What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[Doubeleive]

I do think a vac leak is worth checking for.


I'm just guessing they did plugs and wires when they replaced the lifters?

New lifters
new plug wires
new plugs -twice
that includes a new intake gasket twice
new head gaskets, heads inspected and cleaned by a machine shop (pass)
new cat on bank2
new downstream 02 sensors
new maf
swapped in known good map

as a result the rotational noise I was hearing on bank 1 is gone
previous to doing bank 2 lifters I was getting a lean code on bank2 which has not yet returned but it doesn't have many miles on it since then probably less than 30
still getting random misfires, maf code, maf code is new since bank2 lifters done
swapped the tune 3 times
thats all I think

 

[Doubeleive]

Only thing that stands out is the continuous knock for a couple sessions..?
looks like it feels normal cruising slowly? Once you roll up past 3500 rpms it retards

I don't know if this is the problem, but I bet if you take the starter out and feel it in your hands, you'll want to replace it.
Might be a good time for that maintenance..

I will def give it a look at later this evening, hot as balz outside plus the engine is nice and warmed up now

 

[j91z28d1]

New lifters
new plug wires
new plugs -twice
that includes a new intake gasket twice
new head gaskets, heads inspected and cleaned by a machine shop (pass)
new cat on bank2
new downstream 02 sensors
new maf
swapped in known good map

as a result the rotational noise I was hearing on bank 1 is gone
previous to doing bank 2 lifters I was getting a lean code on bank2 which has not yet returned but it doesn't have many miles on it since then probably less than 30
still getting random misfires, maf code, maf code is new since bank2 lifters done
swapped the tune 3 times
thats all I think

man that's a lot of new stuff.

honestly since a vacuum leak is easy to check for I'd still double check their work. spray around some while watching the short term trims.


so I did have a thought, so the miss fire uses the crank position relative to the knock sensors hear noise. which works because miss fire is from detonation in the combustion chamber near or just before top dead center of the power stroke, but if say it's a lifter or something making the noise the knock sensors are picking up, then the ecm reporting what cyl is missing could be wrong? Just a guess, as I don't fully know how the ecm works it out. but its possible it's leading you to a wrong cyl?

 

[mikez71]

No rush here, I'm still waiting to put my replacement motor mount bolt in
Soon, real soon. I bought a used OEM bolt from ebay and everything. Patina should match..

Cooler days ahead.. My head was thinking about clogged cats and broken transmission parts..
but a little noise (which I never heard) can really cripple the power output!

Maybe the same alien that visited my truck, visited your truck..

 

[Doubeleive]

man that's a lot of new stuff.

honestly since a vacuum leak is easy to check for I'd still double check their work. spray around some while watching the short term trims.


so I did have a thought, so the miss fire uses the crank position relative to the knock sensors hear noise. which works because miss fire is from detonation in the combustion chamber near or just before top dead center of the power stroke, but if say it's a lifter or something making the noise the knock sensors are picking up, then the ecm reporting what cyl is missing could be wrong? Just a guess, as I don't fully know how the ecm works it out. but its possible it's leading you to a wrong cyl?

if it was a vacuum leak wouldn't it be the same vacuum under a load versus no load, revving it in park I get 0 zero misfires even at 5500rpm, this only happens under a load.

 

[mikez71]

Now you make me want to raise the park rev limit..

Could be a separate issue the misfire count, but for sure too much knock retard.
Something is setting the knock sensors off.

 

[Doubeleive]

Now you make me want to raise the park rev limit..

Could be a separate issue the misfire count, but for sure too much knock retard.
Something is setting the knock sensors off.

I suppose while I am under the truck I should take a look at the knock sensors see if one is loose or anything, replacements are about $25 each if I wanted to just throw new ones on there just have to get them from 2 different stores, everywhere has 1 only
I don't know how out of spec one has to be to throw a code. I see the left one is right by the starter.

 

[Writefast]

Fixed my passenger side mirror today. Not too bad a job. Waited till it was hot out because of all the plastic pieces that might crack
View attachment 434755

How did you fix that?? I just ordered two new mirrors.

 

[Doubeleive]

How did you fix that?? I just ordered two new mirrors.

the mirrors can be disassembled on the truck. takes about 15-20 minutes to just swap a motor out, little bit longer to take the motor apart if just replacing the gear.
it's common for the white plastic gear to split open, then it's just spinning it's wheels and not doing anything.

 

[j91z28d1]

if it was a vacuum leak wouldn't it be the same vacuum under a load versus no load, revving it in park I get 0 zero misfires even at 5500rpm, this only happens under a load.

in general there's high vacuum at idle and basically zero vacuum at wot.


when I'm at a loss and something is doing something weird. I tend to default doing whatever simple tests I can do to rule out stuff.

just habit