What did you do to your NBS GMT800 Tahoe/Yukon Today?

[clandr1]

Thanks for all the suggestions Fless, strutaeng, mountie, 6speedblazer, Scottydoggs!
And I'm surely forgetting someone.. sorry if I did!
Good news!

As Fless mentioned my MAF was not reporting right.. Too much at idle, too little at WOT. Alvin of PCMofNC also informed me that MAF sensors age out..

Installed new MAF. Max LTFT now 9.4%, and STFT looks much better. Old left, new right. Honeycomb pattern different. New one has ovalized hex at different angles.
View attachment 483434
View attachment 483435
MAF resistors? look a little different.
Old legs angled 45 degreess, new straight. New resistors larger.
View attachment 483436
View attachment 483437
Idle at stop in drive, the new MAF reads 6.6g/s..(old 8g/s)
Max airflow at 5,184 rpms, new equals 260g/s..(old 213g/s - 226g/s)
Injector duty cycle 17.40ms at 5,184 rpm supposedly 75% duty cycle.

Someone with a LQ9 logged 253g/s at 5200rpm, 20.7ms, 89% duty cycle.
They also logged 265g/s at 5,530 rpm..

Old MAF - airflow signal squiggly, fuel trims jump when driving modes change
View attachment 483439

New MAF - airflow signal smoother, fuel trims change much less
View attachment 483430

I haven't been keeping up with all your posts on this issue, but did you notice a difference when driving? Acceleration, throttle response, etc?

 

[mikez71]

If I didn't have a scanner, I may never have noticed! (I did get a P0101 code one time)
I have not driven much, and it did not drive terribly before..
But I am confident the MAF did fix some issues, and it feels more consistent.

What I first noticed in the logs, fuel trims varied a lot.
(+25% LTFT +20% STFT) (+7% LTFT +30% STFT) (+19% LTFT -18% STFT)

Fuel trim variance is less than half as much now.
LTFT mostly +5% to +9%.. (a few times it spiked to 11.7%)
STFT +/- 10% max, mostly +/- 5%.

Before there was sometimes 7.9deg of knock retard at WOT.
Logs show the MAF reporting 170g/s at 4000rpm in 2nd when knocking.
New MAF reports 200g/s at the same RPM/throttle.
I did not log injector pulse earlier on, but the trims were typically +25 LTFT & +15 STFT when it knocked.

Still a little KR when engine is cold at light throttle, none at WOT!
(A few occasional misfires that hopefully new plugs will fix, probably have some exhaust leaks too..)

Also noticed transmission PCS line pressure was 70% during WOT pull in 1st before.
After new MAF it is 80%.

 

[JoeBlobs]

Installed a battery cut-off on the 'ol beater today. This truck has been driven maybe 3 or 4 times in the past two years, but I just can't bring myself to let er go.

 

[mikez71]

Gotta have a backup vehicle..
It's what you drive when working on the daily driver, and vice-versa...

Once every 6 months is quite infrequent....
You need to work on the daily driver more often!

 

[6speedblazer]

Had a few small things i wanted to get done today.

A crack started on my dash bezel in the escalade and I wanted to stop it before it got worse. Also decided to replace the bulbs in the hvac headunit while I had the dash apart. This truck only had one bulb out, but at 20 years old, I just did them all.

Picked up a 20 dollar hot staple kit off amazon for the bezel repair.

 

[JoeBlobs]

Gotta have a backup vehicle..
It's what you drive when working on the daily driver, and vice-versa...

Once every 6 months is quite infrequent....
You need to work on the daily driver more often!

You ain't wrong my man. The 'ol girl definitely needs some attention. I'm pretty sure the cats are clogged so that'll be a fun one.

 

[mountie]

You ain't wrong my man. The 'ol girl definitely needs some attention. I'm pretty sure the cats are clogged so that'll be a fun one.

At least, you have the time when available, to work on it since you have something else to drive.
( Is that a window wash sprayer under the headlight?? )

 

[JoeBlobs]

At least, you have the time when available, to work on it since you have something else to drive.
( Is that a window wash sprayer under the headlight?? )

haha no thats the battery cutoff switch. Since it sits so long, it's easier for me to flip a switch rather than keep disconnecting and reconnecting the battery.

 

[mountie]

haha no thats the battery cutoff switch. Since it sits so long, it's easier for me to flip a switch rather than keep disconnecting and reconnecting the battery.

Hidden in plain sight.

 

[6speedblazer]

Finally got one set done. Cleaned up and painted 99-02 wiper arms on my 05 denali.
No real reason other than I really wanted a service position.

 

[mikez71]

Had a P0101 MAF code, bought a new MAF, fuel trims improved, knock retard seemed to go away, but now the CEL popped up again!

Two codes now. (every 'fix' always creates two more problems!)
Still the P0101 (just a history code), but now a P0332 knock sensor..

Got freeze frame data, but not sure it will tell me anything...LTFT increased to 16%..
I do notice the exhaust leak @Scottydoggs mentioned, engine quiets down after warming up..
Hoping that can be the cause of this code too...

 

[Fless]

Read your fuel trims at idle. Of course at 3k rpm it's going to be adding fuel and they'll increase.

 

[mikez71]

Just went on another drive with HPTuners...
LTFT between 2.3(bank1) 0.8(bank2) upto 8.6 and 5.5 (at idle)
10.9 is as high as it ever gets driving. At WOT both banks are 7.8...
BUT with the P0332, I notice my ignition timing is retarded ~6-7 degrees at WOT than before..

Not sure why the Tech2 recorded 16% in the freeze frame.
(Previous to code, and after code, I logged a max of 11% LTFT)
Secondary o2's seem to stay mostly rich except after decel fuel cut..

Maybe misfires, I see a few spread out here and there..
But I would think misfires would cause the mixture to read rich, and PCM to adjust trims lean..

 

[Scottydoggs]

Just went on another drive with HPTuners...
LTFT between 2.3(bank1) 0.8(bank2) upto 8.6 and 5.5..
10.9 is as high as it ever gets. WOT both are even at 7.8...

Not sure how the Tech2 recorded 16% in the freeze frame.
Secondary o2's seem to stay mostly rich except after decel fuel cut..

Maybe misfires, I see a few spread out here and there..
But I would think misfires would cause the mixture to read rich, and PCM to adjust trims lean..

how high are the miles? cats could be clogging up. could cause misfires and the rich, but not so much that maf code.

 

[Tonyrodz]

Thanks for all the suggestions Fless, strutaeng, mountie, 6speedblazer, Scottydoggs!
And I'm surely forgetting someone.. sorry if I did!
Good news!

As Fless mentioned my MAF was not reporting right.. Too much at idle, too little at WOT.
Alvin of PCMofNC also informed me that MAF sensors age out..

Installed new MAF. Max LTFT now 9.4%, and STFT also much better. Old left, new right.
Honeycomb pattern looks different. New one has ovalized hex at different angles.. Or it's just deformed from mishandling at the factory..
View attachment 483434
View attachment 483435
MAF resistors? look a little different.
Old legs angled 45 degreess, new straight. One new resistor larger.
View attachment 483436
View attachment 483437
Idle at stop in drive, the new MAF reads 6.6g/s..(old 8g/s)
Max airflow at 5,184 rpms, new equals 260g/s..(old 213g/s - 226g/s)
Injector duty cycle 17.40ms at 5,184 rpm supposedly 75% duty cycle.

Someone with a LQ9 logged 253g/s at 5200rpm, 20.7ms, 89% duty cycle.
They also logged 265g/s at 5,530 rpm..

Old MAF - airflow signal squiggly, fuel trims jump when driving modes change
View attachment 483439

New MAF - airflow signal smoother, fuel trims change much less
View attachment 483430

Did you get an AC Delco maf?

 

[mikez71]

150k miles.. I'll skip backpressure test for now. (misfires don't necessarily happen at WOT or high flow conditions)

Someone else told me:
"P0101 code is from exceeding a calculated airflow value difference from the MAP/VE and the MAF. "

He told me to smoke test the intake. Have ordered an Amazon smoke tester..
I wonder if an evap leak could cause that. (But no evap codes and I know the solenoids click)

 

[mikez71]

Did you get an AC Delco maf?

Delphi.. Apparently OEM is discontinued and Delphi was the OEM manufacturer..

 

[yukon-coRn]

My new to me 01 Yukon came with aftermarket headlights, and while looking under the hood I noticed the driver's side had a busted adjustment screw:



They're some kind of Winpower bright white HID/xenon lights that work pretty good. I unplugged the bulbs from the 2 little ballast/adapter things and JB welded the break above. All good, then reinstalled.

Drove it that night starting at dusk to get dinner & didn't notice anything odd until later that night, the headlights are always on now along with the instrument lights. The headlight switch does nothing. They only turn off when the truck is turned off. I'm wondering if something shorted because I didn't disconnect the battery before unplugging the light in the first place, I've never dealt with these kind of aftermarket lights before. Everything acted normally before all this (except the fog lights were out which I had not investigated yet). Scratching my head on this one....

 

[mountie]

My new to me 01 Yukon came with aftermarket headlights, and while looking under the hood I noticed the driver's side had a busted adjustment screw:

View attachment 483654

They're some kind of Winpower bright white HID/xenon lights that work pretty good. I unplugged the bulbs from the 2 little ballast/adapter things and JB welded the break above. All good, then reinstalled.

Drove it that night starting at dusk to get dinner & didn't notice anything odd until later that night, the headlights are always on now along with the instrument lights. The headlight switch does nothing. They only turn off when the truck is turned off. I'm wondering if something shorted because I didn't disconnect the battery before unplugging the light in the first place, I've never dealt with these kind of aftermarket lights before. Everything acted normally before all this (except the fog lights were out which I had not investigated yet). Scratching my head on this one....

Maybe the headlight switch??

 

[mikez71]

My headlight switch doesn't seem to work either.. Dimmer off button also no work.. Or fog lights..