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1999 Honda CRV Random Misfires-Burned Valves

I’m not new to working on cars, but this one has me a bit confused:

I bought my kid a 1999 CRV AWD automatic after he hydrolocked his 2004 TSX driving through a flooded street.

It ran fine when we got it, it just needed tires and I didn’t know how old the timing belt was. A few weeks after I bought it I put a new timing belt and water pump on it. I also replaced the spark plugs and wires at the same time. A couple weeks later (he drives it every day) he said his CEL popped on. I pulled the codes and I had misfires on all cylinders. The car seemed to run fine so I just cleared the codes. A few days later he said the light came back on but the car seemed to be fine. I thought maybe the distributor was starting to go out but cleared the codes again and did nothing.

About a week later he says it’s running bad. I start it and I can see it has a dead miss. The engine light is flashing and once again: codes are 301, 302,303, and 304. I pulled the spark wires off one at a time with the engine running and cylinder 4 was definitely the one not firing. I tested spark, listened to the injector, then pulled the plug and saw it was wet with fuel. I did a compression test and had 30 psi.

It turned out to be a burned exhaust valve. I pulled the head and sent it to a machine shop for a new valve and full clean/valve job. I reinstalled it and the car seemed to run fine. A week or so later we’re back to having misfires on all cylinders! And this time I can feel an intermittent miss.

I have no idea what to do and I’m afraid if I do nothing I’ll get another burnt valve?

Ideas?

Have you adjusted the valves?

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Probably the most common causes of a burned exhaust valve is the valve clearance is too tight. This means the valve never fully closes. In the fully closed position the heat from the valve is transferred to the valve seat, which keeps the valve cooler. But if it doesn’t ever fully close, well you get the idea. If your engine is configured so measuring the valve clearances makes sense, that’s where to start. If it has hydraulic lifters, that makes it more complicated. If so could be an internal oil passage problem (clog etc) is preventing the lifters from working correctly. You might want to verify the oil pressure is correct using your own shop oil pressure gauge .

Another possibility for burned exhaust valves is the engine is running overly lean. A fuel trim test is where to start.

Did the machine shop check ALL of the valves?

Did the machine shop measure and adjust valve lash on all of the valves . . . ?!

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Two comments
One is to agree with db4690 about whether or not the entire head was serviced. It should have been.

Two is wondering whether or not the machine shop adjusted all of the valves down to 9 clearance. If so, it won’t take long to burn all of the exhaust valves.

I’d say pull the valve cover tomorrow and see if there is some play in ALL of the rocker arms.This will vary based on camshaft position of course. IF hey’re all tight the machine shop screwed up.
It’s also a good idea after 500 to 1000 miles run-in to recheck valve lash adjustment.,

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I adjusted the valves after reinstalling the head, but I’ll check them again today.