DirectParts.com has many neat Installation/Service/How-to articles for our motorcycles. One such article I found useful was the, “Motorcycle Compression: How Much Should I Have? 8/19/2001 by Sisco.

Here is a direct quote from the article:
“Keeping an eye on your compression is a good way to assess the condition of your top-end. Heat and wear gradually reduce the piston-ring and valve seal which keep the pressure in the cylinder causing power loss. Head gaskets eventually begin to leak from the heating and cooling cycles and can blow out unexpectedly. A simple compression test when your motorcycle is new will give you a baseline to compare future checks, but if you are already riding a higher mileage bike, check your service manual for the exact compression specs. Most big motorcycle run about 150 psi. Here's the procedure for checking compression:
· Remove both spark-plugs
· Ground both leads so the coil isn't damaged
· Install compression gauge, even cheap Car-Store gauges work fine
· Hold the throttle wide-open
· Crank the motor over until the gauge settle
If the reading seems low, squirt a bit of oil into the spark-plug hole to give the rings a better seal. If the reading increases the rings are worn and cylinder maintenence is needed. If one cylinder is more than 10 lbs higher than the other, it may have a burnt valve, seat, or the ring/cylinder damage. Since each piston has separate compression and oil control rings, low compression doesn't always correlate with oil burning, but can cause fouled plugs due to incomplete combustion.”

I want to modify Sisco’s procedure a bit. I want to do the compression test without the injectors squirting fuel or the coil being energized. I did a compression test on my 2005 Road Glide with the following changes.

1. Replace or Clean the air filter
2. Remove the right side cover and remove the EFI System Relay
3. Remove both spark plugs
4. Install the compression gauge
5. Turn the Run/Off switch to Run
6. Turn the Ignition switch on
7. Hold the throttle wide open
8. Press the Start button
9. Take the reading after 4 revolutions
Note: The pressure (PSI) rise should be very rapid.

At the conclusion of the test the TSM/TSSM will have the following fault codes:
P0261 – Front Injector Open
P0263 - Rear Injector Open
P1001 – System Relay Coil Open
P1003 – System Relay Contacts Open
Clear the DTC codes using this procedure.


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For those people who are interested, I made a simplified schematic diagram of the EFI fuel supply power line.

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what was your PSI readings? What is in the "normal" range? Also, did you run the test on a cold engine or warmed? When I do this on an auto I warm for a few minutes first.