What you're likely looking for is a way to *override* the ECM's control of the timing, which is not a simple task and should only be done by someone with extensive experience in automotive electronics and engine management. Attempting this incorrectly could severely damage your engine.
Any attempt at altering the spark timing would involve one or more of the following complex methods, none of which are simple "bypass" switches:
* Modifying the ECM programming: This requires specialized equipment and software to reprogram the ECM's internal map. This is the most sophisticated and potentially dangerous method.
* Interfering with the sensor signals: You could potentially alter signals from sensors like the crankshaft position sensor (CKP) or the camshaft position sensor (CMP) to trick the ECM into changing the timing, but this is extremely unreliable and risky. Incorrect signals can cause misfires, engine damage, or even a no-start condition.
* Using an aftermarket ignition system: This replaces the factory system entirely, allowing for more control over spark timing. However, this is not a simple bypass; it's a complete replacement.
* (Only applicable if it has a distributor): Manually adjusting the distributor's mechanical advance mechanism (if it has one, which is less likely on a 1991). This is generally only applicable to older, carbureted systems and not recommended for a fuel-injected system like that in a 1991 Trans Am.
In short: There's no "bypass" switch. Any modification to the spark timing requires advanced knowledge and specialized tools. If you're trying to troubleshoot a timing issue, start by diagnosing the problem using a scan tool to read the ECM's diagnostic trouble codes (DTCs). If you lack the expertise, consult a qualified mechanic.
