1995 E320 Air injection pump not working, please help daignose
 

1995 E320 wagon. :confused:
I will try to organize what I have tested thus far please bear with me:
The air injection pump does not come on.
It is supplied power from the main computer along with the switchover valve. The pump does come on when jumped with 12v from the battery.
There does seem to be continuity to the main computer (the wiring harness is not bad)
The resistance of the electromagnetic clutch of the pump is ~3-4ohms
The Voltage at the pump connector (on cold start) is ~6v only when the swithover valve or ground location is disconnected!. Otherwise it is low (mv).
Questions: is 6v the pump supply voltage, could the switchover valve short the pump, could this be due to incorrect wiring of the new harness - any knowledgeable feedback would be appreciated!
thank You

The pump is only active during the first few minutes of operation following a cold start before the engine goes into closed loop operation in case you're not aware of this.

If it doesn't activate upon a cold start, warmup emissions will be higher. During emission tests, techs are supposed to visually check that the pump is properly configured, but I don't think any states require a functional test.

Duke

Give fuse #7 a twist...

thank you for the reply
It seems that the culpret is very likely the computer - I suspect that before the wiring harness was replaced the old harness shorted and caused problems with the computer. Thus the ~6v output to the pump.

That is why I mentioned the fuse .. a bad fuse contact would also read as low V
I also think you have a bad driver circuit in the ECU, but before final decision
on that , I would test for power again, but this time I would use Bat neg terminal for the test point of the meter neg lead .. this will eliminate the possibility of a bad ground at pump..
Do it with SOV unplugged. SoV and mag coil are in parellel

thank you for the prompt reply!
I did use the battery negative with the sov unplugged (and every other combination I could think of!) - so I think I'm out of luck. As for the computer, must the part number match or are they created equally for a 95 e320's (wagon)?
thanks again (please check my transmission slip post if you get a chance

Why buy a ECU just for the pump??

well, I would prefer the whole air injection system did not exist - but a check eng light is sort of a pain in the rear - especially if we were to decide to sell the car. It also makes my wife feel as though the car is not trustworthy. The cumputer may also be responsible for the upshift delay fault but I havn't figured that one out yet. Do you know any way to disable the air injection system so that it does not cause a fault?
thanks again

<<any way to disable the air injection system so that it does not cause a fault?
thanks again
>>

Can't be done
The ecu does a self test and looks at the 02 sensor to go way lean when the test is initiated ...so..that's that.