Louie928

I had the infamous in-tank fuel pump failure problem about 5 years ago in my '90 GT. The short hose broke and which allowed the external tank pump to ingest some debris which jammed the pump. I got a 170 mile ride home in the cab of a flat bed car hauler. I replaced both pumps and vowed that would not happen to me again. About a year after that incident, I damaged the 2/6 rod bearing and took the car out of commission to fix it. I am now nearing the point of installing the engine. I needed to drain the old fuel out anyway so I figured I might as well check that in-tank pump again to see the condition of the hose. It was broken. The hose had the tensile strength and elasticity of refrigerated Monterey Jack Cheese. The pump is about 5 years old. The car hasn't been driven in 4 years, and the hose is broken. Not a good scene. Sure, the gas was old, but I doubt that old fuel had much to do with the hose disintegrating just sitting there. The original hose isn't compatible with whatever is added to gasoline. Maybe alcohol. Maybe something else.


Here is what I found.
https://rennlist.com/forums/attachme...d=104717&stc=1
Broken hose 640x480.jpg

Since the pump was near new, I decided to fix the hose rather than replace the whole pump with another cheese type hose. Here is the result.
https://rennlist.com/forums/attachme...d=104718&stc=1
NewHose640x480.jpg

The original hose was 12mm inside diameter. 1/2" fuel hose (0.465" ID), 1.25" long, from NAPA fits tightly over the hose barbs on the pump and the external screw fitting. It has to be better at withstanding fuel effects than the useless original stuff. The clamps are Oetiker brand, 7/8" (20/23mm) size P/N 584-2991. They are the same as the original clamps. Regular screw type clamps are too big in outside diameter to fit through the tank hole. I think the spring type clamps would work too, or even plastic tie wraps. All you need is to be sure the pump and screw fitting doesn't separate. You need a 36mm socket to get the pump out of the tank. The seal between the pump and the tank is a square cross section "O" ring. A regular R28 size "O" ring does work for a seal too and is a lot easier to find. I'll be putting a filter between the in-tank pump outlet and the external fuel pump inlet to insure no foreign matter can get into the external pump if the hose come apart.

The stock in-tank pump with poor quality hose is a stalled 928 just waiting for an unpleasant opportunity to happen. I'd suggest checking yours before summer driving season is here.

borland

The hose is not the only part that's poor quality. If you saw the size of that pump's impeller you'd see the secondary pump is pretty worthless.

If I was up to doing it again, I'd delete the in-tank pump and install the strainer instead. You only need a couple gallons of gas for enough static head to prime the primary pump.

borland
90' S4, Slate Metallic

Louie928

That may be a good idea to delete the in-tank pump. Does anyone have any data to show if there is any total flow increase when using an in-tank pump vs. no in-tank pump? The in-tank pump doesn't need to pump appreceable pressure, just get a large quantity of fuel to the external pump inlet.

Jim_H

I could swear Jim B gave me a good reason for the intank pump but I can't remember what it was. As I recall vapor lock may have had something to do with it but I'm not sure why. The only time I haven't driven a Shark home was because of the intank pump... on three different Sharks, all low milers. Let me restate, the only time I haven't driven a Shark home because of mechanical problems...

I am not sure why but as H stated the other day stale gas may be the problem.

Chazz

Does the '87, '88 strainer assembly fit directly, without modifications, into the '89 in-tank pump access hole? It seems from this and other posts in the same vein, that the only risk to this retrograde modification is the possibility of a loss of some power when driving in high ambient temperatures with a low quantity of fuel in the tank. Against this, if the internal pump is retained, there is the risk of complete shutdown at any time - right?

Louie928

I beleive that's right. Possibly, on a hot day, and if your in-tank strainer is a bit clogged, the external pump may pull enough vaccum to cause the fuel to vaporize at the inlet to the pump.

Louie928

I think the anti-vapor lock fix is the main reason for the in tank pump, and not for increased fuel flow. I also think the pump rubber hose deteriorates much faster than usually thought. Maybe only having a safe life of three or four years. It appears to be made of different material than other fuel line hoses and has no woven braid inside. Could be that the stale gas rotted it faster than it should have, but I doubt it. The rubber hose on the outlet of the pump had stale gas in it and it's fine.

The only time I've had to be hauled home was the in-tank pump and a bad coolant pump (separated plastic impeller).

Nicole

Here is an interesting related bit of information from Jörg Austen's book:

In MY 89, along with adding the in-tank pum, the fuel lines were switched to "Polyamid" materials. They might have forgotten to make that change on their new in-tank pump. The defect on mine was ciscovered at around 70k miles, even though it had not caused any trouble.

Well, I hope the newer fuel lines are less likely to cause engine fires...

Garth S

My '88 has the in tank pump, but then, it's an 'euro': Believing this to be an inevitable failure, my long term plan has three paths ...

1) replace the hose as Louie has - but extend the hose to ~3"-6" along with the wires: why - I suspect that the 'wave' action of all that fuel wagging that pump back and forth on a puny 1" piece of hose is far more than the hose can take. Fatigue failure is the likely cause verses chemical degradation, as the bending radius of the assembly is pathetically short - so increase the working radius of the flexible coupling between the pump and flange. Also, a braided sheath would not hurt.

2) thread and/or braze a solid pipe coupling in place of the hose .... no flex!

3) Take the easy way out as Borland said .. use the screen/strainer: Our climate ( here) is quite temperate, so vapour lock is the least of my worries: it should be Sahara conditions or worse before cavitation would be an issue at the external pump.

Which to do ... probably won't know until I too get stranded: depends on how PO'd I am at the time ...

Apoc

When first purchased my 79 had a big problem, it would start fine when cold, and run well, but would NEVER hot start, it was finally tracked down to the in tank fuel pump not running. Sure I live in a hot climate, but 928's are sold around the world so I guess they just did a fix that would apply anywhere.

Steve

Jim_H

You will be PO'd, the failure only happens after purchasing a full tank of gas

Louie928

The in-tank pump fits in an anti slosh well in the tank. There isn't much room for a longer overall pump + hose length than the short hose. I think a solid tube attached to the pump and outlet fitting using either epoxy or urethane adhesive may be a solution. If the NAPA fuel hose gives me trouble, that will be the next step I'll take.

cfc928gt

Last fall both of my pumps failed on my '89GT. As far as I can tell they were original and the car had 65k miles on it. I expected to find the hose on the intank pump broken but it was in perfect condition. I was thinking of going to the '87/'88 single pump setup with just the screen in the tank but ended up replacing both pumps. I called the distributor of the intank pump and they said it was rated at 5-6 psi. I purchased it from Autozone because they sold it for $120 and it has a lifetime warrenty which I fully expect to take advantage of at some point in time. It is the exact porsche part and even has the porsche part # cast into it. It came in a Master Parts box, their part #E8165H.

SharkSkin

I have the strainer and dual external pumps... never a hint of vapor lock. IMHO the in-tank pump is only needed in the most extreme conditions, e.g. Saudi Arabia....

Bill Ball

Interestingly, the in-tank pump in my 89 was perfectly fine at 157K miles when I removed it last month. The hose was intact and very pliable. Strange how some are fine but most are bad. I replaced the pump anyway, just for good measure.

Flexing it back and forth, checking the hose, I managed to get the hose end to pop off the outlet, and it would not go back on securely. So, this thread is helpful since Louie pointed out the crimps are available from Napa.