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T7 Engine Management details?
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Posted by Dean (more from Dean) on Wed, 14 Jul 2004 05:51:08 Share Post by Email
In Reply to: Saab T7 Engine Management details?, perkj, Tue, 13 Jul 2004 23:31:25
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Very complex. General descriptions are floating on the net somewhere. Trouble shooting requires a Tech-II system. But in many cases, running problems can be fixed by attending to plugs and injectors. Sometimes TB needs to be cleaned. The T7 DI does not have the life expectancy of the red T5 DI. A spare DI is always a good idea.

The T5 and T7 systems do not have descrete knock sensors. The DI-ECU monitors the plasma resistance of the spark plug gaps and detects knocking conditions that way. So there are four knock sensors, the plugs. So if the plugs are wrong or fouled, that is trouble. The system can adjust mixture and timing for each cylinder. Overall boost levels can be reduced if neccessary. At lower RPMs, if the system detects that a cylinder did not ignite, it will respark the same fuel charge. I do not think that there is any way that the system can tune running mixture per cylinder. There can be differences in flow rates between injectors from manufacturing variations or fouling. The system can't resolve all of that with the combined exhaust flow o2 sensors. But, it might be able to vary individual injector flow parameters based on knock tuning. But one very quickly gets into speculation, as there is no published material that gets into such issues.

T5 was speed density and you could hijack the boost with a MBC. T7 uses a MAF and MAF flow targets are used instead of boost pressure targets. This compensates for hot humid air or higher altitudes. So also no huge power whan cold like the T5. The T7 uses a motorized TB that also does the criuse control and idle air control. So that is three devices in one. It also serves as a secondary boost control. If the air mass flow rates exceed target flow rates, the ECU does change the wastegate via the BPC, but also will throttle back the TB! So the T7 will fight with a MBC attempt. The TB is also has things to do for TCS, ESP, brake force distribution etc. So the TB servers several sub systems. A long way from an basic TB. If the TB gets fouled, and the motorized throttle can no longer follow or smoothly follow the throttle input and ECU demands, then things can be a mess and the ECU can trip a solenoid that locs the throttle plate up and posts a CEL. In this failsafe mode, you can still drive, but the petal will not get you full throttle and the ECU will not demand boost. So that sucks. The solenoid can be manually reset to restore normal operation if everything else is ok. The TB can get fouled with deposits that interfere with the stepper motor's ability to make it work. So cleaning the TB and a drop of oil in the pivots inside is a good idea. (T5 IACs foul badly over time, so there is a good reason to expect that the T7 TB will foul at small throttle settings that support idle speeds.)

So thats enough for one dose of coffee!

posted by 68.93.19...
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