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Discussion Starter #1 (Edited)
2013 Traverse Stumbles on light acceleration No Codes

I have a 2013 Traverse that stumbles randomly during acceleration.
Replaced the injectors with a set of cleaned referbs. This has eliminated a consistent misfire in cylinder #5. Replaced the plugs and coil packs as well. Performed compression test on all cylinders all around ~160lbs.
The MAP and MAF sensor has been swapped with a known good sensor as well as the throttle body. The PCV and Airfilter have been replaced. The intake valves have been cleaned. The problem remains. Random stumble on light acceleration.

The STFT & LTFT still favors heavily to the negative side. -10 to -15 both banks on LTFT.
What I have noticed is if I disconnect the PCV quick disconnect from the inlet tube, the trims all move quickly to +/- 5 of zero and the car runs ok.

My question is why would this be? Why do I need more air? or why is the car getting more fuel than necessary?


 

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How did you clean your intake valves ? Walnut blast?

When you say "stumbles", might you be describing "Low speed pre-ignition ?

(LSPI) is a premature combustion event, occurring prior to spark ignition
it occurs when engines operate at low speeds and high loads.
It can result in extremely high cylinder-pressures and can lead to heavy knock

Also,
You said fuel trims get better when you disconnect the clean side PCV breather hose from the air intake plenum

Did you also say .. the "stumbles" go away when you disconnect the clean side PCV breather hose from the air intake plenum?


And... regarding fuel trims ...
Did you drill out your dirty side PCV orifice?
Did you drill the fixed dirty side PCV orifice top hole to 1/8" and the 2 bottom holes to 5/64 ?
 

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Discussion Starter #4
Timing Chain and Misfire ?

Identified that @1800-2000RPM the engine will misfire on cylinder #3 at a notable rate.

When you say "stumbles," might you be describing "Low-speed pre-ignition? << I thought it was LSPI but, after reviewing the oil and mode 6 data. I do not believe this to be the case.

Did you also say? The "stumbles" go away when you disconnect the clean side PCV breather hose from the air intake plenum? << I only noted the trims moved closer to zero. I replace the PCV orifice, and this observation is a red herring.


Yes, I did clean the intake with walnuts.


I was convinced it was ignition related, after swapping the trigger wires on the x3 connector for wire #28 & #14 and moving the coil pack connectors from 3 to 5 and noted no change. I can now rule out ignition.

Now I am finding that when I disconnect the timing actuators on Bank1, the misfire counts do not increase. When I connect the actuators, the misfire counts increase.

The car has 82K miles on it,

1. When do you need to replace the chains?

2. Why would the check engine light not eliminate if the chains are stretched to a point where it will misfire?

3. How can I conclusively relate the misfires with the timing chain stretch?



After 2 months of tinkering, this is the first time I can directly relate a misfire to a process. (remove actuator connector > Misfire count does NOT increase) when connected Misfire count does WILL increase)
 

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Discussion Starter #5
It appears one of my problems was the wiring to the injector located under the manifold. After removing the injectors and the wiring on Bank 1. I hand taped each wire pair with cloth loom tape, then replaced the harness. Zero misfires after 100miles.


The next item I have found is a that oil and sludge can affect the CAM actuator performance. Added Seafoam to my oil. Will see how this goes and see if I need to remove and clean the actuators to assure they reacte quickly.


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Conditions for Setting the DTC • The ECM detects that the average of the actual camshaft angle measurements is greater than 10 degrees of the parked position angle on an engine start-up. • The condition exists for greater than 4 seconds, or a cumulative of 30 seconds.



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Conditions for Setting the DTC The ECM detects a specific cylinder misfire rate of greater than 100 counts in less than 17 engine revolutions, and P0087 is set. The condition exists for greater than 4 seconds or for a cumulative of 30 second
 

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Discussion Starter #6
After confirming the Ignition coils were fine
Wiring to the injectors were fine

Plugs were fine
Injectors were fine
Wiring to injectors were fine
PCV was fine
Air filter was fine
EVAP valve was fine
Throttle body was fine


I found that the stumble @ 1800-2000 was caused by the VVT actuators. I pulled all four, removed the screens, cleaned them in acetone, flushed the actuators and then used air to blow them through with the aid of a 9volt battery.
 
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