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2012 Tahoe LT active fuel management issue

Drakecloude96
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Drakecloude96 Enthusiast

Drakecloude96

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Hello everyone. 

I didnt know if this was the right place to post this issue but I did not see a place to post for the Tahoe.

I know we have all talked about the AFM issues one these GM motors. But my issue is different and I cant find anything similar.

So here is the issue. I went to do a tune up and found the clasic oil in the cylinder (#7 for me). However I am getting no missfire, no codes other than an EVAP code thats been there a while. I decided to do the tune up because while I was at cruising speed the RPM's would jump about 75-150 rpm. So I did the plugs, wires, coils, and air filter. Thats when I found the oil. 

So I dont have lifter noise like I see in a lot of cases when you get a stuck lifter on these. I am wondering what I should check before taking the intake off and seeing if the valley gasket is messed up or something like that allowing oil to seep into th cylinder. What are your ideas?

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

Taking the intake off will do nothing.

 

The only way oil will get into that cylinder is from oil getting past the piston rings, past the valve seals or if there is oil pooled up in the bottom of the intake manifold itself.

 

You can stick your hand inside the intake with it still on the truck to feel if there is a pool of oil sitting in the back of the intake. That oil would be from the PCV system, which is very common to see. A 2012 should already have the updated drivers side valve cover design but a catch can could help capture the oil vapors.

 

Honestly not much you can do. Seeing oil on a spark plug is just what happens to these engines. If you did a AFM/DoD delete and re-honed the cylinders with new rings, that would likely stop all oil consumption problems.

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newdude Senior Enthusiast

newdude

Posted
Posted (edited)

Has the driver's side valve cover been replaced?  There was a revision to the PCV baffles to control overactive PCV flow that could pull too much oil into the intake.  An overactive lifter can cause this as well.  

 

Proper functioning PCV should leave not much more than an oil film in the intake.  

Edited by newdude
newdude Senior Enthusiast

newdude

Posted
Posted
On 10/4/2023 at 10:30 PM, Drakecloude96 said:

Drivers side valve cover is the updated one. I have also installed an oil catch can and see no difference so far in the runability. I have had it in for about a week. 

 

 

Your RPM jump, is that during steady state cruising so 55mph for example on the highway?  

Drakecloude96 Enthusiast

Drakecloude96

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  • Author
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On 10/6/2023 at 1:23 PM, newdude said:

 

 

Your RPM jump, is that during steady state cruising so 55mph for example on the highway?  

Correct. There also seems to be a little hesitation now around 35mph

newdude Senior Enthusiast

newdude

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Posted (edited)
39 minutes ago, Drakecloude96 said:

Correct. There also seems to be a little hesitation now around 35mph

 

 

Sounds like you could have a torque converter going and possible 4-5-6 clutch pack wear issues then. 

 

Do you have access to a bi-directional scanner to monitor torque converter slip speed during cruising speeds?   

Edited by newdude
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Drakecloude96 Enthusiast

Drakecloude96

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Posted
4 minutes ago, newdude said:

 

 

Sounds like you could have a torque converter going and possible 4-5-6 clutch pack wear issues then. 

 

Do you have access to a bi-directional scanner to monitor torque converter slip speed during cruising speeds?   

I had a feeling it might be transmission related. I'm not sure if my scanner does that. It's an icarsoft cr max, if anyone has experience with them. I've only had the scanner a month. Haven't had time to go through all the features

newdude Senior Enthusiast

newdude

Posted
Posted
14 hours ago, Drakecloude96 said:

I had a feeling it might be transmission related. I'm not sure if my scanner does that. It's an icarsoft cr max, if anyone has experience with them. I've only had the scanner a month. Haven't had time to go through all the features

 

 

Looking it up quick, it seems like it could do it.  See if it can read transmission data.  Look for TCC slip speed.  

 

Normal converter operation on the 6L80/6L90 should have 0-20rpm slip at steady state throttle so say on the highway doing 55mph for example.  It can be observed though from say 30-80mph.  

 

If its near 60rpm repeating during steady state throttle cruising, the fluid is shot.  

 

If you see around 100rpm erratic slip, you've got internal issues (converter, etc.).  

Drakecloude96 Enthusiast

Drakecloude96

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Posted

Okay. I had a break at work so I took it for a drive. It was kinda hard to tell, the slip was kinda all over. Maybe because I didn't have cruise on, so I was speeding up and slowing down. However I did some reading and saw that one thing to test is the slip speed in gear but not moving and it should be almost 0. Is that true? Mine was 500

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