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How is Coking related to diesel engines?

Diesel engines: head-''decoked''

Diesel engines: head-''decoked''

EGR valve coking and sticking is not uncommon for the 6.0L Power Stroke Ford diesel engines.

Coking deposits in diesel engines are usually a build up of unburned fuel or oil in the exhaust system and related components (valves, turbo, EGR valve). This can be caused by poor fuel quality, over-fueling/leaking injectors, idling for excessive periods of time (especially in cold ambient temperatures), low engine operating temperatures, injection timing (calibration) or oil consumption.

Unburned fuel usually appears as white smoke, but over time the coking condition can result in excessive black smoke. Coking depositis can plug the EBP (exhaust back pressure) sensor tube, foul the EBP sensor, cause the EGR valve to stick open, block the EGR cooler, plug the MAP (manifold absolute pressure) (boost) sensor hose, or cause the variable turbo vanes to stick open (no power/boost) or closed (excessive back-pressure, black smoke, popping noise, bucking). The cause of the coking issue should be identified before replacing parts to prevent re-occurance.

An EGR valve that is coked-up, or clogged with carbon deposits, will reduce it’s ability to allow exhaust gasses to flow through it when it is opened ultimately reducing it’s effectiveness. These deposits may also cause the pintle valve (throttle position sensor) to stick or operate slowly making accurate control of the valve impossible. Should these conditions exist several drive-ability concerns may result. This includes lack of power, smoking, surging and the check engine light may illuminate accompanied by DTC’s P0401, P0402, P0404 or P1335. EGR valve diagnosis may lead to the removal and inspection of the valve.

Cleaning the valve under any circumstance was NOT recommended or a supported practice until now. Since then, TSB # 06-19-6 has been released with guidelines to clean and test the valve for proper operation. If the valve shows signs of excessive coking the root cause of the coking must be identified and corrected. Cleaning of the EGR bore and the intake manifold may also be required.

Clean the valve in a carburetor cleaning solution. You can buy a quart can at the parts store. Then use a spray carb-cleaner to get it surgically clean.

When clean, use compressed air or wipe the valve dry. Install new o-rings and base gasket supplied in the o-ring kit, Ford part number 3C3Z-9P455-AB, and re-install the valve. From this point, continue with diagnostics, verify the valve range and movement, clear all codes and retest. If the valve fails the range and movement test or otherwise fails electrically, replace the valve. Always road test the vehicle to verify the repair. GotEngines.com @ 1-866-320-1065.

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