1972 280 SEL 4.5 fuel pump problem? - Mercedes-Benz Forum

 
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post #1 of 10 (permalink) Old 07-17-2010, 04:46 PM Thread Starter
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1972 280 SEL 4.5 fuel pump problem?

I took my 1972 280 SEL 4.5 out for a spin on the Interstate today and stopped by my office on the way home. When I returned to the car, it wouldn't start. I cranked and cranked and finally decided to put the gas pedal all the way down. It started, but ran pretty rough. On the way home, it stalled when I would stop. I made it home and drove the car into the garage, keeping my foot on the gas so it wouldn't stall. It blew out bluish smoke at idle and finally stalled. When I got out, I noticed a sound coming from just behind the left rear tire. I looked under the car, and the buzzing/humming sound was coming from the fuel pump.

Does the fuel pump run after the car is turned off? Could the fuel pump be failing and creating a fuel pressure problem? A mechanic told me the last time that the car was running way too rich. Also there was a paint-like smell coming from fuel pump area.

Help is appreciated.
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post #2 of 10 (permalink) Old 07-18-2010, 06:11 AM
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Paint-like smell from the fuel pump area? How old is your gas?

I'd suggest taking out your spark plugs to inspect them. If you're running rich, chances are excellent you have fouled plugs. Additionally, if they're oil fouled, you might have an issue with your rings.

What kind of milage are you getting?

And yes, when your turn the key off, the fuel pump should stop.
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post #3 of 10 (permalink) Old 07-18-2010, 01:20 PM
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If you are blowing blue smoke, that means that you are getting way too much fuel. I would suggest that you check the vacuum line to your fuel pressure regulator and change your oil, as it is probably contaminated. Your fuel pressure regulator shoild be replaced if the vacuum line is intact.
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post #4 of 10 (permalink) Old 07-18-2010, 03:23 PM Thread Starter
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The gas is a couple of months old. The compression on all cylinders is good. Mileage has always been poor - 10 to 14 mpg.

What's wierd about the fuel pump is that it made a buzzing sound which slowly went away. I put my hand on the fuel pump and it didn't feel like it was running, but the sound was definitely coming from it.

Today I tried to start the car and the same thing happened. I always started right off, but on the first crank it quickly fires but then nothing. It just seems like this is fuel system related, especially if the fuel pump was making a noise. Could it be a fuel pump relay issues? The fuel pump actually looks quite new.
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post #5 of 10 (permalink) Old 07-18-2010, 03:26 PM Thread Starter
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Thanks. I will check the vacuum line. Any ideas why the fuel pump would make a buzzing sound after the car has been shut off?
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post #6 of 10 (permalink) Old 07-18-2010, 03:52 PM Thread Starter
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Is there a way to clean fouled plugs or should they be replaced?
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post #7 of 10 (permalink) Old 07-19-2010, 03:30 AM
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The SEL's fuel regulators don't have a vacuum input - they're inline, spring regulated devices.

I'm wondering if you have some sort of a clog after the fuel pump. If you hear a buzz but the pump isn't running, maybe it's return pressure going through the pump, back to the tank... Anyone remember if there's a check valve in the pump?

For fouled plugs, I've used acetone (nail polish remover) and mild sand paper to de-foul the things. You may need to regap them though.

I agree with changing the oil too - running rich causes the fuel to mix with the oil in the cylinder, which thins out the oil.
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post #8 of 10 (permalink) Old 07-28-2010, 07:47 PM
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Make sure to check the map sensor make sure the hose isnt cracked, you wont get proper fueling to engine without the right pressure readings had sort of the same problem on my 73 450 sel same engine/trans. Cheers and good luck, bro..
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post #9 of 10 (permalink) Old 07-28-2010, 08:30 PM
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It it suddenly started running like crap, check the ignition points gap and condition, it may be either dirty or out of adjustment and would do exactly that.

With best regards

Al

Check out the W114, W115 /8 enthusiast forum http://www.stroke8.org

My 280SL restoration
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post #10 of 10 (permalink) Old 08-24-2010, 09:03 AM Thread Starter
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Is there a pcv valve on the 1972 4.5 V8?
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