454 EFI Running Awful - Timing? Knock Control? ??

[lakejohanna]

Hello. I've got a 94 Echelon with a 454 EFI-Ski engine. It is actually a salvage project which was previously sunk. I've had it for a couple years, fixed it up, and it was running real well until a few weeks ago when it started running horribly. Summary:

- It starts and idles fine.

- It throttles up under no-load fine.

- The gas is clean and fresh, for certain.

- It has fuel pressure under load

- Compression is fine

- Plug wires are on right

- There are no EFI codes set

- Base timing is set

- Knock sensor replaced

- It pings and/or backfires when throttle is applied under load

- I don't even get enough horsepower to plane

By process of elimination there isn't much left to try. Any suggestions? I'm wondering about the timing advance - given the pre-sunk condition perhaps the distributor isn't behaving? How do you check timing advancement anyway?

There is a module between the knock sensor and the ECM, 805443 - "Spark Control Module", which is no-longer-available or I would have replaced it. Anyone know what it does? Know if it can be replaced with one for a 5.7L?

Thanks - JK

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[areamike]

I say look at timing first.

[EZSnow]

How do you check timing advancement anyway?

Not sure if they are mechanical, vacuum, or electronic advance on those engines, but one way to check it would be to put a timing light on it while it's acting up. Remove the engine hatch and have someone drive the boat while you watch the timing tab with the light. Maybe it's retarding, maybe it's WAY advancing. Maybe it's jumping allover the place. Don't know until you check.

Just don't get you, your clothing, or the timing light cords caught in any of the belts!!