[928uk] S4, GT and GTS engine U-bend fuel hoses

Tue Feb 14 17:46:13 UTC 2023

Unfortunately Martin, even a reputable company like Cohline make rubber hose with cheap steel braid, as well as with stainless steel braid, and an available replacement 928 U-bend hose that is being sold on the Internet uses the Cohline steel braided hose ☹

A typical AN-6 teflon tube with 8mm ID and stainless steel braid has a minimum bend radius of 62mm, so needs 124mm across the U-bend. It just doesn’t work in this tight U application. If there is an affordable U-bend solution using teflon lined tube that has a minimum 7mm inside diameter and meets the tube manufacturer’s minimum bend radius requirement I’d like to hear about it.

Another issue with the U that I didn’t mention is that the original Porsche end fittings are not 90 degrees, they are custom bends, with one being more than 90 degrees and one being less than 90. This is so that the U will be positioned to fit into the small gap between the accelerator cable pulley and the MAF. Aftermarket hoses with new 90 degree fittings can’t achieve this positioning so even with an aftermarket U hose the original look cannot be maintained. If the U-bend has to be in a different position, there is no longer any point in having a U-bend.

Best regards, 

Jonathan

928 GT 1991 Amethyst Metallic

From: Martin Dunks <m.dunks at googlemail.com> 
Sent: 14 February 2023 17:15
To: jonathan at rackowe.net; 928 List <928uk at lists.928.org.uk>
Subject: Re: [928uk] S4, GT and GTS engine U-bend fuel hoses

With regard to real braided hoses rather than braided rubber cheap lookalike stuff, if anybody wanted to keep the U look, they are made from stainless steel,  so won't rust & will be 100% compatible with ethanol/methanol as they are Teflon lined, not rubber.

A suitable heat shrink wrap added would solve any unwanted braided look.

On Tue, 14 Feb 2023, 4:08 pm Jonathan Rackowe via 928uk, <928uk at lists.928.org.uk <mailto:928uk at lists.928.org.uk> > wrote:

Many of you will be aware of the notoriety of the U-bend fuel hose at the
rear of the 32V engine in 928 S4 and GTS cars, a hose which has been
reported to cause engine fires if it fails.

As my 928 GT is now over 30 years old, and we all know that rubber hoses
deteriorate with age, I have been keen to replace this fuel hose for some
time, but unfortunately the part is NLA (No Longer Available) from Porsche.
There have been replacement parts available from suppliers in the USA, and
originally I considered buying one of those, but investigating further I
found that they are either very expensive, having been developed for racecar
applications, or are fairly low quality. I wanted a hose that met DIN73379
type 3E for 100% compatibility with biofuels so that it would be
futureproof, and I didn’t want a steel braid on it which would rust and
prevent me from inspecting the rubber hose. I noted also that parts from the
USA attract import fees and VAT making them even more costly.

The original Porsche 928 hoses were made by German hose manufacturer
Cohline, so I decided to work with a UK supplier of Cohline parts to develop
a high quality replacement hose that I would be happy to put on my own 928
GT. I’m pleased to say that I now have the resulting hose fitted to my 928
GT. The cost was just £35 delivered and if anyone is interested in seeing
pictures or obtaining this Cohline hose for their own car please send me an
email.

For those interested in the issues developing this part, the biggest problem
with the original U-bend fuel hose is the U-bend itself. With just 80mm
approx between the Fuel Pressure Regulator (FPR) and the rear fuel damper,
the U-bend is really sharp and results in a bend radius that is less than
the minimum specified by Cohline for suitable hoses. The possibilities of 90
degree end fittings and smaller diameter hoses with lower minimum bend
radius were discussed, but dismissed because restriction of fuel flow would
be undesirable. Similarly, a straight hose or even a solid fuel line,
between the FPR and damper was investigated, but the two connections at FPR
and damper are nothing like aligned, and it would be necessary to loosen a
fuel rail and the FPR or damper just to fit the hose. The solution we have
come up with is a 360 degree loop with sufficient hose length to satisfy the
minimum bend radius specified by Cohline. The part is made with latest spec
DIN73379 type 3E rubber hose and Cohline end fittings with professionally
crimped sleeves. I’m selling these new fuel hoses on ebay for £38, but happy
to supply them for £35 delivered (in the UK) to anyone on the 928UK list
that wants one.

BTW, the short fuel hose at the front of the engine between the fuel rail
and front fuel damper is still available from Porsche, but inevitably they
will run out of those someday, so if you haven’t yet replaced that one I’d
suggest buying one from Porsche while you still can.

Best regards, 

Jonathan

928 GT 1991 Amethyst Metallic