How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask GM Bob Your Own Question
GM Bob
GM Bob, ASE Master Technician
Category: GMC
Satisfied Customers: 960
Experience:  30 plus years experience as GM technician, ASE Master Technician and GM Certified
70078276
Type Your GMC Question Here...
GM Bob is online now
A new question is answered every 9 seconds

I have a 2007 Yukon xl Denali 6.2. When at idle the service

Customer Question

Dave
I have a 2007 Yukon xl Denali 6.2. When at idle the service stabilitrak and traction control off light comes on. When I hook it up to our tech 2 the codes for engine misfire detected and fuel system lean come up. Sometimes it will say that the camshaft sensor not working properly. Also if you go to misfire graphic at idle it shows multiple misfires on cylinder 7. If I unplug map sensor that is on top of the intake manifold the misfire goes away. I have replaced all the sensors, new throttle body, oil pump, oil sensors, intake manifold gaskets. If you have any ideas that would be great.
Submitted: 10 months ago.
Category: GMC
Expert:  Jeromy Madison replied 10 months ago.

Hello, are you still having an issue with this vehicle?

Customer: replied 10 months ago.
Expert:  Jeromy Madison replied 10 months ago.

I know that you may have thought of this, but have you inspected ALL of your grounds?

Customer: replied 10 months ago.
Yeah. We went online and found a chart that showed all of the ground locations. We checked and they seem fine
Expert:  Jeromy Madison replied 10 months ago.

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?

Customer: replied 10 months ago.
I think it's fine but I can double check it
Expert:  Jeromy Madison replied 10 months ago.

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.

Customer: replied 10 months ago.
Ok I will check it and reply back
Customer: replied 10 months ago.
Checked ground and everything is good. Terminal is ok. Ran a different wire and still the same thing
Expert:  Jeromy Madison replied 10 months ago.

Ok, let me do a little research and see what I can find with on the wiring diagram.

Customer: replied 10 months ago.
Ok thanks
Expert:  Jeromy Madison replied 10 months ago.

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.

Customer: replied 10 months ago.
I have replaced the pcm twice.
Expert:  Jeromy Madison replied 10 months ago.

Man I am very sorry that I don't see anything. I will opt out and maybe someone else can help you.

Customer: replied 10 months ago.
Ok thanks for your help
Expert:  GM Bob replied 10 months ago.

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

Customer: replied 10 months ago.
I have changed spark plugs. Checked all coil packs. Switched coil packs around. Done compression check. Compression was good. The misfire is only at idle. When you get above 1200 rpm the misfire goes away. Or when you unplug map sensor the misfire goes away.
Expert:  GM Bob replied 10 months ago.

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

Expert:  GM Bob replied 10 months ago.

I'm just following up to see how it's going?

Customer: replied 10 months ago.
Since we have been having the bad weather I haven't been able to check o2 sensor yet. Which one do I need to take out again. Also our internet hasn't been working.
Expert:  GM Bob replied 10 months ago.

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

Stay safe

Customer: replied 10 months ago.
There are 2 on the left side. I removed the one closest to the engine and the misfire is still there. If I unplug map sensor the misfire will go away. Why would it do that?
Customer: replied 10 months ago.
Thanks for your help with this
Expert:  GM Bob replied 10 months ago.

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?

Customer: replied 10 months ago.
You don't really feel it. It just shows up on the graph on the tech2. Yes it can do a crankshaft position relearn
Customer: replied 10 months ago.
I left the hole open.
Expert:  GM Bob replied 10 months ago.

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.

Customer: replied 10 months ago.
How do I do the leak down test?
Customer: replied 10 months ago.
One other thing. There's a certain place we drive by every now and then,but every time we go by that place the low oil pressure light comes on. That's the only time that it does that is when we drive by that place
Expert:  GM Bob replied 10 months ago.

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.

http://www.hotrod.com/how-to/engine/116-0406-cylinder-leakdown-tester/

As for the oil light. There has been a problem with the filter under the oil sensor plugging.

Customer: replied 10 months ago.
The sensor behind the intake manifold
Customer: replied 10 months ago.
We checked compression on all the cylinders and they were all close to the same.
Expert:  GM Bob replied 10 months ago.

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

Customer: replied 10 months ago.
No they were all about the same.
Customer: replied 10 months ago.
Within a few psi
Expert:  GM Bob replied 10 months ago.

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.

Customer: replied 10 months ago.
Ok I will try that tomorrow
Expert:  GM Bob replied 10 months ago.

That sounds good just keep me posted.

Thank you

Customer: replied 10 months ago.
The springs all look good. Everything looks normal. Today it kept giving the po174 and po171. Fuel system lean.
Expert:  GM Bob replied 10 months ago.

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?

Customer: replied 10 months ago.
Still misfiring on seven. No aftermarket stuff. All factory. The hose was cracked a little not bad so I replaced it.
Expert:  GM Bob replied 10 months ago.

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

Customer: replied 10 months ago.
Replaced hose before the codes.
Expert:  GM Bob replied 10 months ago.

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

Customer: replied 10 months ago.
Ok will do
Customer: replied 10 months ago.
It will be tomorrow. Has to go out of town today
Expert:  GM Bob replied 10 months ago.

That's ok just keep me posted.

Thank you

Expert:  GM Bob replied 9 months ago.

Just checking to see how its going.

Have you had any luck on fixing your problem?

Please let me know.

Thank you

Related GMC Questions