Misfire - P0301- Cylinder 1 Misfire
 

So far have changed the following:

Plugs
Coils
Injector 1

Attached is the freeze frame data. Any ideas?

Re: Misfire - P0301- Cylinder 1 Misfire
 

Can you feel a misifire? Is peformance suffering?
Did you reset the ECU/idle relearn after replacing those parts to clear CEL?

Do a power balance (drop) test on it:
* With engine idling slowly lift coil pack off spark plug and listen for spark (note spark quality).
* Lift coil pack off further and listen for idle to drop. Idle/rpms should drop and if not there is an issue
* Repeat this procedure by disconnecting the fuel injector harness..again rpms should drop

Do a dry compression test and if compression is low repeat test using a teaspoon of oil in cylinder. With oil added if compression raises it points to faulty compression rings.

Re: Misfire - P0301- Cylinder 1 Misfire
 

Reset the ECU
Disabled the fuel injector of cylinder number 1.

It was the same, no difference.

Went to plug the injector connector back in, and the wire (black) snapped. It looked badly rusted. Could it have been the problem? I have to get a new connector and see if this was the issue.

Re: Misfire - P0301- Cylinder 1 Misfire
 

As in the idle didn't drop (no difference)?
Or are you saying no difference in removing code/solving the issue?

If the injector harness wire snapped that easily..then it's very possible that is what's causing the issue as it likely prevented the cylinder from getting fuel.

Re: Misfire - P0301- Cylinder 1 Misfire
 

Both, it didn't make a difference.

Step 1 - ECU was Reset by removing the fuel injection fuse

Step 2 - The fuel injector connector to cylinder one was removed and there was no change

After the wire broke, injector 1 was disabled, that made it more likely it was a wiring issue.

If issue was spark related and If there was fuel in the cylinder there would be raw fuel coming out tail pipe or the smell of it would be very strong, which was totally absent.

Therefore, I presume cylinder 1 was not getting fuel at all and the broken wire was the culprit which has probably been causing the issue from the beginning. Furthermore, injector was moved from cylinder 1 to another cylinder and all the O-rings have been replaced (Old ones were brittle after 17 years), which eliminated any possibilities of vacuum leaks. Since the code was still cylinder 1, it was confirmation issue was not the injectors.

Initially the problem started when it was raining and humid, the perfect scenario where it takes a lot of current and voltage to overcome the resistance caused by moisture and corrosion. Issue started as intermittent , which was similar to fuel starvation, but became constant after wiring harness was moved around during the troubleshooting process. I suspect the wire broke internally due to corrosion and then simply gave away once it got moved around Anyhow, ordered a new connector and will replace and see if it solves the issue.

I don't have a wiring diagram, but if there was a way to test the wiring for voltage drop it would've been a lot easier.

Will update after this has been completed.

Re: Misfire - P0301- Cylinder 1 Misfire
 

Did you inspect the wiring for the other three cylinders? If one has corroded then likely others may follow.

For future reference..swap coils, plugs and injectors between cylinders to test first before replacing parts.

Re: Misfire - P0301- Cylinder 1 Misfire
 

This is a fourth issue in the general area which is caused by corrosion due to this vehicle being in a climate with salt on roads the first 10 years. The other injectors wiring seems to be okay. If it turns out to be a broken wire was the issue, then I won't be surprised at all. However, finding it was tough.

Re: Misfire - P0301- Cylinder 1 Misfire
 

A compression test was performed to validate it was not an internal issue with the engine. Dry compression test passed with flying colours where all cylinders were within 1 lb psi of each other. The problem cylinder (#1) had the highest reading, which rules out any internal mechanical issues with that cylinder.

Furthermore, the car doesn't burn any oil and/or there's no loss of coolant.

Waiting on new injector connector to arrive next week.

Re: Misfire - P0301- Cylinder 1 Misfire
 

Solved

It was a broken ground wire (brown wire) of the fuel injector connector that had caused the issue. It broke due to rust from years of driving in snowy climates. The engine is running without any issues and NO MORE MISFIRE(S)!!!

A broken wire was hard to find, because there was no visible rust and also the connector didn't show any damage. When the connector was removed multiple times for testing, that's when it finally broke, and then the problem was visible.

Re: Misfire - P0301- Cylinder 1 Misfire
 

Good job.
Always test first before replacing parts.