EHA Valve - Mercedes-Benz Forum
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#1 (permalink) Old 03-22-2010, 03:44 PM
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EHA Valve

How many volts should I be getting at the plug to the EHA valve and the cold start valve on my 1988 190E 2.3? The car was hard to start and would not idle, so I purchased a new eha valve. Thr problem persists so I checked the voltage at the plug. the eha valve plug reads around 4 volts and the cold start valve plug voltage reads around 6 to 7 volts.
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#2 (permalink) Old 03-23-2010, 08:23 AM
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You need to measure current going through the EHA, not voltage!
The cold start valve isn't going to be an issue in terms of idling but it does have a role in terms of rough start.
If I were you, I would actually check the OVP's fuse or simply replace the OVP all together. In my book, it's a maintenance item with a life span of a few years even if the fuse looks good. If the OVP (or fuse) is fubar your car will have a hard start and will die as soon as you start it. If you manage to keep it alive it will eventually stall the car at random.
At this point don't waste your time measuring devices until you replace the OVP. You need proper voltage and in a steady delivery mode before you can even conclude that the EHA is bad or cold start valve has issues. Besides not getting proper voltage to these devices does not mean the devices are bad, it's whatever delivers power to these device that should be suspect.
It will not hurt to check your voltage regulator, heck actually replace that one since it too is a maintenance item, and so is your battery.
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#3 (permalink) Old 03-23-2010, 01:30 PM
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Is there a way to jump your OVP relay im sure its not suggested to check if it is bad


YOU CAN RUN BUT YOULL ONLY DIE...TIRED!!If you insist on driving blind and deaf to the obvious warnings coming from under your Mercedes' hood, the next sound you hear may be a rapping or knock noise from the rod bearings - which will eventually be followed by dead silence as your engine seizes and your Mercedes coasts to a dead stop.LOL
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#4 (permalink) Old 03-23-2010, 01:36 PM
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I wouldn't jump the OVP because:
1. You will have to look carefully at the OVP switching side to figure out the jump pins
2. You must maintain a specific voltage between another set of pins that the Zener diode inside the OVP is supposed to do.
Too much to do at once.
If you suspect OVP, replace it!
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#5 (permalink) Old 03-23-2010, 01:56 PM
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mine is brand new last year tho..


YOU CAN RUN BUT YOULL ONLY DIE...TIRED!!If you insist on driving blind and deaf to the obvious warnings coming from under your Mercedes' hood, the next sound you hear may be a rapping or knock noise from the rod bearings - which will eventually be followed by dead silence as your engine seizes and your Mercedes coasts to a dead stop.LOL
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#6 (permalink) Old 03-23-2010, 02:21 PM
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Originally Posted by panzerbenzer View Post
mine is brand new last year tho..
then check the fuse or how it's seated.
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#7 (permalink) Old 03-23-2010, 02:29 PM
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I just had a very hard starting problem and no power on take off on my 1990 190e 2.6l. I found 1 of my fuel pumps dead and after replacing that still the same problem but I now had 80 pis fuel pressure at the upper and lower chambers of the fuel dist. I checked the OVP relay fuse good but green crap inside and only 1.5v coming out on red/blue wire. I tested the cold start injector with a noid lite and it would not lite so I replaced the OVP relay and now the cold start injector is trigging and now I have power and running again.
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#8 (permalink) Old 03-23-2010, 02:46 PM
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My Snapon vantage says the EHA works on ampsto control fuel. Tech notes sayscommon for the valve to leak,stick mechanically, may cause hard start cold, hesitation, and stalling. do a resistance test with valve unpluged. test leads across valve. 19.50 ohm. (+/- 1.5 ohms) ( I had my EHA valve start leaking from the small hole between the 2 " O" rings last year and found a use fuel dist with the EHA valve on EBAY for $85.
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#9 (permalink) Old 03-23-2010, 02:59 PM
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The amp test for the EHA valve is like this. 1. Disconnect EHA connector and install harness adapter for current testing, Harness adapter is available from Mercedes Benz. 2. if adapter is not availableit may be possibleto use jumper wires to connect meter for current testing. KOEO, Control current should be positive 50 mA, If negative, reverse test leads and continue. KOER with engine at normal operating temp and fuel system in closed loop, check EHA current, EHA current should be fluctuating between a range of 4 and 16 mA. This test is from the Snapon Vantage. ( I would first test the voltage out of the OVP relay first to make sure that the OVP relay is working . the OVP supplys voltage to a lot of control devices. )
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#10 (permalink) Old 03-23-2010, 03:21 PM
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Also current to EHA increases or decreases allowing mixture control in respose to H02S signal.
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