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

[ivin74]

What sensor is taking direct readings indexed from the harmonic balancer?

I would like to know as well.

 

[Fless]

Took it for a drive halfway across town in freezing rain to pick up 4 nearly brand new Blizzaks for a friend.

 

[Rocket Man]

Took it for a drive halfway across town in freezing rain to pick up 4 nearly brand new Blizzaks for a friend.

Is the freezing rain sticking to the roads?

 

[Fless]

Is the freezing rain sticking to the roads?

Yes. It wasn't bad yet, just some slick spots, but when I got home the front of the hood and the mirror caps were covered.

 

[mountie]

Just returned from my mechanic... New starter / old was original/ failed/ ( why it was at shop)...replaced belts....new A/C belt tensioner....Mobil 1 oil.
( Tesioner wasn't bad, but it was original and it takes a beating down there.)
Yesterday I waxed wheels inside my garage, since it wasn't moving due to starter bad.

 

[Rocket Man]

Just returned from my mechanic... New starter / old was original/ failed/ ( why it was at shop)...replaced belts....new A/C belt tensioner....Mobil 1 oil.
( Tesioner wasn't bad, but it was original and it takes a beating down there.)
Yesterday I waxed wheels inside my garage, since it wasn't moving due to starter bad.

Looking good!

 

[iamdub]

The pulley and crankshaft are not machined with keyway/key? I am new to GM and we know there are some GM-specific quirks and features, but I would expect the removal and install of the harmonic balance pulley to be a fail-proof operation. With the pulleys and cam shafts being indexed with a key/keyway, there is only one position for the pulley which would not even matter if the timing chain/cam/crank were not messed with.

Just wondering... What sensor is taking direct readings indexed from the harmonic balancer?

Like I said, I am new to GM and eager to learn more. But right now, I am trying to wrap my head around why the computer would give a hoot where the harmonic balancer pulley is relative to the crankshaft, if the CPS reads off of the flywheel and timing is unchanged.

Thanks for taking the time to get me up to speed on things related to my "new-to-me" 04 Tahoe!

As Mark pointed out, the crank pulley is not keyed. There is nothing taking a reading directly from the pulley/balancer and so the computer does NOT give a hoot where it is in relation to the crankshaft.

even that, I don't understand?

The pulley bottoms out against the crankshaft. Once that happens, it's essentially "floating" as the only pressure applied would be a result of the belt.

Thrust bearings constrain the crank shaft in the forward/backward direction.

So... Hell if I know

Didn't even know a relearn was needed. I replaced mine while I had some bits apart and can't say I noticed any changes in how the engine behaved

It was just my guess since the clocking of the pulley doesn't matter and GM outlined this step for some reason. I'm not so sure the pulley bottoms out on the crankshaft. I think it presses on a certain amount, achieved when specified torque values are met. GM lists an engagement depth spec (something like a ~2mm range, IIRC). Yes, the belt does apply longitudinal pressure on the crankshaft. Maybe the positioning (and manufacturing tolerances) of the accessory drive was factored into their calculating of that engagement depth? Yes, there's a thrust bearing. But, it doesn't hold the crank so tightly that there's no movement. There at least has to be an oil gap.

The CKP sensor is very sensitive to the size of the air gap between it and the teeth on the reluctor wheel. On the old Vortec engines, particularly the 4.3, there was an issue with the CKP sensor misreading and, in more extreme cases, even contacting the reluctor wheel. It was primarily higher-mileage engines being spun to high RPM that had the worst of the problems. IIRC, they ruled it as "loose" manufacturing tolerances in that front cover allowing the sensor to be too close. They released a shim kit to space the CKP sensor out. The kit consisted of (IIRC) two .005" thick shims. You use one and test, then try the other if one wasn't enough.

A CKP relearn is necessary any time the sensor is disturbed or, especially, if shims were added. The PCM has to know the CKP's baseline so it can detect variances and respond accurately. I can see a slight "relocation" of the reluctor wheel being enough change to alter the base signal as expected by the PCM. Is it enough to cause a problem? IMO, not likely. But, for a ~2-minute process, why not have the accuracy?

 

[iamdub]

I would like to know as well.

None. See my guesses/opinions/oral diarrhea above.

 

[MADPINTO08]

Lights in grille

 

[Rocket Man]

Lights in grille
View attachment 361128

Are those RGB? I installed some in my bagged Silverado grill that are hooked to a controller along with my demon eyes that uses an app on my phone so I can CM them all to the paint color -it’s in the red spectrum which of course is illegal to drive with. I run them in a different color when I’m on the road.

 

[MADPINTO08]

Are those RGB? I installed some in my bagged Silverado grill that are hooked to a controller along with my demon eyes that uses an app on my phone so I can CM them all to the paint color -it’s in the red spectrum which of course is illegal to drive with. I run them in a different color when I’m on the road.

Oh nice yeah I was trying to post a video of them flashing all the colors look pretty cool but it’s just something my kids talked me into doing and I think I like it

 

[Rocket Man]

Oh nice yeah I was trying to post a video of them flashing all the colors look pretty cool but it’s just something my kids talked me into doing and I think I like it

You have to host the video on YouTube or something similar and then post a link if you want to share video here.

 

[iddqd]

I was under the impression that it had to be done when the crankshaft sensor was replaced. First time I hear it needs to done when the harmonic balancer is replaced. I do have the Tech 2 to get it done

I attached GM Service manual extract, check out #12.

Basically, the crankshaft does not have a keyway, so balancer can be installed in any position, and since these parts are balanced separately, it can potentially throw off misfire detection due to slight fluctuation in RPM between cylinders.

 

[mattbta]

Dropped the Escalade roof rack end caps, vent caps and a door handle that have been sitting in the garage for many months off at a paint shop for color matching. Truck is 805K, Dark Spiral Gray Metallic....starting to second guess getting the rear vent caps matched instead of just black.

 

[Rocket Man]

I attached GM Service manual extract, check out #12.

Basically, the crankshaft does not have a keyway, so balancer can be installed in any position, and since these parts are balanced separately, it can potentially throw off misfire detection due to slight fluctuation in RPM between cylinders.

I saw where the SM states to perform the relearn but it doesn’t explain why, and even though you say it can potentially throw off misfire detection, I have yet to read anything that actually explains how it can just by R&R’ing the balancer. Why would that cause a slight fluctuation in RPM between cylinders?

 

[iddqd]

I saw where the SM states to perform the relearn but it doesn’t explain why, and even though you say it can potentially throw off misfire detection, I have yet to read anything that actually explains how it can just by R&R’ing the balancer. Why would that cause a slight fluctuation in RPM between cylinders?

My guess would be that the imbalance might cause slow down/speed up at some crankshaft positions. It's been a while since physics classes, I have a feeling it might happen, but I can't explain the physics behind it.

This is what GM has to say on this topic:
DTC P0315
Circuit Description
The crankshaft position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the CKP sensor. The calculated error allows the powertrain control module (PCM) to accurately compensate for reference period variations. This enhances the ability of the PCM to detect misfire events over a wide range of engine speed and load. The PCM stores the Crankshaft Position System Variation values after a learn procedure has been performed. If the actual crankshaft position variation is not within the Crankshaft Position System Variation compensating values stored in the PCM, DTC P0300 may set. If the CKP system variation values are not stored in the PCM memory, DTC P0315 sets.

The CKP system variation learn procedure is also required when the following service procedures have been performed, regardless of whether or not DTC P0315 is set:

• An engine replacement

• A PCM replacement

• A harmonic balancer replacement

• A crankshaft replacement

• A CKP sensor replacement

• Any engine repairs which disturb the crankshaft to CKP sensor relationship.

 

[Rocket Man]

My guess would be that the imbalance might cause slow down/speed up at some crankshaft positions. It's been a while since physics classes, I have a feeling it might happen, but I can't explain the physics behind it.

This is what GM has to say on this topic:
DTC P0315
Circuit Description
The crankshaft position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the CKP sensor. The calculated error allows the powertrain control module (PCM) to accurately compensate for reference period variations. This enhances the ability of the PCM to detect misfire events over a wide range of engine speed and load. The PCM stores the Crankshaft Position System Variation values after a learn procedure has been performed. If the actual crankshaft position variation is not within the Crankshaft Position System Variation compensating values stored in the PCM, DTC P0300 may set. If the CKP system variation values are not stored in the PCM memory, DTC P0315 sets.

The CKP system variation learn procedure is also required when the following service procedures have been performed, regardless of whether or not DTC P0315 is set:

• An engine replacement

• A PCM replacement

• A harmonic balancer replacement

• A crankshaft replacement

• A CKP sensor replacement

• Any engine repairs which disturb the crankshaft to CKP sensor relationship.

Lol. I read that too. It still doesn’t explain why, since they state the balancer is an individually balanced item, and it’s being installed right back in the same position fore and aft. I guess if it was a different balancer or say an under drive one that’s a different size but they say to do it even if you’re putting the same one back on. I know I should just probably say “fine, they said to do it so I will” but my mind wants to understand why. Is it just me?

 

[ratled]

Note to self..... when cleaning the throttle body DON'T drop the nut that bolts it on...... you know that one thats hidden under the throttle body and blocked by the alternator. But if you do, it's a #12-24 coarse thread. GM dosen't carry it anymore, none of the chain auto stores have it and the box hardware stores only go to a #10. Amzon can have it to you in about 3 days though.

Back to your regularly productive reads.....

 

[iddqd]

Note to self..... when cleaning the throttle body DON'T drop the nut that bolts it on...... you know that one thats hidden under the throttle body and blocked by the alternator. But if you do, it's a #12-24 coarse thread. GM dosen't carry it anymore, none of the chain auto stores have it and the box hardware stores only go to a #10. Amzon can have it to you in about 3 days though.

Back to your regularly productive reads.....

I always though American manufacturers switched to metric ages ago. That should be M6 nut. Any local HD definitely has them in stock.
Home Despot web site

 

[mountie]

I always though American manufacturers switched to metric ages ago. That should be M6 nut. Any local HD definitely has them in stock

What area of San Francisco do you hang? I grew up in Marin.