1972 250C - want to convert to fuel injection

[thorsen]

After the restoration of my 250C, I am very happy with my car except for the fuel mileage. 15mpg just seems unreasonable to me for a 2.8 liter car.

I looked into MegaSquirt but I don't really want to go that route. Is there a Mercedes straight-6 with fuel injection that would be a good candidate? Or is there a manifold swap I can do?

Does anyone want to try to talk me into keeping the carbs? I have a set of Webers on now, the engine compression is good, and I replaced the ignition with a Petronix Ignitor and Flame-Thrower coil.

[Skippy]

Didn't a guy on here just post some pics of a fuel injected M130 that he swapped into his 114? I think the thread was titled "They said it couldn't be done" or something like that.

[alabbasi]

If it was me, I would go with an M110 out of a Euro 280SE or E.

[Mike D]

You are not going to increase the MPG by going to a fuel injected M130 or M110.

The facts are that you are pushing a 3400lb. mass around using a 2.8L, late '60's early '70's technology, internal combustion engine.

Megasquirt (or a controller similiar to it) will give you the best optimal fuel mixture but you still cant beat gravity and physics. Your mileage is NEVER going to be similar to a 2500lb vehicle. Of course, the 250C is never going to ride like a tin can on skates either.

Go to a different gear ratio, taller, skinnier tires for a slight increase.

You have a "cruiser" not an "economeister".

Drive less, enjoy it more. Style it brother!

[todds]

He's got a point. For a meaningful mileage increase using the technology of the era you'd have to "downgrade" to a far less powerful diesel or small 4 cyl powerplant. Or you could buy a beetle or something. ;-)

Is 15mpg your highway mileage or city? It's a little low for the highway. Automatic or Manual? A/C?

I'll post a pic of the fuel mileage section of my owner's manual tonight. It's fairly astonishing and I don't get anything like the curve they posted in there. They do say that city driving raises the consumption substantially, while automatics and a/c also effect it to a lesser extent.

[JMURiz]

Originally Posted by Mike D

You are not going to increase the MPG by going to a fuel injected M130 or M110.

The facts are that you are pushing a 3400lb. mass around using a 2.8L, late '60's early '70's technology, internal combustion engine.

Megasquirt (or a controller similar to it) will give you the best optimal fuel mixture but you still cant beat gravity and physics. Your mileage is NEVER going to be similar to a 2500lb vehicle. Of course, the 250C is never going to ride like a tin can on skates either.

Go to a different gear ratio, taller, skinnier tires for a slight increase.

You have a "cruiser" not an "economeister".

Drive less, enjoy it more. Style it brother!

Couldn't have said it better, the best you can do is do an EFI and crank-fire ignition setup but it still won't get more than probably 20-22 on the highway (just a guess). Hopefully in a year I'll be able to give a better answer on that as I'm going to rebuild a euro M110 and to the above mods to it.

[thorsen]

Mine is an automatic with a frequently used A/C. I am seeing 15mpg in mixed city/highway driving, about 50/50 each way.

Thanks for the gut-check MikeD. I was comparing it to my 1970 MGB, but it has no A/C and the safety margin is no contest.

[Skippy]

Originally Posted by thorsen

Is there a Mercedes straight-6 with fuel injection that would be a good candidate? Or is there a manifold swap I can do?

OM603? Or go five cylinder and get a 617.952? That one should be relatively simple to put in a 114 body. Change rear end ratios and you should be in the mid to high 20's of mpg with approximately the same performance you have now.

[alabbasi]

Originally Posted by Skippy

you should be in the mid to high 20's of mpg with approximately the same performance you have now.

Really? I've never driven a 250C but I have driven a 250CE which was a very quick car. It could give a 90 325i a run for it's money.

[Skippy]

I have a turbo 300D and a carbed 250. I haven't put a stopwatch to them, but SOTP I think the 300 is as quick as the 250, maybe a little quicker.

[UT_Tech]

Your 250C should be able to get 20 MPG without any radical surgery. Try running the coast-down test on our website. If your car measures the equivalent of 15mpg in road horsepower then there's a problem.

[cth350]

http://unwiredtools.com/utcoastdown.asp -CTH

[cth350]

Some states consider shifting to neutral like that to be a no-no (a ticket). Not that any cop would know and enforce it.

Define "MPG capability" for me please. What vehicles acheive this theoretical number (or come close)?

-CTH

[thorsen]

Man, this is frustrating as all get out. I know this is the hottest weather we have had this year in Chicago, but I drive somewhere, park, and the fuel that is left in the carb bowls starts to boil. You can see and hear it. The fuel floods the engine so when you go to start it up you have to hold the pedal to the floor until you clear the flood. This doesn't help economy at all. I put my infrared thermometer on the carb and it is reading 150 degrees - not all the extreme for being under the hood.

[mbgingerbread]

I replaced the fuel pump in my 71 280se. The bleed screw on the old pump was removed and an auxiliary fuel line to the return fuel line was attached there using a tee at the return line. I was advised that this line was put there to help out with vapor lock. Since I did not anticipate vapor lock with fuel injection, I left the extra line out. You might check your line from the tank and see if the setup is the same as I had. Maybe adding the line will help with your carburated engine. Good luck.
Where did you order your pertronix unit and coil from?
Thanks,
MBG