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how do you know that, (you never said)
P0303 DTC errors? that?
303 means.
#3 cylinders combustion energy is weak, to a tech it means the piston velocity was week, slow to accelerate, it was.
that can be.
1: spark bad (for gas/petrol engines)
2: injection bad.
3: this cylinder compression bad.
it is NOT just a spark issue, not at all.
it can even be air leaks (vacuum ) near #3 but that cause.
injection rates to seem wrong when ok. lean.
see?
id be all over compression tests.
after all cant burn fuel with weak compression.
it may burn but 303 will keep going.
then spark, cant burn fuel with bad spark
and last is fueling. (air and fuel mix)
in that order, is how it happens in real world.
but we take short cuts, sure, and new spark plugs are prudent fast and only $2 each.
Check these three things in the misfiring cylinder: spark, gas, and compression. One of them is wrong or missing. For spark check the spark plug and wire. Make sure you have spark on the plug wire, a strong blue spark. For gas, the fuel/air mixture may be wrong. Does the fuel injector pulse, putting gas into the cylinder? Possibly you may have a leaking injector or a clogged injector.
If gas and spark seem okay, you need to check compression in the cylinder. Low compression will cause a misfire. If compression is 20 or 25% lower than adjacent cylinders, that could be causing a misfire. For example, say numbers 1 and 3 cylinders had about 150 psi compression. 80% of 150 = 120, so if cylinder 2 is 120psi or less, that could be setting the misfire code. Low compression can be caused by valves not seating well, or bad piston rings, bad head gasket- something in the combustion area of the cylinder is losing compression.
It could be caused by a lot of different things, including a fuel injector, spark plug, spark plug wire, low compression, but in most cases it doesnt get to deep. I would start with checking the spark plug wire to cylinder number 5, then the spark plug. Moisture can cause a misfire so make sure the metal contact points are dry.
Have you measured the compression? Very low compression can be the reason. And the reason for low compression can vary - broken compression ring, worn valve/valve seat... You are sure you are getting a spark, just before the spark plug, right? Have you checked the timing of ignition?
Had there been a distributor like the earlier models it would be the one at fault. However now microchips control that aspect, the problem being synchronizing with the cam shaft rotation, the injector valves being controlled electronically are not opening & closing as per the compression in the cylinders leading to un-synchronized firing. Thus preventing the engine to start & hold a rhythm. This can happen overnight if the insulation has given way due to condensation, contact, etc. It's basically an electrical problem & I am afraid that the wiring will have to be checked thoroughly again meaning repeat of many of the tests which were carried out plus a replacement of the wiring near & around the induction coil & the chip involved. Hope this helps....sodeep
Misfires can be caused by worn or fouled spark plugs, a weak spark
(weak coil, bad spark plug wire), loss of compression, vacuum leaks,
anything that causes an unusually lean fuel mixture (lean misfire), an
EGR valve that is stuck open, dirty fuel injectors, low fuel pressure,
or even bad fuel.
A Random Misfire code usually indicates a vacuum leak or bad gas.
NOTE: If a misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression.
The cylinder is not getting fuel, spark or compression. You have already checked for spark on that cable and it appears to be good. Pull the spark plug and see if it is damaged. You can also switch spark plug and cable to another cylinder and see if the miss travels with the plug and or cable. If so, you'll know its the spark plug/cable that is bad.
You can check for fuel by listening to the fuel injector to see if it clicks. Use an automotive stethoscope or a long screwdriver--put the metal end of the screwdriver on the injector and the other end against your ear and listen to the injector while the engine is cranking or running. You should hear it click for each time it pulses fuel.
If both fuel and spark are good, then you are probably missing compression in that cylinder. You (or a mechanic) will need to pull all the spark plugs and do a engine compression test with a compression test/gage set. Lots of things can lead to poor or zero compression including: broken piston rings, burned/stuck/broken valves, cracked cylinder head or engine block, cracked pistons,etc.
Because one cylinder is "dead", the engine has to work extra hard to start and run against a cylinder that is dragging it down. If you find low/no compression in that cylinder, you will probably have to remove the cylinder head to correct it. A big expensive job. It may be cost effective to replace the whole engine with a rebuilt one.
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