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1987 420 SEL
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2,090 Posts
Discussion Starter #1
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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AMG Forums Moderator
SLK55 (2006) C36 (1995)
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3,288 Posts
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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1991 300 SE
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18,534 Posts
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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Registered
1987 420 SEL
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2,090 Posts
Discussion Starter #4
I do get a hard start symptom sometimes. I'll have to look further into it. Thanks.
 

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1987 420 SEL
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2,090 Posts
Discussion Starter #5
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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1991 300 SE
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18,534 Posts
That’s it. Remember that if you replace it, it must still be adjusted to work correctly.
 

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1991 300 SE
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18,534 Posts
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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1987 420 SEL
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2,090 Posts
Discussion Starter #9
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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Registered
1987 420 SEL
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2,090 Posts
Discussion Starter #11
If the seal is leaking. Does it leak over the EHA valve? Or, could it be leaking from the injector housing? I started the car and then noticed that it appears the fuel is seeping over the black unit (EHA Valve)in a very small amount towards the outer edges of the valve.
 

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1991 300 SE
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18,534 Posts
The valve uses pressure variations to work.

From Steve’s article

“Positive current flows cause enrichened mixtures by leaking down the lower chamber pressure (higher differential pressure).�

The gas is coming out because it’s under pressure and the seal has failed. The loss of fuel and pressure in the system can cause poor engine performance – the EHA may be the weak link in the fuel system chain.
 

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1991 300 SE
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18,534 Posts
THX MBL...

“O ring seal (4)… Check, no fuel must run out with running engine.

Right on.
 

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1987 420 SEL
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2,090 Posts
Discussion Starter #15
So do you think I should try changing the seals first? In the instructions, are they referring to releasing the fuel pressure by opening the fuel lines? If not, what is the process to use to release the pressure? Just playing it safe. Thanks.
 

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Moderator
1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,283 Posts
Hi Prochambers,

In answer to your 1st two questions: Yes & Yes.

I'd always start with the simple stuff first. To quote Eddie: "Most likely it's the little gaskets inside. Open it up slowly (high fuel pressure) and inspect those little gaskets....... I had bad gaskets, but assumed the worst, so my old one is still here.

I think it natural to assume the worse if one is unfamiliar with a particular component or system. For example, I thought my 560 wiring harness had a short last Spring, as my bulb failure light had (to me) an intermittent problem (instead of a bad bulb). Then I read the manual and found the MB lamp has somewhat different operation than 30 years of Volvo experience led me to believe.[:0]

So, yeah, relieve the fuel pressure, and replace the little o-rings first. If the leak is gone, you're good to go. If the unit itself is bad, you'll know straight away.

Cheers, MBL
 

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1987 420 SEL
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2,090 Posts
Discussion Starter #17
That sounds like a good plan to me. I have some old rags in the garage to collect the spilled gas once I open those screws. Let me start pricing the gaskets now. They are only $1.70. The shipping is probably the higher cost.
 

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Moderator
1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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RE: EHA Valve O-Rings Shipping

Hi, it's me again,

Even so, the shipping could be less $ than the fuel to get to R & S Imports in Ft. Washington right near the confluence of I-276 & Rte 309.

http://www.rsimports.mercedescenter.com/mbcenter/b/index.jhtml

Cheers, MBL
 

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1987 420 SEL
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2,090 Posts
Discussion Starter #19
Thanks MBL. I'm closer to the MB dealer in Devon, PA off Rt. 30. I usually run over there at lunch time whenever I need to pick up something quick. I'll give them a call and see what's available.

http://www.mbofdevon.com/mbcenter/b/index.jhtml
 

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420 SEL
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223 Posts
I had the same problem with the valve leaking, I replaced the O ring seals first but still no good. I then replaced the valve assembly with new seals again and it worked fine. Very easy job just be careful of the small amount of fuel that sprays out when you first undo the 2 screws. Good luck....
 
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