Resolved 1G Help with AFPR

[johnny boy 93]

Ok guys,
So I am mounting my AFPR in my car right now and installing it as we speak. Now I am going to do a boost leak test, but other that that I need help tuning. Right now I have the stock injectors but I will be moving up to evo ones in a couple days here. My question to you is what do I set my base fuel pressure at? I know I am supposed to set it without the vacum line on, but I am still lost as to what pressure I set it at, and how to gauge if something is wrong with my system. Also when I switch to the evo injectors will I have to tune with the AFPR again to get idle and proper pressure? And final question how to i pressurize my system without starting the car so I can check for leaks. Thanks guys
John

 

[snowborder714]

1G auto - Spec 42.7psi (Standard value 41 - 46 psi)
1G manual - Spec 36.3psi (Standard value 36 - 38 psi)

You will set it once and not touch it again (unless it is out of spec), even once you install the other injectors.

To check if there is a leak in the fuel system (before you start the car!), use this to turn the fuel pump on:
http://members.shaw.ca/dsm.1000q/Engineprimer/1G/fuelpumptestconn.htm

You can also use that to set your fuel pressure without disconnecting the vacuum line (while the car is off).

 

[1992awdlaser]

1g manual fuel pressure=37
1g auto fuel pressure=43

Do you have something like an safc to tune the injectors with? If not, don't put them on.

 

[CJTurbo]

1g manual fuel pressure=37
1g auto fuel pressure=43

Do you have something like an safc to tune the injectors with? If not, don't put them on.

This is true, you do not tune with the AFPR, you need either DSM Link or an AFC to adjust fuel trims when changing injectors.
Do you have anything to check your fuel trims or O2's?

 

[JDMath]

do we need to crank up the afpr when crank up the boost??

 

[steve]

do we need to crank up the afpr when crank up the boost??

No, The fuel pressure regulator will change the actual fuel pressure 1:1 as manifold pressure changes so that the injectors always have the same pressure across them (the base pressure). The ECU makes sure that you get more fuel injected as the boost goes up since it measures the air flow using the MAF and figures out how much fuel is needed.

You only turn up the base pressure if your injectors are too small so you can get a few more cc's out of them.

 

[JDMath]

No, The fuel pressure regulator will change the actual fuel pressure 1:1 as manifold pressure changes so that the injectors always have the same pressure across them (the base pressure). The ECU makes sure that you get more fuel injected as the boost goes up since it measures the air flow using the MAF and figures out how much fuel is needed.

You only turn up the base pressure if your injectors are too small so you can get a few more cc's out of them.

ooo thanks thats more clear now!! i was thinking that we need to crank it up every time we run more boost, i read somewhere exemple base pressure 37 psi (+ your boost ex: 20 psi) so set the afpr to 57 psi...

so a afpr is not that usefull???

 

[1992awdlaser]

ooo thanks thats more clear now!! i was thinking that we need to crank it up every time we run more boost, i read somewhere exemple base pressure 37 psi (+ your boost ex: 20 psi) so set the afpr to 57 psi...

so a afpr is not that usefull???

It will go up by itself as Steve already said. You set it at 37psi and when you are at 5psi boost the fuel pressure will go up to 42psi. This is why the vacuum line is connected to the fuel pressure regulator.

A fuel pressure regulator is useful to prevent fpr overrun from a 255 pump. It can also be a way to tune the car. More fuel pressure will make the car run richer. Less pressure will make it run leaner. This isn't the ideal way of doing things for a couple of reasons though:

1. You can't tune for a certain air/fuel ratio at a certain rpm like this. It will just add or subtract the extra fuel for the entire rev range. With something like an safc or dsmlink you can change the air/fuel ratio for a specific rpm.

2. This will limit the injector capability. Or work the injectors harder than they are supposed to be.

3. It can also make the fuel pump work harder. Or if the fuel pump is already working too hard and you turn up the fuel pressure then the car can run leaner since the pump would have to work harder to maintain the higher pressure.

 

[steve]

I read somewhere example base pressure 37 psi (+ your boost ex: 20 psi) so set the afpr to 57 psi...

so a afpr is not that usefull???

An AFPR is very useful but in most cases it's used because the factory FPR can't dump enough fuel back to the tank with a big fuel pump to regulate the fuel pressure at idle. This is fuel pressure regulator overrun.

Either the poster was incorrect or you misread the post. Our fuel pressure regulators must adjust the fuel pressure during operation so that the pressure is always:

Fuel Pressure = Base Fuel Pressure + Manifold Pressure

We set the regulator with the reference vacuum line disconnected so Manifold Pressure = 0 psi. Under vacuum the Manifold Pressure is negative, 18 in hg is about -8 psi. So the fuel pressure at idle with the reference vacuum line connected on a 1G should be 36.3 - 8 = 28.3 psi and the pressure with 20 psi boost should be 36.3 + 20 = 56.3 psi

 

[JDMath]

okok now its really clear! thanks a lot guys!

 

[johnny boy 93]

One last question. When I go to pressure test my fuel system, on that connector, which terminal do I connect to the battery? Is there only one lead inside of it or what?
Thanks

 

[steve]

One last question. When I go to pressure test my fuel system, on that connector, which terminal do I connect to the battery? Is there only one lead inside of it or what?
Thanks

http://members.shaw.ca/dsm.1000q/Engineprimer/1G/fuelpumptestconn.htm

check out the rest too.

Virtual Tour of the DSM Engine Bay - 1G Visual Index