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Old 07-17-2002, 11:12 PM
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Can you test an EHA?

Anyone know how to test an electrohydraulic actuator? Tech says it sounds as though I need one, but I hate to throw another $151 bucks at this thing on a gamble. He says it should draw 19 milliamps but even at that it could be bad.
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Old 07-18-2002, 07:04 AM
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Figure 4 shows a doable diyer setup. One multimeter with duty cycle on the left and another not so sophisticated multimeter on the right to measure current.
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Old 07-18-2002, 08:32 AM
Join Date: Mar 2000
Location: Gainesville FL
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I can't imagine anyone who knows the system issuing a statement like that ("He says it should draw 19 milliamps but even at that it could be bad).

The device has a resistance of which I have never checked as its not whats important.

Testing as done in the article verifies control! The EHA valve itself reacts to varying current flow by causing the programmed leak within to grow and fall. More current more fuel passing. To actually test this one must view system and lower chamber pressure. The difference between the pressures is caused by the programmed leak and is called differential pressure. Unplugged (EHA unplugged) differenial pressure is about .4bar. When hot and mechanically adjusted properly, closed loop control will have the leak raising and falling right at zero milliamps which is the same as being disconnected (zero current).

On a car that was failing I viewed a 60ma signal that increased differential pressure to about 1.4bar. The problem was corrosion in a connector that caused the control unit to cycle the cold starting control.

A -60ma signal generated by decel cutoff will drop the differential pressure to zero and stop the engine.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 07-18-2002, 09:52 AM
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Join Date: Aug 2001
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Steve, I printed your article on evaluation of engine controls but admittedly have not read it yet. When I got to the part about needing a DMM with a "duty cycle" I knew I didn't have one. I have a Beckman Industrial DMM but I don't see anything on it to indicate a duty cycle. Anyway, I have one on my must have tools list and will read the article then.
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