System Too Lean P0171 & P0174

[texan]

I'm getting codes for both banks being lean. The car seems to be running fine. Maybe it's not accelerating as hard as normal, I can't really tell. Not long ago, the ECM, throttle body, and rear cat were replaced. It had issues with no throttle response sometimes and then ran terrible when the cat went bad. It ran great after these repairs and still does.

When these new codes occurred, I suspected the rubber/cork gasket that I used on the throttle body. I knew it wasn't the correct material, but it was all I could find at the time, 100 miles from home. I replaced the gasket with one made from the correct rubber material (according to the guy at O'Reillys) a week ago and cleared the codes. It ran great and didn't show any codes, until today. Now I'm getting the same lean codes again. Ideas?

2002 VUE AWD 3.0 V6, 113k miles.

[far2grumpy]

Originally Posted by texan

I'm getting codes for both banks being lean. The car seems to be running fine. Maybe it's not accelerating as hard as normal, I can't really tell. Not long ago, the ECM, throttle body, and rear cat were replaced. It had issues with no throttle response sometimes and then ran terrible when the cat went bad. It ran great after these repairs and still does.

When these new codes occurred, I suspected the rubber/cork gasket that I used on the throttle body. I knew it wasn't the correct material, but it was all I could find at the time, 100 miles from home. I replaced the gasket with one made from the correct rubber material (according to the guy at O'Reillys) a week ago and cleared the codes. It ran great and didn't show any codes, until today. Now I'm getting the same lean codes again. Ideas?

2002 VUE AWD 3.0 V6, 113k miles.

Can you remove the sensors (at least one easily accessible) and check for residue?

Here a few thoughts from FSM re 0171 and 0174:

o A skewed mass air flow (MAF) sensor may set this DTC.
o The system will go lean if an injector is not suppling enough fuel.
o A skewed engine coolant temperature (ECT) may set this DTC.
o The system will go lean during high fuel demand.

[texan]

Originally Posted by far2grumpy

Can you remove the sensors (at least one easily accessible) and check for residue?

Here a few thoughts from FSM re 0171 and 0174:

o A skewed mass air flow (MAF) sensor may set this DTC.
o The system will go lean if an injector is not suppling enough fuel.
o A skewed engine coolant temperature (ECT) may set this DTC.
o The system will go lean during high fuel demand.

Would a faulty injector make both banks go lean? I removed and tested the coolant temp sensor not long ago. I'll try looking at the sensors tomorrow.

[far2grumpy]

Originally Posted by texan

Would a faulty injector make both banks go lean? I removed and tested the coolant temp sensor not long ago. I'll try looking at the sensors tomorrow.

Do you have means to test fuel pressure?

Diminished flow would affect both banks.

My comment about checking sensors for residue was way weak - I should have included a note from FSM regarding anti-seize compound - if used:

Notice: Silicone based products will contaminate the HO2S. Use only a nickel based anti-seize compound that does not contain silicone.

If you didn't use silicone based lubricate during removal of old HO2S, or silicone based anti-seize when installing new one, I'd cross off the list.

[ernesto rex]

Do you feel anything different in the way the transmission shifts? If it feels like it is slipping and then grabbing you might want to give your MAF a real good cleaning or replacement.

ernesto

[fdryer]

And to add my 2-cents here, is there a possibility of a vacuum leak between the maf sensor and main intake manifold? This would cover the flexible coupler for the maf sensor between it and the throttle actuator and the throttle gasket. Any loose coupling here would allow a vacuum/lean mixture as well as the throttle actuator gasket left loose for the same vacuum leak.

[texan]

Originally Posted by ernesto rex

Do you feel anything different in the way the transmission shifts? If it feels like it is slipping and then grabbing you might want to give your MAF a real good cleaning or replacement.

ernesto

No issues with shifting.

[texan]

Originally Posted by fdryer

And to add my 2-cents here, is there a possibility of a vacuum leak between the maf sensor and main intake manifold? This would cover the flexible coupler for the maf sensor between it and the throttle actuator and the throttle gasket. Any loose coupling here would allow a vacuum/lean mixture as well as the throttle actuator gasket left loose for the same vacuum leak.

At 4000 rpm, I can hear what sounds like a vacuum leak, so whatever it is is getting worse. I pulled things apart and looked for faulty seals between the MAF and the throttle body, but everything looks OK. I can see some black residue in a few places around the intake cover plate. Could that be it? I guess I'll put everything back together and make sure everything is clamped tight.

[Someclown]

Originally Posted by texan

I can see some black residue in a few places around the intake cover plate. Could that be it? I guess I'll put everything back together and make sure everything is clamped tight.

Was your thermostat changed ?what do you mean by intake cover plate, the plastic piece on top of the engine? or the aluminum intake, if its the plastic cover take the cover off and check and re-torque the intake bolts to spec.I believe there are six torx bolts.

[texan]

Originally Posted by Someclown

Was your thermostat changed ?what do you mean by intake cover plate, the plastic piece on top of the engine? or the aluminum intake, if its the plastic cover take the cover off and check and re-torque the intake bolts to spec.I believe there are six torx bolts.

Thermostat should have been changed when Saturn of Waco did the 100k service. But then, they also should have changed the leaky valve cover gaskets that are still leaking. I'd go talk to them if they were still in business. I was referring to the aluminum plate. The gasket looks fine. I put it back and tightened it up. I put everything back together, cleared the codes, and went for the a test drive.

No SES light, but the noise is still there at high rpm. I can't tell if it's a vacuum leak, an exhaust leak, or something vibrating. It kinda reminds of the noise my belt tensioner made when the bearing went bad, but it doesn't make the noise if I rev it in neutral. Maybe I'll crawl under it tomorrow and have a look at the exhaust system.

[far2grumpy]

texan ... the lean codes would probably appear if you had a significant vacuum leak.

According to 3.0 documentation - the intake manifold has vacuum controlled switchover valves in each intake runner to improve performance.

GM released at least one service info document pertaining to possible flapper valve noises. It primarily addresses a "clunk" noise but is it possible as the vacuum motors age the valves might make other noises?

I don't have the 3.0 but have attached the bulletin in case you've not seen.

[texan]

Originally Posted by far2grumpy

texan ... the lean codes would probably appear if you had a significant vacuum leak.

According to 3.0 documentation - the intake manifold has vacuum controlled switchover valves in each intake runner to improve performance.

GM released at least one service info document pertaining to possible flapper valve noises. It primarily addresses a "clunk" noise but is it possible as the vacuum motors age the valves might make other noises?

I don't have the 3.0 but have attached the bulletin in case you've not seen.

I haven't noticed any clunks or pops.