauge, also check pressure before the filter incase something is wrong there.

 

Comparisons to the Dmax are worthless. The fuel lines, filters, and fuel system are totally different. The first upgrade to a Dmax is a lift pump, even stock they benefit.

In addition the fueling maps are totally different between a Cummins and the Dmax, its an apples to oranges comparison no matter how its looked at.

 

Another observation regarding ambient temp: Some LPs may be better than others at pumping diesel fuel when the temperatures get get deep down into the negative numbers. My stock in-tank pump normally holds 10-11psi at idle. This morning at -15 degrees it was down to 4psi.