So... I stirred up another conflict while I was researching the proper feeding of Stinky, the wonder truck. In this conflict, I speculated the stock pump was good up to 33 GPH (top limit for AC160s) at 45 PSI - based on the information I could find at the time. It was countered that the stock pump is good for much more, but there is no data to specify how much more. I've talked to a number of people in the diesel business and the common answer was "It depends on your injectors and your tuning." Apparently, I'm speaking Geek and failed to translate what my goal is. I'm not asking if it will work, I can figure that out on my own - if I can just get the silly flow numbers. Here are all the part numbers for the pump:

Motorcraft: PF1
Ford: F81Z9C407AC
Bosch original: 0 580 464 074
Bosch replacement: 69136
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I conducted every internet search possible - zip. I called Ford and they don't have that data. I finally called Bosch (manufacturer) and they have the data, but the pump is proprietary - which makes the data proprietary. He could tell me the pump is spec'd for 50-65 PSI, but no more. I can do a test to see what it pumps at 60 PSI, but this is starting to get silly. Maybe I can conduct a flow test when I'm bored, but I think I'll just settle for a fuel pressure gauge and go from there.

Some might say "But-Tugly, you can get a Walbro 392 or a Bosch 044". I have complete charts on these units and they are really great performers... but they are not rated for durability like the original Bosch pump for the 7.3L. I looked at Air Dogs and Fass systems, but they are rated at 100 GPH and I don't know their durability - plus they're expensive. The 5/16" fuel line to the engine is rated at 72 GPH max. Ford had the original pump special-made for them and I'm not sure we can find a better one for longevity. Many have used twin stock pumps to get the flow and durability they seek, and this has the added benefit of limp-home capability if a pump goes out. Clay has them on the shelf for $150 and I could just tee in a second pump if mine isn't up to the task. That is just too cool.

 

Don't know about the pump capacities, but here's something to consider if you run two pumps in parallel. Make sure to install valves to isolate either pump in case of an internal failure.

Our fire department has a 1951 Mack with an electric fuel pump plumbed around the factory mechanical one. When the mechanical pump failed we couldn't limp home on just the electric because it was circulating fuel. The defective pump essentially formed a bypass around the good one.

While we're on the topic of fuel pumps, can I hijack your thread for a few seconds and ask how much your fuel pressure drops from idle to WOT? I just got the body on my 99 F350, and in a few days of driving I'm seeing 70-75 psi dropping to 45 psi. Is that normal? Also, how long should the fuel bowl hold pressure after key off? Mine drops to zero almost immediately.

 

The Bosch fuel pump has an internal check valve at the outlet, so this problem would not occur.

The Ford manual says 45 is minimum for WOT, so you are in the safe zone. I'd be more concerned about that 75 PSI, the regulator should keep the initial pressure closer to 60-65 - based on what I read (not experience). The last link in my signature has some information on this. I don't have my gauge yet, but you can bet I'll watch those numbers when I get it.

As for holding fuel pressure when the pump is off, I don't know this one yet.

 

Coming from a hot rod/race car building background I am going to tell you something that many may disagree with.

The stock pump is just fine for anything!

See this 4 barrel carbed, bored, stroked, 12.5:1 CR, direct nitrous injected monster (lol), all running on a STOCK base model fuel pump (not even the performance model car).



Camed, bigger injectors, supercharged, bigger motor, STOCK fuel pump:

http://img177.imageshack.us/img177/7...ake2007kj2.jpg


Pretty much the same setup as the black car but with an even bigger motor yet and guess what, stock pump.



My grandfathers V6 buick also received a stock honda dx fuel pump after it burned up its original chevy pump (very very common problem with chevies).


I think your fuel pump will be just fine for anything you ever want to do with your truck.

 

I don't have the answer on the GPH questions BUT here is where Ford SHOULD have put the pump...in the tank.

 

Just for more thinking, Tugly...

... Pumps are nothing more than pressure change devices. They will convert incoming pressure to discharge pressure, and the amount of increased pressure is a constant for any given pump based upon fixed design criteria (i.e. pump motor horsepower, pump motor rpm, impeller design, inlet and outlet line sizes, etc.).

If you run two pumps in parallel, the only way you will increase flow/pressure to the injectors is if the second pump puts out more pressure/flow than the existing. If both pumps are rated at 65 psi max, then that is all the pressure they will generate. Once the discharges are combined, they will be fighting one another and you've not accomplished anything. If you suspect that both pumps will increase the flow through the line to the injectors, you're wrong... unless the new one is better than the old one.

You see, any increase in flow in your existing line will simultaneously increase the pressure in that line because of the fact that friction losses increase with increased flow.
You might be tempted to think that since both pumps are pushing volume that there would be an increase in flow to the injectors, but that is physically impossible unless the pumps are somehow boosted to higher pressures by increasing the amount of pressure on the suction side of the pumps. Therefore, unless you either boost the suction side pressure OR reduce the friction losses downstream of the pump(s) (i.e increasing discharge line size to the injectors, running two parallel lines from the pumps all the way to the engine's feed fuel rails, etc.), you will simply be running with a "hot spare" and the best of the two pumps will be the only one doing all the real work for you - the other, older, weaker pump will simply be overrun by the newer and better performing unit.

Real world example... when I installed my Carter "lift" pump ahead of my stock pump, I boosted my "system" pressure at the entrance to the fuel bowl by about 4-5 psi because that is what was generated by the Carter pump. Since I increased the pressure on the suction side of the stock pump, it continued to contribute the same amount of pressure increase that it had always provided, but the discharge pressure was only higher because of the Carter pump pushing fuel into the stocker's suction side more quickly than the stocker had been able to generate for itself by sucking through the straw. In reality, the Carter pump I used is rated for 7-8 psi discharge pressure, but I only see about half that at the fuel bowl because of increased friction losses which result from the higher flow rate to the fuel bowl. As an extreme comparison for you, if I had installed the lift pump parallel to the stocker, it would never have accomplished anything because it cannot push enough pressure against that generated by the stock pump.

 

Oh... believe me, I gave the in-tank pump a lot of thought. That is the ideal place for the sake of the pump, but not for the sake of maintenance. I up-sized my pump intake line to address the issues I knew would take place with the existing design (I have experience with engineering pumping systems).

Tank/fuel elevation plays an active role in the issues with the "1/4 tank syndrome". When the fuel is higher, there's a little push from the fuel, but when the fuel elevation drops below the pump - that's when vacuum takes place and the quick-disconnects introduce air. Many people may feel the air comes from within the tank, and this is sometimes the case. There is also air coming in from the return line and into the mixing chamber because it's difficult to finally work the air out from a low fuel tank. The FRx is great... at getting all the air back to the mixing chamber to re-introduce into the pump. Doing the Hutch mod, doing away with the quick disconnects, and installing something like the FRx is a comprehensive recipe to address the air-in-fuel issues of the 7.3L. Once this is done, I feel the frame-mounted pump is just fine for the 250/350. I know nothing of 450+

OK guys! Bring on the counterpoints!

 

Your post landed right behind mine above, Tugly, which gives you more food for thought on your plans for pump configuration.

 

I've been mulling over that as well. In situations with twin pumps, there's usually a pressure switch to activate the second pump when the pressure drops to a certain point, but the hysteresis needs to be configured where the shut-off point for the secondary pump is high enough so as not create cyclic activation.

Laymen's terms: If the second pump comes on in parallel, the pressure will jump and that could shut the pump off - then on - then off. There needs to be a pressure setting that indicates when the demand has dropped and it's safe for the second pump to drop out. This is all way too comlicated for use on our trucks, so I need to think this through some more.

I thought about putting them inline, but I have to think that through as well because this would boost the flow and pressure to the point of popping fuel lines due to the line restriction. My goal is not to boost pressure, it is to maintain pressure when the demand exceeds the limits of the pump. The stronger pump will take the bulk of the work, but the weaker pump will augment the stronger pump when the demand climbs. Drawback: The weaker pump runs the risk of dead-heading when the demand is normal. Things like this are why I have no hair.

I wish there was an output from the PCM to indicate high fuel demand and this would kick in the second pump automatically. As Winnie the Poo would say... "Think, think, think." Ultimately, this may be nothing more than a theoretical exercise because there are many in the business who feel I'm over-thinking this and it will work out just fine with the injectors/tunes I have.

 

I actually just installed my gauge today and when I turn the key on it pumps up to 62 then drops pretty quickly. I think that is normal.

I can get some WOT #'s today. I have 160 cc single shots, so not big but now I will be able to see what my pump is doing.

BTW TUGLYI did some more work on my truck this weekend with the injectors. Email sent.

 

Oh for christ sake...

Just to clarify...

The stock fuel pump will supply 238/80 hybrids off a stock fuel system without issue...

The stock fuel pump will even supply 250/200's until you get to the higher power settings.

The stock fuel pump will not even tell the differance between a set of AD's and a set of AC's...

 

Fuel system does not maintain fuel pressure once the pump turns off.

This is normal.

 

JOE, You just made my day. I've been following this thread to see where it would go and got to your post and just broke out laughing. That was perfect. Thanks.

 

Well I added to it, so I would not "appear" to be a complete "****"...

But all I wanted to say was...

For christ sake.

 

I am glad you added it cause that is what it made you "appear"....not everyone on here knows as much as you on this stuff.