Porsche 930 fuel injection service

Our team has been back at work for a few days since their well-earned Christmas break. The competition workshop continues with the 2-litre and Leaf Green ST builds shared in the Twelve Builds of Christmas and the service workshop has several 911 projects on the go, including this 1976 Porsche 911 Turbo.

This 930 has been working through a full restoration at Tuthill Porsche, including a complete bodywork refurbishment. We’re now into the running gear, which can be a sizeable task on early turbocharged cars that have been in storage or laid up for any length of time.

These cars run an early twin-pump fuel system supplying the vacuum operated Bosch CIS (or K-Jetronic) system, with mechanical fuel injectors in the cylinders. The injectors open at a preset pressure, atomising fuel into the inlet tract. The injectors work constantly above the preset pressure: they are not on/off as with later systems. These very fine injectors do not like long periods out of use.

Modern fuel left to go stale is notorious for gumming up the myriad small passageways in the Bosch CIS fuel injection system, so running issues are now quite common on Porsche cars of the period. This car’s history shows that it has had several attempts at repairing running issues over the years.

We dismantled the fuel delivery side of the injection system and sent it for specialist cleaning, and the mechanics are now putting it all back together, checking for vacuum leaks as they go. We’ll use Bosch pressure gauges to ensure the system is all working as intended, before road testing with our lambda probe to verify that it is fuelling properly across the rev range and not allowing the engine to run lean, especially when the boost kicks in.