Q: cylinder 4 misfire code reading?

asked by on June 18, 2016

I have changed all spark plugs and two of the coil packs that were defected. I just did an oil change. Ive heard that it is rare for cylinders to go bad. One mechanic said I would have to replace the whole thing which would cost 2000 dollars which was seemed crazy. Would my next step be to change out fuel injectors/head gaskets or where should I go from here but keeping price in mind so I'm not changing out random parts. Car also seems to be running a little hot but not overheating by any means, would that mean that water pump would have to get changed in the near future. Also when the car is just idling after 8 min or so it starts to smoke out of exhaust my buddy said it was blue but it really is so hard to tell between blue and white. Could that be problem that ties into the cylinder issue. Hope this all helps, looking on cost effective next steps and a mechanics insight??

My car has 142000 miles.
My car has an automatic transmission.

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It is helpful to state what kind of Dodge it is as some motors have pattern failures that other do not. Either way, there are a few simple tests that can be performed on any fuel injected motor to figure out what is going on. As for the cost of repair if a cylinder is bad, 2000 may be correct. But before we go down that route, I can help you figure out exactly what the problem is. On some dodges, it wouldn’t be out of the ordinary for a cylinder to fail at 142,000 miles.

I assuming you have replaced the coil and spark plugs that serve number four cylinder. This is a good first step. You are correct in suspecting the fuel injector next. First use a noid light to see if there is an injector pulse coming from the PCM. If not, you will need to get to the PCM and test for the injector pulse there. If you find injector pulse at the PCM, it is likely a wiring issue, if not, it is likely the PCM. If you have injector pulse at the fuel injector, you should test the resistance of the injector and compare it to some of the others. If it is very different from the others, it is probably bad. I can’t tell you what the resistance value should be because I don’t know exactly what Dodge you have.

Next, if you have injector pulse and the injector has a good resistance value, it maybe clogged. Testing this is easily done by adding propane to the intake manifold while the motor is running. If it responds positively, you are on the right track. Since this is a computer controlled vehicle, it will react fairly quickly to the extra fuel added. Depending on the type of intake system it has, it may run better for a few seconds or thirty, then begin running bad again. What you are looking for is an improvement in how it runs at the moment of adding the propane. This test is often not conclusive to someone that lacks years of experience, so you will have to make the decision whether or not you think replacing the injector is the best next step.

The order you do these tests will be decided by the ease of each test depending on access to tools and the components involved. But you may want to begin with a cylinder leak down test if you feel there is a problem with the cylinder. You are testing for a head gasket failure, a burnt valve, possibly a broken valve spring that won’t close a valve or low compression which indicates a problem with the piston rings.

If it is a head gasket leak, your coolant will get low fairly quickly, but you won’t see any leaks on the ground. If the smoke out the tail pipe is coolant, it will smell sweet. Oil will smell burnt. Think of what burnt oil smells like. Under the right lighting, you can see blue vs white, but this is often difficult to differentiate. I rely on smell more than anything. If the smoke is oil, the oil level will be low as well.

To test a valve, you will need to perform a leak down test of the number four cylinder. Many will hand you a tool with a gauge and a valve, but this tool really isn’t necessary. The easiest way to do this is with a modified version of a compression tester. You will want to screw in the portion of the compression tester into the spark plug hole and put compressed air to it. Keep in mind, you don’t want more than about 50 psi. To much compressed air will simply push the piston down and open the valves. And that brings up an important detail when performing this test, you need to make sure that the cylinder is at top dead center. This ensures the valve are closed.

Once you have accomplished this and compressed air is in the cylinder with the valves closed, you will want to listen out the exhaust pipe at the rear of the car, open the throttle plate to listen in there, and remove the oil filler cap to listen in there as well. You are listening for a hissing sound of air passing. It will be an obvious sound of air moving from the source of the leak. If you hear hissing from the exhaust pipe, you have an exhaust valve problem. Hissing at the throttle plate is an intake problem and hissing from the oil filler hole is a piston ring problem.

Keep in mind, a little sound in the crank case, which is where you are listening through the oil filler hole, is normal. If there is a problem, the hissing will be very obvious.

If you discover a valve problem, remove the valve cover and inspect the valve springs. If one looks different than the others, then this is likely your only problem. If not, the head will need to be removed and the valves repaired.

If you feel like you need assistance with this, feel free to contact a certified mechanic who can diagnose your misfire and make the repairs that are needed.

Good luck.

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