What it is for
Some older GM ignition systems send the trigger signal straight to the ignition module, and the module fires the coil at a fixed timing. The Ignition Bypass function takes that decision away from the module. The trigger goes to the ECU, the ECU works out timing, and it sends an adjusted fire signal back so the module fires the coil at the right moment.
Without bypass enabled, the module keeps firing at its own fixed timing, and changes to your ignition table will have no effect. That is the first thing to suspect if timing refuses to move on one of these setups.
Setup
| Setting | Value |
|---|---|
| Ignition Bypass Output | Any available DPO |
| Pull Up | 5.00 V |
| Active State | High |
All three need to be right for the module to switch into bypass. Once it's running, check with a timing light that the timing you see on the engine matches what the ECU commands; our timing light guide explains how. For the ignition setup itself see Ignition System, and Elite users can refer to Ignition Bypass on Elite.
