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

[Doubeleive]

 

[Grady_Wilson]

It’s like riding a bike, it comes back to you.






When you got it, use it. I am a proficient CDL and equipment operator. It’s in the blood.

I have not had to use my CDL for work for decades, but I keep it because it was a pain to get and you never know when you may need it again.
If nothing else, I have peace of mind that when I tow one of my antique cars in an enclosed trailer I never have to worry about being overweight for my license.
There have been instances where car owners towing to an event that have been pulled over and weighed and given tickets for being overweight for their class C.

Last time I used my CDL for money was when I drove a trash truck from an auction yard in Salt Lake to So Cal.
The striping business owner that bought it had all his CDL guys out on jobs so he asked if I could do him a favor and drive it back.
He paid me for driving, the flight out there and a hotel in St George.

 

[Grady_Wilson]

Washed the Yukon in preparation fir the trip back to WY.
If I leave early enough I will just do the whole drive in one shot, about 16 or 17 hours.
I've done it in one shot about 3 times.

 

[Doubeleive]

I am at a loss, the first run the fuel pressure was up around 55 this time staying in the low 40's like it should, no difference, fuel trims are on 0 under a load

 

[Geotrash]

I am at a loss, the first run the fuel pressure was up around 55 this time staying in the low 40's like it should, no difference, fuel trims are on 0 under a load

Miss under load is almost always a fuel delivery issue. How old is the pump? Or possibly some bad gas?

 

[Doubeleive]

Miss under load is almost always a fuel delivery issue. How old is the pump? Or possibly some bad gas?

it's been doing that over several tanks of gas when I drove it from here to washington and back but the Tech2 did say volatality Low, unless I got bad gas across 3 states
I got gas here, redding, grants pass, salem, astoria. all did the same thing.
Fuel pressure is good I hooked the gauge up and watched it as I had my foot in it a few times. pump is about a year old oem.
first run the fuel pressure was high (50-55) for some reason (maybe because it was cold?)
fuel trims read 0 under a load if that means anything

 

[Doubeleive]

when I stuck my phone out the window I was hoping it would catch the sound of the misfire but to much wind derp....
but I can hear it when it misfires, has a tink sound like if you were dropping small stones onto a metal plate.
I sent a log file to blackbear but not sure when I will hear from them pretty sure they are closed on the weekends.
my speculations are
1. electrical problem with maf
2 injectors (all of them)
3 coil packs (all of them)
4 crank position sensor
really no idea otherwise, just misfire codes and MAF code
I guess i could test the maf pins & harness but have no idea what I am looking for
@swathdiver do you have a diagnostic tree for testing the maf harness?
to me it is acting like the maf is bad i.e. not shifting properly, misfires, lean code.

 

[j91z28d1]

I forget what year it switched but if you have the return less fuel system. can probably see the requested fuel pressure vs the actual to rule out the weird 55psi and then 40psi. if the ecm is asking for it, it is what it is.


do you have access to any higher octane fuel to rule out its just a timing issue black bear got greedy with a worn valve train engine? if you have a 100 octane unleaded pump anywhere, you could put a few gals in on a low tank and see if the miss fire goes away. e85 might work but it can complicate things too


is it still running badly and is it retarding timing lot? one thing I find I don't like about the tech 2 is it just won't display everything I want to see at once. hptuners seems to be the best at logging multiple things at once. you can log like 30 things with just bit of delay



this is the same engine they pulled a head off at the dealer? might watch fuel trims with it idling and spray some brake clean around to check for vac leaks. efi responses to fast to hear a change like back in the carb days, but you'll see the trims and o2 v go crazy if you can watch and spray at the same time and find something.

 

[Geotrash]

when I stuck my phone out the window I was hoping it would catch the sound of the misfire but to much wind derp....
but I can hear it when it misfires, has a tink sound like if you were dropping small stones onto a metal plate.
I sent a log file to blackbear but not sure when I will hear from them pretty sure they are closed on the weekends.
my speculations are
1. electrical problem with maf
2 injectors (all of them)
3 coil packs (all of them)
4 crank position sensor
really no idea otherwise, just misfire codes and MAF code
I guess i could test the maf pins & harness but have no idea what I am looking for
@swathdiver do you have a diagnostic tree for testing the maf harness?
to me it is acting like the maf is bad i.e. not shifting properly, misfires, lean code.

I'll add one more to your list: 5/ MAP sensor. If the sensor is not able to accurately provide the vacuum information to the ECU, strong rich or lean conditions will result across all cylinders.

 

[j91z28d1]

I'll add one more to your list: 5/ MAP sensor. If the sensor is not able to accurately provide the vacuum information to the ECU, strong rich or lean conditions will result across all cylinders.

I still question that it's showing the right value in the live data. no load at 1700 rpm should be a very high vacuum reading. but I'm not even sure which number to go by, map sensor or intake manifold kpa. I'd have to unplug the sensor while running to see which data goes bad and then do the math to see what the vacuum is in something on used to seeing.

that or go look at my own truck data lol. but I don't have it with me today.