1971 911 E Problem

[jerpetrella]

Need help diagnosing new problem...
Drove car today for 40 minutes then all of the sudden the engine at stops, won't idle, it just dies. Has fairly new tune up and fuel system is completely rebuilt.
Any diagnosis would be appreciated.

Thanks,
Michael

[Grady Clay]

Michael,
First, WELCOME to the Pelican Forum
You will find a lot of help here.


Your (non-) running issue sounds suspiciously like a debris-in-front-filter issue.
There is a screen filter element as part of the fuel pick-up fitting assembly in the fuel tank.

This filter can become clogged with fuel debris over the years.

The correction is to remove the filter fitting from the fuel tank and clean it.
This is also an indication of debris in the fuel tank and should be cleaned out.

This is all relatively ‘normal’ service for your 41-YO model. (Mine is older. BTDT)

Again, WELCOME.

Best,
Grady

[Trackrash]

I would check for spark. The CD unit makes a high pitched whine when active. I have had the fuse for the ignition go bad which left me stranded. The CD units are also prone to failure. I had a CD unit that was intermittent, not fun.

[Matt Smith]

Hi Michael, welcome as well.

I'm chasing a similar problem that rears its head after about 30 mins. Thanks Grady for something new to look at as I think it's about time to address fuel delivery at the tank (and lines) as well.
There are so many things to consider with a 40yr old car. It was a lot easier when I drove it daily and it never let me down!

[tpickstone]

Me too - My '69T which has Webers and no CDI box starts and runs fine and then after about 1/2 hour just simply dies, as if it's out of gas or spark. This happens as I am driving up and down my road testing it and I have to leave it, walk home and after leaving it all day it it will start up again and I can make it home but it's usually not happy - dying if I let the revs drop. I have disconnected the fuel line after the filter and the aftermrket pump pushes fuel though at a steady rate.
I too will look at that fuel pickup and if I find anything out I'll report back. Thanks Grady!

[Grady Clay]

Guys,

There are two easy tests:

First is to plumb a ‘Tee’ in a fuel line near the carbs or at the MFI fitting on the fuel filter console that points to the rear of the car.
In either case this is on the engine side of filters.
Use a very long hose to a mechanical pressure gauge - ~5 psi for carbs, ~30 psi for MFI.
Make sure there are absolutely no leaks or ‘seeps’ with the gauge in your lap.
This allows you to monitor the fuel pressure while driving and experiencing the problem.

The other is to plumb the same long hose from the engine compartment (after all filters) forward to the fuel fill on the fender.
With the fuel pump circulating fuel for a while, time the flow into a container.
Spec for MFI is 1800-2000 ml/min. Carbs can be a bit less – fuel pump type dependent.

That screen filter is a common issue.
It is also one of the often neglected maintenance items.

When servicing the screen filter, siphon the gasoline via the fuel level sender.
You will need a new gasket at the fuel level sender. The original gasket was a cork VW part (113.919.133). There is an up-date neoprene Porsche part available (900.028.007.02).

It is not uncommon to find that someone had taken a long screwdriver and destroyed the screen filter in order to get the 911 to run.
If you find this, replace the screen filter with the original brass 911 version, not the plastic 914 version.
The brass screen filter fittings are 901.201.032.01 with 6 mm outlet to fit 7 mm hose and 901.201.032.02 with 8 mm outlet to fit 9 mm hose.

The aluminum sealing washer for the screen filter fitting is 900.123.001.60 Alu 22x27 DIN 7603-VF.

Always use the Norma-Schellen clamp-type fuel line clamps.
The worm-screw type hose clamps will damage the hose.
This is critical with MFI fuel pressures.

Best,
Grady

[beh911]

A straightforward check of your tank's internals is to remove the fuel level sender from the top of the tank and shine a light down there. You will know pretty quickly how bad the debris situation is.

In other words, if you work from the bottom of the tank and remove the intake sleeve to clean it, you may end up doing this repeatedly as the sock will become clogged over and over again after a certain amount of time.

If your tank is as bad as mine was (original tank in ex show car that hardly ran for a couple decades), you will need to have it cleaned or else find another tank.