Braided Fuel Hose for a 72T MFI

[DonDavis]

I've called 3 Porsche shops, 1 BAP and 1 parts supplier as well as our host. I've also seached the archives. No joy.

What size do I need to replace all of the fuel hose on my car? It's the original 30+ year old stuff. 8mm is my guess with a 5mm hose on top of the filter housing. Should I go with the smooth outer surface or stay with braided? Would a 15 foot piece be enough for the whole enchilada?

I don't want to disassemble anything without the replacement hose on hand. Oh, and I should also replace the clamps. Where can I find those?

Thanks and you all rock!

[austin552]

Good question! I am redoing all my 2.2 stuff as well. I am looking for steel braided though. Not sure on the size but I hear transmition hose works for fuel line.

[Jay Auskin]

Pelican has all the fabric braided hose. That's where I got mine. If the clamps are good, you can reuse.

You'll realize you did the right thing by replacing it after you look a little closer at the old stuff when you remove it.

[DonDavis]

I know someone has an idea of which size. 7mm or 8mm?

[vanwyk4257]

I don't have it in front of me, but I think one of my performance products catalogs had the fuel line hose in it. There are two different sizes if I remember correctly.

[Zeke]

5 and 9mm.

[JSDSKI]

Here are the Pelican part numbers: FH-8-13-HP and FH-7-12-HP

Search under "MFI Fuel Hose". There are a lot of threads on this.

[addictionMS]

AN-6 is fine,

Jim

[Grady Clay]

Don,

The fuel hose is 7 mm P/N 999.180.030.50 or supercede. There is also some 9 mm hose 999.180.031.50 or supercede. Only use OEM hose. The larger hose goes from the fuel tank filter screen fitting to the plastic pipe in the tunnel and from the plastic pipe to the fuel pump.

The cold start hose is 4.5 mm 999.180.080.50.

Absolutely use the original Norma-Schellen hose clamps 999.512.174.02 or supercede for the 7 mm hose and 999.512.070.02 or supercedes for the 9 mm hose. The clamps for the cold start hose are 999.512.082.02. NEVER use the common screw hose clamps. They damage the hose and can lead to fuel leaks and fire. Carefully inspect the plastic pipe in the tunnel for damage or wear.

At the fuel pump, you have two pipe-hose assemblies. You can cut off (Dremmel) the swaged clamps and replace them with the above clamps. Be very careful to not nick the pipes. Apparently there is a restrictor piece in the return line to the tank – look for it and keep it in place. It is inside the hose returning from the filter console and under the swaged clamp.

Depending on your purpose, this might be an opportune time to reposition your fuel pump from the hot environment at the waste heater air to the front cross member as the ’69E&S and the ‘70T, E, &S.

Although expensive, a new fuel pump is worthwhile preventive maintenance. Be sure and clean the electrical connections at the pump. Also check for good ground continuity.

Another “while you are there” is to clean the filter screen fitting in the fuel tank and give the tank a good cleaning.

If you want original Porsche, you can order up the part numbers for the pieces and PAG will build them for you. Just more expensive than ordering OEM bulk hose and some OEM clamps.

Best,
Grady

EDIT for a typo.

[asphaltgambler]

What about the oil lines? Does anyone make a ready-to-go set with the fittings in steel braid for the 3.2??

[Grady Clay]

Oil lines is a subject worthy of its own thread. Do some Pelican searching.

Argus is the manufacturer of the Porsche racing oil hoses and other. Search out their web site and post links.
Warren Eads seems to have the ability to make original hoses. Try him at e-mail@spydersports.com
Fax 310-377-0912.

Best,
Grady

[DonDavis]

Thanks Grady!

[Zeke]

Originally posted by Zeke
5 and 9mm.

Let me correct myself. 5mm (which is what Pelican lists instead of 4.5), 7 and 9mm.

Now, that I've finished reading all the search results under "MFI+fuel+hose," I saw where someone asked, and no one answered, "How many feet of each is needed to do the whole rear of the car?"

More importantly, after removing the swaged fittings, how many Norma clamps? Or, are you guys gonna make me crawl under there and finger this out for myself?

After last few weeks and especially the 80 hr. last week, I'm trying to not even look at the car.

[thastings]

Grady,
Has anyone ever seen this 5mm restricter in the return line? I can find no listing for it in the parts book and did not find one in my original hoses. While it makes sense for there to be one in order to maintain the mininum pressure on the MFI pump side of the system, I have never found one, only hear about them on this BBS.
The closest thing to it was the fitting that goes between the fuel filter and the return hose. I did not measure its ID (not that I didn't have an opportunity in the last year), but it looked a lot smaller then the ID of the return hose.
If anyone knows what it looks like, has a part number for it or has a spare one, let me know because I must need one.
I wonder if the fittings for the electric gas pressure gauge I installled in that line provides this restriction?
Terry Hastings

[Grady Clay]

Terry,

No, I have never seen one and I don’t know of a dimension. I don’t think this was on all MFI, possibly just the later ones sometime after the pump was moved to the rear.

My opinion is that it was added to address low fuel pressure under some marginal or adverse condition. Without the restrictor, you can have normal spec fuel pressure. The center fitting at the filter console is the fuel pressure regulator.

If we can find a dimension, a carb jet would work just fine.

After a little searching in my paper manuals and PET6 I found there are three part numbers for similar appearing “fuel return line” for the rear mounted fuel pump.
The 911.356.064.01 seems to be just ’69 to ’71 E/S.
The 911.356.064.02 is ’72- T/E/S/Carrera2.7.
The 911.356.064.30 is ’72- T-K. What is this?

I would guess the .01 part doesn’t have the restrictor.
I would guess the .02 part might have the restrictor.
I don’t know what a ’72- T-K is. It might be the part for the ’73.5 CIS 911T They have separate stuff for the ’72- T-V carbureted engines.

Best,
Grady

[Early_S_Man]

The restrictor is located in the 7 mm ID line next to the 'Tee' ... in the hose that connects to the pump return line. Because of the length of the 'Tee' legs ... you would never see it after you cut off the crimp rings, unless specifically looking for it, since it is 19 mm deep [or so] in the hose! The restrictor is pill-shaped, approx. 7.5 mm OD and 10 mm long, with a drilled hole 1 mm in diameter in the center, with slightly rounded ends.

The only reason I found the restrictor is because I was investigating radial cracks in the 10-year old hose at the ends, and was curious as to the condition of the hose under the crimps ... so I used large wire cutters to trim the removed hose every 1/8" or so, and was quite surprised to find the restrictor! I would surmise that most of those '72 - '76 MFI 'Tee' hose assemblies have gone to the dumpster with the restrictor still hidden away.

[Superman]

Quite frankly, this place rocks. It doesn't just rock a little bit. It rocks bigtime. Years ago when we had a fraction of the membership here, it rocked just as much. We had Warren then, too.

[Grady Clay]

Thanks Warren.

OK, let’s review how this works.

The fuel pump is spec at 110 to 125 liters/hour at 11.8 +/- 3.0 psi. The fuel return (bypass valve) at the filter console determines this pressure. The safety pressure relief valve in the electric fuel pump opens at 28 psi so I don’t think it ever opens under normal circumstances.

While I have never cut apart a bypass valve, it appears to be a spring loaded pressure relief that opens depending proportionally on the differential pressure across the valve. It simply allows enough fuel to return to the tank to maintain 11.8 psi at the MFI pump, assuming zero pressure downstream. If the engine is using all the fuel the electric pump can supply and the pressure drops below 11.8 psi, no fuel is returned to the tank. When the engine isn’t using much fuel (at idle), the bypass valve is at maximum opening and is returning most of the fuel to the tank.

What puzzles me is the restrictor in the return hose limits the return flow at idle but does little for high power operation. The whole point on this fuel circuit is to maintain cool fuel at the MFI pump by circulating back to the tank – particularly at idle. The counter argument is that it possibly significantly raises the fuel pressure at low usage (possibly up to 28 psi) to prevent vapor flash at the MFI pump inlets.


I’ll propose another possible reason for the restrictor:
On fuel systems without the restrictor, when you first turn on the fuel pump prior to starting, there is a noticeable “burp” from the fuel tank as the vapors are purged from the circuit. I will speculate the restrictor simply reduces that noise at the EXPENSE of cooler fuel circulation.

What do you think?

Assuming a 11.8 psi pressure differential across the restrictor, what is the flow rate through the 1.0 mm restrictor?

Best,
Grady

[Zeke]

You two know all this, and postulate about backpressure in a circulating system, but off the top of your head you can't remember how many feet of which hose it takes to replace it all?

OK, now I don't want to know. I'm gonna get under there and yank it all out, find the "pill," and measure the hoses. That way I'll be able to contribute something here to this thread.

(BTW, over the years, I've had quite a bit to do with spray guns including a few airless systems. One set up I made was a circulating airless system so that what I was spraying couldn't sit and the particular pigment being used settle out. This is not a problem with a cup gun, especially with a couple of marbles in the cup. One of the things we found was that it was fairly important where the relief regulator was located along the circuit. I suspect the 1mm jobber downstream had a stabilizing effect on the flow. That's all I can do, suspect.)

[Grady Clay]

Milt,

No, in the shop a mechanic would take the bulk 20M roll of fuel hose and replace hoses and clamps. For that purpose there never was any reason to precisely measure the length of each hose although I’ll bet we had those numbers. For this exercise knowing the lengths is worthwhile.

Yea! You can measure all those hose pieces and we can have the definitive answer to the hose length question. I’ll go study the parts manuals and help. That is a common and important question.

I assume your ’71S has the fuel pump in the rear.

I’m going to ask you and others for some other measurements so we can spec the retro to the front pump location. Very worthwhile – hint, hint.

Best,
Grady