help chris keep his fuel pressure!

Ok guys I have a strange problem (I think its a problem) that needs to get figured out sooner than later.

Setup:

I have done a bit of work on my fueling system, and the car was out of commission for all of this, so I cannot say what caused the problem for sure.

Here is what I have messed with/changed:

1. using B16 manifold with an AEM fuel rail.
2. using AEM adjustable fuel pressure regulator on the rail (set to 36psi ish)
3. using B&M non-damped fuel pressure gauge with a 45 degree fitting on it so I can see the gauge face better.
4. using 6-AN fuel line and fittings from fuel filter to the rail feed
5. using stock injectors with stock o-rings that don't leak
6. using stock fuel return line with stock clamp
7. replaced fuel filter while swapping out all of this stuff. Using a stock fuel filter though.

-- note --

I have painstakingly checked all of these connections, and none of them leak anymore. at one point I had leaky injectors, and needed to tighten down the banjo bolt on the fuel filter, but its all good now. no leaks that I have detected whatsoever.

8. (my primary suspect at this point) replaced fuel pump with walbro 255lph hp in tank pump.

Problem:

When I turn my ignition on, the fuel pump primes (WRRRRRRRRRRR) for a few seconds and then shuts off, like normal. Fuel pressure during the priming is the appropriate amount. However, seconds after the fuel pump stops priming, if I have not cranked the car, the fuel pressure is lost again.

The car will start and run just fine and dandy... but the fuel pressure bounces around on the gauge (I still need a fluid filled gauge) - however, I think that is just due to vibrations because the needle is moving so fast its almost a blur. When I give the car gas and the engine vibrations smooth out the fuel pressure gauge reads a more constant value as well.

As soon as I shut the car off the fuel pressure just dives to 0 after like 1-3 seconds.

I am pretty confused at this point, because there is no fuel leak in the engine bay, and no fuel on the ground anywhere. My thoughts are that possibly the gas tank is not sealed or the gas cap is not sealing properly, so the system is just not able to maintain pressure when the fuel pump is not running.

Does anyone know ways to test these theories? Anybody had a similar experience? I am getting close to just saying screw it and running a fuel cell lol.

Any insight you guys can provide would be helpful. I know before this fuel setup I had the fuel pressure gauge on the filter and maintained fuel pressure like normal for hours when the car was shut off. Now it is doesn't last for 5 seconds.

HALP!

Do you have the correct orifice installed in the regulator? That could cause the pulsations. The AEM that I got came with the orifice for the stock fuel pump installed, but it also came with two others for higher flow...

I believe inspection places have tools that will tell you if the gas cap is sealing properly. You might bring it by and see they will check it out for you. Did you check to make sure the fuel pump is not leaking back into the tank?

the funny thing is that i had the same thing happining with my mallory fpr.
i ran the car for a year like that with no problems.
when i swaped to the skunk2 mani i bought an areomotive fpr and the problem dissapeared.

so based on my experiance i would say the fpr is the coulpreate(sp).

I am guessing you never swaped AEM pressure regulator with stock one to see if the problem goes away. try that and it will tell you if you have a problem with pressure regulator or fuel tank.

the fuel pump has a check valve in it to maintain fuel pressure. This could be leaking back to the tank.

Thanks for the replies.

I think I have an extra stock B16 regulator floating around. Otherwise does anybody know if the stock accord regulator bolts to an AEM B-Series rail?

It sounds like either the regulator could be causing my grief or the fuel tank itself. I don't have the car insured so I cannot drive it around to get it checked, but after testing new regulators I will see how it goes and see if I need to pursue it further.

I just don't see how a restrictive orifice on a regulator would cause an inability to hold pressure. But I have been surprised before!

How do I check if the pump is leaking back into the tank? I don't really understand what would be happening in this case, unless the clamps just came loose and fuel lines wiggled off the barbs a bit, but I find that to be unlikely. :)

I'd look into the gas cap first, with the age of our cars I'm surprised that mine still holds a seal.

Simple things first.

Quote:

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Originally Posted by nswst8

Simple things first.

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sometimes they are the problem.
i used to drive an old nissan that had problems maintaining fuel pressure. turned out to be the line between the cap and tank was leaking.

Quote:

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Originally Posted by bobafett

I just don't see how a restrictive orifice on a regulator would cause an inability to hold pressure. But I have been surprised before!

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It's not that it can't hold pressure, it's that it can't relieve it fast enough, if that makes sense. With a smaller orifice, it will take longer to relieve pressure. You may have the pressure set WAY lower than stock, but since there is back pressure it will appear higher when the pump is running. When the pump shuts off, it will return to the set pressure, regardless of orifice size, provided that there is nothing else wrong.

Ahh interesting point. Well lets hope I can find the box and try installing a larger orifice on there. :)