fuel pressure problem

[69ptcamaro]

I've been chasing a bad hesitation in my car for 6 months. It only happens under a hard load, i.e. slicks on launch or WOT at a high mph on street tires. I don't get to work on the car much due to being away at school, so I haven't had much of a chance to fix the problem.

My setup is a 509 with a AZSM TPI setup. I would estimate the motor to make 600-650 hp. I have a Rick's tank with the Walbro 255lph intank pump. The calculations I did showed that it would support my engine; it is not however. Today we put a fuel pressure guage on the car while driving it. It drops down to under 30 under a hard load and even drops down to 32-35 under a mild load. The pressure also seems to bounce a lot (5-7 psi). I didn't know if this was due to vibration or what. I am using the regulator that came with the AZSM setup. I have it mounted on the outside of the subframe about 5 feet from the fuel rail.

Do I for sure need to go with an aeromotive or something similar? I have about $1500 in the Rick's setup, so I would really like for it to work. Is there anything else that could cause the pressure drop other than the pump being too small?

Thanks for any help. I have a build thread of the car in the projects section for anyone that is interested.

[Vegas69]

If it does it under mild accel then I doubt your pump is working to it's full capacity. Plenty of guys having problems with there Ricks Tanks when say under 1/2 tank on fuel. I'd fill it up and see if the problem persists.

[69ptcamaro]

It's doing it when the gas is completely full. Another thing I forgot to mention is the full pressure goes straight to zero as soon as the pump quits. Should it not hold the pressure for a while before leaking off?

[68Holdon]

What size fuel line did you use. Is it a returnless setup? I would think based on everything I have read that you would need at least a 1/2" supply and return line. I have not read anything about guys having problems with Ricks in tank pumps under a half tank only the external pumps.

[69ptcamaro]

I'm running 1/2" supply and 3/8" return. I have the regulator on the return about 5 feet from the rail. It just acts like the pump can't keep up. The motor may be making more power than I originally planned. I'm not sure what is going on.

[68Holdon]

I have also read a lot that the return line should be at least the same size as the supply line.

[thedugan]

Rob, whats up, what are you doing to your car?

[69ptcamaro]

I have also read a lot that the return line should be at least the same size as the supply line.

Hmmmm..... We have conflicting information. Pretty much everything I have read on the forum and web gave different line sizes for supply and return in respect to horsepower. Here is one site that I believe to be accurate. http://john.my67.net/efi.htm I could most definitely be wrong. I only know what I have read, and I could have read incorrect information.

[69ptcamaro]

Rob, whats up, what are you doing to your car?

I'm drawing a blank right now. I apologize in advance, but where do I know you from?

I have mostly been working out the kinks while driving it some. Not a lot of progress since I moved back to school in August.

[Hammered]

Here is one site that I believe to be accurate. http://john.my67.net/efi.htm

That's my site and I pulled that info from Holley.

Regardless, low pressure is not a return line problem. I would drop the tank and take a look at the pump. It should have a check valve that holds pressure after shutting the car off. That and the low pressure on acceleration could be a faulty internal fluid connection.

[Vegas69]

What size fuel line did you use. Is it a returnless setup? I would think based on everything I have read that you would need at least a 1/2" supply and return line. I have not read anything about guys having problems with Ricks in tank pumps under a half tank only the external pumps.
With two posts your an expert? I have seen it and it's on in tank pumps. Regardless you return should be the same size. I don't think that's the problem here though. I'd check the basics like fuel filters for debris. I also have to question your regulator being on the return side. Finally it is possible your pump is failing. Check the amp draw vs what it shoudl be.

[thedugan]

[QUOTE=69ptcamaro;477000]I'm drawing a blank right now. I apologize in advance, but where do I know you from?

Ha thats funny. More then one Rob around here.

It was directed towards 68holdon..

[68Holdon]

You know Vegas69 you sure do know how to make new members feel welcome!!

[Hammered]

I also have to question your regulator being on the return side.

Isn't this the norm for return systems?

[Vegas69]

Depends on the regulator and application I suppose.

[MonzaRacer]

OK on fuel injection with a return you use the regulator on the return side as its a return regulator it lets a certain amount of fuel/pressure by there by regulating the pressure/volume.
As for this with too large a line you have a collum of fuel weighing X and then subject it to large amounts of G forces, take a gallon of gas and swing your arm in a circle and see how heavy it is underload.
Your Walbro is sufficient but you need a booster pump amidship, let tank pump push/pull fuel then let next pump keep engine fed.
Also make sure you have a good regulated powersupply.
Jacobs Electronics makes good units and they will keep large by huge amps fed with voltage.
Fuel pumps need heavy relays, I use the oval GM relays as they can handle 70 amp surge by design but are like a 40 amp rated unit.
Put a Gmeter on your car, it may be emparting too many Gs to the mass of fuel in a 1/2 in line.
As for needing same size line on return, thats bs. Pretty much any of the setupsI have built the regualtor will bypass no more than 70 percent and it decreases as engine demands go up.
Another way to test this theory block off the return line ifit goes away you may be limiting the engine by having too low a regualtor setting or the TBI may need bigger injectors or the ecm need the software up graded.
But your readings on the fuel psi tell me to go for blocking the return and see what happens, if it goes away yon may need to use a restrictor pill in return to help regualtor keep up as it may let too much fuel back to tank.
Lee Abel
AFTERMARKET PERFORMANCE

[69ptcamaro]

Thanks for all the info Lee and everyone else.

[INTMD8]

I think the biggest clue here is the pressure dropping to zero as soon as the key is off.

First thing I would look at is a leak in the connection from the fuel pump to sending unit. (pressure leak inside fuel tank)