2010 Avalanche, cold hard start

[Rick Verdura]

I have a 2010 avalanche 5.3 flex fuel engine po 172 code cold start hard but other than that it runs great just changed the plugs wires o2 sensors and MAFs sensor still having problems 

[riverbanks]

How were the plugs on that side, equal?

[Jsdirt]

Could have a bad EVAP purge valve, or a flooded charcoal canister from repeated overfilling (going a few clicks past when the pump automatically kicks off).

[Rick Verdura]

Plugs were equal 

[riverbanks]

Ok,so what are symtoms,any or just the light,and you did clear the code?

[riverbanks]

Just reread, sorry,so just a reader or scanner?

[Rick Verdura]

 My fuel trim was high I have reset the computer by disconnecting the battery and it seems to be OK right now I was at 14.7 and above now I’m at a - 0 to 14 or 18 

[Jsdirt]

Hard start cold, with positive fuel trims indicates a lean condition - are you sure you read that code right? Could it have been a 0171 or 0174?

 

In that case you've got a vacuum leak or bad intake gaskets.

[swathdiver]

20 hours ago, Rick Verdura said:

I have a 2010 avalanche 5.3 flex fuel engine po 172 code cold start hard but other than that it runs great just changed the plugs wires o2 sensors and MAFs sensor still having problems 

What brand of O2 sensors did you use?  Did you replace all 4?  Can you monitor their performance with a scan tool?

 

The MAP sensor at idle should be between 19-42 kPa.  The MAF should be between 2-6 g/s at idle.

 

Check for vacuum leaks, broken hoses, connections, intake gaskets.  Did mice make a nest in your air cleaner?

 

Can you check for leaky injector(s)?  What's your fuel pressure when you turn the key on and then at idle?

[Rick Verdura]

Replace all 4 o2 sensors and it is a 172 and175 

[Rick Verdura]

My fuel pressure gauge broke 

[Rick Verdura]

Fuel trims are negative 

[swathdiver]

14 minutes ago, Rick Verdura said:

Fuel trims are negative 

Yeah, that's the P0172 code.  I bet your intake gaskets need changing.  But first make sure you checked the air plenum for cracks and leaks, the part between the airbox and throttle body, check all PCV lines too.

 

Did you use two different part numbers for the O2 sensors?

 

One way to test for the intake gaskets leaking is to use a propane torch, not lit of course, and see if it affects the idle as you move it around each bank of cylinders between the head and intake manifold.  Youtube has other methods too.  Best observed with a scan tool.

[riverbanks]

172,rich,no?

[Jsdirt]

NEGATIVE fuel trims = RICH - ECU is pulling fuel away to correct the RICH condition.

 

POSITIVE fuel trims = LEAN - ECU is ADDING fuel to correct the LEAN condition.

 

Yes, 172, 175 are rich codes.

 

One thing I neglected to mention for rich running is injectors. I guess these are notorious leakers from what other techs have been telling me.

 

Rule of thumb for MAF's is the grams per second at IDLE should be close to the engine in LITERS: I.E. you want to see roughly 5.3 g/s at idle. If you installed an aftermarket MAF, you may want to return it and try another one, even if the data looks good.

 

I've seen guys that scoped a MAF, and everything looked fine, but the vehicle was still plagued with driveability concerns and/or the money light being on. Replacing the MAF mysteriously fixed the issue. Probably something GM threw in there to ensure they get all the money ...