This is regarding a 2002 Honda Accord SE 2.3L 4 cylinder with 160,000 miles. I had a P0303 (misfire cyl #3) for a day or so that stopped on its own. A week later I now have a P0420 (catalytic system below efficiency threshold). When the P0303 was lit, the engine ran rough at idle. The P0420 is generally a steady light, but occasionally the check engine light will start flashing when stopped at a traffic light (idle 7-800), The CEL goes solid once I start driving again.

First, I replaced the plugs. Plugs were worn and had ash, which is consistent with burning some oil. (This car uses a quart of oil every 1200 miles or so.) I then checked spark to the plugs with an in-line tester. Spark seemed good.

Next checked the resistance on the fuel injectors. They were all about 10 ohms. This is 4 ohms or so lower than the minimum in my Haynes manual, but I concluded that the injectors are not the likely cause. My meter may not be that accurate and they're all about the same.

Last, I checked compression. Bad news. #4 202 lbs., #3 85 lbs., #2 194 lbs., and #1 209 lbs. Added a little oil to #3 and re-tested: #3 94 lbs.

Some history. About three years ago, experienced hesitation when accelerating from 55 mph to 70 mph, for example. Mechanic couldn't figure out why. I don't remember the details, but apparently the problem went away. Last year had acceleration problem again. Someone suggested VTEC issue. As part of my investigation, I checked the oil level. I was shocked to find it really low. I change oil every 6000 miles. An oil pressure light never came on. I suppose its my fault but the increase in oil consumption caught me by surprise. Since then I keep a close eye on the oil level, but I assume that running the car with low oil for at least a little while is probably contributing to the low compression in #3.

Haynes says the leakage is occurring at the valves or head gasket.

What is my next step? Pull off the valve cover and inspect? Any idea what a shop would charge to repair? Is this something I can do myself?

I just had shop replace right front ball joint and clean the egr valve (a previous CEL) in the last 3 months. This car is fairly clean and in good condition cosmetically, but it isn't worth so much that I want to spend a couple of thousand on this issue.

 

Compression numbers pretty much answer the question - you could do a leak down test on #3 just for giggles but at the end of the day.....the head has to come off and work done.

 

Okay, thanks. I think at this point I'm just trying to figure out if this something I want to take on. Maybe that's something I need to figure out for myself, but if anyone has any thoughts on cost, complexity, time involved, special tools needed, and the like, I'm listening.

 

My son took my air compressor when I relocated so not presently equipped to do a leak down test. It's one of the fun things about kids, they want your tools.