Troublesome misfire

Good afternoon,

Did they check the compression?

The catalytic converter melted from excess fuel in the exhaust and it overheated. That is common with a misfire.

Did they check the injector to see if it is allowing too much fuel?

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Odd, that a dealer cannot figure out a simple misfire issue. In most cases, you start with a compression test, look for a vacuum leak, verify fuel pressure and that the pressure does not drop with the key off. That would indicate it is leaking and allowing too much fuel.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Roy

They did not check that as far as I know. How can they check the compression? The intake completely covers the spark plugs. Wouldn't it misfire all the time if the compression was off? I drove it 85 miles the other day before it started misfiring. It doesn't have any codes but when I ran a "test" on the Torque app with a wireless OBD it said cylinder 1 had 3 misfire and cylinder 4 had 98 misfire 2 and ,3 cylinder had none. I will take it back to the dealership probably Thursday but was hoping to figure something out sooner. What about the ignition coils?

Did they replace the plugs? When you have them out, you insert the tester for the compression.

https://www.2carpros.com/articles/how-to-test-engine-compression

Torque app does not check the compression.

If you had a coil issue, it would code for it. Anything electronically controlled will code when there is a failure. There are no codes for mechanical failures.

Roy

I will have them check that next. What would cause the compression to be wrong and what would the fix be?

Also would it only misfire after it had run along time? What about the spark knock?

If it has low compression, they need to do a leak down test to see where the compression is leaking.

The head would have to come off after that for the repair.

The spark knock is from unburned fuel in the cylinder and it creates detonation.

Roy

Just got it back yesterday. They did a compression test with results being 149 on three cylinders and 150 on one cylinder. Can't remember which but they said it was good. They did not do a leak down test cause they said I didn't ask for one... but I did. I told them if it looked okay to replace all coil packs and all plugs (NGK iridium). Which they did. I picked it up and drove 110 miles with the AC on in 80 degree heat. No problems no misfires. Until 111 miles. It just cut off while driving no warning. Will turn over but won't start. It now has it's first trouble code of p0304. I noticed a slight scent of antifreeze but didn't see any leaks and it is almost full. And the engine felt relatively cool considering how far I had just driven it.

Okay, It needs to be checked for spark and fuel pressure to see which system has failed.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Roy

I was already thinking fuel problem. Just a hunch. But I will have both checked just to be sure.

Sounds like a plan.

Keep me updated.

Roy

I will thanks for the help.

You are welcome.

always glad to help.

Roy

The shop just called and said there is no fire to the coils and they don't know why. Any ideas? The engine turns over fine and the dash is all lit up but no fire.

OK, got it.

I attached a wiring diagram for you. The voltage for the coils comes from a fuse. I circled it in the diagram to be checked.

It sounds like this guy does not know what he is doing is he cannot figure something this simple.

Roy

They just called and said one of the new Aftermarket coils melted and several fuses we're blown. They replaced the fuses and now it runs but they recommend putting the old original coil packs back in as that doesn't seem to have been original misfire problem and the new coils are crap. So back to square one. But at least it runs again.

That's not good. If they melted that means there was a high current draw. My feelings are that mess may have damaged the PCM.

Roy

He said it runs fair..a little rough cause of the coil. But I don't think they have driven it. He also said they were checking for bad grounds that may have caused it.

I do not believe that. Something happened while he was diagnosing the engine.

Replacement coils do not melt without a reason. You said he had no fire to the coils. I think he jumped power to the coils from an outside source and jumped the wrong wires.

Roy

It died while I was driving it after the new coil packs. It was running fine and then cut off and would not start back up. He is telling me that it would not start because when I was driving it the coil melted and blew several fuses that kept it from firing again.

You never stated that part.

If that is the case, then you have a claim against him for any damage from inferior parts he installed as he stated.

He needs to replace with Nisaan original coils at his expense.

Was the check engine light on? How many miles on the motor?

Roy

No check engine light only a misfire code after the coil melted. 66000 miles. And the dealership just replaced the catalytic converter but said something else likely caused it to go bad. They just didn't know what.

He needs to get to the bottom of the issue.

Roy

I wish. I bought a new car so I wouldn't have to deal with stuff like this for a while... didn't work out that way. Well the dealership didn't fix so I took it to this other shop closer to home (the dealer is 80 miles away) they did the other stuff but I provided the parts. So if the parts are bad that's on me. I am just unsure of who to take it to next. Do I let the shop that has it keep poking around (I have been using them fairly successfully for a few years) or take it back to the dealership.

The converters fail from overheating. If your car has a misfire, it will damage the converter and that sounds like the reason it failed. The dealer should have been able to determine that.

As far as the parts, that's the chance you take in bringing your own parts.

Let him diagnose it for the failure and see. Tell him to check everything such as compression, fuel pressure, injector leak down as well. Something there is causing this issue.

Roy

I will do that tomorrow thanks.

Your welcome

Keep us updated

Roy