3rd cylinder misfire after exhaust pipe install
 

I own a 1996 LX Honda Accord, 4 cylinder. I had to get the car inspected in NY and have the exhaust pipe just before the muffler replaced as there was a quarter size hole in the existing pipe. The mechanic did the inspection and replaced the pipe, charged me $270, but after I drove 2 miles away I noticed the engine was knocking which it was not doing before the mechanic worked on the vehicle and the engine light came on. I took the vehicle back the next day and the mechanic diagnosed the problem as a 3rd cylinder misfire and told me that it was just coincidence (not anything he did) and so charged me another $185 to replace the spark plugs, change the oil and replace a gasket over the spark plug in cylinder three. I drove 2 miles back home and once again noticed the same knocking and the engine light came on again, so I drove it back. The mechanic diagnosed it again with the same problem and continued to stick to his guns that the exhaust pipe has nothing to do with the engine misfire in the 3rd cylinder. I said that perhaps when replacing the pipe he damaged something that resulted in a pressure build up in the system that causes the misfire. He said that was not possible and if that was the case all cylinders would misfire so he recommended that I add a fuel injector cleaner and then he’d check it out after the weekend. I am not happy, but added the fuel injector cleaner and the engine continues to misfire. What is going on? I have an appointment with this guy tomorrow and will not go back to this guy again after he fixes this misfire issue which I believe he/the new pipe installation caused. Any advice on what’s wrong?

First of all for future reference as long as you put the spark plug cables back on the correct cylinder (I, II, III, IIII) from the right (front) side to the left (rear) side, and thread the new plugs in carefully then you should never take the car to a mechanic to replace plugs, cheap plug are $3-$5 dollars each, so you'd spend max $20 dollars on that. As for the gasket I don't know how neccesary that was because that would typically only happen if there was execessive pressure as you said.

Secondly was it actually a "knocking" of metal on metal? Was it just studdering or consistent shaking? A knocking of metal on metal is typically one of three things. A: flywheel problem, essentially knocking the pistons into place instead of just sliding.

B: bad ignition timing (not sure if this could be caused by an exhaust problem) but the spark plugs prematurely ignite and the incorrectly timed ignition in the particular cylinder produces a pinging or knocking sound.

C: Incorrect engine timing (camshaft and crankshaft not correctly aligned) in an interference engine. If only off by a slight bit, the piston will actually knick the exhaust or intake valves. Typically though it is not a slight bit and you car is screwed.

chk plugs and plug wires first....if ok......have them do a compression test ,,dry and wet test

what is the code,,,,,, p0303??

replacing the exh pipe has nothing to do with what you are experiencing ,, no need to even open the hood to do the job

the knocking you hear is it engine knock or under car ?? did they install a non Honda exh pipe and it is not fitting properly ??

Last ,,,, i cannot believe that they only replaced 1 upper plug tube seal , that had to remove the valve cover ,, they should have replaced all 4 seals ,,,

On the LX there are a 8 seals. Pull the plug wire to #3 (second wire from the dist), is there oil on it?

i would ALWAYS replace the top seals first , a lot easier job THEN if that does not fix the problem and only then i would replace the lower rocker arm seals

lower seals are harder to do , upper seals very easy job .

^ I agree. Just wanted the OP to know if the oil came back, get the lower seals changed.