1999-2009 [Subscribe to Daily Digest] |
On my 99^5 4cyl, it is a 4 wire sensor, I think all the O2 sensors may be 4 wire nowadays, and you may have explained the reason - the added wire could well be a ground.(two wires for the heat element, one ground, one sensor voltage).
BTW, the post on gas milage obtained on lower vs higher octane, I have tested this over 6k miles and noted an improvement with the higher grade.
You seen to understand the Trionic mgnmt system better than most.If in the interest of better mpg the Saab engine runs leaner than most engines on light load, this means less timing advance is tolerated, as lean mixtures cause more pinging. But a hemispherical design typically needs more advance to get effective burns due to a slower flame front than other designs. So the timing must be advanced far enough to get optimal efficiency from each combustion, but you can only get that advance with a certain octane grade. Lower octane = retard in timing, and combustion at less than optimal engine timing.
Under boost conditions, the mixture can be enriched to help prevent pinging, but should pinging occur, the timing and/or boost can be altered.
Since the auto runs in non boost far more than boost conditions, I would suspect that the engine mgmt algorithyms are set to produce best fuel ecomony at normal engine load conditions, which is why I believe Saab recommends the 91 octane because it is with this grade that optimal timing can be utilized. It's not as simple as lower octane = more energy, as was in past days (35yrs back) when an engine ran on an ideal fuel/air mixture.
Hence the pinging and dieseling of engines in the early yrs of emmission controls, when lean mixtures in many engine designs necessitated a retardation of the timing as well as the need to run higher octane.
If the Saab engine does run leaner than most, this also explains the use of the capacitive discharge design of the DI, as leaner mixures are more difficult to ignite, and a stronger spark can counteract this and achieve a quicker and consistent burn across all rpm ranges.
posted by 198.81.26...
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
