Misfire code P0303?

1998 FORD MUSTANG

202,000 MILES • 3.8L • 6 CYL • 2WD • AUTOMATIC

MICHAEL RAINEY JR

MEMBER
4 POSTS

I know it's a misfire code in cylinder three. I replaced coil, spark plug, fuel injector, fuel filter. Reset to computer and still getting code. What other things can I do to fix this problem? I noticed that when I was replacing the fuel injector for cylinder three that the spark plug had an excessive amount of fuel. I am going to do a cylinder test on it this weekend. Can you tell me what the PSI should be at as well? Thank you in advance.

Sep 21, 2022 at 3:21 AM

JACOBANDNICKOLAS

✓Experienced Mechanic
110,240 POSTS

Hi,

Make sure the new coil is providing spark to the cylinder. If the plug was wet, it sounds like it wasn't firing.

Here is a link explaining how it's done:

https://www.2carpros.com/articles/how-to-check-for-ignition-spark

If it has spark, then compression needs checked.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-test-engine-compression

Pic 1 below are the directions specific to the vehicle. Note that Ford doesn't provide a specific compression reading. Instead, they provide an acceptable range only. The last pics are the range charts.

Let me know if this helps or if you have other questions.

Take care,

Joe

See pics below.

Images (Click to enlarge)

Professional Diagram for 2CarPros Members
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Sep 21, 2022 at 11:27 AM