190E Fuel Injection/EHA
 

It appears that my 1985 190E has just consumed its third electo-hydraulic actuator in two years: Cold start stumble, no power past 1/4 throttle ( lean-out, backfire, etc). mA current values seem ok, water temp sensor a little pessimistic ( about 1k too high at 20C, system and control pressures spot on. I hate replacing symptoms, so what could be causing this early failure? Also, has anyone ever made their own injector testor?

EHA does only one thing. It is a controlled leak with a limited flow rate.

The way to evaluate EHA is to watch the differential pressure as the EHA current is altered. Total lambda correction of -12ma to +12ma can be viewed by first grounding the O2 sensor input and then grabbing the O2 sensor input with one hand and battery 12v with the other. the control unit sees 0.0v one time and about 1.5-2.5v the other. It causes the control to do the current changes and they will cause about a .2 bar total differential pressure difference one side to the other. (differential pressure should go from .3 bar to .5bar with .4bar being the 0.0ma position.

EHA Evaluation
 

Steve,

I understand the test as you've outlined it, having been a VW CIS technician many years ago ( CIS was VW's version of this Bosch injection system) However; if replacing the EHA makes the symptoms go away ( which it has twice before ) my original question remains: what makes the EHA fail? I sectioned the first failure and discovered that the o-ring that seals the adjuster had disintegrated and clogged the reed valve inside the EHA, keeping it from floating under the direction of the field coil that responds to the input current from the control unit. The replacement unit lasted about 3 months, as has the second replacement. I speculate on possibilities such as contamination/corrosion failures in the fuel lines, voltage spikes/drop-offs, and bad luck. Any possibilities that I'm adjusting the mixture for a weak injector and overloading the EHA, causing it to fail prematurely?