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

[Doubeleive]

maybe it's just my brain but the engine doesn't even sound normal to me anymore, something has changed even just idling something is different and it's not a rattle or tick or anything like that it just sounds different than it has before. could be my imagination....

 

[Doubeleive]

would the specific cylinder misfires correlate with a bank noise causing knock?
kind of wouldn't make sense though because a lot of the misfire are on 2 & 7

 

[Doubeleive]

misc data, in case anything looks off

 

[gooffeyguy]

the thing is there is no reason for this to be tune related at all, I switched it 3 times including going back to what was on it before blackbear sent me any tune and no change.
something is causing this just need to figure it out.

It's that lost 10mm socket rattling around somewhere

 

[mikez71]

^^^ Could be, right?! ^^^

actual timing should be actual.I saw a -12.5 degrees timing shown at one point.
I thought max was -10, but who knows there maybe some other adders or multipliers.

Looking at MY previous normal graphs, timing tends to stay above 16degrees (warmed up),
EXCEPT during shifts, I see spikes down to -5 degrees (final advance) very briefly.
(pretty sure that is a torque management shift setting)

With the loose mount/knock retard, timing advance could stay negative.
Never dipped below -10, but would often be negative once knock retard kicked in.

My indivudal cylinder knocks were all nearly identical, despite it being close to one knock sensor. Could be the vibration just rings the whole block.
(Or I suppose the knock was so continuous it continued throughout all cylinder ignition events evenly.)
About your cylinder misfires, did they move around? I though I saw some different cylinders before it was 7 & 8. Think I read misfires are sensed by the crank speed..

 

[swathdiver]

View attachment 434938

Fuel Pump trims look good, better than mine and about the same as my pickup.

 

[swathdiver]

I'm trying to think, I think mine did something similar a few years ago. Intake gaskets or spark plug gap, can't remember.

 

[Doubeleive]

^^^ Could be, right?! ^^^

actual timing should be actual.I saw a -12.5 degrees timing shown at one point.
I thought max was -10, but who knows there maybe some other adders or multipliers.

Looking at MY previous normal graphs, timing tends to stay above 16degrees, EXCEPT during shifts, I see spikes down to -5 degrees (final advance) very briefly.
(pretty sure that is a torque management shift setting)

With the loose mount/knock retard, timing advance could stay negative.
Never dipped below -10, but would often be negative once knock retard kicked in.

My indivudal cylinder knocks were all nearly identical, despite it being close to one knock sensor. Could be the vibration just rings the whole block.
About your cylinder misfires, did they move around? I though I saw some different cylinders before it was 7 & 8. Think I read misfires are sensed by the crank speed..

they did but 2,7,8 seem to be more than others, 8 has came up alone a few times then it will show random.
just went to check to see if the motor moves in drive/reverse but doesn't appear to budge at all or very very little.
I guess when it cools off later this evening I will get under it and tap around with a mallet

 

[mikez71]

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..

 

[j91z28d1]

I'm trying to think, I think mine did something similar a few years ago. Intake gaskets or spark plug gap, can't remember.

I do think a vac leak is worth checking for.


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

 

[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