Engine and Tranny Issues - Update in OP

[rustycrocker]

I have a 2007 Yukon XL with 160k miles. There are two issues:

Tranny hard shifts from 1-2. I replaced the 1-2 accumulator with a Sonnax pinless accumulator. It decreased the frequency of the hard shift, but it is still happening about 40% of the time. When I replaced the piston, there was only the small spring, the large spring was not installed. Ever seen this? I am considering replacing the Sonnax with the GM OEM accumulator, as it lasted 150k with no issues.

The engine (LMG 5.3 Flex) has a very rough idle, but cleans up around 1500 RPM. There are two codes showing:

P0449 (EEC vent valve solenoid). I replaced the solenoid with with no improvement. Clear the code and it comes back.

P0308 (Cyl 8 misfire). I suspect this is the AFM (Chevy shake).

Anyone care to comment?

TIA

Update 1/2/2023

Cleaned MAF with no improvement. Checked MAF with code reader and 5-6 on idle and 20-23 on acceleration. Pretty close to specs, so MAF is OK. Changed plugs and plug wires. BAM!! No more shudder, tranny shifts great. Looks like that was the issue.

Still have one code, P0499 - Evap Cannister Purge Solenoid. I have replaced the solenoid with no improvement. Maybe the PCM or the wiring?

 

[Dustin Jackson]

With a transmission that old it might just be worn and due for a rebuild, I wouldn't bother throwing parts at it just drive it until it stops driving and then rebuild it.

I don't think cylinder 8 is an AFM cylinder, I think 1,4,6,7 are the AFM ones

 

[rustycrocker]

My son has a 2019 Sierra that had a Cyl 8 Misfire code. We replaced the injector, plug, plug wire and coil, with the same result. It is in the shop now getting new lifters

 

[Dustin Jackson]

@rustycrocker It's totally possible a non-AFM cylinder had a lifter failure. The lifters are just held in with plastic trays. To save money you can tear the engine down yourself to find the problem.

 

[rustycrocker]

My intention is to replace the more inexpensive components on the Yukon (plugs, wires, coil and injector) and see what happens. Worst case, I will do a teardown, as my warranty has long been expired.

I just wanted to get a second opinion.

 

[Geotrash]

@rustycrocker It's totally possible a non-AFM cylinder had a lifter failure. The lifters are just held in with plastic trays. To save money you can tear the engine down yourself to find the problem.

A 2019 should have DFM which is all 8 cylinders

 

[Dustin Jackson]

A 2019 should have DFM which is all 8 cylinders

Wow didn’t know that, future not looking good for us car guys.

But I was talking about our buddy rustys 2007 with #8 misfire

 

[iamdub]

I have a 2007 Yukon XL with 160k miles. There are two issues:

Tranny hard shifts from 1-2. I replaced the 1-2 accumulator with a Sonnax pinless accumulator. It decreased the frequency of the hard shift, but it is still happening about 40% of the time. When I replaced the piston, there was only the small spring, the large spring was not installed. Ever seen this? I am considering replacing the Sonnax with the GM OEM accumulator, as it lasted 150k with no issues.

The engine (LMG 5.3 Flex) has a very rough idle, but cleans up around 1500 RPM. There are two codes showing:

P0449 (EEC vent valve solenoid). I replaced the solenoid with with no improvement. Clear the code and it comes back.

P0308 (Cyl 8 misfire). I suspect this is the AFM (Chevy shake).

Anyone care to comment?

TIA

Ever cleaned the MAF sensor?

 

[rustycrocker]

Ever cleaned the MAF sensor?

NO, but I will try that first.

 

[iamdub]

NO, but I will try that first.

Start with the basics! The PCM uses the MAF as part of its load calculations to adjust shifting characteristics.