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Fuel System Question

On my race car I currently have motor with stock mechanical fuel injection out of a 72 911. Pictured below is the layout of the system that I am using.

I have an ATL fuel cell with a ATL black box. I am using a Holley “Blue” pump and fuel pressure regulator. I have pressure gauges on the inlet and outlet sides of the mechanical pump located in the front of the car. I know that the mechanical pump requires about 14 PSI delivered to it, so I set the regulator so that the gauge before the mechanical pump reads 16psi and the one after reads 12psi. The regulator is the standard one that comes with the pump. I have the return from the pump go into the normal inlet and blocked one of the exits, the other exit goes right back to the fuel cell. The system seams to work great in this configuration. My problem is that I have destroyed three fuel pumps, two aeromotive and one holley. These motor always fail at the same place, they start spraying fuel out between the motor and the base when the seal fails. The Aeromotive service reps have no suggestions for me and that Holley service reps say that they have never seen a pump fail at that point. Does anyone have a suggestion?



Old 01-26-2004, 02:39 PM
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We have the identical setup. One note: the MFI system working pressure is 1 bar (14.7 psi) and the relief valve in the original bosch pump opened at 2 bar. I run 2 bar system pressure, no starvation, no issues.

You are not even putting stress on the pump by running only 16 psi, it's probably good for five or six times that. And you killed two aeromotive and one holley pumps, which seems a little strange.

What kind of fuel are you using? 110 octane moose juice, or pump gas with a bunch of alcohol or oxygenation additives? It almost sounds like the seal is being eaten away.

Before you spend any more money on expensive pumps, consider using a walbro pump inside your black box. See this thread over on the racing board for my comments.

Batt in smugglers box... Where to mount fuel pump?
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Old 01-26-2004, 02:54 PM
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Thanks for the reply. I have used purple cam2 and good ole 93 octane, both of which were overkill with a stock 72 “T” motor anyhow. BTW that motor was a champ, I couldn’t have asked for anything more out of a motor. I ran it hard for a year and a half while setting up the car after who knows how many miles in endured in it’s previous life.
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Old 01-26-2004, 03:11 PM
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I agree with John, is there possibly some fuel incompatibility?

Some questions:
Where is the pump located? Too hot? Getting bumped? Other?
Could there be a voltage issue? I can’t imagine low voltage causing your problem.
You don’t show a filter. Where is it?
Is there appropriate continuous fuel flow in the main circuit (your heavy line in diagram)? With 4 PSI drop across the mechanical pump I would think so.
What is the outlet (return) fitting? As I recall that determined the fuel pressure in a stock configuration. Is that still in place?

You might look at plavan post and consider if something there might be an influence. FYI- Fuel Safe Defects- What you need to know.(Long)

Best,
Grady
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Old 01-26-2004, 03:23 PM
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All the lines are –6 AN lines and fittings. the fuel filter is an inline one between the cell and the pump. The pump is mounted behind the cell and is lower than the fuel cell. There is no heat in that area as all the mechanical items are in the back of the car and the –16 oil lines that put out a little heat are not close enough to cause a problem. When I fire up the fuel pump though, there is a brief time that the pump is obviously pumping a combination of air and fuel before the line is pumping just fuel and the pressure goes up to normal levels. Do you think this may have anything to do with it? I wouldn’t be enough time for the pump to heat up to the point that it would burn a bearing.
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Old 01-26-2004, 03:35 PM
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If I understand your diagram, you have blocked the return to tank outlet. That is your regulator dump/relief. The regulator (my guess), appears to be of a type that dumps what is not need (flow and pressure). It may be a backpressure type regulator, and you are not using it correctly causing a larger differential across your pump than it was designed for. As John stated above, you are stressing your pumps.
Old 01-26-2004, 03:57 PM
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I assume there is a pick-up screen in the cell, inside the “black box”.
Does the cell have a bottom outlet or does the electric pump pull the fuel out the top plate in the cell?
I would recommend the filter be after the electric pump and prior to the MFI mechanical pump.
You show a “restricting” type pressure regulator rather than a “bypass” type that returns excess fuel back to the tank. Could that be an issue?
If the output of the pump is blocked, what will the pressure become? I wouldn’t think that can that “blow” the gaskets?

Your issue is you are destroying electrical pumps by the seal/gasket in the pump failing. I don’t see how that can be other than materials incompatibility (fuel vs. gasket). Keep an open mind.

When these failures have occurred, what did it look like? Give some descriptions. What time span?

Best,
Grady
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Old 01-26-2004, 04:01 PM
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Souk,
You could have it.
Could this be a bypass regulator with the return blocked?
If so, you would think the pressure gauges would indicate excessive pressure.

Best,
Grady
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Old 01-26-2004, 04:07 PM
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As for the question about when it happens. It is sperratic. I have noticed it on the third day of a DE at the Glen and one in the pits at summit point when getting ready for this year’s club race after being fine in the garage the night before and on in the garage after the parade autocross this year. All of these have happened after I put the “black box” in. Well I only used the car once without the “black box” because I had some severe fuel starvation problems even in a “shake down” autocross with the stock pickups.
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Old 01-26-2004, 04:34 PM
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I don't follow you fellas.

He's using a bypass regulator that has two return ports. One of the return ports has a plug in it. The other goes back to the tank.

The diagram does NOT show a "dead-head" type regulator that is essentially a flow restrictor, which can cause the pressure to spike between the pump and the dead head regulator. If this were the case, the fuel pressure gauges on either side of the MFI pump would show the increase.

You are using a Holley BLUE pump? A Holley 12-802-1, with the regulator that came with it?

Improved design for street/strip applications.
Distinctive "BLUE" logo.
Flows 110 GPH (free flow).
Flows 88 GPH at 9 PSI.
Maximum pressure is 14 PSI.
Includes P/N 12-803 fuel pressure regulator

This pump and regulator are only good for 14 psi. This is the problem. You are asking the pump to put out its maximum pressure.



Go with the Walbro pump in the black box.
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Old 01-26-2004, 04:37 PM
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Good suggestion guys however, I have thought about this before. This regulator is designed to feed a dual-feed 4 barrel carb on an American V8. In this configuration, there is no return so wouldn’t the same stress be caused in this configuration?

As for the materials incompatibility, man I just must not be looking hard enough. The Holley pump is rated for gas, and the aeromotive is rated for gas and alcohol.
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Old 01-26-2004, 04:55 PM
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John, I agree that I need a new pump and the in-tank pump is an excellent option thank you.

That being said, the aeromotive pump,

Street / Strip (SS) Fuel Pump, P/N 11203:
For carbureted powerplants making 200-750 HP with standard regulators and up to 1,000 HP with dynamic, bypass style regulators. Ideal for coninuous duty, carbureted applications where more line pressure, flow volume and reliability are desired. Ideal for your daily driver, street rod or demanding ET-bracket race car. On the street or at the track, you expect durability and reliability, along with consistant high performance. The Street / Strip (SS) Fuel Pump delivers high fuel flow at optimal line pressure. This pump is designed to be used with either ou Bypass Regulator; P/N 13301 or one of our Carburetor Adjustable Regulators; P/N 13201 or 13205. Fuel flow exceeds 900 lbs. per hour @ 13.5 Volts -more than 150 gallons per hour. Pump provides 18-20 PSI fuel pressure - perfect for high-G leaving cars. Pumping mechanism features our proprietary composite rotor, stainless steel vanes, and precious ground, heat-treated steel plates. 3/8" NPT ports facilitate easy installation. Alcohol compatible. Ideal for dedicated nitrous fuel delivery. Low amperage draw.

that I purchased makes 18-20 psi, should be plenty
Old 01-26-2004, 05:05 PM
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John,
Your photo looks like the pressure regulator I use on my GT2 914-6. The bottom port is the inlet and the two side ports are connected to each other. I have one side port to each carburetor. Plugging one outlet port shouldn’t be a problem.

The issue here is the pump “blows a gasket.” What can cause that?

Usually these problems turn out to be something outrageously simple, but not always. Let’s us all put our heads to it.

Nein14-6,
You need to give us the best information possible. The specs on the pump would indicate the problem is somewhere else. Improve your diagram with the filter, gauges, and other. List each part, hose, fitting, etc.

Best,
Grady
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Old 01-26-2004, 05:50 PM
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Do you think that the pickup in the “Black Box” has too much restriction?
Old 01-27-2004, 10:34 AM
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Where is the fuel leaving the circuit? Or is that MFI voodoo stuff I wouldn't know anything about?
Old 01-27-2004, 10:39 AM
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Hmm. OK, here's my last guess. The ATL is a top-loading cell. That means that the pump has to pull fuel from the bottom of the cell, up about a foot, around the back of the cell, through the fuel filter and then push it through the system. Based on my own experience, that's a pretty long way. Some guys mount the pump right on top of the cell for a very short run.

The sound you are hearing on startup is cavitation of the pump in air. It probably runs for a couple seconds, makes a pretty loud whir-whir-whir pulsing sound and then there's a pitch change as the fuel gets sucked through. I think that in the time that it's priming, the seal is overheating. The pump uses the fuel as a coolant and when it's sucking air, no cooling is happening.

The same thing happened to me when I was using a Mallory pump, which even had an air-bleed in it that was routed to the return line via a "T" fitting. It would run fine at idle and even high RPMs for a while, but on long sustained stretches, like through the esses at Watkins Glen, the fuel pressure would drop and the motor would lean out.

Good luck! I'm out of gas on this one (pun intended!)
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Old 01-27-2004, 10:54 AM
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John has some good ideas here.

Nein14-6, is the electric fuel pump seal being pushed out, pulled in, or failing in some other way? What did you do with the failed pumps? I’m sure the manufacturers would like them back and tell you how they failed. Record all the numbers on the part and engrave your name. Get them perfectly clean from any fuel and send them via Certified US Mail. Almost all manufacturers want to analyze failures, not suffer lawsuits.
From your diagram it looks like the stock fuel console/filter is not in place, is that true?

Souk, yes, the mechanical pump voodoos the fuel (via steel or plastic pipes) to the injection nozzles in the intake just prior to the valve. That is the art of MFI.

Nein14-6.
You need to find the source of this problem before you make any other changes. The pumps you are using are good equipment and shouldn’t fail in this manner.
My suggestion of the day is to remove the filter prior to the pump as it duplicates the screen in your black box. Please inspect/clean the screen in the tank.
I recommend a real filter just after the electric pump. I use a Bosch 0.450.905.016 from ’74-> CIS. I made silver soldered adaptors to -6 line. Perhaps positioning your fuel pressure gauges between the electric pump and the (new) filter and just prior to the pressure regulator might yield the most information. You could extend the gauges (carefully with -2 SS Teflon hose) so you can see them while driving, Be extremely careful with pressurized (or any) fuel in the cockpit!

You said you plan to go to carburetors. That is OK if cost is the issue. MFI gives more performance and better throttle response. See the threads on MFI.

Best,
Grady

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Old 01-28-2004, 09:58 AM
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