Why misfire on cylinder

Consult your repair manual or factory service manual FSM for all the test ratings. With no indication of a bad coil, a return to the swap methodology sensible method had us switch the 1 and 3 coils, but the miss at 4 remained. One of three waste-spark coils on the Toyota V6. With P continuing despite plug, wire and coil checks, we were done with easy fixes.

On to the next suspect, indicated by the plugs lean read on 4 , misfire behaviors intermittent, heat-related and occurring at consistent rpm and the elimination of other suspects: fuel. Though an injector problem had been suggested earlier, it was best to rule out the ignition parts before moving on to a set of injectors that required some real wrenching to access. Have a few spare O-rings around. Expect to replace gaskets most of the time.

The fuel injector is nestled beneath the rail in this shot, with the rail holding it gently in the injector port. You must be equally as gentle. On this Toyota engine, the gray-top injectors often identified by color should test between 12 and 16 ohms. The Hole 4 shooter read 0. The bad fuel injector was just as dirty and slimy as the other injectors, so the multimeter was necessary to see it for what it was.

Speaking of dirty, a bottle of fuel injector cleaner could save you this job, should the injectors just be clogged and not mechanically toast. Considering all the fingers pointing at the fourth fuel injector, the time involved in the R and R of injectors was too much. Swapping two injectors, then reassembling and replacing the manifold, hoses, brackets and bolts only to see what was very likely the bad 4 injector shift the misfire to 2 was a big waste of time. The price for the failed gamble of just replacing 4 would only be doing the R and R anyway, so it seemed a risk worth taking.

Should this gamble pay off, it would put us in good shape much sooner than doing everything twice. The manifold on this Toyota — a two-piece clamshell type of unit — came off with the usual Toyota ease, and we had it back together in under two hours, torqued to go.

In standard no-drama Toyota style, it fired right up, the misfire gone. Now you do it. Click here to update settings. Learn more about this system and how to recognize problems in it. Ignition issues can lead to a variety of bad symptoms. Discover three examples of ignition system failure points on modern vehicles. Unwise driving habits can lead to unexpected wear or even breakdowns.

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Disconnect the fuel injectors one at a time and look for a change. If you are still having trouble finding the misfiring cylinder, you can disconnect the power to the fuel injectors one at a time to see what effect it has on the engine.

Locate the connector where it attaches to the back of the fuel injector. If you have trouble locating the fuel injectors, consult an application specific repair manual to help you find them. Test your fuel system if the injectors seem fine. Attach a fuel pressure gauge to the fuel pump test fitting at the end of the fuel rail on the engine. Find the appropriate pressure specifications for your vehicle in its repair manual and then compare it to the readings you get when the engine running at an idle, and then at the RPMs specified in the repair manual.

Replacing the fuel pump might require removing it from the fuel tank, so you may want to seek assistance from a professional mechanic. Replace the fuel injector if its not working. If the test light comes on, power is flowing to each injector. If you got an error code specific to your fuel injector, replacing it should solve the problem. Replace the mass air flow or oxygen sensors if they have errors. If your code scanner indicated that there were problems with the mass air flow sensor or oxygen sensor, they may be the cause of your misfire.

The mass air flow sensor is located on the intake pipe, usually just past the air filter. You can remove the oxygen sensor by disconnecting the wires and unscrewing it with an oxygen sensor socket. Make sure to connect the new sensors using the wires you unplugged from the old ones, then secure them in place using the same mounting hardware.

Method 3. Inspect the spark plugs for signs of damage. Use a spark plug socket to remove the plug so you can get a good look at it. The damage you see will help you determine the cause of the misfire. If the spark plug is just old, replacing it may solve the problem.

Make sure to replace and properly gap new spark plugs. A plug that is wet with gasoline or oil means the fuel regulator may have failed, or that there are serious internal issues inside the engine block.

If the plug looks fine, check the gap between the metal sticking out of the end of the plug and the base. You may also need to replace the wire that delivers the spark from the ignition coil to the spark plug. Use a multimeter to test your coil pack. Spark plugs ignite the air and fuel mixture using current transmitted from the coil pack, so a faulty one can result in a misfire.

Many vehicles will provide a specific error code if a coil goes bad, but you can test a coil by disconnecting the spark plug wires and connecting an Ohmmeter to the top two pins. Find the coil packs by running your hands along the spark plug wires moving away from the spark plugs. If the coil needs to be replaced, simply disconnect the rest of the wiring and unbolt it from the bracket.

Insert a new coil and reconnect it the same way the old one was. Do a compression test if air, fuel, and spark seem to be in order. Then remove one of the spark plugs and screw a compression gauge into its place. Turn the key and let the engine turn over four times, then check the reading on the gauge, it will stay at the highest point it reached. Make sure to reinsert the spark plugs after you remove the gauge every time.

Like the temperature test, all of the cylinders should have similar figures except one, if the misfire is being caused by a lack of compression. If the numbers are the same across the board, the problem is not compression related. If numbers are low across two cylinders near each other, it likely means the head gasket is bad in that area. You will need to have the the cylinder head removed from the engine to replace the head gasket. Other signs of a blown head gasket include finding coolant in your oil bright green or pink translucent fluid , bluish exhaust smoke color, and an oil leak where the cylinder head top half of the engine meets the block bottom end.

If you believe your cylinder head gasket has failed, you may want to take the vehicle to a certified repair technician. In the most extreme cases, an engine misfire can be caused by failed piston rings or even damaged cylinders or connecting rods.

If your spark plug was covered in oil, it may have been because the piston rings have failed, allowing the oil to move freely past the cylinder and eliminating compression in that cylinder. If this is the case, the crankshaft, connecting rods, and cylinders will need to be removed from the engine to replace the damaged components.

Hovig Manouchekian. The most common culprit for an engine misfire is lack of spark—usually because the spark plug needs to be replaced. Another common reason would be the spark plug wire, which delivers the spark from the ignition coil to the spark plug, and then the coil itself, which generates the electricity that's sent through the wire into the spark plug. Those are the three most common causes. More extensively, there may be combustion issues inside the engine.

Not Helpful 4 Helpful 4. Ryan Bacigalupi. This is likely due to weak rings.