Just installed -6AN lines from the sending unit -> AEM rail -> AFPR -> stock return line. Also threw in a 450lph fuel pump.
I’m getting really high fuel pressure even with the adjustment screw all the way loosened. Like 88psi. Is this bad? What can I do to get lower idle fuel pressure?

Kai Hefner said:

Just installed -6AN lines from the sending unit -> AEM rail -> AFPR -> stock return line. Also threw in a 450lph fuel pump.
I’m getting really high fuel pressure even with the adjustment screw all the way loosened. Like 88psi. Is this bad? What can I do to get lower idle fuel pressure?

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Assuming this is for one of your 2G Awd cars... It's likely the factory fuel siphon. See link below. Also note the link posted in reply #4 in that thread for further info.

https://www.dsmtuners.com/threads/2g-awd-fuel-siphon-mod.350851/

I did drill that out to 1/8”

It could be one of a few things:
1. Improper return line size (too small).
2. Defective regulator. How does the diaphragm look?
3. If this is a 2G AWD, have you drilled out the siphon orifice? https://www.dsmtuners.com/threads/2g-awd-fuel-siphon-mod.350851/

If you're using a stock AWD sending unit, then I'm almost willing to bet it's #3. You should open the siphon orifice to 7/64".

Is this too small of a return line? I have a -6AN coming out of the regulator but I have a few connectors and a hose to get it to connect back to the stock return line size.

Kai Hefner said:

Is this too small of a return line? I have a -6AN coming out of the regulator but I have a few connectors and a hose to get it to connect back to the stock return line size.

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It's possible there is a restriction caused by all the fittings and adapters that is leading to this issue. I am using a -6 feed and factory hard line return with a re-wired 450. After drilling the siphon the fuel pressure returned to normal. I'd see if there is a kink in the rubber line or any fittings that have a smaller ID than the factory hard line.

The stock return line has always been ok for a 6AN feed, I run exactly the same oem return line currently and have zero issues, however with your fuel pump it might be hard to get it back into the return so you can either restrict the fuel pump side until you need the full amount or do the 6AN return now and be done ready for the future.

I will ask but i am sure you have, when adjusting you took the vac line off and then adjusted right.

Oh! No I’ve had the vac line on the regulator this whole time (this is my first time running through this). Why do I need to take it off?

1. Return hose was kinked.
2. Wasn’t adjusting the afpr with the vac hose off. What pressure am I looking for with the hose off?
I was hitting 30psi at idle.

Kai Hefner said:

Oh! No I’ve had the vac line on the regulator this whole time (this is my first time running through this). Why do I need to take it off?

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Arh thats likely your problem!

You take it off because you need to sat actual fuel pressure as if you leave it connected your setting it to what it sits while at idle which is what ever the fpr is adjusted to, which will be an unknown until its disconnected via the vac line!.

The thing does not know your base pressure as its mechanical so for you to do that you pull the vac line off and set baseline pressure then once vac installed it will then rise with revs,

So to do this, while idling pull the vac line off adjust the screw for the diaphragm to suit 43.5 psi or close to it, mine currently about 44 psi but its as close as i could get and lock it down, THEN you can install the vac line back on and you will be all set

Once thing you want to do is once fully set is turn the engine off and watch the gauge on the fpr, if it drops down to zero you have an issue and if not and goes down slowly then you are ok, just another useful visual to help see if your part is faulty or have a leak in the diaphragm

Thank you, it’s running great now.

Awesome. Glad we sorted this out, make sure to mark this thread as resolved then others may see this in the future and possibly use it as help for them.