1985-1998 [Subscribe to Daily Digest] |
The APC used to be a descrete chunk of electronics. Now it is just a subroutine in the Trionic ECU. The old APC's used a knock sensor. With the DI's there is not a conventional knock sensor. The DI allows the ECU to monitor the in cylinder condtions after the spark to detect and avoid knocking conditions. So there are now 4 knock sensors. For this reason, many off-brand spark plugs don't work well. The ECU can tinker with the timing and mixture of each cylinder to avoid knocking. Either way, the boost is controlled by the BPC solenoid valve which is a variable bleeder valve. In the T5's, from my 95SET experience, this leads to a lot of boost delay. But this can be overcome with a MBC installed in one of two ways that greatly increase boost response. One keeps the APC functions intact and the other bypasses it and provides lots more power as well. the T5 ECU will prevent knocking with mixture control and timing. This alarms many people, but the engines and control systems have no problems. This is not to say that an engine in bad mechanical condition could not suffer or that really bad fuel could not create problems. But there are years of experience with these and the combo is quite bullet proof. Most folks who go in that direction do intake and exhaust mods to make things easier, which lowers temperatures and increases responsiveness and power.
The T5 is a speed density sytem. It guesses air flow from the intake air pressure measured by the manifold absolute temperature MAP sensor. RPMs, and the air intake temperature. This 'rough' guess at air flow gets refined by mapping correction factors at difference flow rates via the O2 sensor feedback. The T7 uses a mass air flow meter (MAF) to get a better first order estimate of air flow and agian maps correction factores for difference operating conditions via the O2 sensor feedback. This is more accurate during transitions etc, and the result is better MPG's which means better combustion which reduces unburnt hydrocarbons and CO2 as well. When the cat converter is hot, the unburn hydrocarbons are toast either way, but the T7 seems to burn more fuel in the cylinders instead of the cat. My 3700 lb 9-5 Aero wagon gets much better mpgs than my 95SET did at 3200 lbs. Also the T7's first order air flow measurement is probably also be being more accurate, allowing for better open loop mixture control before the O2 sensor gets working. So there is less crap being blown into non functional cold cat converter than the T5. So cold start cycle emissions are probably much improved as well. The T7 has a fly by wire type throttle that allows the ECU to control some of the throttle transistions. I suspect that this was done in part to make transitions easier for the ECU. The electric throttle also takes care of cruise control and reducing power in traction control events and by closing the throttle when needed to trim air flow as a boost control mechanisn. The ECU is a very busy box! It also does the ABS logic too.
The Saabs are low emissions vehicles but can't get to the next catagory. This is probably because all turbo and supercharged engines run rich when on boost which blows soot, HCs and CO, carbon monoxide. And turbo engines have relatively low compression ratios, which reduces overall eficiency compared to the NA engines at 10 or 10.5.
The only down side of all of this is that the DI's are full of electronics and fry on top of the engine. So they (RED)fail around 100-110 Kmiles. The black DI's used with the T7's are much more given to dying off a a tender age, from what I can gather.
Hope that this helps.
posted by 65.68.10...
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.
 |
 |
 |
 |
 |
