The car seems like it misses some times and some times it seems fine, Mechanic tested fuel distributor, and says pressure is fine, but when he tested fuel (mass i think) the bottom of the distributor is good, but when he goes to test the top, the car shuts down. Does this sound right to replace whole distributor, or is there another explanation. Thank you.

I would get a 2nd opinion. This item cost tons of $$$ and many mechanics mis-diagnose it.

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'91 300-SEL

I see there is an o ring gasket for the fuel distributor, if that was to go bad, does anybody know if it would reduce the upper mass reading?

I would get a case of Techron, and run a tankful of gas with a couple bottles of the stuff added. See if this helps. If better, keep adding a bottle of techron/tank until problem disappears. If this doesn't help, get a second opinion before replacing the fuel distributor.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

I will, I have been looking on internet and have found rebuilt one for $300 but something just doesnt sound right.

Have you checked your ignition distributor? Those are known to cause idle issues, and much cheaper to replace than a fuel distributor. If it has not been replaced do it, see if that helps, if not it should be replaced anyway. Also the plugs and wires. I had a rough idle on a 103, it was plugs, wires, and distributor, car only had 42k on it, but now it runs wonderfully.
Brian

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Brian W. Heitman

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I have just replaced the wires this week, and the plugs are about four months old, the distributor is not the original but I have not replace since i have had car (3 years) I will try to clean plugs in case something fouled one.

I now have the fun of getting the car from the mechanic and telling him I am not going to have him fix it. I know there is a "diagnostic" charge.

It seems like you are pretty good at figuring things out, I would still pull the distributor cap off and at least take a look at it inside, see if there is any corrosion or arcing. That way you can rule it out. Fuel distributors are pretty dependable unless the car sits and isn't run for awhile. How many miles?
Brian

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Brian W. Heitman

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88k and only about 500 this year

you need to drive that car more often! It is too much fun to it around! ha ha.
Brian

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Brian W. Heitman

www.MBCA.org/northtexas

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its time to get something more practical, it going in the paper this weekend

It is a practical car, I drive mine every day! How much are you going to sell it for? You might try posting it here as there are lots of people that could be interested. That is a great car and you should keep it. It might give you trouble once in awhile, but you will regret selling it.
Brian

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Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!

im puttin it in the paper for $9500 obo 18" amg rims, dvd alpine grey with black top