I have been considering looking for an older Mercedes for a compressed natural gas conversion. Here are my thoughts:

• The CNG conversion kits on the market that work with fuel injected cars assume that the injectors are electrically controlled. The intent is that when running on CNG, the fuel injectors are electrically disabled.
• The above implies that I would want to permanently disable the fuel injector on the car (I would run on CNG exclusively). This sounds scarry on a mechanically injected engine; if you just pull the injector lines and leave the pump I would think there would be mechanical pump failures. And you can't just pull the pump because the timing chain would become slack (I assume they work the same way as my '85 300D)
• I prefer the older cars because of the lesser amount of electronic controls.
• All of this means that it would be easier to use a carburated engine.

Am I thinking correctly about this? I'd like feedback on the feasibility of such a conversion of a mechanically fuel injected engine.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

There should be a way to safely disable the injection pump. Loop the fuel lines and fill with lightweight oil perhaps?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I had a few CNG cars back in europe. They are pretty common there. Had injected and carbureted. It doesn't really matter if you're using gas. The gas goes through the intake manifold, not the fuel supply.
So use whatever you want. Can disable the pump and injectors, by removing the relay.

The one thing to remember is there are drawback to these systems.
The fuel pump has to work so it doesn't get moisture. The injectors if not open for a period of time, will clog with the gas that overheats. Same with carburetor. If the gas stays in the injectors/carburetor in high temp, it will clog.
The modern CNG/LPG systems will use traditional gas at start-up, until the RPMs drop, and then automatically switch to natural gas when the car is warmed up.
An engine on natural gas will consume a little more than it does on traditional gas. About 10% more; though newer modern systems will only provide more gas when driving style changes.
Natural gas doesn't have the additives the traditional gas has. So your engine will need a different kind of oil. It will run colder and dry.
And misfires are like 4th July fireworks. If you have the air filter out and try to adjust the system (which i always had to do) you'll see flames coming out of the intake on misfire... pretty impressive once you get used to it.
Gas systems can be adjusted so they provide less power but more economy. However if you equal the power to the traditional gas you'll have to burn more (but a lot cheaper)


LPG and CNG will run your engine colder, that's why the combined systems allow the engine to warm up quicker using traditional gas. Preferred in cold climates where i come from. Plus, it will allow the injectors and fuel pump to do a workout once in a while and stay lubricated.

Cost-wise a CNG or LPG is awesome, Natural Gas is extracted here in the USA and costs cheap. Doesn't depend too much on wars with middle east and all the political BS. Don't use it in wars too much so it will stay relatively cheap.
CNG is gas compressed at very high pressure, You'll need very heavy gas cylinders in the trunk.
LPG is probably what you need. It's liquid petroleum gas. There negatives and positives about both systems.
And what americans are very concerned about - SAFETY.. forget about it if you get in an rear end accident with your tank full of compressed gas in your trunk.

Cost of installation is ridiculous here in the states. I'm surprised that it's so big. I'm used to these systems and they provide 100% clean emissions (except the oil your burn) and no BS with fuel pumps or injectors or ECU malfunctioning. As long as you have spark on time you're good.
In eastern europe you could get them for 500 euros for a manual system and about 1000 euros for an automatic system with separate injectors in each of the intake channel. And ECU controlled delivery.
I would definitely consider one for my car, but not at over 5000 for a decent one.

I had a 1986 BMW 318 that was missing the ECU, fuel Pump and almost all the injection system. All it had is the distributor that was ghetto connected to the crank shaft sensor, a very home made car. To bring her back to life was just enough to connect a gas hose to the one of the hoses on the intake manifold and i drove it for close to a year Was VERY CHEAP about 2$/week to fill the tank, about 15 years ago in europe. It used the same gas we had at the stove or the water heater
I don't know why people bother with organic oil conversion and diesel engines. Or electric batteries. Gas is so much easier to get than used oil from fast food restaurants and is 100% clean to the enviroment

I have no experience with these people beyond reading the web site but look here.

Also if you search the forums for CNG you will find a few threads about it.

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1972 280SE 4.5