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#1
06-19-2006, 07:43 AM
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Setting 280sl Duty Cycle
Greetings Forum Members,
I would like to check and set the duty cycle of the engine in my 1985 280sl. I have researched the procedure using a digital multimeter. Being my car is a European model it wasn't manufactured with a "live" 3 pin from a Lambda control system in the diagnostic socket. My understanding is that the readings for the duty cycle are taken from #2 and #3 pins. The Lambda system with the frequency valve and O2 sensor was installed during fideralization. In this situation where do I test voltages to determine duty cycle? Would testing the 2 leads to the frequency valve give me the values that I need? Thanks, Knarf
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72 350SL #69 73 450SL Parts Car? 78 450sl Parts Car 79 450SLC - Sold 1985 280sl 87 190E 2.6 - Donated 90 300E-Junked 97 E420 
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#2
06-19-2006, 08:18 AM
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The duty cycle read at the diagnostic socket is actually reading the negative side of the frequency valve. Remembering that duty cycle is arbitraily referenced one would do the same thing at the negative side of the frequency valve for the same reading.
The scope/DVOM would be hooked with the positive lead of the instrument to the negative side of teh valve and the negative side of teh instrument to ground. With a scope one will see voltage high when the valve is not commanded, and voltage low when the valve is commanded. In this set up duty cycle ON would be greatest when the reading was low most of the time. In the normal BOSCH frequency valve task the higher on time lowers the lower chamber pressure and thus richens the mixture. On "grey market" cars the frequency valve often had a different type of function so I would look carefully at where it is hydraulically attached. If it is spliced into the control pressure circuit you will be much better off without it if you can do so legally.
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Steve Brotherton Continental Imports Gainesville FL Bosch Master, ASE Master, L1 33 years MB technician
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#3
06-19-2006, 09:55 AM
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Setting 280sl Duty Cycle
On "grey market" cars the frequency valve often had a different type of function so I would look carefully at where it is hydraulically attached. If it is spliced into the control pressure circuit you will be much better off without it if you can do so legally.[/QUOTE]
Steve, I have just read another language! If you have a moment, could you explain this in simple terms as to what this is/what it does? Duty cycle? I've got a Grey market 280SL and this is totally greek to me and obviously mine is fitted with this, the extent of my knowledge of this part is I have the plug! What is it and does it have to be adjusted-disconnected "much better off without it if you can do so legally". Legally? Thanks in advance. Brian.
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#4
06-19-2006, 10:22 AM
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Steve,
Thank You for responding. My valve is spliced into the fuel distributor. There is a blue and a red lead going to it from the Lombda system control box. What's the safest way to determine which lead is negative? I don't want to short anything out. If I decide to remove the frequency valve should any other component(s) of the system also be disabled? Thanks, Knarf
__________________
72 350SL #69 73 450SL Parts Car? 78 450sl Parts Car 79 450SLC - Sold 1985 280sl 87 190E 2.6 - Donated 90 300E-Junked 97 E420
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Linear Mode
