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M103 spark advance map
Yesterday I ran some tests to characterize the spark advance - engine revs curve with a dial back timing light using the OE US model 750 ohm resistor and zero (shorted the plug) and infinite (removed the resistor) resistance.
The shorted plug case is supposed to represent the least rate of advance and least total advance, and the open circuit case the highest advance rate and most total advance. For all cases the initial timing was 9 and the vacuum line to the EZL module was removed and plugged, but prior tests indicated maximum vacuum advance of 14 degrees. Figure reading error is plus/minus one degree and 100 revs, but might be a little more at high revs since the mark tended to jump around a little more. 750 ohm OE resistor: 17@1500 21@2000 27@2500 (maximum) 27@3000 27@3500 Zero ohm - plug shorted 09@1500 13@2000 18@2500 19@3500 21@4000 (maximum) Infinite ohm - open circuit 16@1500 21@2000 27@2500 28@3500 (maximum) It's possible that once the bulk of timing is in the advance continues to increase at a very low rate to higher revs, but it is difficult to discern. The resistor is still out, but I haven't noticed a SOTP improvement in performance that has been reported in other discussions. If anyone else can run a similar test, it would be nice to have another data set as a sanity check. Duke |
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Duke,
I realise you replied to one of the threads I posted regarding this subject some time ago. I posted the same thread in different forums so you may be interested to read the various other replies. They can be found at: Those with M102 & M103 "free power upgrade" must read! Read this if you have done the "free horsepower upgrade" http://www.benzworld.org/forums/forums/thread-view.asp?tid=242608 http://www.benzworld.org/forums/forums/thread-view.asp?tid=555023 http://forums.mbworld.org/forums/showthread.php?t=42712 http://forums.mbworld.org/forums/showthread.php?t=42715 I have since been running both my M102 and M103 with the different value R16 as described in those threads. Note that in my case the greatest ignition advance was not obtained with R16 removed but with a higher value (and a different value for each engine) to that fitted originally. The original values for my Aussie delivered cars were lower than those fitted to the equivalent European or US models due to the low octane (91RON) unleaded fuel available here at the time they were sold new. We now have higher octane fuel available (95 and 98RON). I have found that my M103 does require the higher octane fuel to avoid pinging with the more advanced timing, however since my original threads were posted I have found that the M102 is quite happy running regular fuel even with the more advanced timing. As for noticing any difference in the seat of the pants, I recently had cause to set the M103 back to the original setting due to the unavailability of the higher octane fuel. In doing this I did perceive a loss of mid range torque at wider throttle openings compared to when running the more advanced timing. Back when I changed from the original setting to the more advanced setting the difference was not so obvious. Greg
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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership). 107.026: 500SLC, 4-speed auto, thistle green, green velour. 124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex. 201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather. 201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex. 201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather. |
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I've been thinking about puting in a 1K pot with a calibrated dial. I could experiment.
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Regards Warren Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL ENTER > = (HP RPN) Not part of the in-crowd since 1952. |
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Quote:
But what's more astounding is that the open circuit condition, that I've read many rave review about, seems to have virtually no impact on timing advancement, and therefore engine performance. This is quite a discrepancy. What could be the explanation for this?
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Steven 1989 260E (276K miles) 1995 E320 (50K miles) |
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