Fuel Presure Question Here.

[Bill Z]

I have this technical fuel pressure question.

If the electronics of the ECM vary the pulse with to the injectors so they spray more or less fuel into the engine, then why does the fuel pressure regulator have a vacuum connection that adjusts the pressure?

It seems to me that with a constant fuel pressure the pulse with should be sufficient to run the engine at all RPMs.

What would happen if I set my regulator to, say 35 pounds and kept the vacuum off?

 

[VermontTy]

Re: Fuel Presure Question Here.

I'm probably not the best to answer this, but if I were to guess, I'd say that it would be like turning on and off a garden hose quickly (idle) and turning on and off a fire hose quickly (WOT). With more fuel pressure, for a given pulse, you'll get more fuel. The truck probably needs more fuel pressure to provide adequate fueling at WOT. If it didn't have increased fuel pressure at WOT, you'd max out your injectors (100% Duty Cycle) on the 35lb set pressure.

 

[leroy]

Re: Fuel Presure Question Here.

That is a good question!

In my opinion, it is to keep the injector nozzle pressure consistent. Injector flow is more predictable with a constant nozzle pressure. Suppose you could run 30 lbs. of boost. You would only have 5 psi nozzle pressure with 35 psi fuel pressure, and, like Adam said, you would run out of injector quickly.

Jim

 

[jamnut]

Re: Fuel Presure Question Here.

I'm new to the Sy/Ty world, but not to the car world. Leroy is correct, thay call it boost refrenced. Your fuel pressure should rise with your boost to keep the same base pressure when you subtract boost refrenced pressure. We even do it on boosted & squeezed cars, the nitrous pressure needs to be refrenced with your boost or you can lean out while spraying under boost & BOOM.

Almost all high quality aftermarket fuel pressure regulators have a boost port for refrencing.

 

[Bill Z]

Re: Fuel Presure Question Here.

OK. So the fuel pressure we set with no vacuum is sort of a mid point? At idle, the actual pressure drops with vacuum connected and at boost it goes past mid point appropriately.

Is that sound right?

What pressure do any of you daily drivers of stock injector Typhoons set your regulators with no vacuum attached for best performance? I realize the 50#ers will have to set theirs appropriately.

 

[AUSyTyIN]

Re: Fuel Presure Question Here.

The ECU ignores the O2 sensor at WOT, and goes by pre-set values for how long the injector should stay open. An AFPR controls how much fuel gets shot through in that amount of time.

 

[Bill Z]

Re: Fuel Presure Question Here.

The ECU ignores the O2 sensor at WOT, and goes by pre-set values for how long the injector should stay open. An AFPR controls how much fuel gets shot through in that amount of time.

So, in boost (positive pressure on the AFPR) the regulator applies max fuel pressure for max fuel? OK, what IS that pressure for the stock Typhoon?

And what do I have to set my AFPR to with no vacuum to get that pressure at boost?

 

[leroy]

Re: Fuel Presure Question Here.

35-40 lbs. is a good start. Make adjustments as needed depending on blm's or wot performance.

Jim

 

[AUSyTyIN]

Re: Fuel Presure Question Here.

35-40 lbs. is a good start. Make adjustments as needed depending on blm's or wot performance.

Jim

Yup, datamaster will tell you everything you need to know :tup:

 

[Bill Z]

Re: Fuel Presure Question Here.

Yup, datamaster will tell you everything you need to know :tup:

I just started using Datamaster. Still learning. Where does Datamaster tell me the fuel pressure or what it should be set to? That would really help.

 

[AUSyTyIN]

Re: Fuel Presure Question Here.

It doesn't. It tells you the what the O2 sensor is reading though. You want your O2's to be around .920's