Electric start valve problem

[944cabby]

Chaps, on my martini 924 the previous owner had disconnected the connector on the electrc start valve (on the inlet manifold) and crudely attached two wires to it which go directly to the battery to start the engine up when the ignition is turned on.
It has also been converted from points to electronic ignition.
She starts and runs ok by this method but when started you have to pull the wires off the battery for it to tick over correctly.
If i try and start her by reconnecting the electric start valve it just turns over and won't fire up.
Can anyone give me any idea where the wiring from this electric start connector goes to (ignition barrel?Fuse box?) so that i can try and trace the fault.
Also did the early 924's have guide tubes for the oil dipstick?There doesn't appear to be one on mine.
Thanks in anticipation,
Ade.

 

[924nutter]

Power directly from the ignition barrel just the same as the indicators. Disconnect the earth and route a wire to the thermotime switch plug. There are two terminals on the plug, the other should go to earth. The thermo time switch is at the back of the cylinder head below the oil pressure sender, and good luck reaching it. It is an absolute pig.

The principle of operation is this: as its name implies, the thermo-time-switch switches with time or temperature, but switches the earth return, not the supply. If the coolant is above 80 deg celsius, as stamped on the brass body, the earth is broken and the cold start injector will not function. If the coolant is below the switching temperature it allows the fifth injector to supply fuel for between 4 and 10 seconds to give extra enrichment for a cold start. The control pressure regulator, that rectangular block on the inlet manifold, piped into the metering unit, reduces system pressure when cold and thus the damping pressure on the airflow plate allowing a larger deflection for a given air flow. Fuel flow is directly controlled by the plate angle, so obviously a bigger deflection squirts more fuel in. Coming from the 944, it may surpise you to learn that the Bosch Jetronic on the 924 fuels all cylinders continuously, not sequencially like the 944, the fuel pooling behind the inlet valve when it is closed, and atominsing in the spray from the injector when it opens.
The camshaft has exactly the same valve timing as the carburettor 2.0 litre Audi 100 ( I have both the Audi and the 924 manuals) and is unusual to find the inlet valve opening so far before before top dead centre, about 46 degrees if memory serves me correctly; typically on the Golf and Audi injected units of that era the inlet only opens one or two deg before, so it is easy to understand my belief as to why the 924 struggles for economy, as the atomisation of the fuel is not particularly well optimised.

 

[geoff Ives]

Try www.porsche924-owners-club.co.uk/downloads.htm and look in the section for 'Hot start problem. It is worthwhile for any 924 owner to download this one.

 

[924nutter]

There should be a guide tube for the dip-stick. It is an interference fit in the block, and extends upwards to be supported against vibration by the triangular bracket, that itself supports the inlet manifold. It is secured to the top of that bracket with a "p" clip or cleat, call it what you will.