2012 Yukon XLT with mystery rough idle and misfire codes

gotliebk

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Vehicle History: Purchased in 2012 and driven until Aug 2020 without any significant issues beyond routine maintenance. Oil used throughout is AMSOIL Signature Series 5W-30 on extended change cycles (every 15k-20K miles).

All spark plugs and wires changed at 1/20/2018(115K) with AC Delco 41-110 plugs.

Transmission flushed by dealer at 1/23/2019 (139K)

New battery from Batteries+ on 7/2/2019 (Duracell SLI48AGM)

Front and rear brakes from O’Reilly’s and installed by me on 7/28/2019 (149K)

Vehicle slowly developed a rough idle in August of 2020 with an intermittent P0303 OBD code (Cylinder 3 Misfire). Code would only set during long periods of idling but would reset itself after 30-50 miles of driving. No noticeable issues other than at idle with transmission engaged. Over a 5 month span, the code only set three times and cleared on its own without being reset. Rough idle was really only detectable with vehicle in Drive or Reverse and fully stopped.

Jan 2021 Plugs Changed for Cylinders 1,3,5,7 - No change in Idle roughness. No OBD-II codes.

Vehicle passes emissions inspection on 4/08/21 (181,984) at local lube shop. No OBD-II codes.

On 4/29/21 Vehicle fuel injection system power flushed by same lube shop. No OBD-II codes. Still rough idle.

In May of 2021 vehicle displayed a new code of P0300 (Random Cylinder Misfire) and would not reset on it’s own. The following actions were taken to eliminate this code.

Replaced all 8 Ignition Coils with Duralast C1512-8 5/17/2021

Replaced all 8 fuel injectors with AC-Delco 217-3411 5/23/2021 (2nds ordered off of EBAY)

Checked fuel injector electrical function with noid light after replacement on all cylinders— all injector leads firing.

Checked fuel pressure using OBD scan tool(not actual gauge). Static pressure was 58-60psi and running pressure was 43psi.

Replaced both Primary S1 O2 Sensors with Bosch 15200 6/03/2021

Replaced MAP sensor with Duralast SU9491 6/03/2021

Replaced MAF Sensor with Duralast DL-3091 6/03/2021

After sensor replacement all codes cleared but rough idle continued. No codes displayed for two months of driving. Rough idle worsened but still no codes.

Replaced Throttle Body and Sensor with Duralast TB1032D 8/3/2021.

Performed Idle Position Relearn Procedure (but not sure this actually works without advanced diagnostic tool)

Rough idle was diminished but not eliminated. Cylinder 3 Misfire code showed as pending but MIL was not set.

Cylinder 3 misfire (P0303) code resurfaced on 8/5/2021 while driving. Mil was set.

8/13/2021 Vehicle taken to dealer for recalled airbag replacement. While there I had them compression test the engine. Engine produced 135psi on all cylinders but cylinder three failed a “leak down” test. Dealer tech said it was due to “camshaft roller failure” without opening any covers. I declined to let them investigate further as it took them three days just to get that far.

After getting the vehicle home from the dealer, I removed the entire intake manifold and replaced the intake manifold gaskets on both sides. While I had the intake out, I noticed that some of the bolts holding down the “valley cover” or “valley pan” were loose so I torqued them down. These bolts were in the vicinity of cylinders 1 and 3. Also while cleaning the manifold, I noticed significant amount of oil in the manifold. Cleaned the manifold completely and re-installed it. Still rough idle. Still had a permanent P0303 code.

(Is it possible the oil in the manifold was just from the compression check at the dealership?)

8/24/2021 Since it was due, I changed the oil myself. I dropped several ounces of Seafoam in the existing oil and drove it a few hundred miles prior to changing it out. Oil was black but still very slippery to the touch (Amsoil usually is).

9/3/2021 Removed the driver side valve cover and inspected the rockers and pushrods. Turned the engine using a 24mm socket and breaker bar. All valves (including #3) seemed to be tight (minimal play) and all traveled up/down to matching levels with no slack on the springs. I’m thinking this eliminates a collapsed lifter or a worn down lobe on the camshaft. While cleaning the valve cover, I noticed the crankcase breather tube (which runs to the top of the intake manifold) had some oil in it as well. Not a lot but enough to clean off the tube. Also pulled plugs 1,3,5 and inspected. They were a little dirty but mostly dry. Cylinder 1 had some minor wet oil on the threads. Again I'm thinking this was from the compression check at the dealership just a few weeks back.

9/4/2021 Went a little old school. With engine at idle, I sprayed carb cleaner on all the injector bases, suction lines and at the base of the intake manifold looking for suction leaks. No sprays affected the idle of the motor. Also checked the spark on the #3 cylinder by shocking myself on the lead when I tried to hold it against a ground. Anyone got a video of how this is supposed to done correctly?

At this point, I'm left with little to go forward with. It drives beautifully, emits no smoke, doesn't seem to burn oil. It just idles like crap and throws misfire codes (either unknown cylinder or #3). Where should I go next? Wiring harness? Re-examine some of the previous steps I've taken? Buy a more expensive scan tool that gives me more info?
 

wsteele

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A couple of observations.

Cylinder number 3 is not an AFM lifter, so it would not be collapsed. If the lifter roller seized, it will grind down the cam in time, such that you will get a misfire. There is a thread that just completed where this exact thing happened. Post #66 in thread below. Further down you will see what the camshaft looked like.


The other observation is why are you doing an extended oil change interval? I don't care what magic oil/filter you use, that is a very bad idea with an AFM engine. The good news is it doesn't sound like you have any AFM lifter issues, yet.

When you had the plug out checking for spark, how did it look (ash, carbon, etc. build up, light tan/grey insulator, etc.), what was the gap?
 

swathdiver

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Vehicle History: Purchased in 2012 and driven until Aug 2020 without any significant issues beyond routine maintenance. Oil used throughout is AMSOIL Signature Series 5W-30 on extended change cycles (every 15k-20K miles).

All spark plugs and wires changed at 1/20/2018(115K) with AC Delco 41-110 plugs.

Transmission flushed by dealer at 1/23/2019 (139K)

New battery from Batteries+ on 7/2/2019 (Duracell SLI48AGM)

Front and rear brakes from O’Reilly’s and installed by me on 7/28/2019 (149K)

Vehicle slowly developed a rough idle in August of 2020 with an intermittent P0303 OBD code (Cylinder 3 Misfire). Code would only set during long periods of idling but would reset itself after 30-50 miles of driving. No noticeable issues other than at idle with transmission engaged. Over a 5 month span, the code only set three times and cleared on its own without being reset. Rough idle was really only detectable with vehicle in Drive or Reverse and fully stopped.

Jan 2021 Plugs Changed for Cylinders 1,3,5,7 - No change in Idle roughness. No OBD-II codes.

Vehicle passes emissions inspection on 4/08/21 (181,984) at local lube shop. No OBD-II codes.

On 4/29/21 Vehicle fuel injection system power flushed by same lube shop. No OBD-II codes. Still rough idle.

In May of 2021 vehicle displayed a new code of P0300 (Random Cylinder Misfire) and would not reset on it’s own. The following actions were taken to eliminate this code.

Replaced all 8 Ignition Coils with Duralast C1512-8 5/17/2021

Replaced all 8 fuel injectors with AC-Delco 217-3411 5/23/2021 (2nds ordered off of EBAY)

Checked fuel injector electrical function with noid light after replacement on all cylinders— all injector leads firing.

Checked fuel pressure using OBD scan tool(not actual gauge). Static pressure was 58-60psi and running pressure was 43psi.

Replaced both Primary S1 O2 Sensors with Bosch 15200 6/03/2021

Replaced MAP sensor with Duralast SU9491 6/03/2021

Replaced MAF Sensor with Duralast DL-3091 6/03/2021

After sensor replacement all codes cleared but rough idle continued. No codes displayed for two months of driving. Rough idle worsened but still no codes.

Replaced Throttle Body and Sensor with Duralast TB1032D 8/3/2021.

Performed Idle Position Relearn Procedure (but not sure this actually works without advanced diagnostic tool)

Rough idle was diminished but not eliminated. Cylinder 3 Misfire code showed as pending but MIL was not set.

Cylinder 3 misfire (P0303) code resurfaced on 8/5/2021 while driving. Mil was set.

8/13/2021 Vehicle taken to dealer for recalled airbag replacement. While there I had them compression test the engine. Engine produced 135psi on all cylinders but cylinder three failed a “leak down” test. Dealer tech said it was due to “camshaft roller failure” without opening any covers. I declined to let them investigate further as it took them three days just to get that far.

After getting the vehicle home from the dealer, I removed the entire intake manifold and replaced the intake manifold gaskets on both sides. While I had the intake out, I noticed that some of the bolts holding down the “valley cover” or “valley pan” were loose so I torqued them down. These bolts were in the vicinity of cylinders 1 and 3. Also while cleaning the manifold, I noticed significant amount of oil in the manifold. Cleaned the manifold completely and re-installed it. Still rough idle. Still had a permanent P0303 code.

(Is it possible the oil in the manifold was just from the compression check at the dealership?)

8/24/2021 Since it was due, I changed the oil myself. I dropped several ounces of Seafoam in the existing oil and drove it a few hundred miles prior to changing it out. Oil was black but still very slippery to the touch (Amsoil usually is).

9/3/2021 Removed the driver side valve cover and inspected the rockers and pushrods. Turned the engine using a 24mm socket and breaker bar. All valves (including #3) seemed to be tight (minimal play) and all traveled up/down to matching levels with no slack on the springs. I’m thinking this eliminates a collapsed lifter or a worn down lobe on the camshaft. While cleaning the valve cover, I noticed the crankcase breather tube (which runs to the top of the intake manifold) had some oil in it as well. Not a lot but enough to clean off the tube. Also pulled plugs 1,3,5 and inspected. They were a little dirty but mostly dry. Cylinder 1 had some minor wet oil on the threads. Again I'm thinking this was from the compression check at the dealership just a few weeks back.

9/4/2021 Went a little old school. With engine at idle, I sprayed carb cleaner on all the injector bases, suction lines and at the base of the intake manifold looking for suction leaks. No sprays affected the idle of the motor. Also checked the spark on the #3 cylinder by shocking myself on the lead when I tried to hold it against a ground. Anyone got a video of how this is supposed to done correctly?

At this point, I'm left with little to go forward with. It drives beautifully, emits no smoke, doesn't seem to burn oil. It just idles like crap and throws misfire codes (either unknown cylinder or #3). Where should I go next? Wiring harness? Re-examine some of the previous steps I've taken? Buy a more expensive scan tool that gives me more info?
There's very likely a mechanical problem with cylinder number three. You've eliminated everything else. Time to pull the head for a looksee. Bent valve, bent pushrod, cracked piston or ring, leaky head gasket and most likely, a partially collapsed lifter. Yes, even the regular lifters can fail. If all that looks good, then maybe the dealer was right about the camshaft. If your receipt shows the name of the technician who did the work, if yours were mine, I'd seek that guy out and talk to him in person.
 

gotliebk

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A couple of observations.

Cylinder number 3 is not an AFM lifter, so it would not be collapsed. If the lifter roller seized, it will grind down the cam in time, such that you will get a misfire. There is a thread that just completed where this exact thing happened. Post #66 in thread below. Further down you will see what the camshaft looked like.


The other observation is why are you doing an extended oil change interval? I don't care what magic oil/filter you use, that is a very bad idea with an AFM engine. The good news is it doesn't sound like you have any AFM lifter issues, yet.

When you had the plug out checking for spark, how did it look (ash, carbon, etc. build up, light tan/grey insulator, etc.), what was the gap?
Firstly, thank you very much for reading this long post and responding. I read the thread you shared with interest and it gave me some more things to check inside the motor. I'm not ready to pull the head yet until I do a little more less invasive probing. As for the extended cycle on the oil changes, I've been doing that for 20+ years on all my vehicles (98 Suburban with 290K, 06 Monte Carlo with 249K) with very good results. This particular vehicle made it to 180K before it began exhibiting any problems at all. If it turns out this is a mechanical wear issue, I will end up rethinking the extended change cycle for the oil. On the plugs, the points were black but didn't have significant carbon buildup on them. I think the fresh oil on the threads of #1 was from the dealer tech putting oil in the cylinder for the leakdown check(can't be sure). I couldn't find my gap gauge so I didn't check it but it's on my list to pull them all again and just inspect, clean and check them. Thanks for asking good questions.
 

gotliebk

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There's very likely a mechanical problem with cylinder number three. You've eliminated everything else. Time to pull the head for a looksee. Bent valve, bent pushrod, cracked piston or ring, leaky head gasket and most likely, a partially collapsed lifter. Yes, even the regular lifters can fail. If all that looks good, then maybe the dealer was right about the camshaft. If your receipt shows the name of the technician who did the work, if yours were mine, I'd seek that guy out and talk to him in person.
Thanks for reading my lengthy post and responding. I'm not quite ready to pull the head just yet but I'm considering it as part of the plan. I think I'm going to pull the intake manifold and valley cover and do some more wear inspection first. My inspection of the rockers and pushrods from above didn't show me anything that I need to investigate deeper. If the camshaft lobe was flattened I would expect some play in the rocker arm above as I rotated the motor. I didn't see any. All good thoughts though.
 

swathdiver

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Thanks for reading my lengthy post and responding. I'm not quite ready to pull the head just yet but I'm considering it as part of the plan. I think I'm going to pull the intake manifold and valley cover and do some more wear inspection first. My inspection of the rockers and pushrods from above didn't show me anything that I need to investigate deeper. If the camshaft lobe was flattened I would expect some play in the rocker arm above as I rotated the motor. I didn't see any. All good thoughts though.
I hope you'll follow Wes' advice and send off an oil sample for analysis. You might also pick up a bore inspection camera and have a look at the chambers and pistons and anywhere else it will go. Some of them are as small as 7mm nowadays. Keep us posted.
 

89Suburban

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Better invest in a catch can to keep that oil out of the intake. Once you find out what is wrong here of course.
 

wsteele

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Firstly, thank you very much for reading this long post and responding. I read the thread you shared with interest and it gave me some more things to check inside the motor. I'm not ready to pull the head yet until I do a little more less invasive probing. As for the extended cycle on the oil changes, I've been doing that for 20+ years on all my vehicles (98 Suburban with 290K, 06 Monte Carlo with 249K) with very good results. This particular vehicle made it to 180K before it began exhibiting any problems at all. If it turns out this is a mechanical wear issue, I will end up rethinking the extended change cycle for the oil. On the plugs, the points were black but didn't have significant carbon buildup on them. I think the fresh oil on the threads of #1 was from the dealer tech putting oil in the cylinder for the leakdown check(can't be sure). I couldn't find my gap gauge so I didn't check it but it's on my list to pull them all again and just inspect, clean and check them. Thanks for asking good questions.
Sorry if I sounded kind of pedantic on the extended oil change interval thing, but I think these AFM engines are kind of a different breed as it pertains to oil cleanliness and reliability of the DoD lifters and oil manifold, at least in the earlier generation versions. But it only matters that you have confidence in your process.

Did the shop indicate where the leak down was failing (bottom or top end)?

Anyway, it sounds like you are going to go about it in a very methodical way, so best of luck.

I agree with the advice to send an oil sample to Blackstone, it is a very check diagnostic data point and very reliable.
 

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