7.3L Start of Injection Offset

[Power Hungry]

Hey all...

It occurred to me that many folks don't understand how the SOI Offset table functions in relation to overall timing. It's a little bit tricky to get your head around since the SOI offset is calculated in milliseconds (actually, in microseconds) of delay between the time the injector is energized and the time that fuel actually starts to flow from the nozzle.

It's important to understand this and how it relates to the flow characteristics of the injector if you want o have any chance of the timing table values to actually mean anything.

The table itself takes into account the engine oil temp (EOT), which affects viscosity and how slowly the oil flows, and ICP, which affects the movement of the injector plunger. The higher the ICP, the faster the injector moves. The higher the EOT, the faster the oil flows.

In the normal operation range (from idle to moderate load at operating temp), the table is fairly flat. However, as ICP climbs, the offset reduces a little bit to account for the faster travel of the plunger. Also, also EOT drops and viscosity increases, the offset is also increased to account for the slower flow of the engine oil.

I've attached a spreadsheet below which calculates the actual degrees of injection offset based on the current engine speed and the offset time in milliseconds. This is useful to get an idea of just how much timing is be compensated for at various engine speeds, and how it affects overall timing.

I hope this helps.