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Of all the Bosch systems,the KE Jetronic may be the most confusing to troubleshoot.The system combines electronics with mechanical fuel flow control.An analysis of driveability symptoms may point to either a mechanical or electrical problem,or not distinguish between the two.What follows is a logical sequence for analizing any driveability problem.

Verify Engine Condition

Run a compression test and/or cylinder leakage test.Check the valve adjustment and camshaft condition.Then verify the condition of the ignition system.If all of these test okay,then check the injection system.

Test Fuel Pressure

As in all fuel injection systems,any thorough system test must begin with fuel pressure.Connect a pressure gauge between the cold-start valve and the port on the lower chambers of the fuel distributor.Disconnect the electrical connector on the electrohydraulic actuator.Then activate the fuel pump.The pressure indictated should be between 75 and 82 psi.

If the pressure is too low,check the fuel pump volume.The pump should be able to deliver 0.5 gpm (gallons per minute) or more.If the volume is low,check the fuel filter and the line for kinks.If the pressure is low but the volume is acceptable,replace the system pressure regulator.

If the fuel pressure is high,disconnect the return line from the system pressure regulator and repeat the test.Ensure that the fuel from the regulator is captured in an approved container.If the fuel pressure remains high,replace the pressure regulator.If the pressure drops,clean or repair the return line.

The next step is to measure lower chamber differential pressure or the difference between the pressure in the lower chambers of the fuel distributor and system pressure.This measurement is done in two steps.The first step is to simulate pressure in the lower chambers with no correction based on engine temperature and exhaust oxygen.

Disconnect the electrical connector on the differential pressure regulator and close the valve on the pressure gauge.Activate the fuel pump;the differential pressure should be between 2.9 and 7.0 psi.If the pressure does not meet these specs,disconnect the return line from the lower chamber of the fuel distributor.A volume of approximately 5 ounces per minute should flow through the return line.If the pressure is wrong but the flow is correct,replace the differential pressure regulator.If the flow is incorrect,replace the fuel distributor.

If the first part of the test yields the correct pressure,then reconnect the differential pressure regulator with an ammeter in series and proceed with the second part of the test.The second step is to simulate the differential pressure of a cold engine.Disconnect the coolant temperature sensor and place a 15,000 ohm resistor across the terminals.Activate the fuel pump.Differential pressure should be between 10.0 and 17.5 psi.The ammeter should read between 50 and 80 milliamps.

If the pressure is wrong but the current is correct,replace the differential pressure regulator.

If both the ammeter and pressure readings are incorrect,check the resistance through the differential pressure regulator.If the resistance is greater than 21.5 ohms or less than 17.5 ohms,replace the differential pressure regulator.

If the resistance reading is correct,check the ECU power and grounds.Also check the ground for the temperature sensor.If these are OK,replace the ECU.

Test Rest Pressure

Rest or residual pressure is a measurement of the KE systems ability to retain pressure after the engine has been shut off.Open the valve on the pressure gauge and energize the fuel pump for about 30 seconds.Shut off the fuel pump and monitor the pressure for 10 minutes.The pressure should not drop below 38 psi.If the pressure drops too low,remove the differential pressure regulator and inspect the O-rings.If the O-rings are functioning properly or the pressure continues to drop when the test is repeated after replacement,pinch off the system pressure regulator return line.Repeat the test.If the pressure holds,replace the system pressure regulator.If the pressure still fails,replace the electrohydraulic actuator.

Test Injectors for Equal Flow

The injector equal flow test is an effort to determine how much contamination or restriction there is in the injectors.Remove the injectors from the intake manifold leaving them attached to the fuel lines.Place the nozzle of each injector in a graduated cylinder;energize the fuel pump.Push down on the airflow sensor plate.Flow the injectors for 30 seconds and let go of the plate.The volume should only vary 10% for all the injectors.

Replace any injectors that flowed 10% less than the rest of the injectors.

A helpful reference for troubleshooting:

Bosch Fuel Injection and Engine Management by Charles O. Probst

http://www.amazon.com/exec/obidos/tg/detail/-/0837603005/103-7517399-0753439?vi=glance#reader_0837603005