fuel return questions (testing)

[1Gina2G]

Just finished replacing the entire fuel system thanks to all the help on here, and I've been wondering a few things about the return.

I still have my factory fuel regulator, and I was wondering is the fuel regulator always open inside? I wanted to do a leak test to see if any gas was coming out where it wasnt supposed to, and it seems as if no gas is going through the regulator and into the return line it's connected with.

I'm ASSUMING it never passed through the regulator as the rail was FULL of gas & pressure.

I've researched and I can't find anyway to test out a regulator, was wondering if something changes with the engine running, to make fuel pass through? I have no idea if my regulators any good or not.

 

[jcarmichael]

The pressure coming from the fuel pump pushing through the small lines might push it open, and the diaphragm, just opens to 43 psi but I'd imagine theres always a hole there, it could be clogged from particles from your gas tank that the filter didn't stop. worse case scenario if your near a junk yard grab another one. I haven't heard of them going bad, unless you run a wallsboro with them and blow the diaphragm.

on a side note do you have your vacuum line hooked up to your regulator?

 

[1Gina2G]

The pressure coming from the fuel pump pushing through the small lines might push it open, and the diaphragm, just opens to 43 psi but I'd imagine theres always a hole there, it could be clogged from particles from your gas tank that the filter didn't stop. worse case scenario if your near a junk yard grab another one. I haven't heard of them going bad, unless you run a wallsboro with them and blow the diaphragm.

on a side note do you have your vacuum line hooked up to your regulator?

So the regulator will hold the pressure inside the rail up to 43 psi, and once it exceeds thats when it will pass fuel through the regulator?

I think I may be still confused. The regulator deffinatley has the vaccum line connected to the fuel pressure solenoid though. Please note I'm JUST testing out everything fuel related, not trying to start up the engine yet. So could that be why I'm not seeing anything coming out the return?

The only thing I've come across is that if gas is coming through the vacuum hole, that the regulator needs to be changed.

Is the method I described the ideal way to test? I only did it once and not sure what I got the pressure to, but I didnt want too much gas in the rail, mostly was just checking the feed line, but everything still needs to get checked out.

 

[Calan]

The FPR uses a spring pushing against a diaphragm to basically create a restriction in the fuel flow going from the pump, through the rail, and back to the tank. This restriction to flow maintains pressure on the pump side of the FPR (in the rail) at some preset level (roughly 43psi for a 2G DSM).

In addition to the spring, there is also a vacuum source tied to the FPR, which increases or decreases the pressure on the diaphragm, depending on whether you are in vac or boost. This maintains a constant fuel pressure on the supply side of the injectors, relative to the air pressure entering the cylinders. This is called a rising rate regulator, or 1-to-1 regulated system.

This makes it easy for the ECU. Rather than trying to do a lot of calculations to adjust the injector pulse width based on how much resistance the injectors have to overcome, it can simply assume that the resistance is always the same, since the fuel pressure is constantly changing to match the intake pressure.

 

[1Gina2G]

Thanks for the detailed explanation of the fuel regulator, always glad to learn anything about these cars.

So from what I can tell, due to the pressure involved, I won't be able to test the fuel regulator without having the engine running, correct? Would that be a bad idea at all?

 

[jcarmichael]

You should be able to test it, my afpr can be set with the motor off it may change a bit when the cars on but not much, as long as your fuel pumps running you should be getting fuel past the regulator or else the fuel would have no where else to go but pressurize and end up finding a hole to go through. imagine a water hose that you put a kink into it creates more pressure which is what the spring and diaphram due. if you had the kink done to where no water got past the water hose would expand until it exploded assuming you had enough force to create that, so you should be getting fuel past the regulator if the fuel pump is coming on. however the only way to get the fuel pump on in my car is to turn it on through link I suppose you could hook up direct power to it and get it to come on that way as well.

 

[1Gina2G]

You should be able to test it, my afpr can be set with the motor off it may change a bit when the cars on but not much, as long as your fuel pumps running you should be getting fuel past the regulator or else the fuel would have no where else to go but pressurize and end up finding a hole to go through. imagine a water hose that you put a kink into it creates more pressure which is what the spring and diaphram due. if you had the kink done to where no water got past the water hose would expand until it exploded assuming you had enough force to create that, so you should be getting fuel past the regulator if the fuel pump is coming on. however the only way to get the fuel pump on in my car is to turn it on through link I suppose you could hook up direct power to it and get it to come on that way as well.

couldn't I just unplug the starter, and maybe the injectors as well? would this be a bad idea?

last time all I did was disconnect the starter so nothing would turn over, and turn the key to power the pump. you can hear the pump whine and fill the line with gas, and I stopped as soon as I heard the flow of gas slow down, as I was sure it had reached the rail. I didn't want to risk overflowing anything.

Just worried about something poping a seal. But it needs to be able to hold the pressure anyways I guess. I just didn't like the sound of the pump slowing up slightly because of the pressure, but at the same time it'd be a nice relief to see the fuel make it through the pressure regulator.

 

[jcarmichael]

I wouldn't pull the injectors out unless you mean out of the intake, if you really want to see it get past the regulator take the return line off right after the regulator but be prepared for a mess from the gas coming out. I doubt the regulators bad if it is it would be the diaphragm being blown out which would just make your fuel pressure higher then 43 psi possibly causing the car to bog down. if you think it could be an issue it would be a good time to upgrade to a adjustable fuel pressure regulator or just go to the junk yard and pull a couple of them fpr make sure they are off of 2gs. as the 1g's manual turbo are 37 and autos are 39 I believe.

 

[1Gina2G]

Well when I was talking about disconnecting the starter and the injectors, I was just talking about the wires, electrically speaking. So the injectors wouldn't pulse anything with the key turn.

no idea if this is a legit way of testing.

 

[jcarmichael]

http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html


this might help in this case, since your trying to get fuel to go through but not actually start the motor.

it would be just like doing a compression test, where you pull your MPI fuse out causing the injectors not to fire.

 

[Calan]

You can disconnect the return line after the regulator, and run a hose from the regulator output to a bucket. You can then turn the pump on via the fuel pump check terminal on the firewall, ECMLink (for those that have it), or by applying 12v directly to the pump where it connects to the harness. Mark the bucket at a 1 or 2 gallon point, and then time how long it takes to fill it that much. Divide gallons pumped by elapsed time (in seconds), and multiply it by 3600 to get gallons per hour. You can then convert that into any other units you want of course.

It helps to have someone up front at the bucket to watch (guard) the hose, and someone manning the pump so it can be killed quickly if needed. Be safe, and be prepared for it to come out faster than you expect. .

Although not exactly precise due to voltage variations, filter restriction, etc.... it will at least give you an idea if your pump is flowing somewhere in the ball park of what it should for the voltage you are supplying it. You can also use a vacuum pump or an air compressor to supply some vacuum or "boost" to the regulator (low pressure - don't go crazy with it), and watch how it effects the flow.

If you are meticulous about measuring the voltage, amount of air pressure you are injecting, and measuring the flow, you can look up expected flow rates on a chart for the pump you are running and get some pretty useful information.

As usual, YMMV.