Tach Filter test procedure for “NO Start” on Howell TBI systems with Vacuum Advance

Tach Filter Test Procedure

Tools needed for procedure:

• Test Light
• Flat blade precision and small flat blade screw driver
• 5/64 drill bit or similar

Directions:

1. Remove White wire of the Howell harness from the negative side of the coil or Tach Output.
2. Turn ignition ON engine Off
3. Attach Test light clip to 12 volt side of Battery or some sort of direct Battery power source
4. With the other end of the Test light probe, Rapidly Tap On and Tap Off the white wire that was removed from the negative side of the coil.
5. Listen for the Fuel Pump to run and the injectors to click.
6. If the injectors are clicking and the fuel pump is running , then you have an Ignition issue.
7. If the injectors are not clicking and the fuel pump is NOT running, then we need to proceed to next step.
8. Leave white wire disconnected from coil and safely set aside from shorting out.
9. Locate ECM and find the B5 location of the small ecm connector of the harness.

NOTE: All Tap On tests will be using the same procedure as above,Test Light clip attached to Battery Power source

1. B5 is the purple wire in the small connector located above, and Tap rapidly On and Off the purple wire terminal, making sure the ECM connectors are attached to ECM and Key On,Engine Off.
2. Listen for the Fuel Pump to run and the injectors to click.
3. If the injectors are clicking and the fuel pump is running, then you have a BAD Tach Filter. Follow the purple wire back into the main harness and locate shrink tube covered circuit board. Order new Tach Filter from Howell. New filter will have instructions on how to replace it.

If the injectors are not clicking and the fuel pump is NOT running, then we need to proceed to next step.

1. Because the Filter might interfere with the next Test, we need to remove the Purple Filter wire for proper diagnosis. Remove the Purple wire from the connector and insert a drill bit into the B5 location as shown below.

1. Tap rapidly On and Off the drill bit, making sure the ECM connectors are attached to ECM and Key On,Engine Off.

If the injectors are clicking and the fuel pump is running, then you have a BAD Tach Filter.

If the injectors are not clicking and the fuel pump is NOT running, then we have a BAD ECM and it will need to be replaced, be sure to transfer the two chips located in old ECM over and into new ECM.  Chips are located under the cover that is being held by two 1/4 inch hex head screws on top of ECM.