1995 smog data trending

[3Q Jay]

Preface: this is on the daughter's '95 (was wife's when new). I have a maintenance log from day one, every oil change and all other service recorded.this engine has had full plenum and egr cleaning in dec 2006 at ~150k miles. O2 sensor changed at ~125k dec 2004.

15MPH test:Date Apr2005 Mar2007 Apr2009 Apr2009 May2009odometer 130417 158175 176361 176541 176888rpm 1730 1707 1718 1676 1736%CO2 14.9 14.5 15.0 15.0 13.9%O2 0.1 0.0 0.0 0.1 1.1HC (87max) 71 87 87 87 24CO (0.51max) 0.15 0.11 0.12 0.17 0.04NO (701 max) 700 214 506 474 129

25MPH test:Date Apr2005 Mar2007 Apr2009 Apr2009 May2009odometer 130417 158175 176361 176541 176888rpm 1763 1703 1703 1618 1718%CO2 15.0 14.6 15.1 15.1 13.9%O2 0.0 0.0 0.0 0.0 1.0HC (52max) 46 52 60 54 31CO (0.49max) 0.11 0.03 0.07 0.07 0.02NO (730 max) 191 173 425 304 48

Notice the decrease in NO from test1 to test 2, especially on the low speed test--went from marginal failure to factor of >3 improvement. this is what meticulous egr cleaning will do for you.Notice also that two years later in test 3 the NOx has increased by a factor of 2! this is in part due to reasons we'll discuss below, but the point here is that even after cleaning the passages to spotless, they eventually gunk up again.

Now, examine the HC: the upward trend from test 1 to 2 and to 3 over a course of 4 years. engine was maintained in tune during this time (NGK bkr6e-11 plugs), but it wasn't enough and for the first time the car did not pass smog in Apr this year (test #3). The plugs had almost 2 years and 25k on them at the time of test #3, so I replaced them for test #4.

Test #4 was almost good enough to pass, but you know all about 'almost'......

what else is going on here? well for one thing, i have run high phosphorous motor oil (Shell rotella T synth 5w-40) for the last 3 years. side note: this is a really good oil for your engine (a bit thick, but for hard driving in warm climates it offers fine protection), but NOT so good for cats (remember it is a diesel truck oil by trade). Research taught me that high phosphorous *may* poison the cats (not like leaded gas would, but could eventually be problematic)

So, i reinstalled conventional dino oil along with the fresh NGKs for test #4. thinking if the contamination was transient, a few hard runs might abrade the phosphorous enough to reenergise the cats. again, not quite.

Test #5 is with a new main cat (pre-cat is still original).

I do not propose to anyone that you should just go slap on a new cat to pass smog. in my case, i used a fault tree type approach to exonerate other paths including intake, injectors, fuel pressure, vacuum leaks, timing, sensors.