2016 Yukon Denali P0300 & P0106

[cnunez]

Hey all,
Pulling onto the highway lastnight and was accelerated to merge when the truck downshifted and began hesitating. Had a flashing CEL and immobilizer light was on.

After getting towed home and scanning the car I had the following codes.
P0300 Random/mult. Cyl Misfire.
P0106/P0106PD MAP/BARO Ckt range/perf.
After having the vehicle off waiting for a tow it would not start.

A little history on the vehicle.
Car now has roughly 91k. Has an ecu/tcu tune for over a year with AFM/DOD delete (was done around 60k). AFE Stage 2 dryflo (truck was tuned with intake installed). Oil change and air filter cleaning every 5k.
I just did an oil and filter change with RP 5W30, new Delco plugs and exhaust donut gaskets to fix exhaust leak at 87k end of June. Car ran perfect after tune up and just made a round trip from CT to FL last month with no hiccups.

Not sure if anyone has had similar issues and has any idea where I should start looking.
I'm not convinced it's plugs or wires since I got a random/mult cyl Misfire? I've read about possible valve spring issues. The car wasn't making any ticking noises so not sure if I had an afm failure either.

Any advice is greatly appreciated and sorry for the morning novel!

-Chris

 

[cnunez]

Had a mechanic friend plug in his scanner since mine only reads codes. Checked the fuel trims and looks like it may be a failed cat.
Hoping to drop the Y pipe tonight and see if it runs better.
I think it would make sense since I went to accelerate and the car started misfiring when it was driving normal previously.
Will keep the post updated incase someone else ever has similar symptoms

 

[cnunez]

This thread has been a bit of a self update but I'll share anyway.
Loosened the nuts to both headers and started the truck. It runs rough with the exhaust disconnected of course but idle bounces around 750 and it doesn't stall now.
Going to drop the Y pipe and inspect the cats with a scope.
Strangely the Misfire code did not come back BUT the P0106 for the MAP won't delete. I think I need a few drive cycles before it will?
Just alittle weary about buying a Y pipe if not needed. Will update with pics soon.

 

[Doubeleive]

might want to replace that map sensor just for good measure there only about $25 or so plug-n-play, cat failing at 91k would be a little early but it can happen, sucks because right now there up in price. aftermarket cat's are double the price they were pre-covid

 

[cnunez]

might want to replace that map sensor just for good measure there only about $25 or so plug-n-play, cat failing at 91k would be a little early but it can happen, sucks because right now there up in price. aftermarket cat's are double the price they were pre-covid

Yes was thinking the same on the sensor. Found it so strange that the car idled nearly fine with the cats disconnected. I would think if there were no exhaust blockage then it would still run poorly/stall with them disconnected

 

[cnunez]

Another update folks....
Pulled the Y-pipe and checked all cats. Nothing collapsed and they are relatively clear.
Pulled the passenger side valve cover over since we heard some ticking. Cyl4 valve spring was broken. My scope wasn't small enough to fit into the cylinder. Will be putting a stock spring in and running the motor. If everything is fine I'll be upgrading all springs.

 

[cnunez]

Replacement valve spring went in lastnight. Truck is up and running. No CEL, No Misfire or other noises. Think it's safe to say everything else is healthy.
Will be ordering a full set of springs tonight and swapping them all out ASAP

 

[G00se]

Replacement valve spring went in lastnight. Truck is up and running. No CEL, No Misfire or other noises. Think it's safe to say everything else is healthy.
Will be ordering a full set of springs tonight and swapping them all out ASAP

Mine is at the dealer now getting two broken valve springs replaced. 86k mi, very similar symptoms. Yours gives me hope! Fingers crossed though.

 

[cnunez]

Mine is at the dealer now getting two broken valve springs replaced. 86k mi, very similar symptoms. Yours gives me hope! Fingers crossed though.

Good luck!

 

[G00se]

Good luck!

Fixed! Now flapper valve is broken. Dealer wanted $1700 for new exhaust. It’s always something. Maybe good excuse to go aftermarket.