A Flooded Engine

There is something else that can cause a loss of compression that does not involve a mechanical failure. Your cylinders can actually lose compression due to too much fuel getting into the cylinder; this is referred to as flooding. This washes the oil away from the cylinder walls, so the piston rings can’t seal.

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When you try to start an engine with this condition, it spins very fast and doesn’t sound normal at all. It sounds like it has no compression. A quick way to confirm this is to remove the spark plugs. If they’re wet with fuel, you might have a flooded engine. A flooded engine has no compression, hence the no-start. Remove the spark plugs and leave them out to dry.

Once you’ve done that or once you install new plugs, you need to start the engine in a special way called “clear flood mode”. On a fuel-injected engine, if you depress the gas pedal, usually past 80%, the fuel system goes into what’s called clear-flood mode.

During this time, the computer shuts off the fuel injectors so no more fuel is delivered while you crank the engine; hence, you can clear the flood. I usually jump in, mash the gas to the floor and start cranking. Don’t crank for too long at a time, because you can burn up a starter doing this.

After a few cranks, you might notice the engine trying to start. Keep cranking till it does. Once it starts, there will likely be a big cloud of smoke and a lot of fumes, so be sure to do this in a well-ventilated area. Probably the most common cause of this failure is short tripping, meaning driving a short distance and shutting the engine off. This does not allow for a full warm-up and fools the fuel injection system when you go to restart it later. It adds too much fuel, and thus you get the flooded condition.

This happens a lot on Hondas. I can’t tell you how many times a car gets towed into the shop only for me to crank it in clear-flood mode for a bit and fire up. This really freaks tow-truck drivers out BTW.

Here is a quick video explaining everything:

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