Decarbon procedure

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Thanks to Doug Lewis.

There is a decarbon proceedure for Explorer's and Rangers with 4.0L engines. The trick is to make it work for the SHO. Carbon fouling and dropped cylinders are really bad for a few reasons:


In a DIS system, two spark plugs fire at once. One is on the compression stroke and one is on the exhaust stroke. The coil is in the middle and the plugs are each end of the secondary windings. The block completes the circuit. The problem is that when one side of the circuit opens up, it takes out the other side. If you drop two cylinders from the engine, you pump a ton of raw fuel into the cats. We all know what happens when you overheat the converters ... don't we.

Our engines have a quench area at the top and bottom of the combustion chamber. If this area gets a high concentration of carbon build-up, it will hit the piston when it gets to TDC. This sounds like a bottom end knock. Plus, it's not too good on the bearings.

The carbon that accumulates in the combustion chamber takes up combustion chamber volume, reducing chamber volume and raising compression. This could cause the cylinder to pre-ignite or ping.


The procedure is not too complicated, so here goes.

Find the canister purge port on the intake manifold. It's the one near the Idle Air Bypass (IAB) valve, opposite the throttle body. Remove the hose and attach a length of vacuum hose to it. Start and warm the engine. Take a can of Top Engine Cleaner (I use Ford Carb Cleaner and Engine Tune Up -- 16 oz. Blue can). Rev engine and hold about 3000rpm. Use the vacuum hose to suck the cleaner into the engine. It will cough, spit and sputter, while pumping out white smelly smoke from the exhaust. Inject half the can of cleaner into the engine slowly, then suck in the rest of the can quickly and to try to make the engine stall. If it doesn't, then shut it off. Let this cook for about fifteen min. Start the engine and rev until it will idle. Fill the can with water and repeat the steps. Then drive the hell out of it until the smoking stops (about 5 miles of hard acceleration). This should take care of the carbon.