Thursday, January 22, 2009

Porsche 924: sputters but won't start

This seems to be a common problem with the early 924's. You turn the key, the engine turns over, but all you get is a sputter but the engine won't run. Thankfully, there is a common answer to this problem. But before looking at the answers, you have to understand the way the 2.0 liter engine is designed to work.

During all start conditions, cold or hot, the thermo-time switch provides ground to the cold start valve, and the ignition switch provides battery voltage to the other side of the cold start valve for as long as the ignition switch is held in the start position. As long as both the ground and the battery voltage are applied to the valve it will remain open, and spray extra fuel into the intake manifold. This extra fuel is necessary to aid in starting the engine.

During a cold start, the time the ground is supplied by the thermo-time switch can be as much as ten seconds. After that the thermo-time switch "times-out," and the ground is removed. Even if you continue cranking the engine after the ten-second time-out period, only battery voltage is supplied to the valve, the ground is removed. Without the ground, the valve will close, and the extra fuel flow is cut off. This is to prevent flooding of the engine. After the thermo-time switch has cooled down, the ground is once again applied to the valve during cranking, and the normal start cycle is in place.

Hot Start Problem Fix by David Russell

With that in mind, it would make sense that one of three components would be the culprit: the thermo-time switch, cold start valve, or any of the wires/connectors. Checking the wires and connections would be the easiest fix. But if the switch or valve needs replacing, you'd better have a few dollars ready. The following table shares the cheapest prices I could find as of 1/23/09.





Thermo-Time Switch


Auto Barn


Cold Start Valve


Auto Parts Way


But who am I? I'm no technical genius of a mechanic. But there are plenty of mechanics who have willingly offered helpful tips about this problem. And hopefully, their advice will help you solve the problem.

Hot Start Problem Fix by David Russell
Porsche 924 poor idle from cold by Dave Ward
My car won’t start/won’t run when it’s cold!

And if you don't have the manual, check out the picture and diagram available here on page 4.

1 comment:

dad said...