Just for my education, what is the difference between the R24W and R24Y? I know the Y has fuel shutoff functionality. But is there anything else?
Brad
Hi Brad
Oh there is a lot of difference, because the two FIPs were used on two markets with very different emission regulations.
The R24Y was used only on the US market and in the 1970-71 model years of the 280SL. The US emission regulations were aimed at reducing NOx, and this was achieved by MB by reducing the burn temperature. To do this the amount of injected fuel was increased and the ignition was artificially retarded at low revs with special relays and vacuum drives - both with a lower burn temperature as a result. Also, like for the earlier US market FIPs, the R24Y also included a stop solenoid, shutting off fuel supply with no accelerator input.
The R24Y is therefore not designed for accurate injection volumes, but rather to push as much fuel as possible into the engine, which is not preferred, if you today, without the rest of the US emission systems installed, want to make your 280SL run as smooth as possible and with a reasonable fuel economy. Especially in Europe, 280SL owners with re-imported US configuration cars prefer to replace the R24Y with something else, eg. the R24W.
The R24W was designed for the exact opposite emission configuration, as it was designed for the 1971 model year of the 280SL on the Swedish market (which has lead to the German nick name “die Schweden Pumpe”). Sweden had just as the first European country (the rest followed soon after) introduced strict emission control regulations, but not on NOx but instead on CO. To reduce the CO in the exhaust gasses, you have to control and reduce the amount of fuel you inject, but still achieve the same performance of the engine. The R24W is therefore a refined version of the otherwise used R25 FIP in the late 280SL on the rest of the European markets, and therefore the most preferred FIP to install in your late 280SL, especially if you are coming from a R24Y and want to make your engine run as smooth and precise as possible. The R24W is also much easier to find compared to the R25, which was only used in the late European 280SLs, whereas the R24W was also used in the late 280SE on the European markets, before MB migrated to the D-jetronic systems across all of their fuel injected models in the early 1970s. The R24W therefore was produced in much higher numbers than the R25, and more R24W FIPs are therefore available today sourced from scrapped 280SE’s, whereas not many European 280SL’s have been scrapped and thus the R25 is a very rare bird to find, not already installed in an existing European late 280SL.
Finally, like the R25, the R24W does not have a stop solenoid, and neither a start solenoid, though the R24Y does not have that either, as it was eliminated before these late FIPs were developed.
But I can highly recommend getting rid of the US config R24Y and instead install a R24W, if you want to get as much out of your late 280SL engine, unless you have a (rare) European late 280SL with a R25, where the advantage of the R24W only will be a slightly improved fuel economy and precision.
Hope this gives a good overview of the differences.
Cheers,
Christian
Ps: I have just replaced the R24Y with a R24W in my manual 1970 280SL, and I am very satisfied. I have an extra R24W on the shelf for a future transplantation into my automatic 1971 280SL, which currently has a R24Y installed, though with “racing specs” giving high performance but a miserable fuel economy!
