911T 2.2 power loss when crusing at 90

First of all Hi, second yeah I live in Belgium so don't wory aboutthe 90mph cruising.

My problem is that the car runs perfectly well in town, and on winding single lane highways. I only have a problem when cruising on a three lane highway at speed, when the fuel guage drops below 2/3 full!!

The car will slowly loose power and speed, and then cough and splutter to a halt. After a minute at the side of the road everything returns to normal!

This appears to be due to fuel starvation. Even though my local specialist has fitted a new fuel pump the problem persists.

Can it really be due to a problem in the fuel tank?

Any suggestions will be gratefully received.

Thanks.

Nick,

Yes, I think it can be due to rust in the fuel tank!

Does your car have a fuel filter? If it does, replace it, and cut open the old one to find out whether or not it was full of rust to any extent. If you find more than a minimal amount of rust, then the following scenario could/should explain your problem.

The problem that may exist in the fuel tank is that there is a very fine brass 'strainer' screen, cylindrical in shape, mounted coaxial to the steel fuel line, clamped in place by the large aluminum hex nut around the flange/header at the outlet to the tank. The strainer is in the form of a long cylindrical tube, about 2 cm in diameter and 10-12 cm long, sticking straight up into the tank. If the tank has a large amount of rust in it, my suspicion is that as long as there is sufficient fuel, say above 1/3 tank, the rust is continually sloshed around and dispersed enough to allow sufficient flow into the tubular brass screen filter ... but when below 1/3 tank the fuel in the 'well' at the bottom of the tank becomes more densely contaminated with rust particles in suspension, that the flow capacity of the partly clogged fine brass screen filter is not sufficient to keep up with the Weber or Zenith carburetors' float chambers demand at a 90 mph speed.

If you find rust in the fuel filter, have the fuel tank drained by removing the aluminum nut around the fuel supply outlet, remove the steel supply line, and the brass screen. Then, flush out as much of the rust as possible. Remove the fuel tank ant take to a local aviation shop and see if they can treat and seal the tank. There are special compounds just for treating rust in the fuel tanks, and aviation mechanics do it all of the time because of the special problem it presents to private aircraft operation ... your stalled engine problem ... equals a crashed airplane if it happens in the air!

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Warren Hall
1973 911S Targa


[This message has been edited by Early_S_Man (edited 09-03-2000).]

If rust and clogged fuel filter are not the cause, perhaps the tank venting system has failed? (i.e. - maybe pulling fuel out of the fuel tank is incorrectly causing a vacuum in the tank.)

Here in the USA, a fuel tank is vented through a charcoal canister which is supposed to capture fuel vapors to prevent them from escaping into the atmosphere. If the canister is plugged or the hoses to it are crimped, you would have a gradually increasing vacuum which would eventually starve the engine.

You could test this theory by removing the gas tank filler cap and leaving it off during your next 90 MPH cruise (don't try this when you have a full fuel tank, however).

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Bob Thayer
1971 911T
rthayer@hdrinc.com