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High Nox - How much should I retard the timing? 200

posted by  Bean on  Mon Feb 2 06:45 CST 2004
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last visit: Mon Aug 30 03:53 CST 2010
[RELATED]

'87 245DL, M47, 235k

I failed my emissions test for high NOx, both CO and HC were in spec thankfully. I am going to try to correct the problem (vac leaks probably) but just in case I don't find anything I plan on retarding my timing.

HC: 1.96 Limit: 2.25
CO: 12.65 Limit: 23.74
NOx: 4.28 Limit: 3.25

Two questions:
1) How much should I retard the timing? Should I bring it back to "0" degrees?

2) I have heard that by retarding the timing, NOx and CO will go down but HC will go up...my HC reading is 1.96 which is just under the 2.25 limit. How much higher will the HC go up? Does anyone who has done this have any before and after data?? I don't want to retard too much to lower my NOx only to have my HC go out of spec! The car is only going to be on the road for a few more months before she gets parted out and sent on to rusty Volvo heaven.

Thanks for any and all advice,
Bean

--
'80 242GT 91k, '94 945T 110k






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