I have an Accel Thruster system. Manual says to input the fuel pressure, however, with the vacuum line on the FPR the fuel pressure varies from idle to under load / acceleration. So, do I leave it alone or disable the vacuum line? I have an adjustable FPR so I can put it where I want it.

 

That is a good question. you would think that variable(fuel pressure) or constant is needed to determine the WOT or PE calculation to provide adequate fuel on top end.
Much like base pulse constant(FP/CID and injector size). I am guessing you place in 43 lbs for TPI. Most FI engines have VAFPR. TBI may be only applcation that does not.

 

Just got this response from Tech Support at Accel:

The vacuum line is required to maintain a constant pressure drop across the injector. As the throttle is opened and manifold pressure increases, pressure from the regulator will increase proportionately. The Thruster software is calibrated to work with a vacuum referenced fuel pressure regulator.

Regards,
Dave Seidel
Accel-DFI


Makes sense but I just was not sure.

 

I would use 43 lbs for input value. As manifold pressure increases(lesser vac) it allows greater fuel pressure. At WOT 43 lbs is available (no VAC or 100 MAP). At idle it will reduce fuel pressure which helps manage idle.

 

I guess I need to know more about your engine setup but...

If you have upped your injector size for engine mods, than adjust as Ronny said to control idle pressure, tuning fuel via computer as necessary, IOW enter idle pressure being used, vac line connected.

If on the other hand you are wanting to boost fuel pressure to meet demand, then set idle pressure @ 43 w/vacuum connected & tune in the extra pressure @ higher kpa. Enter 43 as the fuel pressure.

The second would be my preferred approach & IMO that is what they were trying to say.
Either way, enter the actual idle pressure w/vacuum line connected.

 

Tnx. I was in the middle of starting to tune and getting the VE table set when this thought came up and I thought it best to ask some questions and possibly avoid doing this twice.

I'll stick with stock pressure. Just wondered about the effect of the vacuum line.

 

At WOT you will hit 0 vac or 100 map and that enables 43 lbs FP. Under vac at idle depending on spring it will pull FP down to say 15 lbs. My understanduiing is that your definition file may be sensitive to changing FP or BPC as well as BPC is comprised of CID/FP/ and injector size. Does your definition file Thruster have a VAC/MAP vs BPC table to account for lesser FP at various MAP/VAC levels?

XCH did I explain ?

 

Don't think so. According to Accel tech support the ECM is set to adjust for the changes to fuel pressure.

 

Each FPR will respond differently to change in FP based upon VAC. Maybe the changes are not enought to warrent concern. My EFI Aeromotive comes with 2 different springs. The spring rate differs as to how they respond to VAC. They may base their file on the FPR they sell.