stock lift pump pressure

[rkrausff29]

Hi i have a 2006 6 speed manual it idles at 12 psi and in 6th gear on on hill to the floor it drops to 2 psi with a new fuel filter in

 

[PWong]

FYI

https://www.turbodieselregister.com/threads/251005-07-5-9-still-acting-up

 

[AllianceDiesel]

3rd gens are measured by flow not pressure

 

[Killgore]

rkrausff29, I am idling at 9 psi and at WOT she drops to about 5 psi. I do have a GDP MK-2 with a Big Line Kit and a GDP Max-Flo Filter Inlet Kit. I am unaware of if/how much this might influence my pressures, but with less restriction I would assume there would be less pressure.
- Ed

 

[cerberusiam]

Hi i have a 2006 6 speed manual it idles at 12 psi and in 6th gear on on hill to the floor it drops to 2 psi with a new fuel filter in

As a rule with a stock engine 8-9 psi at idle and 5 psi full load. Might want to try a different gauge just to verify it isn't the gauge. Depending on what gauge you have it make make a difference.

3rd gens are measured by flow not pressure

Pressure is a function of flow. Flow with no restriction means squat in a pressurized system, totally unreliable.

 

[rkrausff29]

Ok thanks everyone.

 

[AllianceDiesel]

So where is the fuel pressure spec in the manual? All I find is flow.

 

[sag2]

You will not find one. It has always been a flow spec.

 

[PWong]

It's the pressure to create the flow.
Without pressure forget the flow!
5psi at WOT = Excellent/more than needed flow to meet the max demand of CP3

 

[PWong]

but with less restriction I would assume there would be less pressure.
- Ed

It depends on where are you measuring the pressure, before or after the filters.
The pressure before the CP3 after the filters would be the one we are interested to monitor.
In this case with more restrictions on filters would implies less pressure.

 

[Killgore]

PWong, you're right. I'm measuring at both the CP3 and prior to the primary.

 

[AllianceDiesel]

A pressure washer has lots of pressure but takes forever to fill a bucket compared to a low pressure garden hose with lots of flow.

 

[Killgore]

Now that is comparing apples and oranges due to the difference in the size of the orifice.

 

[Prairie Dog]

True there is no pressure spec. but we know that a normally healthy setup makes a certain amount and if it doesn't, it's a sign that something is wrong.

 

[AH64ID]

I called Bosch on a pressure spec and was told -5 to +15, with 12 being ideal but not mandatory.

I idle at 9 and on a 415rwhp tune can dip as low as 3-4 WOT at upper rpms.

The CP3 is more concerned with flow than pressure, but pressure is the measure of that flow.

Try to stay at 2 or higher, mainly for gauge accuracy, and you will be fine.

 

[PWong]

A pressure washer has lots of pressure but takes forever to fill a bucket compared to a low pressure garden hose with lots of flow.

So we would use a low pressure garden hose to fill up bucket.
What if we want to fill up the bucket faster because the demand of water increase???
We can add another low pressure garden hose.
Or we can add a pump to increase the pressure of the existing hose so more water can be delivered to the bucket (CP3).

The performance of a lift pump is measured by it's ability to deliver fuel in volume per second or per minute.

 

[PWong]

I called Bosch on a pressure spec and was told -5 to +15, with 12 being ideal but not mandatory.

CP3 is doing some lifting work when the pressure is negative and this is the result of a lift pump failing to provide 100% of the lifting work.

 

[AH64ID]

CP3 is doing some lifting work when the pressure is negative and this is the result of a lift pump failing to provide 100% of the lifting work.

Yes it is, but the flow is adequate for the CP3 to do it's job.

 

[cerberusiam]

A pressure washer has lots of pressure but takes forever to fill a bucket compared to a low pressure garden hose with lots of flow.

A faiing lift pump won't provide the CP-3 enough fuel wih the system closed where it will meet flow spec with the line unhooked.

Cannot talk flow with talking pressure which is a measure of restriction in a SPECIFIC system, it makes no sense to do so.

Bosch specs -5 to +15 as a range for the CP-3, only as a generic operating range, but NOT a specific number for the Dodge platform because they do not know the restrictions imposed by the low pressure fuel supply system. I can guarantee at -5 psi in a Dodge truck you will have problems, but, not at +15 psi.

Given a stock LP and fuel supply system 3 psi is the magic lowest number you want to see. Lower than that the CP-3 starts robbing lube\cooling flow to supply the rail. When it drops to far the ECU starts stretching duration then things get hot and smoky.

 

[Killgore]

Cerb, would you address the issue of cavitation? At approximately what psi does it become a factor in damage to the pump? Thanks.

- Ed