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5.3 Stabilitrak/#6 misfire puzzle

arupert

By arupert
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arupert New Member

arupert

Posted
Posted

 

Stabilitrak and #6 cylinder misfire:.......pull valve cover and one of the #6 rockers loose and never moved. pulled cylinder head, found collasped AFM lifter...thought AWESOME!.....problem found. Replaced lifter and reinstalled everything else. Cranked it up, same idiot lights and still misfiring. Pulled the valve cove to watch the rockers....both moved up and down 2 cycles and just stopped!....no movement at all????? What could possibly be controlling the lifters or preventing them from moving?......struggling with figuring oout whats going on here....any help would be greatly appreciated!

 

 

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Sounds like the AFM system is screwing up. No idea how to fix it, but, you pretty much know it has to be that.

cwxpro Enthusiast

cwxpro

Posted
Posted

AFM ... is a misnomer in that it is the valves that are controlled, and only indirectly, fuel. It is the stepchild of a
General Motors attempt called DOD ... displacement on demand ... to produce an engine that would run well with selected cylinders shut down.

The first version was tried on V8 Cadillacs in 1981. it was an enormous and embarrassing failure.

 

Not long after GM fielded AFM, trouble began again. Couple of examples. Google for more.

 

........................................................................................................................................................................................................................................

 

http://partsblog.olathetoyota.com/4920/gmc-chevy-afm-oil-consumption/

 

 

 

........................................................................................................................................................................................................................................

 

Plug the Vin in here to see if it's covered.

 

https://recalls.gm.com/#/

 

........................................................................................................................................................................................................................................

 

AFM uses computer driven solenoids under the valley cover to control valve action by turning on or off, engine oil under system pressure, to

the valve lifters. GM doesn't release failure statistics but it appears about 52,000 trucks may have been affected. If the ECM program is faulty and

signals the solenoids at the wrong time, it will damage lifters and bend valves. There would be damaging heat buildup and other stress effects as well.

Or, the valves wouldn't open when they should.

 

If this went on for sufficient time, pressure and reduced oil supply could result in flattened cam lobes and lifter damage. There are numerous possibilities.

 

Horribly dirty oil ... wrong viscosity and service (additive package) oil ... air in the oil delivery system and lifters ... pushrod blockage and damage ... damaged

rocker arms ... all could account for your symptoms ... but the ECM is most likely root cause.

 

 

Some component pictures here:

 

https://www.google.com/#q=displacement+on+demand

 

This is a widespread and serious problem and given their culpability in the Cobalt ignition matter ... they have tried to minimize its damage by being as

quiet about it as possible.

 

But they have to fear a class-action suit ... so they are undoubtedly making an effort to resolve it ...

 

You should find out what it is and what they intend to do about it.

 

Good luck,You'll find it.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

AFM ... is a misnomer in that it is the valves that are controlled, and only indirectly, fuel. It is the stepchild of a

General Motors attempt called DOD ... displacement on demand ... to produce an engine that would run well with selected cylinders shut down.

The first version was tried on V8 Cadillacs in 1981. it was an enormous and embarrassing failure.

 

Not long after GM fielded AFM, trouble began again. Couple of examples. Google for more.

 

........................................................................................................................................................................................................................................

 

http://partsblog.olathetoyota.com/4920/gmc-chevy-afm-oil-consumption/

 

 

 

........................................................................................................................................................................................................................................

 

Plug the Vin in here to see if it's covered.

 

https://recalls.gm.com/#/

 

........................................................................................................................................................................................................................................

 

AFM uses computer driven solenoids under the valley cover to control valve action by turning on or off, engine oil under system pressure, to

the valve lifters. GM doesn't release failure statistics but it appears about 52,000 trucks may have been affected. If the ECM program is faulty and

signals the solenoids at the wrong time, it will damage lifters and bend valves. There would be damaging heat buildup and other stress effects as well.

Or, the valves wouldn't open when they should.

 

If this went on for sufficient time, pressure and reduced oil supply could result in flattened cam lobes and lifter damage. There are numerous possibilities.

 

Horribly dirty oil ... wrong viscosity and service (additive package) oil ... air in the oil delivery system and lifters ... pushrod blockage and damage ... damaged

rocker arms ... all could account for your symptoms ... but the ECM is most likely root cause.

 

 

Some component pictures here:

 

https://www.google.com/#q=displacement+on+demand

 

This is a widespread and serious problem and given their culpability in the Cobalt ignition matter ... they have tried to minimize its damage by being as

quiet about it as possible.

 

But they have to fear a class-action suit ... so they are undoubtedly making an effort to resolve it ...

 

You should find out what it is and what they intend to do about it.

 

Good luck,You'll find it.

 

 

Don't see how it can bend valves or damage push rods. The solenoid does not create lift, it simply either provides oil to the lifter or it allows the lifter to retain the oil, which means the lifter will now be able to open the valve once the camshaft lobe pushes the lifter up. It cannot change cam timing on just one cylinder.

I would be interested in hearing how you come to the conclusion that GM does not release failure statistics. Just because they don't publish numbers does not mean they will not provide them. You have to ask in order to receive.

In order to have heat damage to valves, the valves have to be held open, not kept closed. In order to hold valves open too long, you need to be able to change the duration of the camshaft. The lobes on the camshaft are not adjustable.

 

I seriously doubt the ECM is the root cause. If it is the programming in the ECM doing this, then it will happen ALL the time, not just once in a while. Firmware code is not dynamic, it does not change and then return back to original programming.

There is so much wrong logically with the post that it loses all credibility to me. The post reads like a summary of many posts that someone is just accepting as being completely accurate. Don't see how it can be.

 

I am not saying AFM is working correctly, I am saying that the post is inaccurate and will take the OP down the wrong path, with the wrong attitude.

cwxpro Enthusiast

cwxpro

Posted
Posted

Bugs in code are common. Neither is hardware perfect. These are opinions. Chacun a son gout.

 

You might find this interesting, or not. If you wish to verify, Case No. CJ-2008-7969, District Court of Oklahoma County, State of Oklahoma.

........................................................................................................................................................................................................................................................................

 

Toyota's killer firmware: Bad design and its consequences
Michael Dunn -October 28, 2013

119 Comments

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On Thursday October 24, 2013, an Oklahoma court ruled against Toyota in a case of unintended acceleration that lead to the death of one the occupants. Central to the trial was the Engine Control Module's (ECM) firmware.

Embedded software used to be low-level code we'd bang together using C or assembler. These days, even a relatively straightforward, albeit critical, task like throttle control is likely to use a sophisticated RTOS and tens of thousands of lines of code.

With all this sophistication, standards and practices for design, coding, and testing become paramount – especially when the function involved is safety-critical. Failure is not an option. It is something to be contained and benign.

So what happens when an automaker decides to wing it and play by their own rules? To disregard the rigorous standards, best practices, and checks and balances required of such software (and hardware) design? People are killed, reputations ruined, and billions of dollars are paid out. That's what happens. Here's the story of some software that arguably never should have been.

Check out this related
EE Live! 2014 session:Killer Apps: Embedded Software's Greatest Hit Jobs

For the bulk of this research, EDN consulted Michael Barr, CTO and co-founder of Barr Group, an embedded systems consulting firm, last week. As a primary expert witness for the plaintiffs, the in-depth analysis conducted by Barr and his colleagues illuminates a shameful example of software design and development, and provides a cautionary tale to all involved in safety-critical development, whether that be for automotive, medical, aerospace, or anywhere else where failure is not tolerable. Barr is an experienced developer, consultant, former professor, editor, blogger, and author.

Barr's ultimate conclusions were that:

  • Toyota’s electronic throttle control system (ETCS) source code is of unreasonable quality.
  • Toyota’s source code is defective and contains bugs, including bugs that can cause unintended acceleration (UA).
  • Code-quality metrics predict presence of additional bugs.
  • Toyota’s fail safes are defective and inadequate (referring to them as a “house of cards” safety architecture).
  • Misbehaviors of Toyota’s ETCS are a cause of UA.

A damning summary to say the least. Let's look at what lead him to these conclusions:


Hardware

Although the investigation focused almost entirely on software, there is at least one HW factor: Toyota claimed the 2005 Camry's main CPU had error detecting and correcting (EDAC) RAM. It didn't. EDAC, or at least parity RAM, is relatively easy and low-cost insurance for safety-critical systems.

Other cases of throttle malfunction have been linked to tin whiskers in the accelerator pedal sensor. This does not seem to have been the case here.

 

Toyota_ECMsm.jpg

The Camry ECM board. U2 is a NEC (now Renesas) V850 microcontroller.

Software

The ECM software formed the core of the technical investigation. What follows is a list of the key findings.

Mirroring (where key data is written to redundant variables) was not always done. This gains extra significance in light of …

Stack overflow. Toyota claimed only 41% of the allocated stack space was being used. Barr's investigation showed that 94% was closer to the truth. On top of that, stack-killing, MISRA-C rule-violating recursion was found in the code, and the CPU doesn't incorporate memory protection to guard against stack overflow.

Two key items were not mirrored: The RTOS' critical internal data structures; and—the most important bytes of all, the final result of all this firmware—the TargetThrottleAngle global variable.

Although Toyota had performed a stack analysis, Barr concluded the automaker had completely botched it. Toyota missed some of the calls made via pointer, missed stack usage by library and assembly functions (about 350 in total), and missed RTOS use during task switching. They also failed to perform run-time stack monitoring.

Toyota's ETCS used a version of OSEK, which is an automotive standard RTOS API. For some reason, though, the CPU vendor-supplied version was not certified compliant.

Unintentional RTOS task shutdown was heavily investigated as a potential source of the UA. As single bits in memory control each task, corruption due to HW or SW faults will suspend needed tasks or start unwanted ones. Vehicle tests confirmed that one particular dead task would result in loss of throttle control, and that the driver might have to fully remove their foot from the brake during an unintended acceleration event before being able to end the unwanted acceleration.

A litany of other faults were found in the code, including buffer overflow, unsafe casting, and race conditions between tasks.

 

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

All of the stuff you quoted was in regards to tens of thousands if not hundreds of thousands of vehicles, not just a couple. The Toyota stuff actually proves my point, the ecm will not make errors just because. It was a flaw in the logic, and effected all vehicles with that ECM/Firmware content. I would imagine that if GM had a code issue in the ECM, it would have popped up by now in ALL vehicles using that firmware.

  • 6 years later...
Idontknowanymore New Member

Idontknowanymore

Posted
Posted

09 gmc sierra 5.3l, 6 minths ago check engine light came on blinking, dash screen said stablelink and tracktion control off. engine running rough at idle, trouble code cylinder 6 misfire. shop replaced lifter and head gasket, cost me $1100, part and labor warranty for 3 years included. Bought diablo tuner to deactivate afm/dod. Dash screen showed that it was in v8 mode all the time after that. Win in my book!!!! Not so fast...

All was fine until 2 weeks ago, same exact symtoms/issue, shop replaced same parts as the first time, truck was running fine. Check engine light came on after a few miles down the street.hooked up my scanner, trouble codes p0171 & p0174 (bank 1& bank 2 running lean) truck felt like it was running fine though. Brought truck back to the shop. They smog tested it, supposidly no vaccum leaks. Cleared code. Drove home, shut truck off, truck was off long enough to cool down completely. Drive to the store later that day, light came back on,same codes. Brought truck back to shop next day, they can not figure out why its throwing those 2 codes after 5 hours looking at the truck.

   I restored factory tune, light when away. Came back a few miles later, lol. Switched back and forth between stock tune and diablo tune because installing the diablo tune is the only way to turn off afm/dod. Every time i switched tunes light will go away on the first drive and will come back on the second drive after shutting the truck off. Didnt seem like it was hurting anything to drive it with the light on,truck was running perfectly fine. Just came back from the store and on the way home, guess what!!! Dash lit up and now truck is misfiring again and it limped half way home.... i dont have the slightest clue on what to do beside take the truck back to the shop and see if its still covered under their parts and labor warranty they gave me... im at a complete loss...any help at all would be appriciated, thanks

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