I have replaced the ECU, #7 coil, plugs and wires. The car still shakes at idle and under acceleration has no power. The mechanic that I use, now thinks that it could be either a week valve spring or a bent valve. How do I know that these will fix the problem or is it likely that this is just another guess at the problem.
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Re: dead cylinder/ misfiring cylinder
Wow the first thing should have been a compression check i would not go any further with out doing it should have been done first before changing all those parts if it has good compression then go from there
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scan test for misfire code/s than move spark plug and wire to other cylinders, clear and recheck misfire info, if it moved than replace plugs or wires, if it didnt change, check ignition coil for output, if ok , than check compression, if ok , than check injector circuit with noid light, and measure injector impedence, if ok back pressure test exhaust for plugged cat.
It could be couple problems: -Misfire. (Include bad injector, Coil, spark plug wire) -Lost compression due to broken valves, cylinder wall and head or gasket.
Solution: 1 -Do compression test. - If not with in specification (Too low) Need rebuild engine due to broken valve, blow out gasket or even broken cylinder wall. -All cylinder has good compression: Now need to check Spark plug, wire and all injector. Injector must be with in specification (In Ohm) Follow its manual.
I am having the same issue on Mitsubishi Galant 02. Clattering on acceleration, herky jerky idle. Pulled a code multiple cylinder misfire. My mechanic's diagnosis is bad valve cover gasket causing oil to seap into the spark plugs and bad timing belt, which I have not replaced at 150k miles. I do however know my fuel injectors do need cleaning, he hasn't ruled that out either. Have you pulled any code on it? I have read on engine knock sensor going out on some of these also. Hope this helps some.
In modern cars so much can go wrong to indicate an issue and a computer in the car can get confused as to what is really occurring. In most cars a misfire indicates either an incorrect firing order, shorted wires, bad plugs, or bad coil. Since you have replaced the wires and plugs we can rule those out. Im also assuming after the second engine code you pulled #2 plug and made sure it wasnt fouled with oil, was gapped correctly, and reinserted. To produce a sufficient spark for combustion the alternator sends power to a "Coil" which is in reality a storage point that then sends an amplified electrical current down the spark plug wire to the cylinder to fire the plug. If the car is truly misfiring you will notice a rough idle, fluctuating RPM's, and lack of acceleration. If you are experiencing any of these I would look at replacing the coil. If you arent experiencing any of these I would have the code cleared again and complete one drive cycle 100 miles and then have codes read again. If you still get a Misfire error some other causes known to occur with Rio's are fuel filter issues, gas caps, and fuel injector issues. Although rare, these can cause issues with the cars fuel delivery and emissions which can confuse the sensor in the ECU. I would try injector cleaner, replace the fuel filter, and gas cap . If funds are an issue then based on symptoms I would start with injector cleaner first $3, Filter $12, Gas cap $12, Coil $48 to $200+