'05 Tahoe 5.3 / P0171 / Rough Idle / Misses

[Bwaite27]

Long story short (as possible) - I recently replaced the fuel pump/ sending unit, all fuel lines and nearly all evap lines because of a P0455 code. Dash kept telling me to tighten fuel cap, so I will likely be replacing the gas cap and fuel fill neck as well, cuz at this point, why not?! I also replaced the intake manifold gaskets. Yesterday morning, I replaced the vapor canister purge valve on top of the intake and cleared the code again. This morning, check engine light back on with new code, P0171. I've checked all the hoses for cracks, found nothing. Sprayed starting fluid around all possible leak spots with no fluctuations in idle. MAF sensor is reading temp accurately. She's idling pretty rough and seems to be missing a bit when accelerating. Anyone have any ideas on what I should check next?

 

[strutaeng]

Ouch! So the lean code started after you replaced the fuel pump or after you replaced the manifold gaskets? Does your scanner give you live data?

Maybe one of the intake manifold gaskets didn't seal properly. There's a pretty easy way to tell why watching fuel trims while accelerating the engine to rule a vacuum leak or not.

 

[Bwaite27]

Ouch! So the lean code started after you replaced the fuel pump or after you replaced the manifold gaskets? Does your scanner give you live data?

Maybe one of the intake manifold gaskets did seal properly. There's a pretty easy way to tell why watching fuel trims while accelerating the engine to rule a vacuum leak or not.

Thanks for the response! So the 171 code I've had since I got the truck about 2 yrs ago. I replaced the 2 upper O2 sensors (OEM parts) before I even put it on the road, it didn't change anything. Then it randomly started telling me to "TIGHTEN FUEL CAP" on the dash, so I replaced that. It kept happening so I checked the code and it was a 455, no more 171. About a month ago, I did all of the aforementioned work at the same time. Now my 455 code is gone and the 171 is back again.

 

[strutaeng]

The EVAP code and the lean code are 2 separate issues. Take it back to the shop and ask them if they could re check their work if the P0171 code wasn't there before you dropped it off.

 

[Ibustbravo]

Here is some info from alldata on that pid.. HPtuners can fix'er up.. And a picture showing it's bank 1. Looks like an air leak. You don't want to turn that pid off, you want to see the error but for testing or with a swap.. it's useful.

Conditions for Clearing the MIL/DTC​

DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.

Diagnostic Aids​

• Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.
• The normal Short Term Fuel Trim and Long Term Fuel Trim parameters should be between +10 and −10 % with 0 % the optimum, with the engine running at operating temperature.
• Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.
• A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.
• Inspect the air filter for being the correct one for this application. Make sure that the engine oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated.
• Certain aftermarket air filters may cause a DTC to set.
• Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set.
• Certain aftermarket exhaust system components may cause a DTC to set.

 

[Bwaite27]

The EVAP code and the lean code are 2 separate issues. Take it back to the shop and ask them if they could re check their work if the P0171 code wasn't there before you dropped it off.

I did all this myself, so it would be me having to re-check all that work. I'm really not interested in going through all that again. Lol And yeah, I'm aware they're different, but it just seemed odd that one disappeared for a while during the time that the other was showing up. I've been driving around with a 10 day sticker from the DMV for 2 yrs now and it's time to renew my registration. But I cant until I get it inspected, which I obviously can't do with a light on. So it's down to the wire here. Lol I've put a lot of my time and money into this thing. It's a labor of love, though. I inherited this truck from my grandfather.

 

[Bwaite27]

Here is some info from alldata on that pid.. HPtuners can fix'er up.. And a picture showing it's bank 1. Looks like an air leak. You don't want to turn that pid off, you want to see the error but for testing or with a swap.. it's useful.

Conditions for Clearing the MIL/DTC​

DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.

Diagnostic Aids​

• Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.
• The normal Short Term Fuel Trim and Long Term Fuel Trim parameters should be between +10 and −10 % with 0 % the optimum, with the engine running at operating temperature.
• Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.
• A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.
• Inspect the air filter for being the correct one for this application. Make sure that the engine oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated.
• Certain aftermarket air filters may cause a DTC to set.
• Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set.
• Certain aftermarket exhaust system components may cause a DTC to set.

Thanks a lot! That's some good info there. I actually did check some of that, other things I wasn't aware of, so I'll do some digging. Much obliged!

 

[strutaeng]

Understand.

In the future, the EVAP system checks aren't performed when the gas tank is less then 15% or more than 85% full. So you can clear the code, and keep the gas tank topped off and drive it like that and it won't set the code...just saying

 

[Ibustbravo]

Thanks a lot! That's some good info there. I actually did check some of that, other things I wasn't aware of, so I'll do some digging. Much obliged!

NP... Here's the torque specs for the intake.

Intake Manifold Bolt Caution: Refer to Fastener Caution. Tighten: Tighten the bolts a first pass in the sequence shown to 5 Nm (44 lb in). Tighten the bolts a final pass in the sequence shown to 10 Nm (89 lb in).

 

[Bwaite27]

Understand.

In the future, the EVAP system checks aren't performed when the gas tank is less then 15% or more than 85% full. So you can clear the code, and keep the gas tank topped off and drive it like that and it won't set the code...just saying

Understand.

In the future, the EVAP system checks aren't performed when the gas tank is less then 15% or more than 85% full. So you can clear the code, and keep the gas tank topped off and drive it like that and it won't set the code...just saying

I think I'm pickin up what yur puttin down. Wink wink, nudge nudge. Lmao Thank you kindly