[W126 Coupe] Emissions question

[Alexander Hochhausl]

You may want to check your EHA (Electronic Hydraulic Actuator). This
controls your mixture. A broken EHA, depending on how it broke
internally, can result in the engine running very rich, or very lean. On
my car I had the opposite problem – ultra low emissions, but no power.
Mine failed on the lean side. The EHA is mounted on the intake airflow
sensor, opposite the airflow position sensor. I paid $80 for a new one
on Ebay, usually they run around $150 new. Buy a new one, you don’t know
you are buying a bad used one, as the car will run on a bad one, so the
seller does not necessarily know its good or bad. For me the new EHA
solved my problem, and the motor ran like new! I hope that helps – good
luck.
 
BTW: a power tip: Depending how handy you are with electro/mechanical
projects: I added a switch on my throttle linkage that over-rides the
ECU and controls the EHA via an adjustable variable resistor inside the
car (by the shifter). During normal driving, the mixture is per the ECU.
During emissions testing it is per the ECU 
 but at ½ throttle + I can
adjust the mixture to run rich. For about $100, it adds a
distinguishable amount of power. Hard to say how much, but from gut feel
I would say around 10-20 Hp. Get the Bosch manual for the fuel injection
– it describes the theory of operation, from that you can deduce how to
override the controls. If you can’t I will be selling (very cheap) plans
on how to do this soon.
 
I stumbled across this benefit as a byproduct of my supercharger
addition project (adding 100+ Hp). This is still in its experimental
stage – stay tuned for final details, Dyno run and do-it-yourself plans!
 
To be sure though – you do not want to run rich too long. It will kill
your cats – and you will never pass emissions!
 
All the best!
 
AHPE
’89 506 SESC (my supercharged version pushing around 375 HP – looking
for the 400 HP threshold)
 
-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com
[mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of richard jaffe
Sent: Friday, February 23, 2007 8:43 PM
To: mbCOUPES at MBCOUPES.COM
Subject: [W126 Coupe] Emissions question
 
Hello All:
 
The following are the test results of the emissions test performed this
afternoon on my 85 Euro 500 SEC:
 
               25/25 test
50/25 test
 
                      reading             allowed         result
reading        allowed        result
HC ppm             212                 137              Fail
216             140             Fail
CO %               1.86                 0.87             Fail
1.85             0.79           Fail
NOx ppm          1028                 956              Fail
1036            1046           Pass
RPM                1302                 2500 max
1357            2500 max
CO+CO2 %       15.5                  6.0 min
15.5             6.0 min
 
The following items are new: 8 fuel injectors w/ air tubes, Beru spark
plugs, Beru ignition wires, Distributor cap and rotor button, ICM and
various vacuum hoses and vacuum connector, 1 can BG 44 intake system
cleaner.
 
The car now runs great. Just can't seem to satisfy the clean air nazis
in this state. Is the mixture too rich?
Any ideas how to rectify this situation? Oh yeah, the car does have
catalytic converters.
 
Rich Jaffe
85 Euro 500 SEC 259K
83 300 SD         192K
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