Check timing with a light

[Carl Froehlich]

Recently an RV owner complained about extremely high CHT on his dual electronic ignition engine. The ignitions use a crank sensor and nothing unusual was found. With a timing light however timing (with the manifold pressure line disconnected) was somewhere between 41 and 45 degrees BTDC with the engine at 800 RPM, not the expected 21 or so. This timing was observed on both ignitions.

The ignitions were sent in for repair and now all is well.

This is the first I?ve seen of this happening, but as the manifold sensors failed in both ignitions I suspect it is happening on other people?s RVs.

Recommend doing a real timing light check at each Condition Inspection, and as one of the first steps when high CHTs have you scratching your head.

Carl

[crabandy]

I had a manifold pressure sensor go bad and did not catch it until I was verifying my crank sensors (SDS) with a timing light. Thankfully the upper and lower manifold pressure values reverted to base timing as programmed.

[rv6ejguy]

This why we generally recommend to use low MAP for advance only. If you lose a MAP hose, you just get the straight and safe rpm timing curve. Not sure what the other EI manufacturers are doing but I saw a curve from one with crazy amounts of advance, like 36 degrees up to 2200 rpm on the rpm table- relying on the MAP sensor to pull it down. Bad strategy IMO.

[scard]

Same event on my lightspeed a couple of years ago.

[DanH]

What brand Carl?