Purpose of EHA Valve - Mercedes-Benz Forum
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#1 (permalink) Old 03-20-2005, 03:40 PM
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Purpose of EHA Valve

I was looking over my engine bay yesterday and noticed that my EHA (Electro Hydraulic Actuator)Valve is leaking. What purpose does this valve serve? Here is a link to show picture:

https://www.autohausaz.com/membersonly/lookup_parts.cfm?SubcategoryID=6124&Qualifier=Fuel Distributor Pressure Regulator EHA Valve&CFID=630646&CFTOKEN=12660145

Any advise greatly appreciated!
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#2 (permalink) Old 03-21-2005, 12:13 AM
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RE: Purpose of EHA Valve

Most likely it's the little gaskets inside. Open it up slowly (high fuel pressure) and inspect those little gaskets. If it's the valve itself, i can lend you my spare to try it (or buy it). I had bad gaskets, but assumed the worst, so my old one is still here.

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Previously: 560 SEC RennTech/AMG (1990), 420 SEL (1987).
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#3 (permalink) Old 03-21-2005, 12:20 AM
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RE: Purpose of EHA Valve

This is from a February 2001 article by Steve Brotherton, an MB tech at Continental Imports from ImportCar online magazine.

“The EHA is the final servo device for applying the corrections intended by the control system. All forms of enrichment are accomplished by increasing the differential pressure within the fuel distributor. The EHA acts as a controlled leak depending on current. Positive current flows cause enrichened mixtures by leaking down the lower chamber pressure (higher differential pressure). Negative current flows cause lean mixtures and, on deceleration, a negative 60ma causes fuel shut-off.�

As you can see if the valve is sticking, damaged,leaking, or otherwise not working correctly, the adjustments needed for the engine to run smoothly are not taking place which may result in a rough or high idle, hard starting, stalling, and poor acceleration.
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#4 (permalink) Old 03-21-2005, 08:33 AM
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RE: Purpose of EHA Valve

I do get a hard start symptom sometimes. I'll have to look further into it. Thanks.
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#5 (permalink) Old 03-21-2005, 09:59 AM
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RE: Purpose of EHA Valve

I noticed that it seems that the leak is coming off the top of the EHA Valve. Maybe it's seeping up and coming back down onto the black cover seen in the attached picture.
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#6 (permalink) Old 03-21-2005, 12:00 PM
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RE: Purpose of EHA Valve

That’s it. Remember that if you replace it, it must still be adjusted to work correctly.
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#7 (permalink) Old 03-21-2005, 12:05 PM
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RE: Purpose of EHA Valve

Who does the adjusting?
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#8 (permalink) Old 03-21-2005, 12:14 PM
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RE: Purpose of EHA Valve

I mechanic can, I guess – someone else may know as I’ve never done it – I recall reading somewhere about the adjustment while searching for your answer. As eddie noted above, if only replacing the seal, assuming the actuator is working otherwise correctly, perhaps the adjustment will not be needed – in other words, you’re just replacing the seal, not the entire unit.
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#9 (permalink) Old 03-21-2005, 01:16 PM
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RE: Purpose of EHA Valve

I guess i'll leave that up to someone who actually has the proper equipment to make the adjustments. Besides, I don't like messing with gasoline like that anyway!
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#10 (permalink) Old 03-21-2005, 02:32 PM
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RE: Purpose of EHA Valve

Good idea – so you’re going to just have the seal replaced?
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