2012 Tahoe LT active fuel management issue

Drakecloude96 · September 22, 2023

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 · September 22, 2023

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.

Drakecloude96 · September 23, 2023

Thats good information. I will check that out. Is there anything else I should be checking?

swathdiver · September 23, 2023

Do a compression test on each of the cylinders.

Drakecloude96 · September 27, 2023

There was a bunch of oil in the intake. I cleaned it out and will be installing a catch can to see if that makes a difference.

newdude · September 27, 2023

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 September 27, 2023 by newdude

Drakecloude96 · October 5, 2023

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.

newdude · October 6, 2023

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 · October 11, 2023

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 · October 11, 2023

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 October 11, 2023 by newdude

Drakecloude96 · October 11, 2023

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 · October 12, 2023

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 · October 12, 2023

On 10/11/2023 at 8:57 AM, newdude said:

I will take a look after work tonight and update. Thank you

Drakecloude96 · October 12, 2023

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

Drakecloude96 · October 12, 2023

Also I will note, I checked the fluid. It was at proper level. Maybe a little dark. I can't smell very well but it did possibly smell off from what tranny fluid smells like new