How can I retard timing on a 1990 300E, 6cyl, 3L ?

Want to try and reduce NOx by 150. Changed EGR valve and works fine. Cleaned pipe from EGR to manifold. Vaccum is present at EGR.

HC ppm Limit 52 Reading 1
CO2 Limit 0.29 Reading1.0
NO ppm Limit 578 Reading 678 FAIL
RPM 1603 Valid
Dilution 13.4 Valid.
Curb Idle test, all pass

Any thing else I should look for?
Thanks

 

you can't retard the ignition timing...can't do it...

 

Timing is most likely set by the position of the "cut out" on the reluctor ring mounted on the flywheel.

Although NOx output is in relationshipo with (high) engine combustion temperature (retarding will assist) changing the timing will increase HC.

Assuming the installation is capable of achieving the required PASS level something must be wrong.

You indicate that the EGR system is fully operational. Note: This works by diluting the engine inlet charge with exhaust gas and thus reduces the potential for such high combustion temps. and therefore reduces NOx.

So the next "culprit" must be the catalytic converter. The cat both reduces the exhaust gas (to reduce NOx to N2) and then oxides it to turn HC into CO2. Since both NOx and HC are above the limit it looks as though your cat (I assume one is fitted) must be ineffective.

Looks like you need a new cat., Note:L the old cat is worth something at the scrap yard!

Stuart