I’ve owned this car for nearly 15 years, and it has 53,000 miles on it now. It lives in a garage, in Northern California, where it’s rarely very hot and never very cold. It’s in great condition. I’ve replaced the timing belt a while ago and the shocks because it was time, also the accessory belts. Over the years I’ve had to replace both oxygen sensors after they reported in with a check engine light code. In the past 8 months I have had a recurring check engine light with a P0304 code (misfire on cylinder 4). All the jobs I’ve done are listed here.
- Cleaned every electric ground I could find
- Added a bottle of injector cleaner to tank of gas
- Swapped coil packs (there are 2, one for 1 and 4, 1 for 2 and 3). One coil sits on top of the sparkplug of 4 so no wires involved. No change at all.
- Replaced all spark plugs (no change)
- Removed and had injector of cylinder 4 professionally cleaned. They reported it was dripping and the internal filter was dirty. No change.
- Replaced fuel filter. It was dirty. No change, but it took 100 miles for the light to go on again.
- Discovered belt driving alternator was sort of loose, tightened it up.
- More injector cleaner (Techron).
After each step I reset the check engine light and then drive it. The light returns within 25 to 40 miles except for the time after the fuel filter replacement.
I have not yet checked the compression because I don’t have a reliable tester. It seems so unlikely that it’s compression with only 53,000 miles on the engine and I really never drive it that hard.
My next thought is that there’s enough junk in the fuel tank that I should replace the fuel filter again, because the last time I did it there was really a lot of black powdery stuff that came out of the old filter. But I admit I’m floundering.