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Posted by: Kerrys914 Sep 1 2003, 05:32 PM

Hey guys. I read somewhere that the FI fule pump doesn't suck the fuel from the tank, is this true?

The fuel pump must be located below the lowest point in the tank to make use of all the tanks capacity???

I (PO modification) currently have the fuel pump located below/near the battery shelf. Is this too high?

Cheers
Kerry

Posted by: vsg914 Sep 1 2003, 05:50 PM

Kerry, you need to move the fuel pump out of the engine compartment. It's too hot. It will vapor lock!
Ask me how I know?.

Posted by: URY914 Sep 1 2003, 06:08 PM

There was a factory recall to move the pump to the front under the tank. I don't know if a recall every runs out but someone here will know.

Yes, move it to the front soon and replace ALL the fuel lines cause this probably hasn't been done.

PAul

Posted by: Brad Roberts Sep 2 2003, 12:53 AM

Its funny. I have only seen 2-3 914's in Northern Ca. that have had the pumps moved. It just doesnt get hot enough here to warrant the move. I put them right back where the factory installed them.


B

Posted by: redshift Sep 2 2003, 01:16 AM

It matters here.




M

Posted by: Racer Chris Sep 2 2003, 02:51 AM

The factory lines in the tunnel weren't designed to handle the FI pressure, in addition to age and fatigue, so they definitely need to be replaced. It's not too hard to mount the pump near the steering rack above the metal tray there. You might have to hammer a bulge into the tray to get it to fit back on afterwards.

Posted by: Kerrys914 Sep 2 2003, 05:59 AM

I'll look into that next weekend. Is there any issues with just extending the fuel pump wires to the front trunk?

Cheers
Kerry

Posted by: Racer Chris Sep 2 2003, 07:45 AM

Thats the easy way.

Posted by: Kerrys914 Sep 2 2003, 10:15 AM

But is it the correct way?

Posted by: zeppelin71 Sep 2 2003, 10:38 AM

Can someone please explain what vapor lock is? How does it affect the pump? I'm super curious...

cheers,
Markus

Posted by: ArtechnikA Sep 2 2003, 10:41 AM

fuel pumps pump liquid - they don't have enough displacement ability to pump gas (vapor)

gasoline boils (turns to vapor) at about 140F - once the gasoline in your pump and fuel lines turns into a big vapor bubble, it won't pump very well - and if it could - the car won't run on it.

with an EFI car that runs the pump a few seconds when you turn the key, you can turn it on and off lots of times in the hopes that you can suck through enough cool(er) fuel from the tank and fuel lloop to re-establish a hydraulic head abd be able to start pumping again.

Posted by: boxstr Sep 2 2003, 10:45 AM

What started out to be a quick move the fuel filter to a better position in the access hole, this is a 75. I split one of the fuel lines that goes to the fuel tank. Lucky me, full tank. So off to the store and a couple of 5 gal cans and hose. After a mouth full of gas and filling both gas cans and various other containers, the tank was empty.
Out it came and I figured lets get this stuff to a better access area. I looked at some old photos of Porsche 914 GT race cars and VOILA. They are mounted right front trunk location.
I purchased ten feet of fuel line, this car is carbed so FI hose was not needed. New hose clamps, filters and a search for a 90 degree hose fitting to go oin the FACET fuel pump, so I don't have the big loop in the hose that you see in the pic. Put everythin in place bolted and screwed and it works great.
Know off to look for that 90 degree fitting. Good luck, it works for me.
CCLINFUELPUMPRELOCATIONVILLE


Attached image(s)

Posted by: Racer Chris Sep 2 2003, 04:24 PM

The "correct" way would be to remove the entire wiring harness and redo the wires that make the fuel pump circuit so they follow the most direct route.

Posted by: Dave_Darling Sep 2 2003, 04:56 PM

Nope, no such recall.

The factory put the pump under the tank in the 75-76 cars. And there was a recall to replace the fuel lines under the battery, as well as adding a battery cover. But no recall to move the pump.

I personally, if I thought it was going to be an issue (and I don't think it will), would run an extra wire in the main wiring harness for fuel pump power. This can be avoided if you've got carbs and are not using the stock FI's way of running the pump.

--DD

Posted by: Kerrys914 Sep 2 2003, 05:09 PM

So if I extend the (+) signal to the front and just ground the other side of the pump, will that work?

Cheers
Kerry

Posted by: Dave_Darling Sep 2 2003, 05:19 PM

Yup! After all, that's the way the wiring goes. Power supply (switched by the EFI computer and pump relay or by the dual relay) to one pin on the pump, ground (all the time) to the other.

--DD

Posted by: zeppelin71 Sep 3 2003, 12:16 PM

ArtechnikA - thanks for the explanation, so moving the fuel pump done simply to lower the temperature in which it is operating (?). Does the pressure the gas is kept under while running through the gas line keep it from turning into vapor when it approached the engine?

Posted by: Brad Roberts Sep 3 2003, 12:19 PM

My solution for this (and what Porsche recommended).. turn the fuel pressure up on the stock pump mounted in the stock position. Pretty easy. I bump them up to 32lbs.



B

Posted by: ArtechnikA Sep 3 2003, 12:30 PM

there are several factors involved, and several opinions (hi Brad!).

yes, mostly it's done to move the pump, which can generate and retain quite a bit of heat all on its own, to a cooler location - in the stock location, the right side heat exchanger dump valve is blowing hot air right on it.... also, it's much easier to push a fluid than to pull it, and if you're really close to vaporisation point to start with, lowering the infeed pressure by sucking on it doesn't help. so keeping the inlet line short, and directly above the line, helps prevent fuel boiling.

increasing the fuel pressure also helps prevent vapor lock in the loop, but i'm not sure it does very much to reduce vapor in the feed line.

Brad's probably right that the factory approach to the early cars was to increase the pressure (rather than recall a lot of cars and move it on their own dime) -- but later cars ('75 & '76?) saw the factory move the pump to the front.

Posted by: Brad Roberts Sep 3 2003, 12:34 PM

He he he...


It just scares me telling people to move their pumps to the front and PRESSURIZE a 30 year old line running down the center of a the car. I run our race car fuel pumps up front... but we run all new lines.


B

Posted by: zeppelin71 Sep 3 2003, 02:07 PM

yah - new lines are on the way Glad I understand this now... so I read the 73/74 (I think) had extra air scoops underneath the car to help reduce vapor lock. Sounds like that didn't work too well if they ended up moving the pump in later model years.

cheers,
Markus

Posted by: ArtechnikA Sep 3 2003, 02:54 PM

they added the flaps to improve the effectiveness of the cooling system; even early cars can benefit from them.

'75 brought with it the catalytic convertor and A LOT more heat.