1973 450 SEL Fuel Economy - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 05-22-2004, 03:34 PM Thread Starter
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1973 450 SEL Fuel Economy

Hi folks. I have a 1973 450 SEL and I have terrible fuel economy. I think its somewhere between 8.5 and 9.5 miles to the gallon. What are some things I can do to improve this?

I believe the ECU is bad because it does not respond to the knob turning in either direction. Also, I need a new fan clutch. These right now are my priority to replace, are there any other things you guys suggest I look into?

I am aware of a huge leak on the port side because an exhaust manifold bolt is missing. I need to take the head off and redrill the hole. Is the gap a major cause of poor mileage as well?

Please help!


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post #2 of 3 (permalink) Old 05-22-2004, 04:29 PM
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RE: 1973 450 SEL Fuel Economy

I have the same car except newer - 1978 with CIS MFI, but my 1972 280SE 4.5 has the same engine.

Remember that the engine combined with the hefty curb weight earns this car on average 19.9L/100 km (11.8 mpg) fuel economy, so for starts, you are not that far off of the factory specs.

I don't think the exhaust manifold bolt missing would attribute to it that much. Be careful drilling into the head. Hate to hear a horror story come out of that.

Read up on how to adjust the D-Jetronic - and I know it is possible because my 4.5 has the same system. Remember that new ECU's are very expensive so start with cheaper avenues. If you need help with this I can post some instructions from my Bosch FI book. Also take a look at your injectors, they are not hard to remove and inspect - perhaps they are worn out. Still pricey to replace but not as much as an ECU.

Maybe start looking at things like gaving the tires inflated to specs and trying to accelerate a little slower. Avoid using the kickdown. I know how fun these cars can be if you want to give them a little juice but it will cost you later.

Something I just learned as well. Be careful what spark plugs you place into these engies. They demand high temperature plugs.

Try other standard things like FI cleaners - Lucas makes some good stuff. Maybe a new air filter...the usual.

Good luck and let me know!

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post #3 of 3 (permalink) Old 06-28-2004, 02:11 AM
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RE: 1973 450 SEL Fuel Economy

Throughout the 16 years' use of my 1980 450 I've averaged 17/18 mpg# around town and 20/21 mpg on country trips.
My 1973 450 however uses more - viz 16/17 mpg city and 18/19mpg country.
Ten years ago I had a 6.9 and that did 13/14mpg city and 17/18 mpg country.
Each time the fuel consumption rose from those averages I had the cars' fuel systems retuned so I guess they should be about average rates - and whilst I don't hammer my cars, I don't nurse them either.
# Imperial.

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