Member luckymike asked me to explain how Lambda control was originally set and whether it is possible to set it back to the correct setting after the Lambda adjustment screw has been tinkered with.
Consider that the “duty cycle adjustment“ is actually, as I said, an adjustment of the EHA‘s operating range … and that, when that adjustment was originally done, everything was new & clean & (supposed to be) well working. Under these conditions the Lambda adjustment screw was set to the position at which the EHA current fluctuated around zero milliamp (EHA baffle plate fluctuating around its currentless rest position), which is represented by a duty cycle fluctuating around 50%.
Contrary to common belief, that adjustment was done irrespectively of o2 sensor voltage and exhaust emissions
. The EHA current (fluctuating around zero milliamp) was the only parameter for the adjustment. …
Exhaust emissions were checked after
the adjustment was done.
they were according to specification, everything was fine … and the Lambda adjustment tower was sealed with a (difficult to remove
they were not
according to specification, there was either a fuel combustion affecting problem (not necessarily with the injection system
) or a problem with the o2 sensor or with the CAT or an exhaust leak between cylinder head & CAT. … In such a (very rare) case the exhaust emissions were, of course, not
corrected by turning the Lambda adjustment screw but by fixing the problem that caused the emissions to be out of spec while the EHA current was fluctuating around zero milliamp (duty cycle fluctuating around 50%).
Conversely, the duty cycle indicates, according to its purpose, whether there is/are (a) fuel combustion or Lambda control affecting problem(s) or not … which after ~30 years is often the case, of course.
If you know
that the Lambda adjustment screw has never been tinkered with, or exactly how far it has been turned in what direction in relation to its original setting, or what the duty cycle reading was each time before & after the Lambda adjustment screw was touched, then the duty cycle can still be used as a reliable basis for diagnoses … which, depending on its value/range, points to or excludes specific potential problems. After fixing all problems
, if any, the EHA current, respectively the duty cycle, not only can but should be readjust according to the procedures in post 2.
If you do not know
whether the Lambda adjustment screw has been turned or how far it has been turned in what direction, then, as I said in post 40, “valuable diagnostic information is gone for good (!) and everything that has an effect on fuel combustion (see examples under “Please note“ in post #2) has to be checked first before further touching the adjustment screw, in order to reliably restore a proper condition of the system“ !
It may sound like a broken record, but this post should further help to realize that the Lambda duty cycle is a provider of diagnostic information
… and not
something that should be ignored or simply readjusted via Lambda adjustment screw. I continuously see the latter being suggested here at BW instead of first checking/fixing all
potential problems that can cause the duty cycle reading to deviate from the above mentioned setting range. The duty cycle should primarily be readjusted by fixing the problem(s) that cause(s) its deviation !
This post should also help to understand that using the o2 sensor voltage or exhaust emissions as parameters for adjustments via adjustment tower
(instead of the EHA current, or at least the duty cycle) is a bad idea !
… It may get the car through an emission test, but shorten the engine‘s life !