What does this piece do? Mine began leaking fuel a while ago and I thought it was just the o-rings, so I replaced them and weeks later the leak was back. Today I went out and bought 2 of them used and I noticed there is a flat screw on the back. I decided to unscrew it on the one that I was replacing to see what it was, and nothing....Is that just a screw or does it control something?

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1990 190E 3.0L

the eha modulates pressure so the system can react to the o2 sensor. that screw is the base setting and, if adjusted, is done in VERY SMALL increments. like 1/16 turn. the leak is coming from the around the pins and you need a new eha. good luck, chuck.

Yeah I got the new eha....2 of them, and I swapped the leaking one out already. How would I be able to tell just by driving if the screw needs adjusting, also, would the eha give a cause to fail a smog check?

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1990 190E 3.0L

Yes it can if the internal diaphragm is broken or nonfunctional....

A brand new EHA requires no adjustment. I checked pressures immediately when I installed my new one and it was dead on spec. So leave it alone!!!

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

just to add-when i said new, i meant new in the box, not different used 1s. good luck, chuck.

I bought 2 used ones. Now here is the issue I just ran into today. My CEL came on and gave me 17 flashes, which is something to do with the O2 sensor not reading or something to that effect. I'm guessing its the EHA I put on. Any way to rectify this? What about turning that screw? I still have the other EHA I could try.

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1990 190E 3.0L

If the codes are telling you O2 sensor, then look there. The EHA has probably nothing to do with it, or possibly just triggered the already problematic sensor.

Used EHA's are a complete crapshoot. Pressures have no indication for proper function unfortunately, so you either test it by the seat of your pants, or flow test each injector to check for proper fuel quantities and work your way backwards if it does not meet specs.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Yeah, I had to get the used ones though beause mine was leaking pretty bad. In fact, right when I turn the car on, engine off, I could see the fuel immediately start coming out of the top where the EHA meets the fuel distributor. Funny how that happens even with the o-rings in place because when I put the used one on using the same o-rings, not a drop of fuel escapes. The used ones were taken from 2 190e' s at a junk yard. I took them off the cars myself....well not really but the guy took them off and gave them to me.

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1990 190E 3.0L