2G How to set fuel pressure with an AFPR?

[dboyle23]

So I installed an Aeromotive AFPR, but how do I set the pressure?

The nut on top doesn't change anything.

 

[Archer Fabrications]

I'm not sure I agree with your assessment.

The point of a FPR is to maintain a set pressure even with changes in the incoming feed pressure and the variable demands from the injectors. Some amount of pulsation is going to result from both and the dynamic response of the FPR but if the pressure changes when the voltage is higher and you have low duty cycling of the injectors from what you set with the car off I suggest you have other things also going on.

We tested it and got different readings.

If what you are saying was true, the readings would have yielded the same base pressure regardless if the car was on or off, we are talking about base pressures, and they don't match. The point of the FPR’s VAC SOURCE is what allows the dynamic changes With base there should be no dynamic change happening.

With activating pump via DSMLink, you have no injector response, vs running where there is voltage and consumption applied to your base calculations (without vac).

Not only that, you will have a weak pump feed drawing off straight battery with the car off (12V) vs with the car on (14V). Your pump will be stronger while the car is actually on thus allowing you to set a proper base pressure. Assuming you have a rewired pump.

 

[Jason99GSX]

Yup very easy! Loosen the nut on top. And tighten down the Allen bolt to increase pressure, if you have DSM link you can leave everything hooked up. Turn the key on, leave the car “off” and turn the fuel pump on in link to set your pressure.

 

[steve]

We tested it and got different readings.

I don't doubt you. However I've done it with several cars over the years and there should be no difference between engine on or engine off if the FPR is working correctly.

If what you are saying was true, the readings would have yeilded the same base pressure regardless if the car was on or off, we are talking about base pressures..... and they dont match. The point of the FPR’s VAC SOURCE is what allows the dynamic changes With base there should be no dymaic change happening.

I think you misunderstood what I meant by Dynamic Changes. Yes, the vacuum line is a dynamic manifold reference and the FPR has to track it well but each injector pulse and changes in the voltage to the pump cause the FPR to vary the flow out the return port to adjust. I believe of the three manifold has the biggest swings but moderate timescales, injectors perhaps moderate changes but shortest timebase, and voltage changes small changes over relatively long timescales.

With activating pump via link, you have no injector response, vs running where there is voltage and consumption applied to your base calculations (without vac)
Not only that, you will have a weak pump feed drawing off straight battery with the car off (12V) vs with the car on (14V). Your pump will be stronger while the car is actually on thus allowing you to set a proper base pressure. Assuming you have a rewired pump

I don't disagree that these happen, they do but I believe Injector response is a red herring, at idle the pulse width is the shortest therefor the least impact (local pressure drop due to injectors opening) short of being off so the pump flow rate due to higher voltage should dominate if there is a difference. The question then is why.

The point is that if the FPR can deal with low pump flow rates (due to low voltage) and regulate the pressure, then if the pressure changes with higher voltage (higher flow rates) the regulator isn't regulating for some reason. In fact, some fuel systems are designed to run the pumps at lower voltages until the injector duty cycle rises because the full flow overruns the ability of the FPR to dump the excess back to the tank.

Anyway, it's a smart idea to check both ways and if your car's pressure rises when it's running adjust it back since that's what matters.

 

[Archer Fabrications]

Yup very easy! Loosen the nut on top. And tighten down the Allen bolt to increase pressure, if you have DSM link you can leave everything hooked up. Turn the key on, leave the car “off” and turn the fuel pump on in link to set your pressure.

Thats what we are arguing

 

[steve]

No we are discussing your statement that "If you simply activate fuel pump via link. You will end up with a higher base then you should if you do it that way".