Codes P0300 and P0302, misfiring, RPM's fluctuations on cold start

Hi,

On this engine, each cylinder has its own ignition coil. What can happens is where the coils go down through the valve cover, there is a tube that has seals on it. If the seals fail, oil can then leak into the spark plug tube that the coil is mounted to. If that happens, it can cause a misfire by causing the rubber boot on the coil to fail and short.

The easiest thing to do is remove the coil packs and inspect for oil on them.

If you look at the attached pic, it shows where the coil goes down through the valve cover to connect to the spark plug. That is where I feel the leak may be located.

I noted that you indicated cylinder 3 (P0302) has the misfire. If you look at pic 2, I highlighted the number 2 coil pack. Facing the front of the vehicle, it will be on your right.

Let me know if you have other questions or need help.

Take care,
Joe

Hi,

The fuel trims are a bit high (indicate the computer is removing fuel). But, they are not completely out of spec. I have a question. I'm not familiar with your scan tool. What is the fuel pressure?

The next thing I find of interest is that the new codes indicate misfires all on the same bank or side of the engine. It could be related to a fuel balance issue or pressure issue. Let me know if you have checked and what the pressure is in PS. If I'm reading the scanner correctly, it's nearly 1500psi, which would blow the system apart. If you look at the attached pic, it shows what pressure should be.

Also, in your second pic, it shows long term fuel trims as really high. Bank 2 (where cylinders 2, 4' and 6 are located, it is excessive. The system is extremely rich. We need to check fuel pressure.

Follow the attached link above and let me know what you find.

Joe

Hi,

Okay, that is within spec. Did you try switching the coil from cylinder 2 with a different one to see if the misfire chances cylinders?

Let me know.

Joe

Okay, if you still have the same problem, I'm starting to question if it is a fuel injector issue. If possible, follow this link and let me know the results:

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

Let me know.
Joe

Hi,

I understand. I was thinking something could be causing it to stick open. As far as further diagnosis, the next thing would be to check engine compression. If the cylinder is low, that also can cause a misfire.

I'm sorry. I feel like I just keep adding more to do, but I'm trying to touch on all the things that can cause the misfire. If it isn't ignition and seems limited to one specific cylinder, then it leads me to believe it is fuel related or a compression issue.

If you can, here is a link that shows how to test compression in general:

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

Here are the manufacturer's directions which include the specs:

__________________________

2010 GMC Truck Acadia AWD V6-3.6L
Engine Compression
Vehicle Powertrain Management Tune-up and Engine Performance Checks Compression Check Testing and Inspection Component Tests and General Diagnostics Engine Compression
ENGINE COMPRESSION
Engine Compression Test

Tools Required

J 39313 Spark Plug Port Adapter

A compression pressure test of the engine cylinders determines the condition of the rings, the valves and the head gasket.

1. Run the engine until it reaches normal operating temperature. The battery must be at or near full charge.
2. Turn the engine OFF.

Important: Remove the powertrain control module (PCM) and the ignition fuse from the instrument panel (I/P) fuse block.

3. Disable the ignition.
4. Disable the fuel systems.
5. Remove the spark plugs from all cylinders.
6. Remove the air duct from the throttle body.
7. Block the throttle plate in open position.
8. Measure the engine compression, using the following procedure:

1. Thread the J 39313 into the spark plug hole.
2. Thread the compression gage into the J 39313.
3. Have an assistant crank the engine through, at least 4 compression strokes, in the testing cylinder.
4. Check and record the readings on the gage at each stroke.
5. Remove the compression gage from the J 39313.
6. Remove the J 39313 from the spark plug hole.
7. Repeat the compression test for each cylinder.

9. Record the compression readings from all of the cylinders.

* The lowest reading should not be less than 70 percent of the highest reading.
* No cylinder reading should be less than 965 kPa (140 psi).

10. The following are examples of measurement problems:

* When the compression measurement is normal, the compression builds up quickly and evenly to specified compression on each cylinder.
* When low compression is caused by the piston rings, compression is low on the first stroke and tends to build up on the following strokes, but does not reach normal. Compression improves considerably with the addition of oil. Use approximately 3 squirts of oil from a plunger-type oiler.
* When low compression is caused by the valves, the measurement is low on the first stroke and does not build up even with the addition of oil.
* Leaking head gaskets will provide the same results as worn valves but engine coolant may be identified in the crankcase. In addition, a leaking head gasket will give low readings on paired cylinders.

11. Remove the block from the throttle plate.
12. Install the air duct to the throttle body.
13. Install the spark plugs.
14. Install the powertrain control module (PCM).
15. Install the ignition fuses to the I/P fuse block.

___________________________________________

Let me know if you are comfortable doing this.

Take care,
Joe

Hi,

To be honest, it would be odd. However, it is really based on how the vehicle was maintained. Other than that, we need to check the injectors.

Let me know.

Take care,
Joe

Hi,

There is a lot of carbon. However, if that was causing the valve not to seal, it would have been evident with the compression test. I will tell you that 140 is what they indicate compression should not be lower than. Just for curiosity, were the cylinders at 140 the ones that have the misfire issue?

Also, and I may have already asked if you have a live data scan tool, have you checked the signal from the engine coolant temp sensor? (ECT see pic 1) Also, have you confirmed there are no engine vacuum leaks when it's cold?

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know.
Joe

Hi,

At this point, what I would have to watch live data to determine if it is actually an ignition issue or mechanical issue.

Based on the compression, the work you have done, no vacuum leaks, fuel pressure within spec, and the fuel injection is working, that leaves the possibility of a weak valve spring or if the carbon is causing issues on and off. I would think it would have to be related to a mechanical issue.

Also, if it was a sensor, I don't see why it would affect cylinder 2. By chance, have you been able to check the fuel injector?

Let me know. Also, I will be having surgery tomorrow (Monday). Please hang in there and I'll get back to you as soon as I can. If it is more than a day or two, Ken, the site owner, will likely get back to you.

Take care,

Joe

I have seen a bad MAF sensor cause the misfire issue without throwing a code, also I would service the throttle bore. Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car:

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

and

https://www.2carpros.com/articles/throttle-actuator-service

After the work please clear the codes.

https://youtu.be/ahK_eucFi-k

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.