P0172, P0175 too rich, 07 6.2 about to throw in the towel

[chucksrt]

I have a 07 Yukon denali xl with 120,000 miles on it. I started getting a check engine light a month or two ago. I researched it and replaced items that are common to causing this issue. I didn't care if it was the fault or not because of the miles i just figured the new parts would help it regardless. I started by replacing the EVAP purge solenoid. That actually seemed to help me fill the tank to full better? I then replaced the mass air flow sensor, again, i have cleaned it but thought a new one wouldn't hurt. Then i replaced the MAP sensor. I know that they can be a common point of failure. It seemed to run better but still had the C.E.L. i took it to a friends shop and he wasn't much help. He pretty much looked it up on Mitchell and said it sounds like the fuel injectors are bad. I bought a used set of injectors and sent then to FIC to be cleaned and flow tested. I received them yesterday and installed them and on my maiden voyage the codes returned in pending. I am at a loss!? I am going to take it to GMC to look at ir bur i do not know what else to check. Any thoughts or have you run into a similar issue where something else fixed it?

 

Sent from my SM-G935P using Tapatalk

[wildcatter]

Your fuel tank vent is plugged.Remove the vent filter and solenoid and clean both.Also check to ensure the solenoid is working.Check the vapor canister as well for plugging or flooded.

[chucksrt]

I just finally got my spare down and will brr replacing the vent valve assembly, but i wanted to know if that could cause it not to start? It has an issue that is getting worst. If i drive and turn it off and let it sit for 20 minutes or so it will have a really hard time starting initialy. If i turn the key off and restart it it will fire right up. Almost as if it doesn't have fuel. If i drive and stop and restart it 5 minutes later it starts right up. The only codes are the ones i have mentioned already.

 

Sent from my SM-G935P using Tapatalk

[Jsdirt]

A plugged fuel tank vent would starve the engine of fuel. He has the opposite problem. A soggy charcoal canister, or raw fuel in the line would definitely cause his issue though.

[chucksrt]

My gas guage just acted funny. I started the car and it said low fuel and i could swear i had over a quarter tank. I finished my trip, turned the vehicle off waited a second and turned the key back to the run position and sure enough the guage read over a quarter tank.

 

Sent from my SM-G935P using Tapatalk

[chucksrt]

Your fuel tank vent is plugged.Remove the vent filter and solenoid and clean both.Also check to ensure the solenoid is working.Check the vapor canister as well for plugging or flooded.

Could this also cause an extended crank? I started my car after sitting all day and it cranked for a while before it started. And the pending code (P0172,P0175) came on just as i started driving.

 

Sent from my SM-G935P using Tapatalk

[Jsdirt]

Weak pump would be throwing lean codes, not rich. This is more like a failed pressure regulator if anything fuel delivery related. Like 15HDriver said, if the f/p sensor is bad, it could be tricking the system into thinking you have low pressure, when you do not - could have full pump duty cycle running at all times. These are returnless systems, so pressure can get way up there.

 

Not sure if this is internally regulated (in tank - part of fuel pump assembly), or duty cycle controlled system - I'd have to look into that. I'd say if it has a fuel pressure sensor, then it's duty cycle controlled.

 

Definitely need scan tool data to at least get some direction on this one.

[wildcatter]

Shouldn't cause extended cranking,but definitely filling problems.Since you have both issues, I would check to see if you are getting raw fuel in the vapor line from the tank to the engine.

[Jsdirt]

Not likely unless the tank is filled up until it's coming out the filler neck, and the valve failed at the same time.

 

From here it sounds like you may have a failing fuel pump. Get a pressure gauge on there, and see where it sits at idle, snap-throttle, and shut down. Pressure should increase slightly on a snap, and hold steady for at least 5 minutes when shut down. 55-60 is what you're looking for if memory serves correctly ...

 

Thing is, normally a failing fuel pump will throw lean codes.

[newdude]

P0172 or P0175

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be more than approximately −20 percent with the engine running at operating temperature.

 

• • If the value is not more than −20 percent, inspect for the following:

• With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19–42 kPa.
  • Refer to DTC P0106 if the MAP sensor parameter is not between 19–42 kPa.
• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2–6 g/s at idle.
  • Refer to DTC P0101 or P1101 or DTC P0102 or P0103 if the MAF sensor parameter is not within 2–6 g/s at idle.
• Vacuum hoses for splits, kinks, and improper connections
• The air intake duct for being collapsed or restricted
• The air filter for being dirty or restricted
• Objects blocking the throttle body
• Excessive fuel in the crankcase due to leaking fuel injectors
• The evaporative emissions control system for improper operation
• Excessive fuel pressure
• Malfunctioning fuel injectors
• Fuel contamination
• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit shorted to voltage

 

[Dnt]

probably just a vacuum leak find it and get it fixed. Should get another 120k no problem

[chucksrt]

I ordered the EVAP vent valve assembly so i went out last night to drop the spare tire so i could be ready to install it when it came and i noticed the smell of raw fuel. As my luck would have it the spare is seized and won't come down! So i need to find a way to get the spare out of my way so i can replace the vent valve and find the source of the smell

 

Sent from my SM-G935P using Tapatalk

[Jsdirt]

As far as the running / starting problems go, you could have a bad "new" MAF sensor. At this stage, that seems to be the only suspect component. Need a multimeter that reads Hz (Hertz) to properly diagnose.

 

Here ya go: http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/testing-the-maf-sensor-1

[chucksrt]

 

P0172 or P0175

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be more than approximately −20 percent with the engine running at operating temperature.

 

• If the value is not more than −20 percent, inspect for the following:

• With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19–42 kPa.
  • Refer to DTC P0106 if the MAP sensor parameter is not between 19–42 kPa.
• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2–6 g/s at idle.
  • Refer to DTC P0101 or P1101 or DTC P0102 or P0103 if the MAF sensor parameter is not within 2–6 g/s at idle.
• Vacuum hoses for splits, kinks, and improper connections
• The air intake duct for being collapsed or restricted
• The air filter for being dirty or restricted
• Objects blocking the throttle body
• Excessive fuel in the crankcase due to leaking fuel injectors
• The evaporative emissions control system for improper operation
• Excessive fuel pressure
• Malfunctioning fuel injectors
• Fuel contamination
• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit shorted to voltage

I have replace most of the parts in that list. My buddies shop checked the fuel trim and said it was ok. I will chdck the wiring to the af sensors.

 

Sent from my SM-G935P using Tapatalk

[chucksrt]

Just for full disclosure i wanted to add a list of odd issues it has had.

It sometimes would crank and not start, very intermediate

Just last week it started cranking excessively long and stumbled when it finally started, until it idled itself smooth.

My fuel tank is hard to fill to full? I can fill it and the nozzle shuts off and still be able to ad 4-5 more gallons after if i let it sit for a minute.

Idle has a ever so slight stumble? I have installed new plugs and magnecore wires within the last 10,000 miles and there are no cylinder misfires. That is all i can think of at the time although i am sure there is other stuff. Lol

 

Sent from my SM-G935P using Tapatalk

[Jsdirt]

Vacuum leaks will not cause a rich code - they cause lean conditions / lean codes - just FYI.

 

 

Some things to check:

 

o2 sensor operation - a sensor stuck rich (high mV).

 

Coolant temp sensor - should be close to intake temp sensor reading upon cold startup. Both should be close to ambient.

 

 

One more thing. IF you're going to throw in the towel and let someone else fix it, DO NOT go to a GM dealer. Plenty of small garages out there that are 100x more capable of fixing the issue than the dealer is. Trust me on that one.

 

 

EDIT just to say, double check o2 sensor operation by forcing a lean condition - disconnecting the vacuum booster line to the power brakes should make the o2 dive lean (lower mV) quickly.