6.7 fuel pressures

[Gearjam'r]

I am looking for the fuel pressure at idle and running at highway speeds(65/70). I'm seeing 5. 5/6. 5 now at idle.

I did change my FASS filters when I got home tonight and it was still at 5. 5/6. 5 at idle.

I will be changing the factory filter tomorrow with one of the new NanoNet filters. Is this the norm or should it be higher?

 

[CKelley1]

I hate to laugh at you but the stock pump is 10x better than the fass. the cp3 will put out full power and last as long with MINUS 5 psi to the pump as +20 psi. that is its published specifications. the pressure is about 6 to 8 psi on stock so you are good. take that fass junk off and sell it. add a filter like the one in the pix and do not change the filters until the pressure drops to 2 psi under load. and you will never need to change the stock filter. another thing if you have the gauge hooked in at the fass, move it to the cp3 where it belongs. need part numbers and how to on the filter pm me.
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[EDankievitch]

I'm showing 13-15 psi at idle and 10-12 psi under load with the stock in tank pump. I think there is a pressure relief/ regulator on the return line back to the tank that keeps the pressure more or less steady.

 

[AH64ID]

The OEM pump has an in-tank regulator that opens at around 8-9 psi.

There are always a few trucks that read higher, and it makes me think their regulator isn't functioning properly.

 

[cerberusiam]

That pressure is low for a FASS. Are you measuring at the pump or the CP-3, I am inferring you have it a t the CP-3. If changing the factory filter makes a large difference I would be examing where you purchase fuel very closely.



You want to maintain 20-25 psi at all times to the CP-3 inlet. That will supply the gear rotor pump with enough fuel to keep the cavitation from battering the gears, end plates, and nose of the drive into fine particles to feed into the injectors. For the most part 15-22 psi works just as well as you don't normally see full flow all the time. The basic rule for optimal gear pump performance is head pressure at 25-30% of output pressure. Case pressure in the CP-3 is around 75 psi on a stock build.



For a stock engine in a stock configuration a minumum of 3 psi is the lowest reccomended pressure to see consistently for any length of time. Below that the COV is robbing lube\cooling flow to feed the rail. Imagine what is happening at -5 psi, , like no lube and cooling.



Sounds like you either have a bady plugged filter or the FASS motor is giving up.

 

[AH64ID]

Per Bosch the pressure rating for a CP3 is -5 to +15 psi, with 12-15 at idle being optimal. With 415 rwhp, 3 fuel filters, and a stock in-tank pump I rarely dip below 5 psi, and haven't seen below 4 more than a couple times and never below 3. I run ±8. 5 at idle, and normal cruise is ±7.

Most recommend a minimum of 2-3 psi for gauge accuracy reasons. I am not aware of anyone running a vaccum/pressure gauge.

The CP3 uses flow for cooling and lube, not pressure (Duramax doesn't even have a LP on the CP3) (Yes there are a few differences).

 

[cerberusiam]

It is worthy to note the -5 to +15 psi is CP-3 operating range not a platform recommendation, there is a difference.

The cooling\lube flow is drawn from the same reservoir as the rail pressure supply and is in fact totally reliant on case pressure for its flow. Once case pressure drops below 40 psi the COV reduces lube\cooling flow by roughly 75% to maintain rail pressure.

A Duramax pump has a different gear rotor pump, larger lines, and the CP-3 sits below the tank in the truck. Much more conducive for fuel delivery via suction than the Dodge platform. It is also worthy to note the addition of an LP to Duramax engine is worth 40-50 HP by itself, and, Duramx CP-3's suffer more failures from cavitation than the Dodge implementation.

 

[AH64ID]

Isn't the CP3 in the valley on the duramax? Even with a low slung engine I don't see how that is below the tank. But yes there are some differences, but the point is the CP3 doesn't need a lot of pressure it just needs flow.

The 40 psi for lube/cooling is created by the pump thou, not the lift pump. Operating at the higher end of design spec is good, but it should have adequate cooling/lube at the lower end of the operating range as well.

 

[mpaulson]

I'm running the fass frame mount pump with two filters and it is also running through the stock filter and at idle I am around 18 psi and at full throttle on a climb I am around 12 psi. The psi is read just ahead of the Cp3 pump.

 

[cerberusiam]

Isn't the CP3 in the valley on the duramax?

You are correct, I though it was mounted low on the left. Still, just eyeballing it looks like the pump is at or just below the top of the tank with the way things are situated in the platform. With larger lines that is still a better siphon position than the Dodge platform.

For the most part you are correct that flow is more than adequate to keep the rail supplied and lube\cooling flowing. Only at the extremes of operation will the drop offs occur. Calculated risk by the manufacturer on duty cycle of the engine to keep costs down.

Talking to Relentless Diesel and Floor It diesel, the single biggest problem seems to be the cavitation the lack of adequate flow to the gear rotor pump causes. Even then its not a huge issue, just one of the main reasons for the CP-3 failures. The ramifications are what sending the metal into the injectors does. The CP-3 is one thing but costs quickly escalate when you have to replace the rail, corss over tubes, and injectors due to metal contamination.

IMO, if you are going to the expense of running a FASS then set it up for the most benefit.

 

[AH64ID]

IMO, if you are going to the expense of running a FASS then set it up for the most benefit.

Agreed. When I upgrade my pump I plan to set it for 12 psi at idle and let it ride.