Theta

Not to steal this away from DF, but just to put things into perspective (a bit) here, this is a very isolated failure.

The fix comes in the form of a new exhaust part number, which should have some sort of heat protection/dampening on the butterfly joint. It is my belief that 2015 models came with this near the get-go looking at the part numbers, and after NPP stock from 2014 was depleted.

I would highly doubt that 99.9% of everyone here will ever see these issues. DF is a track junkie (not a bad thing at all), and so is finding the weak spots in the design of the car here and there - he (and others who track) are a most helpful tool to show what does/does not function correctly at the bleeding edge.

Zajac, I agree with most of what you've said, taking into account what I've written above. If you don't mind though, I'll take it line-by line.

1) DF drives harder than most, that's for sure, and spends a good deal of money tracking this thing. I can see where the problem was coming in after realizing he and I were talking about two completely different problems. Funny enough, the valves have other electrical problems which I won't go into here. Just funny to me...

2) Correct (to date). Most likely will never be an issue for those 99.9% of owners.

3) They regulate the attenuation and backpressure for the pulses in V4 mode. The best way to eliminate this mode (unless you'd like to keep it) is with the OBD tool (Range AFM Disabler), or with a tune. The tune, obviously, voids the powertrain warranty (to an extent we won't go into here as I'm sure you won't mind). Or, as you've said, you can move the valves out of the stream. This, however, will cause potential issues with noise and backpressure. V4 mode is quite unpleasant-sounding without the AFM attenuation.

4) The CCM checks for both a response and a presence on the AFM and NPP valves. The lack of a response on the AFM valves causes a DTC and a MIL, as opposed to the NPP only flagging a DTC. So, yes - correct.

5) Exactly - looks like this is the case from the melting of the housing that DF was good enough to post.

6) See 3.

7) I doubt you will see any changes to the actuators, but perhaps a small amount of heat isolation will prevent failures for heavily-tracked vehicles. Otherwise, as we all know, there is very little incentive to 'fix' a problem that can be attributed to 0.1% or less of the buying public. A majority of the tracked cars are Z06s, which have those valves removed (and for an obvious reason now that this is public).



Again, thanks for this DF - doubt we would have seen anything if not for the problems you were having. A shame the actuators aren't being changed, but that was a snowball's chance in hell of a shot.

leadville1

I have my exhaust wrapped in DEI heat wrap. I did over 600 miles two weeks ago in the Advanced Instructor group and didn't have any issues. I may just be lucky.

If you wrap the exhaust you also don't get the overheating in the tranny fluid. I changed out to Redline, DEI wrap and put in the Z06 cooler inlets and I rarely see the temp on the tranny go over 200 degrees (M7).

The DEI wrap worked wonders in keeping temps down

FYREANT

Any pictures of your wrapping so we can see how much is actually covered?

sigelitest

Would u mind sending me the part numbers of what u ordered to me in a pm?

Theta

I was able to duplicate this issue after a good amount of heat buildup, and was able to figure out a few things about the electrical signature of the actuators while I was at it.

Suffice to say, I was able to burn out an AFM actuator (after quite a bit of trying), and get an NPP actuator to panic from raising the temperature enough that the positive pulse signal was no longer effective at operating it. After cooling, the actuator returned to normal, while, of course, the AFM actuator remained lifeless.

At least this way, DF has some backup on this issue - it's re-produceable, but it does take some doing (hot lapping at 4500+ rpm heavy loads).

sigelitest

I looked up the part numbers with the dealer and there are no GM notes associated with the new part numbers. they say that means there is normally a change to the manufacturer of the part not the design. I did my exhaust swap yesterday and noticed the actuators are mounted on stand offs and the metal from the actuator does not contact the valve coupling until it closes the valve so there should be no direct contact when it is open. The melted actuator in the picture looks like it came from around the coupling. could there be an issue with it trying to close while u are driving? am I missing something. i thought it only came into play during v4 mode. can u force v4 mode off?

sigelitest

I wrapped mine also. all the way to the joint of the h pipe.
all the heat from the exhaust is trapped up around the trans.
made sense to me. I will check the trans temp today and report
The actuators are mounted up high and That seems to be where all the heat stays

Theta

It's becoming clear that the new part numbers are identical to the old ones - valves and all. The actuators are still the same (electrically and physically). I've ordered from a few different batches just in case.

There's a bit more to the story with regard to when they're engaging. We already know from the last 18 months of testing exactly when/where/how they're activating on both the M7 and A6/A8 (obviously with the latter being far more intrusive). The bar and cup design touches more often than you would think on a stock C7, and much more so on the A6/A8.

As for forcing AFM/V4 off, yes - there are ways to do this ranging from products that plug into the OBD2 port to the full removal of all DoD/AFM components in the engine and elimination of the V4 system entirely. Unfortunately, this still doesn't remove the checks that the CCM performs on the AFM valves - if the valves are dead, stuck, panicked, or simply unplugged, you will have a CEL/MIL and a stored DTC.

descartesfool

I took some pictures of the new mufflers that came with actuators that were supposed to have "insulated inlets" per a GM Brand Quality Manager for Corvette and Camaro. She gave the shop foreman the new part numbers and dealer ordered parts. I picked them up at the dealer and took them home to look for any evidence of the so-called "insulated inlets" and found no evidence of any change whatsoever.


Part numbers are the new correct ones they said to order and are engraved on the exhaust pipe, so no error in part ordering. Stand-off height on the actuators is the same, air-gap when mounted is the same, mounting flange on top of valve in exhaust pipe is the same, all metal, no insulation, and metal cup part with return spring contacts the actuator as it did in the original part that failed.


So this new part also failed as I reported in my new thread, which I made since now the car also added and "Engine Overheat -Idle Engine" issue to the overheating on track party for me.

Theta

Great pics - thanks for the update. Caught this right before bed, but glad to be able to see this up close and in detail.

I will compare the butterfly section at length to see if there's any change to the ID that would indicate an integrated heat shield / double-wall of some sort. Regardless, it still appears to do nothing to dissipate or decouple the heat from the butterfly/spring section...

Actuators are exactly the same, but you already knew that.

descartesfool

Once I had the parts home I got my wife to help me warp then exhaust pipes fully with some DEI Titanium heat wrap. Anyone who has tried to do this with the mufflers still on the car will know how difficult it is to do due to so little clearance above the axles. Since dealer was nice enough to let me have the parts to take home, this was the prfect opportunity. Purpose is to reduce heat radiation from exhaust pipes into the transmission which always goes to over 300 F on track for me and pins the transmission temperature guage. Radiation from the two exhaust pipes that run by the transmission at the back of the car is certainly not the primary source of heat generation, but perhaps this wrap was going to help. Turns out it did not. Tranny temp still went into the red zone. Temp rise might have been a little slower, and perhaps it was not as much over 300F as before. You don't know from the gauge how much higher than 300 F (150 C) the transmission is because gauge doesn't read any higher. Temp overheat on the manual transmission is 325 F, and I didn't get a code or warning at any of my 4 track days so far with the car, so transmission temperature is somewhere between 300 and 325 F, way too hot for comfort and longevity. Z51 might have a transmission cooler, but it is not effective enough obviously to match Tadge's track capability statement, Pro Driver flat out continuously in 86 F or less outdoor temperature.


Wrap also did nothing to prevent failure of the AFM actuators. Not that I expected that as the actuator is in direct contact with the metal cup connected to the AFM valve. All in all, a complete engineering design failure on the part of GM in terms of these actuators. They can't take the heat!

sigelitest

I bought a new set thinking they were different so I cut the valves off the old set. I will sell the valve section shipped to anywhere in the U.S. For 120.00 pm me. I figure someone might want to test these or mount them under the car somewhere

Theta

Hmm... This would make things much easier on me and resolve the issue of having the entire NPP exhaust system laid out in my garage for the last 4 months of testing...

Stupid question here, but would you want to sell me just one in the name of science?

sigelitest

Pm sent bud. Think this is a way around the problem. I wasted money thinking they upgraded

sigelitest

If they we're smart they would have put the other actuator on the other exhaust tip. There is not as much heat after the muffler. Then it would have closed one off and closed the other side off in v4 mode with the center hole in it. Wonder if it could be modded that way. Any problems with the aftermarket exhausts

Theta

Didn't get a PM, but it could be in limbo here.

There is very little room for the NPP valve(s) after the muffler and before the tip, so there was no way they could double-stack like that. I get what you're saying, though - BMW uses something similar to what you're referring to.

The goal was to alter the input flow into the mufflers in order to give a specific resonance at each given plot of RPM/load. In theory, it would work quite well. In reality, they were placed above an overheating transmission (which was unexpected by the design team, to say the least) and at a point where a great deal of heat would rise and stay due to the 'up and over' design of the exhaust.

Aftermarket exhausts are not immune from this issue, sadly. However, there is a manufacturer that makes a system without the AFM butterflies/valves, and I'm heading in that direction.

The hope is to continue work on the coding of the CCM to eliminate the checks/CELs, or to create a 'dummy' spring load for the actuators (instead of using the full 2.5" round assemblies tucked up).

baron95

My car is a 2015 Z51 NPP and the AFM actuators fried just the same.

I did a few track days before they failed on an autocross fun drive.

My thinking is that since my car is an A8 and the transmission overheats in only 10-12 minutes on track, forcing me to park the car, my AFM valves never got as much heat time as yours. So it took them longer to cook.

My dealer is waiting for parts. If anyone has any suggestions on what I should ask/tell the dealer when the parts come in, it will be much appreciated.

leadville1

Do you have the Z06 Cooler ducts in the rear fenders, they make a big difference in cooling. I have no issues and I am not being gentle on the car.

descartesfool

I have some on the bench, but not installed because GM Brand Quality manager keeps asking via my service manager to confirm my car is not modified each time I take it in to have the AFM actuators replaced so I haven't put a single part on my Z51. The 4th time I took it in they said it was the heat wrap tape on the pipes that likely caused the failure of the actuators and they made the service manager instruct the tech to remove it. Then of course the actuators failed again as obviously the heat wrap tape had nothing to do with the electronic AFM actuators failing. 5 failures so far and no hope of any fix from GM.

smilence

I haven't taken my car to the dealer yet so I don't know the root cause for sure, but I had the similar issue after my 3rd track day in my life.I'm totally beginner and falls into slower half of solo/beginner group, yes, with the C7 so I might be the poorest driver here.

After running five 20mins sessions with high rpm (at least 1 hour break between them), I got a CEL, and metal clanking noise from rear end, especially when switching to v4 mode, I assume it's the AFM failure you guys talked about. I also heard a different rattling noise from rear end, when accelerating with 50% gas pedal on street.

To be honest, this is really disappointing, considering that might also happen for my future track events.