Miata Technical Service Bulletin

Category Applicable Model(s) Subject
Bulletin No. 004/93
Issued 6/3/93
B Listed Below Engine noise due to carbon accumulation

Applicable Models/Vins

1990 - 93 Protege
1992 - 93 MX-3 (V-6)
1990 - 93 MX-5
1989 - 93 B2600
1989 - 93 MPV (4 cyl.)


If engine noise is heard on initial start-up and decreases as the vehicle achieves operating temperature, carbon may have accumulated in the combustion chamber and on the piston tops.
NOTE: Additives in some fuels and continuous "short trips" may contribute to carbon accumulation.

The noise that occurs is similar to Hydraulic Lash Adjusters (HLA) noise. However, unlike HLA, the noise will peak and decrease as the engine RMP increases. Before beginning HLA diagnostics or replacement, perform the carbon cleaning process described in this bulletin.

Vehicles exhibiting the above symptoms should be repaired according to the instructions below. Inform the customer that the noise does not contribute to engine deterioration and the use of gas treatment to prevent carbon accumulation will prevent reoccurrence of the noise.

Repair Information

Carbon accumulation can be removed using Mazda Top Engine Cleaner (P/N 0000 77 2025) which is available through your parts department. The cleaner should be induced through a throttle body vacuum port with the vehicle idling. Diagrams are attached to assist you in locating the correct port.

Carefully read and follow the instructions that come with the cleaner. Recommended induction procedures are as follows:

  1. Operate engine to normal operating temperature then turn engine off.
  2. To inject the cleaner into the engine, use the canister purge vacuum port. This will allow even distribution of the cleaner. Refer to pages 3 of 10 through 9 of 10 for the vacuum port locations.

CAUTION: The Mazda Top Engine Cleaner must be fed into the engine through the correct vacuum line and at a feed rate not less than 1.5 minutes per half container with an orifice (P/N E5B6 13 986) in the feeding hose. A faster feed rate may result in liquid accumulation in a cylinder resulting in hydraulic lock-up and engine damage.


  1. Place the other end of the hose in the container of top engine cleaner.
  2. Restart engine.

WARNING: An excessive amount of exhaust smoke will be produced in the next procedure. Use an exhaust hose to vent the smoke.

  1. Allow idle to stabilize. Then feed the cleaner into the engine by releasing the pliers while idling up and down (between 1500 - 3000 rpm) a few times until 1/2 of the cleaner is used. At this point, let the idle drop. The engine should stall. If it doesn't, turn engine off.
  2. Let the vehicle sit for at least one hour or up to 24 hours. The chemical's cleaning ability increases the longer it is allowed to saturate the carbon.
  3. To flush the remaining carbon from the engine, repeat steps 2 to 5 using the remaining 1/2 of the cleaner. DO NOT let the engine stall. Increase the idle up and down between 1500-2000 rpm.
  4. Remove your feeding tube and reconnect the original line.
  5. Take the vehicle on a 3 or 4 mile performance (i.e. full RPM range) test drive to remove any remaining cleaner or carbon.

NOTE: After verifying the noise has been eliminated, change the oil, oil filter and raise the engine RPM several times to circulate new oil throughout the engine.
As a preventative measure, use a known gas treatment additive to prevent repeat carbon accumulation (example: Chevron Techron).

Instructions for using Top Engine Cleaner

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