How to test 99 subaru forester ignition coil

SOURCE: misfire code

Many things can cause a misfire,but basic mechanical checks or tests can be made relatively inexpensively.Compression testing the cylinders with a compression gauge will verify the general condition of the engine's piston rings and valve sealing capabilities.A leakdown test is similar to a compression check except that a leak down test is directed more towards verifying specifically the valve's sealing capabilities.A valve can burn or a bad seal occur between valve and seat...causing a misfire.Valves and piston rings are mechanical in nature,but there are many other possible causes.Vacuum leak,ignition problems,fuel problems,sensor problem,etc etc.Good luck.

xalint1

• 152 Answers
• Posted on Dec 12, 2008

SOURCE: Check Engine Light

Hello engelhard58
I have attached a link that can give you some of the reasons why your getting that code.I hope you able to get your answer out of that.
Mean of the code=P0420 Catalyst System Efficiency Below Threshold.
Link to site

SOURCE: check engine light subaru forester 03

try ebay or used i would just replace the one downstream one frist

SOURCE: how do i change the spark plugs on a 99 subaru forester?

Subaru Forester Spark plug removal: First, you must remove the air cleaner housing Move the tube from the air cleaner and the intake on top of the engine by loosening the hose clamps at each end. It is still attached to a hose underneath but can be put out of the way

Remove the top of the air cleaner and the filter.

Remove the two 12mm bolts at each side of the bottom.

The side of the bottom is rubber gasketed to the inside fender - just rotate slightly each way to loosen and pull off and put off to the side - there is still a wire attached.

Now pull off the spark plug caps on the side of the engine. This is a boxer engine which means the plugs are in a horizontal position on the sides. It is good to have a pair of spark plug pliers to do this as they are really difficult to remove. (spark plug pliers form a circle on the end when closed and are nice to grasp the caps with). Now you will need a 3/8 drive socket wrench, a 2" extension and a 5/8 deep socket Connect the extension and socket and feed it into the spark plug hole and over the spark plug. It is really deep inside. Now attach the wrench and remove the spark plug making sure you keep the tools level so as not to torque the plug side ways. Once the plug is real loose, unattach the wrench and hand loosen the plug with the extension because the wrench won't fit to remove the extension and socket attached. Remove the extension and socket and then spark plug. Put in the new plug reversing the steps.

SOURCE: Subaru forester 2001 code P0328 Knock sensor and

Replace knock sensor.