K-Jetronic Troubleshooting Basics

K-Jetronic Troubleshooting Basics

>My 81 Euro 928 is very hard to get going in the mornings. Almost seems to
>flood then takes after about 10 attempts to start. Churns for ages without a
>hint of firing.

Your '81 Euro should have K-Jetronic CIS injection.

First, don't automatically assume it is the fuel system. Check for vacuum leaks. Is the spark strong? If the spark is weak, check: wires, coil, distributor cap, spark plugs.

If you don't have the test equipment and understanding of the K-Jetronic system, find a mechanic that does (even better if they also know the 928). The K-Jetronic system is pervasive among German autos, so Mercedes or VW mechanics should be able to service the system. This info would help them.

Good luck,
'93 GTS

Per the Porsche Workshop manual, the fuel system testing is:

a. Fuel pump rate: at least 1120 cc/30 sec. (have you changed the fuel filter?)

b. Control Pressure "Cold" for warm-up control (p/n 928.606.109.05, Bosch p/n 0438.140.087): proper operation is a linear rate of vacuum as follows:

Maximum vacuum: 1.4 bar (kp/(cm x cm))at 10C ambient up to 3.2 bar at 40C ambient.

Minimum vacuum: 1.0 bar at 10C at 10C ambient up to 2.9 bar at 40C ambient.

c. Control pressure "Warm:"

Test with pressure (without vacuum) 2.8 to 3.2 bar

Connect vacuum pump for test on intake pressure connection of warm-up control. Test pressure 460 - 600 mbar (350-450 mmHg): 3.4 - 3.8 bar

d. System pressure: testing value: 5.2 - 5.8 bar, adjusting value: 5.3 - 5.5 bar

Leak test (engine warm)

Minimum pressure after:
10 minutes: 2.7 bar
20 minutes: 2.6 bar
30 minutes: 2.5 bar

e. Fuel injectors opening pressure: 3.0 - 4.1 bar

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