AFM and Rich Spark Plugs

jfm762 · January 23, 2015

Hello All,

My first post, I do apologize for the length. I have a 2014 Silverado z71 crew cab, 5.3 3:42 rear gear with no modifications. Vehicle has 4000 miles on it now. Since new I haven't liked the way the AFM worked. It often runs rough when in V4 mode and on occasion, I have noticed that when on an incline when I accelerate, the truck bogs down and AFM will not disengage V4 mode. The accelerator has to be near floored or the truck put in manual to get back in V8. Not a safe situation on icy hills in Pennsylvania. I read computer but no errors reported. I then pulled spark plugs to see if they would shed light on the rough running,. What I noticed was that all the odd cylinders, driver side, are rich. All the even, passenger side, were perfect.

Brought the vehicle to dealer explaining the situation and showing pics of plugs and asking if they could disengage AFM. Was told vehicle is operating normally and as far as rich plugs, that must be how GM intended it to run. As far as the AFM, they could not Disengage unless authorized by GM. Not the answer I was looking for. After doing some reading on forums, I figured I would go with range unit to disable AFM, but wanted to see what was causing rich plugs first.. I have been driving in manual M5 for the past 300 miles occasionally having to switch to M6 on faster intermediate roads and I must say the truck drives so much better. I even get 1 mpg better around town. I recently read the plugs again and the odd side is burning much better, but not perfect. Have been unable to find any other reason for rich plugs.

I have tried to contact GM to explain the situation but that did not go well. I simply asked if AFM could be disengaged in manual mode M6. The first person I talked to had no idea what I was talking about. She transferred me to another person who had no idea what I was talking about but said "We build the vehicles and sell them to the dealers who in turn sell them to you. If you have any problems bring it back to dealer. And any modifications to the vehicle are illegal (Yes she said illegal) and would void the warranty". I guess along with quality, GM has passed on Customer assistance. What ever happened to let see what the problem is and try to come up with a solution.

Has anyone else had similar problems with AFM and done a read on their plugs?

Any help is greatly appreciated.

LongrangeLauber · January 23, 2015

I disabled mine in the first 1k miles with the range unit. I have 4300 on the truck as we speak. Power is always there, but I have never checked the plugs

fondupot · January 23, 2015

I used the range unit for a while, but eventually decided to have it tuned out completely with a custom tuner. No more AFM.

07Softail · January 24, 2015

I disabled mine in the first 1k miles with the range unit. I have 4300 on the truck as we speak. Power is always there, but I have never checked the plugs

Haven't read the plugs but I just bought a Range AFM Disabler from a member here and love it. I will eventually get the tune done when I do the cam and long tubes and a set of Cometic .030 head gaskets for better squish.

RT

thefishhawk · January 24, 2015

Idk but your AFM is exactly the opposite of mine and I have the same truck setup. I wish mine would stay engaged more, the slightest change in the grade of the road will disable it. Can't believe you have to mash the pedal to get it to drop out. What it really needs is selectable modes.

jfm762 · January 24, 2015

Fishhawk

I agree it needs selectable modes. That is why I drive in manual M5 and switch to M6 when speeds excede 50. Just wish AFM didn't engage in M6

gone_fishing · January 24, 2015

I then pulled spark plugs to see if they would shed light on the rough running,. What I noticed was that all the odd cylinders, driver side, are rich. All the even, passenger side, were perfect.

I might not be understanding you correctly but are you saying 4 plugs looked good and 4 didn't? All 4 plugs from the driver side of the motor are rich and the other 4 plugs from the passenger side are fine? I'm not sure if the new Ecotec motors follow the same order as other small blocks (as in this diagram) but I do know that when in V4 mode, 2 cylinders from one side of the motor are used along with 2 from the other (hence V4). If V4 mode was causing the plugs for the deactivated cylinders to look different then the activated cylinders then it wouldn't be just all 4 from one side. It would be plugs #2/#8 (passenger side) and #3/#5 (driver side) being different compared to the plugs #4/#6 (passenger side) and #1/#7 (driver side)

jfm762 · January 24, 2015

Gone Fishing

I do understand that in V4 mode that 2 cylinders from each side are deactivated. Another reason this is so strange. All I can say is that cylinders 1 3 5 7 spark plugs were rich. 2 4 6 8 are or near perfect.

that is why I asked if anyone else with similar problems had taken a plug reading. After running in manual mode M5 for some time, plugs look better but I cant get a true reading as I do on occasion have to switch to manual mode M6. I would post pics but the file size is too large. I will try to compress images and post if interested.

gone_fishing · January 24, 2015

Gone Fishing

I do understand that in V4 mode that 2 cylinders from each side are deactivated. Another reason this is so strange. All I can say is that cylinders 1 3 5 7 spark plugs were rich. 2 4 6 8 are or near perfect.

that is why I asked if anyone else with similar problems had taken a plug reading. After running in manual mode M5 for some time, plugs look better but I cant get a true reading as I do on occasion have to switch to manual mode M6. I would post pics but the file size is too large. I will try to compress images and post if interested.

Ahhhh.....I see. Yes that does seem strange