see the old DeCarbon TSB thread has self destructed.

I like 1 qt of acetone, cheap paint store variety, mixed with 1 cup of kerosene instead of the expensive Ford or Seafoam stuff.
I suck it into the throttle body plate gap with an 1/8" tube at 2k rpm. engine off. let soak 1 hour
out on freeway for hard run.
every 20k > 30k miles more often if all city slow speed cold engine driving.

watch the tailgaters

Engine - Carbon Knock On Acceleration
Article No:
01-19-7

10/01/01
^ ENGINE - 4.0L OHV - CARBON KNOCK ON ACCELERATION

^ NOISE - CARBON KNOCK ON ACCELERATION - VEHICLES EQUIPPED WITH 4.0L OHV ENGINE ONLY

FORD:
1990-1997 AEROSTAR
1990-2000 EXPLORER, RANGER

ISSUE
Some vehicles equipped with the 4.0L OHV engine may exhibit an engine noise which may be perceived by the customer as a piston/connecting rod bearing knock. This carbon knock is heard only under load during the drive cycle. Carbon knock is a customer drive duty-cycle phenomenon that cannot be repaired with an engine exchange. This may be caused by carbon build-up within the combustion chamber.

ACTION
Verify condition. If normal diagnostics fail to correct the condition, de-carbon the combustion chamber to help quiet the carbon knock noise. Refer to the following Service Procedure for details.

SERVICE PROCEDURE
1. Use Motorcraft Carburetor Tune-up Cleaner PM-3.

2. Carbon removal:
a. Disconnect canister purge line from throttle body.
b. Attach a vacuum line to the canister purge port.
c. At hot engine idle, allow the engine to ingest 1/2 to 2/3 of a can of Motorcraft Carburetor Tune-up Cleaner. Use caution not to ingest too quickly due to potential hydro-lock issues.
d Shut engine off and allow it to soak for one hour.
e. Start engine, allow engine to ingest the remainder of the Motorcraft Carburetor Tune-up Gleaner.
f. Remove vacuum line and re-install canister purge line.
g. Road test vehicle at 3500 RPM for 2-3 miles.
h. Repeat above procedure two times for a total of three times.
i. Change oil and filter.

3. Review the customers' driving habits. The recommended drive cycle should include daily periods of engine operation above 3,000 RPM, such as a brisk acceleration from a stop position. This will break/burn the carbon off the piston head.

4. Use regular unleaded fuel, 87 Octane. Mid-grade and Premium fuels may increase the probability of carbon buildup, leading to a knock noise.

PARTS BLOCK
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage