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for serious carbon buildup in the EGR i use oven cleaner, like easy off or something like that. drives my wife nuts cause she never has any oven cleaner under the sink. for the egr, youll want to clean the valve itself, mounted to the head behind the intake manifold, the tube that connects it to the upper plenum, take off the upper plenum itself and clean that passage with a bottle brush, and as much as you can get from the head itself.

i had the same thing happen to me once, EGR vacuum hose popped off, causing spark knock much like you are describing. my two cents


>>>*Good tips here, I might add that the setting slightly retarded may actually be correct for the combination.

Another possibility is the engine may have an aftermarket RV style cam, this can also require a tad less timing advance due to increased cylinder pressures. Normally most by themselves don't really affect the required setting, but add in other changes and the effect begins to stack up.

Of course as mentioned the head was likely surfaced, and increased compression enters into the mix, too.

It is certainly possible that a small retard of the timing will be a better setting, not affect power any, and result in even some small economy increase.....*EB

*Beats the he** outa me!....*LOL**...