GM V8 Engine recall

[Frenchy]

What's the AFM?

Active fuel management. Essentially is what GM uses to shut off half the engine while it's running

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[got3fords]

Active fuel management. Essentially is what GM uses to shut off half the engine while it's running

Heck, I thought that stuff died with the unreliable Cadillac V8-6-4 .

 

[Buckbull]

Heck, I thought that stuff died with the unreliable Cadillac V8-6-4 .

It should have.

 

[Langwilliams]

I hear the Hemi engines have that same AFM under a different name. My friend ordered a tuner just to turn that feature off.

 

[dtech]

Ford uses it on 5.0, Mazda, Honda, toyota, gm, ram also. Like the Chrysler lean burn the 8 6 4 Cadillac was conceptually sound but the microprocessor technology at the time wasn't up to the task. Today processor speeds are orders of magnitude better allowing for stuff like DI to be effective.

 

[NotBudule2]

I worked at a Caddy dealer during the 8 6 4 engine, the complaints and one reason why they did away with it was when in the 6 cylinder mode, it felt like it had a bad miss, 8 and 4 were fine, 6 ?... I got a nice 81 Coupe somebody traded dirt cheap from there, disabled the 864 and drove it for years...

 

[Frenchy]

From what I remember with both Chevy and GMC Trucks with Active Fuel Management, they loved to take a dump on lifters all the time. It was usually the collapse able lifters for the cylinders that would get shut off. I remember having to replace a set on an engine that had less than 5,000 miles on it. Not a fun task at all......

 

[Dgc333]

I hear the Hemi engines have that same AFM under a different name. My friend ordered a tuner just to turn that feature off.

Yep, it's called Multiple Displacement System or MDS. I got the Hemi in my hot rod because one of the MDS lifters failed and wiped out the cam. When I rebuilt the engine I replaced all the MDS lifters with standard lifters, removed the MDS solenoids and plugged the ports.

FWIW, my son's wife had a Tahoe with a 5.3 LS. They were at a friend's house and the car would not go into reverse but would move forward. They pushed the car into the road and drove home. Next day at his shop he dropped the tranny pan and opened the valve body. The check balls in the valve body that were traditionally steel were plastic and one was work and had stuck in the port it controls. New check ball and all was well. Two weeks later one of the AFM lifters stuck, the push rod jumped out of the rocker jammed and bent. He replaced the lifter and push rod drove the Tahoe to the local Ford dealer and traded it for an Explorer.

 

[Langwilliams]

Yep, it's called Multiple Displacement System or MDS

When I read this fuel saving system was coming I figured they'd just turn off two injectors, then four. Rotating the ones turned off to even wear but I'm no engineer (my three boys are) so there might be problems with the simple solution.

 

[RangerBill]

When I read this fuel saving system was coming I figured they'd just turn off two injectors, then four. Rotating the ones turned off to even wear but I'm no engineer (my three boys are) so there might be problems with the simple solution.

You would also have to open the valves so the disabled cylinders no longer have any compression that the active cylinders would be fighting against.

 

[Frenchy]

You would also have to open the valves so the disabled cylinders no longer have any compression that the active cylinders would be fighting against.

Lol talk to the GM Engineers about that. They deactivate the lifters for the cylinders keeping the valves closed when turning off half the engine. Along with that no spark and no fuel to said cylinders.

 

[RangerBill]

Lol talk to the GM Engineers about that. They deactivate the lifters for the cylinders keeping the valves closed when turning off half the engine. Along with that no spark and no fuel to said cylinders.

You're right, I mis-remembered on the operation of that system.

 

[Dgc333]

Lol talk to the GM Engineers about that. They deactivate the lifters for the cylinders keeping the valves closed when turning off half the engine. Along with that no spark and no fuel to said cylinders.

That is the way the Hemi MDS system works too. Here are a couple of pictures of what happens when one of the lifters fail.

I speculate that when a cylinder deactivates the load of the cam pushing on the lifter against the valve springs goes away. When it reactivates there is a sharp increase in load. Over time the needle bearings in the lifter take a beating and one fails resulting in the roller not rolling over the cam and the lifter and cam lobe are ground away.

When I rebuilt the engine these parts came from I got rid of the whole MDS system.

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[dtech]

Oil Geek youtube vid on GM recall and oil viscosity, it's long and probably not a lot of new info for those who know oil, but one thing I found of interest early on in the vid is the geek advocates doing the 1st oil change at much lower miles than standard prescribed interval . Also the test on the engine is looking for a DTC code that comes from comparing camshaft speed to that of the crankshaft, when Hyundai was having their massive recall for crankshaft wear the test they did was inserting a sonic probe into the oil dipstick and recording noises,if passed you got a new dipstick which allowed for increased oil capacity but later on they figured out how to use the knock sensor to detect impending crankshaft failure. And as frequently mentioned pursuit of higher mpg is at the root of all this.

 

[OGMix376]

Why not just cut spark and cut fuel, let those unused cylinders just cycle as normal? With the shut off cylinders just be fighting compression anyway if the valves are shut off anyway?
(Or at the engines non interference? So the valves are just locked in the open position during inactivity.)
I never dealt with that system but I’ve heard they were doing stuff like that..
((My initial thoughts when hearing about that idea of a cylinder shut off system… sounds like a lot of engines are going to be blowing up?.))

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