PontiacBonnevilleClub.com

Original topic here:
viewtopic.php?f=18&t=5600

P0171 - Fuel Trim System Lean Bank 1
P0440 - EVAP system (sorry, don't have the actual text of the code)

a while back I posted about having two codes - P0171 and P0440 - and the concensus was that I had a vaccuum leak somewhere. Since the car has been running fine I haven't spent a lot of time on it...until recently.

The car needs to be inspected and after a weekend of looking I can't find a leak. Since everyone, myself included, thinks it's a leak I'm going to take it and have a smoke test done on it to try and pin point where the leak is.

My question this time round, would the leak that's causing the P0440 likely be the same leak that's causing the P0171 or are they different systems?

Thanks!

Completely different systems. The P0440 has to do with the Evaporative Emissions system, that controls the gasoline fumes in your fuel tank. The other one means that your engine is running more lean than the computer can adjust for, meaning it can't give enough fuel to keep it at the proper air/fuel ratio. Do you have any mods? Also, can you get access to a fuel pressure gauge? If you can, check your fuel pressure with the car off, key off; car off, key on; and at idle on the schrader valve on the fuel rail. Wouldn't hurt to change the fuel filter as well, as that could be causing (or contributing to) the lean condition.

no, no engine mods. I'll check my records tonight but I'm reasonably sure the fuel filter is a year or so old. I'll ask around and try to find a fuel pressure guage....what kind of pressure should I be looking for?

As the evap system pulls and checks the ability to hold vacuum, it's possible, but probably not likely that the two are related. If there was a leak in the vacuum line for the system large enough to lean out the fuel, it should be pretty easy to find.

I too had the P0440 code just weeks before my car was due for it's 2 year
admission check (cash grab). I had this same problem a few years ago and
the guys here helpped me with it. Turns out my gas cap wasn't on tight, but
as for the admission check the gas cap finally had to be replaced.
Just my 2 cents...

Just wanted to follow-up with this and post the results of what ended up fixing my problems.

The P0171 was caused by a vaccuum leak in the Supercharger Bypass Valve Actuator. New one from the dealer is approx $260, found online for $150, found at a salvage yard for $3

The P0440 ended up being a combination of vaccuum leaks at the U-bend hose attached to the EVAP Canister Purge Solenoid (GM# 24506665 - $17) and the EVAP Canister Purge Solenoid itself ($30 from Advance Auto).