P0171 Troubleshooting - Evap System Diagrams?

[spfautsch]

I'm having trouble finding anything in the service manuals pertaining to the EVAP system. I'm looking for a diagram but maybe someone can chime in as to where it might be in the FSM or whether my troubleshooting method is valid.

Having a P0171 setting while idling on my 221k mile 2006 TB EXT. Runs fine, no missing but maybe a little down on power. Fuel pressure is 58psi running and does not leak down when off. MAP at idle is 32-33kpa. LTFTs are generally positive by 5-10% across all load cells, but after long periods of warm idling (load cells 17 & 37) trims will sometimes swing north of 25% and set the code. Initially I thought it might be loose intake bolts, but after snugging them up nothing changed.

Same after removing the brake booster hose and plugging w/ my finger.

My next item was the MAF, and it was / is dirty. I used some electronics cleaner on it still no difference.

So I wanted to eliminate the EVAP system as a possibility. As I've searched through the 2006 Ranier manual from Mooseman's sticky extensively I can find nothing about the fuel or EVAP system. Maybe I just haven't looked hard enough, but I believe (correct me if I'm wrong) that removing the plastic quick-disconnect line and plugging the nipple on the throttle body should completely take the EVAP system out of the picture?

I'm leaning towards it being the MAF, and have one on the way but wanted to eliminate all other possibilities. I don't think the O2 sensor is the problem because it's switching correctly and the downstream O2 reads as expected and there are no other codes.

There's no SAIS on this one (pretty sure none of the long wheelbase have SAIS).

 

[spfautsch]

Forgot to mention that the PCV hoses are both connected, and not cracked. Have sprayed carb cleaner around everything I can get to and can detect no change.

The only thing I've done recently is changed what looked like the original spark plugs and boots about 1500 miles back.

 

[azswiss]

Charm.li has the following diagram for vacuum & vapor hoses:
https://charm.li/Buick/2006/Rainier...sis/#Diagrams/Vacuum and Vapor Hose Diagrams/

 

[Mooseman]

P0171 specifically says it's running lean. With LTFT that high, I'd be doing testing using carb cleaner or propane to find a vacuum leak. It could be anywhere including intake gaskets, throttle body gasket, fuel injector seals, PCV hose, etc. There is a SAIS on your 2006 TB unless it's been deleted. It could be the valve or, if deleted, the cover plate and gasket. The original plate has a history of cracking and causing leaks.

Also check for an exhaust leak that could allow air to be sucked back into the exhaust falsely causing a lean condition.

 

[spfautsch]

There is a SAIS on your 2006 TB unless it's been deleted.

I've worked on about a half-dozen long wheelbase 'Voys and none have had a secondary air system including the two I own. I've had this one for 15 years and rebuilt the trans twice. There were no provisions left behind from a SAIS being deleted.

Conversely every short wheelbase I've worked on has had a secondary air system. I'm fairly sure the mandate was based on GVWR and big boys weren't required to have it.

Also check for an exhaust leak that could allow air to be sucked back into the exhaust falsely causing a lean condition.

It's not an exhaust leak. The size of leak required to make the sensor read lean would be unmistakably loud and this thing is still stone stock and purrs like a kitten. See if you can find the episode of Engine Masters where they tested this theory - think it was a comparison of wideband 02 sensors. Very much worth a watch.

 

[Mooseman]

But do check the SAIS plate cover on the head. It has been shown to cause a lean condition when cracked.

It is strange that your 06 never came with the SAIS but EXT's of the last year for this model are a rare bird so it's possible it was excluded. I know that 02-03 never came with it and was introduced to the 04 model year.

 

[spfautsch]

I'll pull it and give it a look, thanks!

A friend of mine recently bought an '04 EXT with the 5.3 and it also has no secondary air system. If the option wasn't based solely on GVWR then perhaps it was something specific to what market it was manufactured for as most of what I see were sold in the Midwest. There are so many of these things still on the road here it's mind boggling as to why GM ever killed the platform. Today if you want a 7 passenger vehicle with a V8 that can actually tow something you're gonna spend north of $85k for a Suburban / Yukon. I live in a small rural town of ~3k and there are about10 long wheelbase ones around I see regularly, and several dozen short. In fact you can barely drive the 2 mile stretch of main street without passing two shorts.

As most of my other vehicles I've tuned on were equipped with secondary air, I found it surprising when from a cold start the TB switched to closed loop after less than 30 seconds of runtime.

 

[Mooseman]

That explains it, it's only on the 4.2L I6 that had SAIS. I don't remember any LS engine equipped vehicle with SAIS. I deleted mine (4.2) years ago with no ill effect. I don't even know why they added it since the V8 never got it and it does go to closed loop fairly fast so . Pretty pointless and failure prone system.

If you're working on a V8, forget everything I said about a blockoff plate or SAIS.

 

[spfautsch]

No, this one is an Altas 4.2. Bought used in 2014 w/ 114k miles on it, currently 221k. As mentioned I've had the trans out more than once and there's no evidence of it having provisions for SAIS. I guess the only sure way to tell is to identify the RPO code and search the build sticker.

The whole point of it was to light the exothermic reaction off in the cat(s) faster than would happen without the additional oxygen. I'm sure GM would've omitted it across the board if not mandated due to cost per unit, but it's been commonplace since 1974.

Here's my current and past lineup of GM goodness as pertains to AIR / SAIS
2000 GMC Jimmy 4dr 4.3 v6 - no AIR (sold @ 150k miles)
2001 Chev S-10 4.3 v6 - AIR - set P0410 code around 40k miles - deleted in the tune (sold @ 265k miles)
1995 Corvette 5.7 LT-1 - AIR equipped and was working when I deleted @ 150k miles in 2016 to use the power circuit for electric water pump
2001 Corvette 5.7 LS-1 - AIR equipped and working as designed @ 147k miles
2006 Chev TB EXT 4.2 - no SAIS
2006 GMC Envoy XL 5.3 LH6 - no SAIS

The TB in question is in storage while waiting on the MAF cartridge but I'll go grab it tomorrow and pull the bock-off plate and inspect. I'm highly doubtful it's the culprit but it's easy to get to and only two nuts.

 

[spfautsch]

The check valve block-off plate gasket isn't the issue. Broke out my extremely high-tech exhaust leak detector (a section of 3/8 hose used as a stethoscope) and no exhaust leak can be heard. It would have to be a big one to move the needle on trims. I could see if the gasket blew out completely, possibly. But the visible part of gasket looks intact and nothing can be heard underneath it.

Sadly the MAF is being delivered USPS, so I may get it this month and I may not. I'm leaning towards this being the problem b/c I've neglected to change the air filter for a while and there was visible build-up on the first visible component in the MAF that wouldn't come off with cleaner alone.