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  #1  
Old 08-12-2018, 12:21 PM
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Join Date: Aug 2018
Location: Maine
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R107 fuel harmonic

I have a 1979 450 SL, with 140kmiles. It runs fine aside from an annoying intermittent problem. Every once in a while it will start this fairly loud whooing, almost foghorn like sound. It took a while to narrow it down,because initially it would stop soon after the vehicle stopped. But recently it has changed it's characteristics some, and the other day I was able to search around a bit more. Originally it seemed to be coming from under the air cleaner housing. But now has moved to under mid-body of car. When this happens I can actually feel the fuel supply line in the engine bay,right where it changes from hose to hard line vibrating. By wiggling the line back and forth I can change the sound of the harmonic. Now I'mtrying to figure out if my problem is in the fuel distributor system,or back aft. I've already changed the fuel pump and filter, because I thought it may have been fuel pump related. Any ideas or input greatly appreciated.
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Old 08-12-2018, 01:37 PM
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Location: Texas Hill Country
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Have you replaced the fuel accumulator? One of its jobs in addition to maintaining fuel pressure when the engine is stopped is to dampen pulsation in the fuel system.
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  #3  
Old 08-12-2018, 01:50 PM
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No, I have not. I thought of doing that while I was down there,but decided against it for no reason other than I was in a hurry. Sounds like a logical source. Guess I'll order one.Thanks.
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Old 08-12-2018, 02:58 PM
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No promises it'll fix the issue at hand, but it's certainly a contender. When they fail they can cause strange issues or no symptoms at all for some people. The most common complaint is warm starting issues where the car's sat for 15-30 mins and either refuses to start, cranks for longer than normal, or "chugs" for a few seconds when restarted. When working properly, the M117 should be "diesel" fast starting, basically a flick of the key hot or cold and it should just about jump to life.
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'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'86 300SDL - "The Diseasel" 186K
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
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  #5  
Old 08-12-2018, 06:47 PM
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Join Date: Aug 2018
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Diseasel300, Thank you.Yes, I also have experienced it being a bit balky at starting when warm. Other times fires right up. I have only had this car for3 months,still feeling my way around it. Learning all the time.Thank you for the help and I'll let you know how it works out....
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  #6  
Old 08-16-2018, 05:15 PM
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Join Date: Aug 2018
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R107 harmonic

Diseasel, well replaced the fuel accumulator this morning. No luck still making the harmonic intermittently, so no change.The only things I haven't changed back there now are the fuel damper and tank screen. It shows no signs of starving for fuel so I don't think it's the screen. Could be that little damper though?????
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