944 Tech

H20.....Oh No!

by Steve Grosekemper, San Diego Region

As a Porsche technician, quote I hear with some regularity is "I went out to the car this morning and it just wouldn't start." But, when I heard it from two customers driving the exact same cars, on two consecutive days, I thought it odd.

The cars in question were 1986 Porsche 944 Turbos. The problem we discovered after a short diagnosis was that the DME (Digital Motor Electronics) computer had failed. The computer was receiving all the right signals from its sensors as well as getting the required voltage; however, it was not sending any impulses to the injectors or to the coil.

When we find a failure such as this we like to know the reason for the failure so history does not repeat itself. The investigation into the DME  failure was a short one. Upon removal of the DME we noticed a leak, not from the car, but from the computer. Computers are like cats, they hate getting wet!

The computers (Turbos have 2) sit in front of the passenger foot well, which is right below the battery. What had happened to these two cars was their battery trays had rusted through. It rained on Monday, the cars came in on Tuesday and Wednesday respectively.

What we wanted to know at this point was why they rusted through, and what can be done to prevent this extremely expensive failure in the future. So up to the battery tray we went to continue our investigation. What we found resembled a compost pile! Wet decomposing leaves and dirt had formed a paste and clogged the water drain that normally keeps the battery tray clean and dry.

Because the water could not escape it mixed with the normal battery acid and etched its way through the metal.

Prevention would be simple: Don't park under trees, and do rinse out the battery tray vent when you wash the car!

If the tray is rinsed out regularly, no debris will be able to clog the drain and your computer, like your cat, will stay dry and happy! 

Good luck!