Porsche Enthusiasts Club Forum

Hi guys, I have a dilemma ... my 85 924 has been on sorn since 2004, and tucked up in the garage, it's been started and run regularly, but now with my imminent house move, it's got to be moved for an Mot and service. I'm finding it starts and runs when the fuel pump 'kill switch' is in the off position, and will run for about 20/30 seconds, when the switch is on, and the fuel pump runs, the car refuses to start, and petrol smell within the engine becomes strong as it appears to 'flood'... the pump can be heard pressurizing the pipes and stops as soon as you stop pulling the starter. As soon as the fuel pump is 'killed' by my switch, the car starts immediately on the turn of the key, and again runs on the petrol that has been sprayed into the manifold via the injectors... for again about 30 seconds... any suggestions please?

Hard to know without knowing who fitted this kill switch.

But, being a 924, I would be tempted to say it is not a kill switch, but a commonly installed "hot start fix switch", which is designed to add extra fuel via the cold start injector when used to overcome an issue with 924's suffering with fuel vapour in the injector lines and a lack of hot'ish start enrichment on 924's which caused many hot start issues right from when the cars were new.

So what I think is happening, is when you are using the kill switch, you are actually dumping extra fuel into the manifold via the cold start injector.

Hi john thanks for the reply, it is indeed a 'kill switch' I fitted it into the fuel pump 12 volt positive feed when I first bought the car, it completely isolates the fuel pump from power, seemed to be the ultimate anti theft/ anti driveway device I could think of when I first got the car... have never needed a hot start fix on this car, only once did I change the spring ball valve attached to the pump feed when I had a hot start problem many years ago.... it's been fine ever since. The keyswitch to switch off the fuel pump has always been part of my alarm/ imobliser system to protect the car.

In that case, the cause sounds like a warm up regulator which is causing very high fuel pressure, a fuel metering head which is stuck (or its valve) which is causing high fuel pressure at the injectors.

Problem is, to be sure, you really need to hook up a CIS system pressure tester to look at the control and system pressures to see what is going on, as well as checking out the other basics such as the spray patern and flow of the injectors at different fuel metering flap positions.

Yes I was starting to think that the 12 year old petrol in the pipes and metering head may indeed be gumming up the system... looks like it's going to have to be extracted from its garage and towed to my indie for rectification ....