DaveK

This morning, on the way to work my car stalled. What happened was :

I exited the motorway and came to the end of the slip road, where there are two lanes to turn right and there was a queue in each lane. I stopped in the right hand lane - but then decided to move to the left lane which simply meant swinging left and moving forward about one car length. As I stopped (probably braked quite hard even though I wasn't moving all that fast) the car stalled.

The car was probably 80-90% of fully warm at that point.

When I got to work, I tried to replicate this in the carpark by moving forward a few metres and then braking. I managed to make it stall once in about 10 attempts. About half the other times, it didn't stall, but the revs did drop to about 500rpm and then bounce up to about 1200 before settling to steady idle.

Idle is usually rock solid - although I do rarely get what feels like a split second hesitation at a steady motorway speed (although it's not done that for over a month).

I've had the car about 6 months ('02 car with 28k miles on it now) and have wondered if my coil packs might need replacing.

Could that be the cause - or any other ideas?

Macster

From my reading UK Porsche forums a UK Porsche always need coil packs...

Seriously, that is not a coil pack failure symptom I'm familiar with.

One thing that jumps out at me is this occurred under some braking which causes me to suspect fuel level in the gas tank.

I won't go into detail but the tank is a rather Rube Goldberg-like contraption that has an odd shape that IIRC at half tank and lower has the tank divided into two compartments, basins might might be a better description. These are not directly connected not at their lowest points at least.

Because they are not directly connected at their lowest or very low points, at some fuel level the two basins can't share/mix fuel. Special fuel lines that direct some output from the fuel pump run into each basin and by some siphoning effect manage to extract fuel from the basins with the end result the full capacity of the fuel tank including the considerable amount represented by these two basins is utilized.

However, I could see with this setup considerable agitation of the fuel remaining the basins is a side effect -- the lower the fuel level the more agaitation likely -- and under some conditions the fuel might get a bit aerated and if any "bad gas" exists or a bit of water this gets agitated into the good gas with the possibility a bit of air perhaps, bad gas or gas with a few fine/tiny drops of drops of water in it gets ingested with the result the fuel supply is momentarily interrupted and the result is what you felt.

(I have experienced total engine cut off -- not with my Porsches thankfully -- when I was driving a vehicle with a low gas level and rounded a sharp corner. Some water in the gas tank -- a rather common thing at least when tanks were steel (and this one was) -- was ingested by the fuel pump and made it to the inline fuel filter located in teh engine compartment. This fuel filter's housing was transparent and upon close examination I noticed a few tiny drops of rusty colored water on the filter element. This filter element had an affinity for the water which then blocked the flow of gas through the filter. I had the filter blown out with air and after installing the filter the engine started up and then I filled up the tank and never let it get that low again.)

Porsche does caution against hard cornering with low fuel level and perhaps the level was just low enough that the hard braking sufficient to somehow result in a brief interruption in the supply of gasoline to the engine?

One possible test would be to fill the tank and try to reproduce the symptom. If you are unsuccessful then low fuel level played a role.

If the symptom appears with the tank not low...then something else the cause.

Sincerely,

Macster.

DaveK

I'd say fuel level is a good guess - because it does only seem to behave this way if I pull away just for a few metres and then stop quickly. However, I have about 75% full tank at the moment, so it would be hard to explain this time.

I just checked the fault codes with durametric and nothing has been logged. I'll have to see how it goes - at the moment, it's clearly not something that's easy to reproduce. My other car is going for a service on 10th May, and it's likely the turbo will come along for the lift back. So I'll get the mechanic to take a quick look then.

Macster

75% full gas tank is a pretty full gas tank and if the symptom arises from fuel supply the momentary interruption of it or just the inclusion of air which can see the fuel pressure perhaps drop enough the fuel delivered by the injectors is less than the Ecu allows for. The amount of fuel delivered by each injector very dependent upon fuel pressure and length of time the injector is open.

Have you recently run the gas tank level down to under 1/2 tank, or better yet, even lower and upon refill confirmed that the tank accepted 1/2 tank's or say even 3/4's tank of fuel?

The reason I ask is there possibly is a condition where the fuel tank pickup is acting up and even with some fuel showing the fuel pick up may be sucking air, so to speak, once in a great while under some special conditions and a hard acceleration followed very quickly by a hard brake may just be that special condition.

But I'd not tear into the gas tank and fuel supply system unless you had more indications this activity warranted, more to go on than my suspicions and theories.

It will be interesting to learn what your mechanic thinks about the symptom and the possible causes.

Sincerely,

Macster.