GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello, are you still having an issue with this vehicle?
I know that you may have thought of this, but have you inspected ALL of your grounds?
What is the condition of the ground terminal at the battery? The wire is in good condition and there are not cracks or anything with the terminal?
If it were me, I would replace it to be sure that is not the issue. The things you described are very, very common with a bad ground.
The computer will put out false codes and read things incorrectly if it is not getting the ground signal that it wants.
Ok, let me do a little research and see what I can find with on the wiring diagram.
I have done some research and investigated the wiring diagram for a while and there is real relationship between those things.
This leads me to agree with what I read from others and that is the pcm is bad.
I have seen several issues like this and found that the pcm is the cause. Several unrelated issues randomly appearing.
I wish I had the magic answer but that is where I would look at this point.
Man I am very sorry that I don't see anything. I will opt out and maybe someone else can help you.
Hello my name is ***** ***** I can help.
Can you post your VIN#
When you set a misfire code it will disable stabilitrak and traction control.
I need to ask have you looked at the spark plug? Have you check for spark? Have you done a compression test?
If you done more let me know.
Sorry for so many questions.
Please get back with me
Do you have any engine noise?
Have you done a leak down test on the cylinder?
Have seen valve not seating.
I have had a valve spring broken causing misfire with no noise.
Also found a catalytic converter cause one cylinder to misfire.
If you remove the front O2 sensor and check for misfire. If they are gone you have a bad converter
When you cause other codes the misfire chart goes to default and does not work in some cases.
Let me know if this helps
I'm just following up to see how it's going?
Sorry to hear about the bad weather.
The O2 sensor to remove is on the left side. The side that #7 is misfiring.
It is the one before the converter.
Also leave it electrically plugged in.
Thank you for getting back with me
The reason it stops misfire is because you are setting a map code. The ECM disregards ***** ***** because of the new code set.
You did leave the O2 sensor hole open on the exhaust?
Do you feel the misfire or is it just showing up on the scan tool?
Can your scan tool do a crankshaft position (CKP) variation learn procedure with a scan tool?
Ok do the relearn. But I don't think it will help
Need to do a leak down test. Checking for bad valve not seating.
Need to inspect the valve springs and make sure the rocker arms are moving the same amount when cranking.
When you did the compression test what was it? Did you compare the other cylinders?
Here is The tool GM uses for leak down test.
J35667-a cylinder head leak down tester.
Here is a link on how to do it.
As for the oil light. There has been a problem with the filter under the oil sensor plugging.
Yes the sensor on the back side.
What is close anything more than 10-20 psi different. May have a bad valve or broken spring
With a bad spring or a valve seat starting to go bad. May not find it with a compression test.
At lest pull the valve cover a look at the spring and move meant.
That sounds good just keep me posted.
Sorry for the delay just got home.
Did this happen after you removed the valve cover?
If so make sure the vacuum hose going to the valve cover is not cracked.
Is it still misfiring on just #7?
Do you have a factory air filter to intake system?
Do you have any aftermarket system on this truck?
You replaced the hose before or after the lean codes?
Need to do a leak down test on #7
I don't know if you can do this.
If you have a hose that will screw into the spark plug hole. The other end hooks to shop air.
Need to back off both rocker arms. Apply air to the cylinder. There should be no air leaking out past the valves.
If you hear air in the exhaust or intake you have a bad valve
Does your scan tool display fuel trim? Short and long term
Let me know what your reading are in closed loop.
At idle and at a steady 1500 rpm
That's ok just keep me posted.
Just checking to see how its going.
Have you had any luck on fixing your problem?
Please let me know.