PPV AFM ?’s

[5strmtrp]

I understand what AFM does, just not sure of it’s specifics.

Does it only turn on above a predetermined speed?

Is it always active say at surface street speeds, above 25 MPH?

I’m getting a stumble at surface street speeds. It doesn’t matter if I’m on the throttle/maintaining speed or I’ve just come off coasting and resuming/gaining speed. I do feel a slight change at highway speeds and have been told it’s the AFM, but it’s only a guess.

The Tahoe is a retired police service vehicle/SSV, 4 wheel drive 5.3 6 speed trans.

Truck has 110,000 ish miles on it.
I’m thinking it might need plugs and wires but have not determined if it needs them yet.

I am lucky enough to have gotten in touch with the PD it was in service by and have gotten a decent service history on it. No record of problems regarding what I mentioned. It was used as a Crime Scene vehicle driven by 1 officer 24/7.


Suggestions comments fixes really needed.

Thanks

Paul

 

[iamdub]

There are a various parameters required for AFM to engage ranging from engine temperature to vehicle speed. The most pertinent to your case is vehicle speed and engine load.

Most PPVs/SSVs don't have it, but does yours have the DIC control switches to the right of the instrument panel? If so, you can cycle through the displays until it shows "V8" or "V4". Drive around when the stumble happens and not happens and compare it to the engine mode.

Other than that, I think you can keep AFM from engaging by putting the trans in "M4". You'd need to know the approximate vehicle speeds, engine RPMs and throttle amounts where the stumble happens for an accurate comparison. If it never happens in M4, shift to M5 or M6 and retest. If the stumbling returns, it's likely an AFM issue.

If your plugs are original at 110K miles, it couldn't hurt to change them. But I don't think that'd make any real improvement in the stumbling.

 

[R3cord303]

I understand what AFM does, just not sure of it’s specifics.

Does it only turn on above a predetermined speed?

Is it always active say at surface street speeds, above 25 MPH?

I’m getting a stumble at surface street speeds. It doesn’t matter if I’m on the throttle/maintaining speed or I’ve just come off coasting and resuming/gaining speed. I do feel a slight change at highway speeds and have been told it’s the AFM, but it’s only a guess.

The Tahoe is a retired police service vehicle/SSV, 4 wheel drive 5.3 6 speed trans.

Truck has 110,000 ish miles on it.
I’m thinking it might need plugs and wires but have not determined if it needs them yet.

I am lucky enough to have gotten in touch with the PD it was in service by and have gotten a decent service history on it. No record of problems regarding what I mentioned. It was used as a Crime Scene vehicle driven by 1 officer 24/7.


Suggestions comments fixes really needed.

Thanks

Paul

When I still had AFM on my 2007, I could feel it engage and disengage. At low speeds it would feel like it was stumbling when in v4 mode but I think it was just because it didn't run as good on half the cylinders, combined with shot motor mounts. The stock ones are oil filled and will collapse after some time. you can replace them with mounts for a hummer h3 with the 5.3. At highway speeds when kicking into v4 mode it would also sound a bit different and shake ever so slightly more. Then after passing someone one day an afm lifter failed it it had a dead miss in #4.

 

[5strmtrp]

I was under the assumption that all trucks had the AFM in them. Learned something new!


My truck doesn’t have the DIC switch, however like most of us know the wires are there. It’s on my list of improvements for this truck.

I’ll see if driving it in Manual mode makes a difference. That I fixed a few weeks back as my shift had the wires snipped.

There are a various parameters required for AFM to engage ranging from engine temperature to vehicle speed. The most pertinent to your case is vehicle speed and engine load.

Most PPVs/SSVs don't have it, but does yours have the DIC control switches to the right of the instrument panel? If so, you can cycle through the displays until it shows "V8" or "V4". Drive around when the stumble happens and not happens and compare it to the engine mode.

Other than that, I think you can keep AFM from engaging by putting the trans in "M4". You'd need to know the approximate vehicle speeds, engine RPMs and throttle amounts where the stumble happens for an accurate comparison. If it never happens in M4, shift to M5 or M6 and retest. If the stumbling returns, it's likely an AFM issue.

If your plugs are original at 110K miles, it couldn't hurt to change them. But I don't think that'd make any real improvement in the stumbling.

 

[5strmtrp]

I also was wondering if it could be motor mounts. It idles fine do not see the motor moving around.

My other thought was one of the coils starting to fail or getting weak if that’s such a thing.

thanks

Paul

When I still had AFM on my 2007, I could feel it engage and disengage. At low speeds it would feel like it was stumbling when in v4 mode but I think it was just because it didn't run as good on half the cylinders, combined with shot motor mounts. The stock ones are oil filled and will collapse after some time. you can replace them with mounts for a hummer h3 with the 5.3. At highway speeds when kicking into v4 mode it would also sound a bit different and shake ever so slightly more. Then after passing someone one day an afm lifter failed it it had a dead miss in #4.

 

[avalonandl]

At 110 k you need pplugs and wires. You could check the coils and the connectors make sure no corrosion.

I doubt the AFM is causing the issue.

 

[R3cord303]

I also was wondering if it could be motor mounts. It idles fine do not see the motor moving around.

My other thought was one of the coils starting to fail or getting weak if that’s such a thing.

thanks

Paul

If they’re the OG oil filled ones they could for sure contribute

 

[jatPPV2012]

Just adding to this post. Sorry I'm a recent new member (Feb 14 join date).
I have a retired Florida FHP 2012 PPV Tahoe which I recently bought at an auction and it does have AFM so I'm assuming all Tahoes including SSV and PPVs have AFM. When I'm driving, I notice it kicks in at various speeds above 25 MPH. I've driven as slow as 45 MPH and see it switch to V4 mode so its not set at a predetermined speed.

 

[Miami-Dade]

I was under the assumption that all trucks had the AFM in them. Learned something new!

Just adding to this post. Sorry I'm a recent new member (Feb 14 join date).
I have a retired Florida FHP 2012 PPV Tahoe which I recently bought at an auction and it does have AFM so I'm assuming all Tahoes including SSV and PPVs have AFM. When I'm driving, I notice it kicks in at various speeds above 25 MPH. I've driven as slow as 45 MPH and see it switch to V4 mode so its not set at a predetermined speed.

Last year spoke to a Leo from the FHP who was getting his 2013 Tahoe serviced at the dealer while I there. I asked him if all the PPV Tahoe's in the fleet have AFM and his answer was yes.

 

[2011SSVHOE]

My 2011 SSV has AFM, with no problems