Newbie with 2005 Envoy XL 5.3

[Joel Phelps]

Hey guys, newbie here. A few weeks ago I picked up a 2005 Envoy XL, 5.3l 4x4. Had 100,350 miles on it. Thought it was a pretty good deal. Now I am hesitant to make that claim. I like this thing, BUT, its going to be the death of me.

Week 1, battery died. No biggy. It was the original.
Week 2, started noticing my rpms jumping at cruising speeds, bad torque converter. Well that wasn't cheap
Week 3, day 2 after getting back from TC replacement. Getting a slight hesitation at cruising speeds. Also similar to what I was feeling with the bad TC. Took it back in and no codes. They recommended new plugs wires etc.
Week 4, officially started this last Saturday. I pulled it into the garage with a backseat full of new parts, and a lofty expectation this wouldn't take to much and we would get this done....

SO..... A number of hours later (wont disclose actual hours as is slightly embarrassing but did include a trip back to autozone for 2 more spark plugs after some ummm...fell...) SO, plugs and wires changed, MAF cleaned, Throttle body cleaned (lord it was bad), new air filter, oil change, and was going to be a new fuel filter till I spent half an hour looking for the damn thing only to realize mine is a model that has it integrated inside the fuel tank......

Did some slight low to no cost cosmetic changes to the outside while I was at it and yesterday morning took it out and to see how she ran.... And you could tell the difference. Smooth as silk idle and acceleration, a noticeable gain in restored HP, and after 20 minutes of driving, IT STILL HAD THE FREAKING HESITATION/MISS/WHAT THE CRAP IS THIS THING DOING?!?!?

SO...All that is said to say and ask this. Between 1600-2200 RPMS, which equates to 55-70 mph, when I am at a constant cruising speed without significant acceleration, every couple of minutes I am getting a jerk feeling almost like a miss or hesitation. The RPMs stay constant so not thinking any transmission issues. Also not throwing any codes and its otherwise running very well. Any ideas thoughts or suggestions? Could it possibly have something to do with this DOD mess?

 

[BRomanJr]

Congratulations on your "New to you" Truck.
It could be the DOD/AFM. The easiest way to temporarily disable it is to unplug the electrical connector on the vacuum switch mounted to the Brake Vacuum Booster (this will eventually turn on the CEL/SES light) unplug it after you start it, then the start-up self test won't trip the light right away.

See if this cures or changes that jerk/miss/hesitation you feel.

The next thing that might cause this is the Upstream O2 sensors (1 on each side) be warned the electrical plugs are a pain to get to.

 

[Joel Phelps]

Ok, first thank you! 2nd. I pulled the connector off. Drove a 30 mile round trip with no issues. SO, preliminarily that worked. So finally getting somewhere. However, that just raises more questions

Why am feeling it, and besides getting a tune and/or leaving the connector off and killing it completely, how do I stop making it very noticeable when it goes in and out?

Or, has someone come up with a way to run these things with a tune that doesn't eventually lead to lifter failure?

 

[Mooseman]

I used to feel the same jerk when it switched from 8 to 4 cylinders, until I tuned it out. I also eventually replaced the entire valvevetrain (seperate story). You should be able to avoid lifter failure by tuning it out. In the meanwhile, you can just leave that sensor unplugged and continue monitoring. You'll know what a CEL is for.

And MPG won't be affected that much really. Useless system.

 

[Joel Phelps]

Thanks. Your threads were what got me considering the DOD issue. was not mentioned at all when I took it in to check codes etc.

 

[Shaw520]

When properly disabled,..(don't ask me how bc I don't know), some have claimed same or better gas mileage.

 

[BRomanJr]

Excuse my long read:
My theory is that DOD/AFM is designed, calibrated and programmed for a clean engine. When in 4cyl mode, the unused (deactivated) cylinders collect oil in the rings from the increased suction in the cylinders (valves never open). As the cylinders are re-activated that oil gets blasted with combustion gases and a small amount of that oil is super-heated and gets stuck to the rings, some burns and goes out the exhaust. Drivers have noted that after odometer mileage approaches and exceeds ~100k miles that a puff of blue smoke is exhausted every time when going back to 8cyl mode. (YMMV)

The amount that collects in the rings must be so small that the engine runs properly for many thousands of miles. Once the rings start to stick (these engines are known to use lots of oil as they age) the compression and power variances between 4cyl and 8cyl modes becomes more than the programming has allowed for and the transition is no longer smooth. At this point the sticky rings allow more oil to pass and the problem can worsen.

Disabling the system essentially stops the process from progressing and logic would predict that over time those rings on the deactivation cylinders may get cleaner or at least no worse. I also think that the deactivated cylinders lose a bit of compression because of the sticky rings and that fuel economy probably worsens as the engine is no longer putting out power as smooth as it used to.

Would like to hear others' thoughts on this.

 

[Mooseman]

That actually makes sense given they use more oil with DoD active. Once deactivated, oil consumption goes down.

The lifters usually fail when trying to return to 8 cyl. mode and it stays collapsed. By not activating, they don't collapse so no failure theoretically.

 

[Reprise]

Would like to hear others' thoughts on this.

While the first time I've seen this reasoning on DoD and why it fails...what you posted makes sense and sounds logical. Nothing I can add to it (thankfully, my '03 doesn't have this tech)

Thank you for sharing it with the community.

 

[Joel Phelps]

Just figured I would do a weekly follow up. Have had the plug off for one week. No issues at all. And actually getting better MPGs. Now that might be due to the new plugs, wires, air filter, MAF and throttle body clean, but still gained almost a full MPG.

So I guess the next step is doing a little more research on a tune.

 

[BRomanJr]

While the first time I've seen this reasoning on DoD and why it fails...what you posted makes sense and sounds logical. Nothing I can add to it (thankfully, my '03 doesn't have this tech)

Thank you for sharing it with the community.

My recent experience and continued research on AFM (DOD) culminated when my brother bought a barely running 2006 Trailblazer LT 5.3. That's another story.

I can also clarify, my current 2004 Envoy XUV has the 5.3 just prior to DOD (now AFM) and used to wish I had the "better" 5.3. That is until I read about it more and found very few positive attributes once the vehicle exceeded 100,000 miles.
The XUV now has well over 200k and going strong. I am much happier that I don't have DOD.

 

[northcreek]

Just figured I would do a weekly follow up. Have had the plug off for one week. No issues at all. And actually getting better MPGs. Now that might be due to the new plugs, wires, air filter, MAF and throttle body clean, but still gained almost a full MPG.

So I guess the next step is doing a little more research on a tune.

You can do the tune to eliminate AFM activation or buy a RANGE unit that just plugs into the obdII port. I have had one on my 5.3 for several years without a hitch....Mike.
saw this one on ebay>> https://www.ebay.com/itm/RANGE-TECH...ash=item2a9314b012:g:B7YAAOSwi0xZ8UXf&vxp=mtr