What to Tune First

[joecar]

IFR is flat for MAP-referenced FPR.
IFR is sloped for un-referenced FPR.

[Dirktdolman]

Dirktdolman,

Does your FPR have a MAP reference (i.e. air hose connecting FPR to intake manifold)...?
YES

Did you measure rail pressure (with MAP reference hose disconnected), is it 43.5 psi...?
I have not. Will RPM change this pressure (more fuel being used)?

Do your injectors flow 21 lb/hr at 43.5 psi (3 bar)...?
I am only going by what I have found on Witchhunter and other site about the OEM injectors I have.

[joecar]

Does your FPR have a MAP reference (i.e. air hose connecting FPR to intake manifold)...?
YES

Ok, so your IFR will be flat (as you saw in your tune file).

Did you measure rail pressure (with MAP reference hose disconnected), is it 43.5 psi...?
I have not. Will RPM change this pressure (more fuel being used)?

The FPR regulates rail pressure, so rail pressure will not be influenced by RPM changes...

if FPR was un-referenced, then rail pressure would be constant (+/- 1 psi is acceptable);
if FPR is MAP-referenced, then FPR pressure equals FPR base pressure (contant) plus MAP...
i.e. rail pressure follows MAP.

( note: to measure rail pressure, temporarily disconnect the FPR reference hose, and measure the rail pressure. )

Do your injectors flow 21 lb/hr at 43.5 psi (3 bar)...?
I am only going by what I have found on Witchhunter and other site about the OEM injectors I have.

We need to know if they are rated at 43.5 psi or at some other pressure.

[joecar]

If your rail pressure measures 58 psi (say)...

and if the injectors are rated at 43.5 psi...

then you have to scale the flowrate by multiplying it by sqrt(58/43.5)... (the spreadsheet does this).

[Dirktdolman]

Based on what I have found on the net about this OEM numbered injector it rated 220 cc at 3 bar (21 lb/hr at 43.5 psi). I just check and my pressure with the vacuum line to the FPR disconnected is 53 PSI.

This is my new calculation

[joecar]

You measured 53 psi (it should be 58 psi)...? What vehicle do you have...?

[Dirktdolman]

03 2500 HD 6.0l New pump and FPR. Maybe my gauge is bad. It is about 20 yrs old

[joecar]

Is that a GMC Sierra or a Chevrolet Silverado, and which platform (C or K)...?

[Dirktdolman]

03 Chevrolet Silverado K2500 HD 6.0L Automatic 4X4

[joecar]

The service manual give these specs (for key-on engine-off several times):

55-62 psi VIN: V, T, U

48-54 psi VIN: Z

VIN = engine code in VIN (8th letter/digit).