What PSI does an MFI FUEL pump (not injector pump) put out/need?

[Eric P]

Anyone know? I'd like to install a replacement pumpin the front by the fuel cell.

[pwd72s]

Eric, I try not to be one of those "do a search" guys...but in this case I am. Do a search. If memory serves, the topic is on replacing fuel lines on an early 911. Look for posts by Grady Clay.
This thread goes on for many pages, and is one of the best tech threads I've read here. In it, Grady mentions fuel pumps, PSI needed, even the parts numbers of MFI and Carb fuel pumps...
If you find it, I hope your printer has lots of ink, because I think you'll be using it.

[Eric P]

Thanks for the guidance. I have searched under MFI fuel pump, fuel pump PSI, and a few others but only came up with either CIS info or carb info. I'll look for Grady's stuff.

Thx

[Jays72T]

Try this:

fuel line info

[pwd72s]

Ahhh, the computer literate among us comes to the rescue! Thanks!

[Paul Thomas]

I am frequently wrong, but i think it is only about 12psi.

Paul

[Grady Clay]

Eric,

The specs are:
Regulated pressure; 14.2 PSI, 0.8±0.2 Bar (note the inconsistency)
Flow rate; 125 liters/hour
Porsche P/N; 901.608.105.00
Bosch P/N; 058097 0001
Current draw; 3.5A @ 12V
RPM; 2800

For MFI use with a fuel cell, do some Pelican searching. Post some images; there is a lot of important stuff to be learned.

With a race 911, I would use stock stuff or a slightly higher flow fuel pump and an adjustable regulator in the return circuit. You might consider an integral “surge cell” within your fuel cell. The Bosch pumps can run in/under the fuel.

Best,
Grady
gradyclay@hotmail.com

[Paul Thomas]

See what i mean?

[Eric P]

THANKS! I search Grady and found all kinds of stuff but hadn't come to this yet...plus I probably would have passed over this one given its subject line...

[pwd72s]

Eric, Thank Grady...we are very fortunate that he decided to start posting here.

[Grady Clay]

Eric,

This is one of the failures of the Pelican Search Function. There needs to be some clear instructions on how to use it.

If I go to the “Forum Jump” menu and choose “Search Forums” I get to a screen where I can enter both a username “Grady Clay” in this case and a set of subject keywords, “MFI+flow” and the thread cited above is 11th on the list (they are chronological on last post).

One of the best features of the Pelican Forum is the archive. Understanding how to search it is critical. There is an invaluable resource here.

Best,
Grady

PS, If it weren’t for guys like pwd72s donking on me ….
Thanks Paul.

[Eric P]

Yes, very fortunate. Thanks Grady, on multiple levels...

[Eric P]

Okay, I've searched for this answer too but no luck:

Can I put a comparable spec (PSI and flow) pump in front and just leave the stock fuel pump in place? Basically either running both pumps at once or disabling the stock pump. This would save me $ and effort (trying to replumb the system in back).

My stock pump is working but for some reason I don't trust it.

[304065]

No. The rotor-type pump will interfere with the flow. If you put a modern 1.0-2.0 bar pump up by the crossmember you should remove the rear pump and change out the hoses from the steel lines in the tunnel to the steel lines through the engine compartment rails. Stock performance, good reliability, fewer leaks, fewer things to go wrong.

One half day with the left rear wheel removed carefully supported on jack stands and you are there.

[Eric P]

John, I didn't want to have to do that but so be it! Sounds like you have done this. What pump?

Did you stainless and AN stuff or "just" the factory type lines?

E

[Zeke]

I'm not John, but I used the factory type hoses from Pelican and the proper clamps, which is the key to no leaks and long lasting lines (no cuts). Sorry, I can't recommend a substitute pump, but I'm all ears as the Bosch unit is over $400!!.

There are not too many pumps available with the features of the Bosch, i.e., a circulating system and a return line(3 nipples). Sure, most modern cars have this, but those pumps run at much higher pressures.

[304065]

Eric, you are taking me back to the old, old days.

MFI Fuel System Re-Engineering Questions

Today I use an ATL 17 gallon fuel cell with a "Black Box" or three-door surge tank in the cell, with an integral Walbro fuel pump that will move 255 liters per hour. I fixed it in this thread. Fuel Starvation at Watkins Glen

Anyway, if I had it to do over again, I would use Earl's fittings and kevlar-braided black hose, and keep the weight as low as possible.

One design criteria that I used which has served me well is to have NO JUNCTIONS in any place you can't see easily. I use continuous pieces of hose from the top of the fuel cell all the way to the MFI fuel filter console. When a hose leaks, it likely leaks from a connector, not from the middle of a hose. It's not a small task to pull -6an all the way from the front through the tunnel around the heat exchangers up through the frame rail and into the engine compartment, but it's worth it to not worry about leaking fittings.

Good luck!

[Grady Clay]

Eric,

Lots of good advice here.

Let’s drop back a step or two and define the criteria and design a fuel supply system that fits your needs and budget. You don’t want a Space Shuttle level system because none of us mortals could afford it. On the other and there is a huge amount of Factory and Independent race technology available, much at very acceptable cost.

First, in the fuel supply circuit you don’t want two pumps in series. The pressures are additive and there is a high pressure limit for MFI. Turbos do this to overcome the boost pressure and get higher flow from the CIS nozzles, not an issue with MFI. The optimum is there needs to be appropriate pressure and excess fuel flow under all circumstances.

OK, what and why is there an optimum?

The reason for having pressure at the inlet of the MFI pump is to prevent cavitation during the piston pump inlet phase. If that happened the MFI pump doesn’t meter the fuel properly and a lean condition results. Sometimes this happens with disastrous results. On the other hand, MFI doesn’t like too much pressure because it starts to effect mixture at idle. I think about 1.4 bar is about the practical limit.

The other side is fuel flow. Obviously there needs to be enough for every maximum HP situation. The fuel is used to cool the MFI pump. This is also part of preventing fuel vaporization at the MFI pump inlet. I think at maximum fuel usage, about 20% still should be returned to the fuel tank. This also purges any gas bubbles that might interfere with fuel metering. There probably is an upper limit to how fast the fuel is circulated before causing bubbled to form on the (low pressure) leeward side of fittings and such. I don’t know where that is.

Diagram for us your proposed fuel system and let us critique it and help optimize an affordable system. This is in the finest tradition of engineering.

I think the basic criteria are:
1) It has to work perfectly under all conditions.
2) Must be safe.
3) Be easily diagnosed and serviced.
4) Be within a realistic budget.
5) Comply with the rules.

Of course there are also things like “coolness factor.”

Best,
Grady

[Eric P]

Grady,

This is great info, thanks. I've tried to get through some of the other treads on this but after 4 pages I was a big scrambled. Let me work on it over the weekend and I'll post.

Thanks,
E

[David E. Clark]

Please take a look at the Ultimate MFI resources thread and add your links and resources. It will make a great resource for all of us.