substitute fuel pump

[inaminit]

Helping a friend with his 1974 911. We have installed the original engine, and removed a turbo engine and both the turbo fuel pumps. I have ordered a generic Bosch pump from our host, but delivery is 3 weeks away, and we may need to move the car around before then. I am thinking about putting back the rear pump from the turbo that is a 0-580-254-994 for now. I do not have any info on what pressures are needed for a 74 CIS and if this pump can do the job. Can anyone help me with this? Thanks in advance

[boyt911sc]

Are you installing a 2.7 CIS motor to replace a 930 motor? The 2.7 uses a single FP compared to the 930 with two (2) FP’s. The 930 FP’s are installed in series and both should work at the same time.

If I understood your post correctly, you only need a single FP for your normally aspirated 2.7 CIS motor. Any of the two (2) FP’s used in the 930 set up will be adequate for 2.7 application. You need a single FP with a minimum flow rate of 1 liter per 30 sec. or 2 liter per min. (minimum). And you have to revise or eliminate one of the FP temporarily to allow the fuel to flow through unobstructively.

Tony

[spuggy]

My CIS 930 ran fine in stock trim with the single original 230K 911 fuel pump. I thought it was noisy and swapped it out at turbo upgrade time for an 044 for more headroom. It was no quieter - and made no difference to any of the CIS tuning issues either. Car made >400 FWHP with a single pump for years before going EFI.

2 pumps on a 930 was the original way the factory did it - but in practice, just more things to go wrong - especially if you don't address the way the factory wired the rear pump, which is problematic. Added to which, original 930 rear pumps are spendy, if you can even find one.

And factory-fitted pumps are much lower spec than the motorsport pump. Which is both widely-available and usually much cheaper - made in much larger quantities.

Bosch rate the 044 as 200l/h @ 5 bar with a max current draw of 15.5A, but this seems to be very conservative; they typically test very differently, with some rating them 258 l/h @ 5 bar/285 l/h @ 3 bar.



You would need to address both line fittings and electrical connection differences though.

Bosch says, in their motorsport/universal pump program document (eg http://www.lucasinjection.com/_borders/fuelpumps.pdf):

Purpose and Function
Modern EFI fuel systems circulate as much as 200 litres per hour (~ 3 litres / min ) of fuel at pressures between 2.5 - 3.5 bar ( 250 - 350 kpa ) Modern electric fuel pumps are “Positive Displacement” type pumps, this means that the pump cannot produce pressure unless it is acting upon a restriction. The only restriction in the system should be the fuel pressure regulator. The regulator controls the system pressure; the pressure ability or flow volume capacity of the fuel pump will not alter the system pressure.

So if swapping in a 2.7 motor with CIS, that'll take care of pressure regulation.

According to the Bosch cross-reference I have (eg https://jenniskens.livedsl.nl/Technical/Tips/Files/Bosch%20Fuel%20pump%20crossref.pdf), the rear pump for a turbo 80-94 is 0-580-254-979 - which is still a current part #.

The 0-580-254-994 you quote might be for earlier cars - cross-ref says that was superceded by 0-580-254-953, which the motorsport fuel pump document documents as a 175l/h 5 bar pump

[inaminit]

Update- I swapped in the turbo rear fuel pump into the rear position, and removed the front pump, and the test readings are way low-40 psi system, and 15 psi control, engine off. Then , I measured the pump static pressure at the fuel filter outlet-80-85 psi.
What other tests can we run? What could cause such a drop in pressure through the fuel distributor?Right now the car will fire up on start, but not catch and run, so I know it has spark. Prior to getting the engine back from the builder, it ran perfectly on a test stand. Thanks for your help!

[boyt911sc]

Originally Posted by inaminit

Update- I swapped in the turbo rear fuel pump into the rear position, and removed the front pump, and the test readings are way low-40 psi system, and 15 psi control, engine off. Then , I measured the pump static pressure at the fuel filter outlet-80-85 psi.
What other tests can we run? What could cause such a drop in pressure through the fuel distributor?Right now the car will fire up on start, but not catch and run, so I know it has spark. Prior to getting the engine back from the builder, it ran perfectly on a test stand. Thanks for your help!

Have you checked the PPV (primary pressure valve)?

Tony

[inaminit]

No I have not checked the PPV. How do you check it or test it for good function?

[boyt911sc]

Originally Posted by inaminit

No I have not checked the PPV. How do you check it or test it for good function?

The System Pressure is determined by the PPV setting. So adding or subtracting the amount of shim/s installed at the PPV will give you resultant SP.

Tony

[inaminit]

I have been reading from Jim's CIS Primer-actually the k-jetronic troubleshooting guide-it looks as if you can relieve pressure and unscrew the valve body to add shims or seals. Can this be done with the engine in the car?
Tony-would you kindly pm me your phone number- I would like to order some parts.
Thanks!

[boyt911sc]

Originally Posted by inaminit

I have been reading from Jim's CIS Primer-actually the k-jetronic troubleshooting guide-it looks as if you can relieve pressure and unscrew the valve body to add shims or seals. Can this be done with the engine in the car?
Tony-would you kindly pm me your phone number- I would like to order some parts.
Thanks!

Test the residual fuel pressure loss. These are the three (3) most likely culprit/s.
a). Defective fuel accumulator.
b). Defective fuel pump check valve.
c). Defective primary pressure valve seal.

In your case, if might be a leaking valve seal allowing the pressure fuel to bleed out. So you definitely need to test and inspect the condition of the PPV’s o-ring seal. PM sent.

Tony