450 SL -75 US version (D-jet) way too high CO (8 !)

ej!

I have had this car just 2 months and it has just failed its MOT due to too high CO 8 (should below 4) whilst idling.

Actions so far:
New thermostat/oil/temp sensor plus checked plugs/distributor/trigger points/vacuum hose/cold start valve. Today I tried lowering CO by turning the knob on the ECU whilst at a garage - the CO did not change a bit despite turning the knob.

Anyone had similar issue? Could it be something with the throttle switch? Any ideas appreciated.

Regards
Patrik

...if you can`t change the CO on the ECU, first thing to do is to adjust the throttle Switch !

Hi Patrik,

your are actually on the wrong of my 2 web sites. My D-Jetronic web site shows how to adjust idle-contact on throttle switch: jetronic.org/en/d-jetronic/maintenance#Leerlaufkontakt

Only when that one is closed in idle-run rheostat on ECU will work. Having said that the next probable issue will be a detuned MAP sensor. It is a nightmare on US cars. If you notice that the black cap on your MAP sensor is missing, askew ... : Then someone has detuned it on the screw. I have seen and retuend many such MAP sensors during our workshops. Some are even leaking vacuum after they have been detuned and some are irrepairable. Especially the ones that were sold by Daimler from 90s and early 2000s production in France by Bosch could be completely wrong.

Hej!

Sorry for delay - been away on mini vacation.

After adjusting the TPS the "knob" on the ECU does now have an impact. A HUGE thank you for the advice.

Whilst driving to the garage yesterday to test CO I ended up in 15 min queue having to idle - engine died. Eventually got i going with starter cables. Got back home not able to start. Charged battery but no luck. Used starter cables again and it did fire up. So battery probably gone.

I also noticed that the temp gauge needle is only moving slightly. Thermostat is new and I have done basic test on thermo time sensor, aux fan sensor and EFI water temp sensor. Is there another sensor for the temp gauge in instrument cluster?

Kind regards
Patrik

Hi Patrik,

yes there is a separate sensor just for water temp display.