Reading the plugs

[andywehrle]

We put Vibrant to bed for the winter last week. When I removed each plug to squirt MMO in each cylinder I noticed that #1 & #3 were burning rich and #2 & #4 were burning clean.

Any ideas what the engine is telling me?

Andy

[ArtJ]

If those two plugs are from the rear 2 cylinders (not positive of location)
they could normally run cooler due to tilt of engine. Maybe trying a
hotter plug will help. Others have recommended hotter plugs in recent
threads.

[andywehrle]

It's not the rear two plugs that are running rich. It's the #1 and #3. that seems weird to me. Not sure what she's telling me.

[CalebD]

For the sake of clarity the plugs are numbered 1 - 4 starting from the flywheel side back to the transmission - sequentially. The firing order is 1 - 2 - 4 - 3.
I would guess you might have your ignition cables to the plugs mixed up given the firing order they were designed to use.
FWIW our 43 year old A4 gets fouled spark plugs frequently enough - likely because we don't let the engine get up to operating temp often enough and perhaps some valves and rings are a bit worn. Spark plugs are cheap compared to pulling the engine for an overhaul.

[andywehrle]

OK, thanks for the refresher. I'll triple check the firing order next time I'm aboard - maybe this weekend. If it's wrong, it wouldn't be the first time I've seen what I wanted to see instead of what was there.

[sastanley]

andy,

I notice that #2 & #4 on mine seem to slightly more fouled than #1 & #3. However, when I pull each of the plug wires with the engine running, I cannot discern a difference in the amount of power one cylinder makes over the others, so the physical state of the plug is inconclusive. - When I put the plugs back in, I rotate them too.

If you have any of the old Chilton's books for one of your cars, they had a section in them on spark plugs with great pictures to explain what was going on inside the cylinder based on the observations of the spark plug(s).

[rigspelt]

That got me trying this google search, which turned up some great photos and references: "spark plug diagnosis".

[sastanley]

Rigs, the images that show up on the top of the list are the old Chilton's pics that someone must have scanned in...great detective work!