[SOLVED] 2012 6.2L Yukon Denali XL 172000 miles? Need help and cannot figure this very random problem out.

[testdepth]

Truck sits all night and get in to go to the store in the morning. Drive about two miles from home and engine is not fully at 210F yet with gas tank full. Stop at stop sign and turn left. Slowly accelerate but truck starts acting like it will shut off. Sort of like running out of gas as RPMs bounce up and down and engine stumbles. I slowly pull to the side of the road and stop and shift back to park. The truck settles out at idle and is fine driving the rest of the day. This scenario has happened randomly since last year. Sometimes it goes weeks or months without a problem and then it will do the above. Never throws a code or check engine light.

This truck runs fine 99% of the time with no other issues or problems.

02 sensors are original with 172000 miles but I don't know if they would cause this??

 

[Joseph Garcia]

When you say 'never throws a code', what are you using to look for a trouble code?

If you want to get to the source of your issue more quickly, use a quality bi-directional scanner, where you can monitor items in real time, like your O2 sensors, and check for deep trouble codes. Otherwise, you will be firing the parts cannon, hoping to stumble onto a solution.

 

[SpareParts]

Long shot but check wiring.
Jiggle and move every wire you can see. Check plugs.
Could be at a certain temp every thing has expanded just right to cause a momentary short or loss of communication.
That could cause the ECU to shift its perimeters and pulling over and letting it run till it straightens out fixes or masks the problem.
Long shot but odd things happen.

Not reading 210 after 2 miles is normal, i believe.
Do you let it warm up at all before driving?
I let mine warm up to the first mark on the gauge between cold and 210 before i drive. Takes about 2 miles after that to get to 210.

 

[Doubeleive]

shouldn't be hard to figure out since it is a repeatable cold start issue.
I would start with something simple like monitoring the fuel pressure, you can get a $35 harbor freight tester, connect it and stick the gauge up under the hood gap so you can see it while driving.
key on / engine 0ff should read 50+ psi
engine running pressure is normally 42/43 psi, which may rise with acceleration.
so if the pressure is dropping just driving normal, not messing around trying to make it go less then it could be a fuel pump issue, which will typically not throw a code.
other than that you could connect a decent scanner and monitor the injectors, spark count and see if anything else raises it's head.
one thing I would recommend in any case is be sure your battery terminals are clean and tight. you could have a poor connection cold then as it heats up it creates expansion and the problem goes away.

02 sensors are rated for 100k so that is a maintenance item that needs to be done, regardless
delphi's are fine when available, that's what will come in a ac delco box anyway. rockauto probably has the best deal
when the 02 sensors are replaced use a obd tool to clear the computer or disconnect the battery. that resets the computer to learn the new sensors otherwise it just uses the previous sensor data.

 

[testdepth]

When you say 'never throws a code', what are you using to look for a trouble code?

If you want to get to the source of your issue more quickly, use a quality bi-directional scanner, where you can monitor items in real time, like your O2 sensors, and check for deep trouble codes. Otherwise, you will be firing the parts cannon, hoping to stumble onto a solution.

TOPDON bidirectional scanner

Already fired parts cannon because there is no information about this problem anywhere on the internet. Replaced within the last 6mos

OEM fuel pump and sensor
OEM crank sensor
OEM fuel injector sensor
OEM coolant temp sensor
Throttle body
MAF sensor
Coil packs
Spark plugs
OEM negative battery cable
Valve cover gaskets and grommets
Radiator and both hoses
Installed AFM delete into OBD port
Added additional ground from front of engine block to the driver side fire wall
OEM braided ground strap from engine block to driver side fire wall
I drove it while cold intentionally trying to recreate this problem by driving at different speeds, while at low speed jerking the steering left and right, hard breaking, running over bumps, running around the roundabout in both directions. This truck never missed a beat the whole time. Drove normal and would not stutter, stumble or die.
While it was running I tugged on and shook every wire under the hood and nothing happened.

FRUSTRATED

@SpareParts

 

[testdepth]

Long shot but check wiring.
Jiggle and move every wire you can see. Check plugs.
Could be at a certain temp every thing has expanded just right to cause a momentary short or loss of communication.
That could cause the ECU to shift its perimeters and pulling over and letting it run till it straightens out fixes or masks the problem.
Long shot but odd things happen.

Not reading 210 after 2 miles is normal, i believe.
Do you let it warm up at all before driving?
I let mine warm up to the first mark on the gauge between cold and 210 before i drive. Takes about 2 miles after that to get to 210.

Usually we just get in and go but may have to let it warm up and see if that changes what happens

 

[testdepth]

shouldn't be hard to figure out since it is a repeatable cold start issue.
I would start with something simple like monitoring the fuel pressure, you can get a $35 harbor freight tester, connect it and stick the gauge up under the hood gap so you can see it while driving.
key on / engine 0ff should read 50+ psi
engine running pressure is normally 42/43 psi, which may rise with acceleration.
so if the pressure is dropping just driving normal, not messing around trying to make it go less then it could be a fuel pump issue, which will typically not throw a code.
other than that you could connect a decent scanner and monitor the injectors, spark count and see if anything else raises it's head.
one thing I would recommend in any case is be sure your battery terminals are clean and tight. you could have a poor connection cold then as it heats up it creates expansion and the problem goes away.

02 sensors are rated for 100k so that is a maintenance item that needs to be done, regardless
delphi's are fine when available, that's what will come in a ac delco box anyway. rockauto probably has the best deal
when the 02 sensors are replaced use a obd tool to clear the computer or disconnect the battery. that resets the computer to learn the new sensors otherwise it just uses the previous sensor data.

I've already checked the fuel pressures and they are good.

I'll change the 02 sensors next.

 

[Doubeleive]

I've already checked the fuel pressures and they are good.

I'll change the 02 sensors next.

I've already checked the fuel pressures and they are good.

I'll change the 02 sensors next.

if it is electrical/fuel/air then the scanner should make it pretty evident, hook the scanner up, bring up the live data and watch that data when the problem is happening
looks like you are throwing parts at it without diagnosing the cause. The scanner is a good way to sort that out.
the computer will allow x amount of things to happen before it decides to throw a code, that translates into poor driveability.

 

[Gearz]

There is a cluster of grounds on the left lower side of the engine in back of the power steering pump that are hard to see unless you have a lift. The grounds are known to cause issues so remove and check for corrosion or wires pulling out of eyelets. Worth a try? The fuse box under the has corrosion issues also and can cause intermittent problems.

 

[Bronson357]

Mine does the same only when below 60° or so outside. Sometimes when it's real cold it will take 20 min to run OK. I have it tracked down to intake manifold gaskets. I will report back,may be a while probably won't do them until spring and it won't act up until winter

 

[testdepth]

Mine does the same only when below 60° or so outside. Sometimes when it's real cold it will take 20 min to run OK. I have it tracked down to intake manifold gaskets. I will report back,may be a while probably won't do them until spring and it won't act up until winter

Would that mean you have a vacuum leak at your intake manifold?

 

[Bronson357]

Yes exactly, may not be your problem but sounds like mine and yours

 

[rdezs]

Kind of sounds like the vapor canister purge solenoid on the intake manifold..... Takes about 3 minutes to swap it out, should probably be changed anyway due to age.

You should be able to see it functioning on the live data on a bidirectional scanner to either confirm or rule it out.

The ground on the driver's side of the block down low behind the power steering pump is an important one.

Age of the battery cables? They do tend to fail from inside out. Positive and negative.

 

[testdepth]

Kind of sounds like the vapor canister purge solenoid on the intake manifold..... Takes about 3 minutes to swap it out, should probably be changed anyway due to age.

You should be able to see it functioning on the live data on a bidirectional scanner to either confirm or rule it out.

The ground on the driver's side of the block down low behind the power steering pump is an important one.

Age of the battery cables? They do tend to fail from inside out. Positive and negative.

Purge solenoid takes about a minute to test. Unplug electrical and unplug the line to the canister. Start the car and if there is vacuum at the solenoid it's bad. Mine is brand new.

Negative battery cable is brand new.

 

[testdepth]

Just installed a brand new DELPHI OEM MAF sensor. Next will be all 4 O2 sensors (these are the factory originals now 14yrs old).

 

[swathdiver]

Just installed a brand new DELPHI OEM MAF sensor. Next will be all 4 O2 sensors (these are the factory originals now 14yrs old).

Aftermarket sensors do not play nice with the computers on these trucks. You are introducing new problems with aftermarket sensors.

If it came in a Delphi box, it's not GM/ACDelco. We see this especially with the oxygen sensors. Delphi is an OE supplier but the sensor in their box does not look like the Delphi sensor in an GM/ACDelco bag/box.

My first thought upon reading your original post was an electrical problem or torque converter. The rpms shouldn't bounce around and usually only do that with a failing converter.

A depleted or weak battery can cause all kinds of gremlins like this too, even internally corroded battery cables.

 

[testdepth]

Aftermarket sensors do not play nice with the computers on these trucks. You are introducing new problems with aftermarket sensors.

If it came in a Delphi box, it's not GM/ACDelco. We see this especially with the oxygen sensors. Delphi is an OE supplier but the sensor in their box does not look like the Delphi sensor in an GM/ACDelco bag/box.

My first thought upon reading your original post was an electrical problem or torque converter. The rpms shouldn't bounce around and usually only do that with a failing converter.

A depleted or weak battery can cause all kinds of gremlins like this too, even internally corroded battery cables.

The sensor I received in the Delphi box is a brand new Delphi sensor stamped DELPHI on the part. The best GM MAF sensor replacements are OEM parts from AC Delco or Delphi, ensuring precise calibration and preventing poor engine performance, stalling, or false codes common with aftermarket brands.

 

[Charlie207]

Purge solenoid takes about a minute to test. Unplug electrical and unplug the line to the canister. Start the car and if there is vacuum at the solenoid it's bad. Mine is brand new.

Negative battery cable is brand new.

Can you explain this a little more? Where is the "Bad" vacuum coming from?

I'm having intermittent stalling issues, similar to your initial description, and I've been fighting this for a while. It's more pronounced with really cold weather.

 

[testdepth]

@Charlie207

At minute 3:14 (do not need to remove harness as he did). Disconnect the electrical plug and the line that runs to the EVAP canister. Start the truck and place your finger like he does and check for suction. Suction means it's bad.

 

[Fless]

These valves can also be intermittent, so that's something to watch for.