1976 Mercedes Benz 450sl Problem with surging

  • 1976 MERCEDES BENZ 450SL
Engine Mechanical problem
1976 Mercedes Benz 450sl V8 Front Wheel Drive Automatic 117000 miles

We bought this car which was sitting for about two years. We did a tune up and replaced the vaccuum lines. We also put in a new fuel pump. It starts up fine sounds good but then when it gets to about 175 degrees the engine starts to surge and dies on acceleration. We can't figure out the problem can you help with this? Thanks Norma
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have the same problem?
Tuesday, July 13th, 2010 AT 8:25 AM

1 Reply

You've still got a vacuum leak, and it's connected to one of the thermovacuum switches.

There are two switches that screw into the intake manifold of the car. These are both controlled by engine heat. When the engine is warm enough, the switch opens and allows vacuum through. The pipes coming off these switches is small, brittle, and easily broken. It's a common failure point.

In case you haven't already, get yourself a MityVac hand vacuum pump. The lines in these cars can look flawless and still leak like a sieve. The only way to be sure is to connect a vacuum pump to them and verify they hold vacuum. That hand pump will be the best $30 you ever spend on this car.
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Friday, September 24th, 2010 AT 2:04 PM

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