Fitfits

It's an '07 with 150k miles on it. It started misfiring ever so slightly a couple of months ago. Finally it got bad enough to start setting random misfire codes. So like any reasonable person I changed the plugs and coil packs. I thought I fixed it for about 5 minutes until it started to misfire again. It also doesn't want to accelerate. Any ideas? I'm lost... Thanks.

manxman

Adjust the valve clearance and your problems will go away. Valve clearance adjustment is part of normal maintenance for all Fits.

Fitfits

I don't understand...how could misadjusted valves cause random misfires??

manxman

Obviously, in the 150 K miles on your engine, the valve clearance has never been adjusted. That maintenance procedure should have been done a very long time ago,and you are lucky that the engine runs at all. Over time and miles, the exhaust valves tighten up and don't allow enough exhaust out of the cylinders for efficient combustion of each new cycle of each cylinder. At the same time, the intake valve adjustment becomes looser which further upsets the balance of fuel/air mixture in the cylinder. Miss-fires occur when there is an imbalance of fuel and air for each combustion stroke of the engine. Too much fuel, with too much old exhaust from the previous cycle, and not enough air, the spark plug won't ignite the charge in the cylinder, and/or the combustion is incomplete and can't deliver the usual amount of force to keep the engine running smoothly.

But don't take my word for it- see a mechanic and get the job done. You are only about 100 K late.

claymore

When the exhaust valve beats itself into the valve seat it causes the tip of the valve to be physically higher out of the head decreasing the amount of clearance between the valve tip and the cam follower. This causes the exhaust valve to open FURTHER not less. The result is a lean condition which results in a misfire. The symptoms of a valve clearance issue is rough idle, stalling and misfire. With that many miles it surely needs an adjustment.

Fitfits

I understand that the valves are way overdue for adjustment. However, if that's what's causing the problem wouldn't the misfire be constant rather than random and intermittent?

claymore

Nope this is a common problem and the misfire is intermittent depending on load.

m90polk1

Have you checked the car while running with a scan tool that shows live data, there should be live data stream of your engine running that can help you diagnose it. What codes are you getting and is it a misfire on one or multiple cylinders. Did you replace with genuine Honda OEM coil packs? Also did you check the wiring from coils to PCM, if you did check pcm output to coils? I'm pretty sure it should lead you in the right direction .

claymore

LOL ^^^^^ you haven't been around Fits much right. This is a common Fit problem which can be fixed by adjusting the valve clearances. With that many miles and never having been done it surely needs it. My own needed adjustment after only 25,000 and he has 100,000 more miles than that.

m90polk1

But wouldn't you have valve tapping noise coming from the the head because of clearance issues?