jdub;1003290 said:
Not if you understand how it works
In the words of the late Arthur Clarke: "Any sufficiently advanced technology is indistinguishable from magic"
Those old enough to have dealt with carburetors and centrifugal/vacuum advance distributors will remember how two things were required when setting ignition timing:
1) Idle speed had to be correct to prevent mechanical advance.
2) Vacuum advance had to be defeated.
Idle speed was checked and set manually while defeating vacuum advance usually involved disconnecting the vacuum line from the distributor. It's no different with the TCCS except it's done for you electronically. When T and E are jumped the ECU does two things in relation to timing:
1) Idle is brought to the correct rpm and held there.
2) The ESA (Electronic Spark Advance) System is disabled.
Neither of these things can happen if the IDL contact is open. Barring other problems that's mainly why it's important to check codes prior to setting timing.
Btw I often see various and conflicting terms used when talking about ignition timing. "Base" timing for example. The correct terms are as follows:
1) Initial Timing: timing resulting from the physical position of the CPS/distributor when T and E are jumped. Initial Timing is what you set with a light.
2) Basic Timing: timing calculated on engine load (airflow) and speed (rpm). Basic Timing is added to Initial Timing whenever T and E are *not* jumped. Basic Timing is what replaces centrifugal and vacuum (speed and load) advance in conventional ignition
3) Corrected Timing: timing calculated using the trim inputs. Coolant temp, idle contact, knock, AC on, O2 sensor idle stabilization correction, etc. Corrected Timing can be an additive or subtractive (advance or retard) angle from Basic Timing and is the timing sent to the igniter. Put another way Initial Timing + Basic Timing + or - Corrected Timing = IGt.
The same type of thing applies to injection duration but I'll leave that for another thread.
