W108 CNG Conversion: 1970 Mercedes-Benz 280SE
The Paul Bracq styled W108 generation Mercedes-Benz S-Class is (in my humble opinion) one of the better ways to get into a vintage sedan for a semi-daily driver. The performance is acceptable, ride is comfortable, build quality is exemplary, but most importantly — drive one and you’ll look like a boss. Today’s W108 has a 6-cylinder gasoline engine that has been converted to run on CNG (compressed natural gas) and some rust along the doors that needs to be investigated. I wonder if you can get those California CNG carpool lane stickers for this thing? Find this 1970 Mercedes-Benz 280SE offered for $5,900 in Pasadena, CA via craigslist.
From the seller:
1970 mercedes benz 280se
condition: good
cylinders: 6 cylinders
fuel: other
odometer: 140000
title status: clean
transmission: automatic
type: sedan
1970 mercedes benz 280se. 6 cylinder car. converted to cng. I believe it is out of cng gas it starts on starter fluid than immediately dies. Again it runs on cng fuel. I am not sure why it was converted and i do not have any prior history for the car. Clean interior. Runs and drives. Body has some rust bubbles on doors. Clean title. Original radio $5900 cash no low offers please. This is a project car priced very low. I am not interested in 4k 5k offers so please do not ask
See a better way to drive CNG? tips@dailyturismo.com
I’m confused, the 220se has a Bosch mechanical injector pump that used a 3 dimensional cam to pump fuel into the intake ports depending on RPM, load, and throttle opening much like the injection pumps on old Diesel engines except for the throttle position part of course. Obviously you can’t pump a gas the way you can a liquid so I don’t see how the injection system can be converted.
I suppose you could just put a CNG carburetor on the intake manifold and do an abandon in place on the injection system, but that would be a real shame.
Arg
280 se not 220. I have a 220se with the same system rotting away so it was one of those slips.
Yeah…i’m not sure either. Most CNG conversions are going to be a fumigation style system, not some kind of multi-point port injection setup, and the engine looks stock to me. Would have been nice to see a pic of the CNG tanks and filler cap, which would been very obvious.
My wild guess is that it’s supposed to be some sort of throttle-body setup, with the industrial-looking thing to the left of, and slightly below, the intake manifold/throttle body providing the gas for combustion. I don’t know exactly how the gas gets from the thing into the manifold, and I don’t know whether the gas head (or whatever it is) is, or could be, regulated by the gas pedal lever that (per original design) is connected both to throttle and the MFI system. It looks like it was hacked to do that.
The reason I think this–it looks like the MFI system is still connected on the intake side, but with no connection to the gas. (For comparison, pics 121-132 of this basketcase car show the MFI system: https://bringatrailer.com/listing/1969-mercedes-benz-280se-coupe-3/) They must have also found a way to disconnect the gas pedal from the MFI on the driver side of the engine, or you’d think the system would seize without any fluid, and keep the pedal/lever stuck. Unless they have given up on power brakes, the booster is still getting vacuum off the original intake manifold, assuming the thing runs.
Maybe somebody gave an estimate to overhaul the MFI that was just too rich for a 4-door like this, so they went all “taxi” on it. I don’t think I’d feel too comfortable driving this, or even trying to start it, although I quit smoking a long time ago. I’m not that risk averse–if they’d hooked up nitrous, I’d be preparing a spot in my $5k fantasy garage–but they say gas makes you slower.