Power for relocated fuel pump

[rching]

I'm moving my fuel pump from the rear of a 73.5 CIS to the front by the tank. Is there a good place to pick up the power for that since the fuse panel is right above? TIA

[ossiblue]

On my former 73.5, I used either the fuse for the sunroof option or the power window option (can't remember exactly which one) since my car had neither of those options and the fuses were unused. I do remember that whichever one I used, it was a switched hot.

[chrismorse]

Hi Randy,

I just did the fuel pump move to the front on my 74. I came off of fuse #12 with a lead to an in line circuit breaker, thent on the pump. I needed to remove the old pump mount to put some Wevo rear bar mounts in.

Just curious, how did you route the high pressure fuel back to the cis??

chris

[RWebb]

I'm also interested in pics...

BTW - are you putting it on the cross-member for the front suspension? Sounds like you are putting it closer to the fuse box...


Search on "fuel pump front relocate" yields:

Fuel Pump Relocation
- fittings fabbed

Need pictures of 85+ front fuel pump mounting for 74 upgrade
- pics & PET parts diagram

Problems with my 3,0 SC in 1972 911 swap
- polarity & other problems

HELP Please! with another 1973 3.2L implant
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39 hits total; I only looked at about 10 of them.

[rching]

I'm going to try and mount a new Pierberg Fuel Pump to the front crossmember. My old pump is not working well so I thought I might as well mount a new one in a better position and replace all the fuel lines while I'm at it. This is all under the car so the 10 mm supply from the tank will go to the metal line in the tunnel. It will exit, same 10 mm but will have to adapt to 8 mm metal line that goes to the fuel accumulater / fuel filter. It's after the accumulator that there is higher pressure isn't it? I will do the engine compartment lines at another time. I want to check my injectors and try to use my ultrasonic to clean up any crap in them, using all the info about "how to" from this forum. I have pics but nothing of the finished results, ..yet. 2 day jobs, golf and 2 911's, one up on 4 jack stands. But having fun. Thanks for all the help from the forum, so far.

[rolls 912]

I would also recommend you put a filter between the tank and the pump.

[rching]

Good idea about the filter. I'll have to look into an inline one. I've been advised to flare the ends of my steel tunnel line so another task requiring me to look for a flaring tool and see if I have room to do it. And I thought I had it figured out! : )

[Grady Clay]

Randy,

It is an excellent idea to relocate a rear-mounted fuel pump to the front suspension cross member.
This was a mistake ‘Porsche Engineer Von Stülpnagel’* made in ’71 and not corrected until 1986 or so.

With CIS, be sure to use proper pressure-rated hose and fittings (screw fitting are far best).
The high pressure can push a hose and hose clamp off a non-barb fitting.
Bad things happen quickly.

I think your ’73.5 has the fuel line ‘loose’ (retained by clips and rubber sleeves) in the tunnel.
If so, you can slide the pipe several inches fore & aft if you remove the support grommets at either end.
This will allow you to silver-solder proper metric fuel line threaded fittings to the pipe.
You can easily have these made using used threaded fitting from old hose assemblies or even a used fuel filter.
The support grommets are ‘split-type’ so you can install new over the pipe with the new fittings in place.
This allows proper screw-type fuel fittings like all the later 911s.

Do some planning and use Factory spare-part hose assemblies from later 911s.
This makes future repair easy and a nice ‘Factory appearing’ installation.


It is not usually prudent to put a fine-filter on the inlet side of the pump.
This can lead to the pump running with a bit of cavitation all the time and shorten its life.
The fuel tank has a screen filter in the tank (center bottom) for CIS and in the outlet fitting for earlier tanks.
This is adequate protection for all fuel pumps.

Use the opportunity to thoroughly clean your fuel tank.
Do not let anyone talk you into putting ‘sealant’ in a CIS tank.
It will become non-functional.

Depending on your fuel pump choice, you may want to use your existing polarized fuel pump electrical connector.
There is a large OD, small wire grommet designed for this situation.
This allows a large (~20 mm) hole in the sheet metal for the connector to pass through while filling with the grommet and the power and ground wires.

Be sure to use the vibration-isolating rubber mounts or the fuel pump noise will drive you nuts.
Make the installation with ‘ease-of-service’ in mind.

Best,
Grady

* ‘Porsche Engineer Von Stülpnagel’ was an invention of ours to describe some of Porsche’s ill-fated designs and changes.
The (probably misguided) idea was that Nazi General Carl-Heinrich Von Stülpnagel was so incompetent about his own anatomy that when he shot himself he only succeeded in blinding himself.

Some of the most notable of ‘his’ design changes were the ’72 ‘install the 915 transmission input shaft seal and then build the transmission around it’.
Others include this fuel pump move and building the 911 engine around the oil return tubes.
There are more.
G.

[RWebb]

Grady - what are your thoughts on which fuse, and what wires to use on the installation/relocation on his '73.5?

[rching]

Grady, great info! Do you have suggestion for a fuel pump with a check valve? the Pierberg Unit from Pelican has no check valve so that's another issue to try and resolve before buying the pump. I searched a little for check valves so if I find that, then i can still use the Pierberg Pelican Pump.
thanks,

[Grady Clay]

Randy,

A ’73.5 fuel pump in the rear has a short wiring harness from the pump polarized connector to a pair of single-contact connectors (I think alongside the transmission near the tub bulkhead).
In the little harness, the power wire is blue and the ground is black.
On the car side of the two connectors, in the main harness the ground is brown and ends up at the chassis ground stud behind the electrical panel in the engine compartment.
The switched power is a red/green wire from the ‘hot’ (not fused) side of Fuse #7 of Fuse Box I (10-terminal).

I’m in favor of replacing the wires in the small fuel pump harness (blue and black) to the same colors as in the main chassis harness (red/green and brown).
This makes future trouble-shooting easier.


This ‘hot’ side of Fuse #7 is still an appropriate place to get switched power for a front mounted fuel pump, only add an in-line fuse/circuit breaker.
It is equally appropriate to put a red/green wire from the existing ‘hot’ side Fuse #7 to the ‘hot’ side of unused Fuse #9 or #10.
The fused side of Fuse #9 or #10 can then feed power to the front fuel pump using a red/green wire.

The fuel pump ground (brown wire) can go to the chassis ground stud under the cowl or near the left battery.
I would make a nice, neat black heat-shrink covered new little harness without intermediate connectors.

Be sure you have the correct polarity at the pump.
Mark the polarity before you disconnect the original pump - I don't think either the connector or the pump are marked + & -.


I don’t know what size fuse to use. It depends on the pump.
I’m sure Warren had the pump info in his notes.
Important is to know the ‘running’ current the pump draws.
More so is the ‘starting’ current and the ‘stall’ current (probably the same).

The original wire size to the pump is not particularly large, 1.5 mm I think.
I think a 25 A fuse is suitable for that wire but I would be more comfortable with 2.0 mm wire if the color-codes could be found.

Knowing the actual numbers for the pump current may allow use of a 16 A fuse.
That is proper for a 1.5 mm wire.

Critical is the fuse never ‘blow’ during normal operation, even at very hot temperature environment.
The car will immediately stop (in the middle of high-speed traffic) if the fuse blows.
The sole purpose of the fuse is to protect the wiring.

I might consider using a relay for the same reason we install headlight relays – to protect the switches at the driver.
The ‘pro’ is the fuel pump current goes directly from the battery/alternator, through the relay (and fuse) to the pump.
This reduces the current through the ignition switch contacts.
The ‘con’ is this adds another component which can fail, stopping the car.

Best,
Grady

For reference: The ’73.5 wiring diagram pages are in Workshop Manual 911 (’72-’83) 4810.21, Volume IV, Assembly Group 9, Supplement XXVII (1973), pages 0.1-2/13 and 0.1-2/15.
These are the last of the ‘wiring diagrams’. Starting in ’74 they become ‘current flow diagrams’.
G.

[BoxsterGT]

I make up custom Flare fittings that will slip over your steel fuel line. Once flared you can use the standard ball nose fuel fittings to connect wherever you need to go.

I use these for my "944 Fuel Hose Fix" if you want to do a search. Shaun 84 Targa & Jeremy D are some of the Pelicans using these on their 911s with success.

I can also make up custom crimped fuel lines such as this one for the fuel pump..........




Please email me for details. No PMs as I cannot send photos via PM and its almost always full.

Len at Autosportengineering dot com