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Cylinder 3 misfiringvery little compression measured at 65
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Posted on Jan 02, 2017
SOURCE: misfire in cylinder 3
I recently had that (po303) misfire in cyl. 3 on my 2002 Mazda MPV LX with the 6cyl. 3.0 ford duratec engine (the only engine installed that year). 75k miles. The engine was studdering while at idle and upon accelleration. It was worse when the AC was on. The check engine light came on. I went to Advanced Auto Parts. They loaned me a code reading handheld computer. An Actron OBD II. PO303 misfire in cyl.3 was the verdict. I then got on the internet to do some research. Found that the problem could be a number of things. Coil packs and/or wiring harness, spark plugs, egr valve and/or ports, fuel pump or filter, fuel injectors etc. etc.. I decided to try what I thought was the simpilist remedy first. I purchased new spark plugs, retrieved some tools from the garage and opened the hood. Though I've performed all the other routine maintenance items like oil changes, battery maintenance, air filter etc., I never really looked for or noticed the spark plugs or their location. The front bank of 3 plugs was a breeze to change out but the rear bank....well they havn't been changed yet. Not so simple. At that point I decided that since I would have to remove the intake manifold and all the wires,hoses and etc. would have to be unattached, I might as well change the 3 coil packs and recondition the 6 fuel injectors while I had it apart. The cost and hassle of those fixes then lead me back to do what my old school, auto mechanic all his life father, alway told me. "Look at the easy fixes first". Many of us think that since everything nowadays is so complex that the fix must be complex also. Well, I then purchased a bottle of Chevron Techron Fuel Injector Cleaner. So many other brands were on the shelf to choose from. Seafoam, Lucas, Shell, CRC, STP, etc., etc.. Through netsurfing I discovered an old CARTALK Q & A. They kinda gave a halfhearted nod to the Chevron product. It stuck with me so I tried it. Within 10 miles the engine began to run better. The more I drove the better the performance. The Check engine light went off. No more misfire in cyl. 3 and no more code po303.
Posted on Dec 07, 2008
Posted on Feb 14, 2009
I have changed a few cylinder heads under warranty for this type of problem. The exhaust valve guides wear, this causes the exhaust valve to seat badly, giving low compression. if one cylinder compresion reading is more than about 50 psi below the others, then this warrants head removal. It is quite a job, due to the fact that the camshft id chain driven. If you are up for it then once the head is removed, poor liquid into the exhaust ports and see if it leaks out through any of the exhaust valves.
Posted on Jul 23, 2009
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