Posted to Technical Discussion Forum on 1/3/2013
OK, this may be a long story, but here goes...
This vehicle came to me as prep for state inspection. No
MIL, but when I ran my scan tool, of course two codes were
present. P0301 and P0171. Customer was complaining of small
shake at cold startup and adding coolant every 2 weeks or
P0301 has been fixed with a fresh head gasket, as the gasket
coolant leak was fouling the number 1 cylinder plug, causing
the misfire at startup, also warped the head to the point
where the plug sleeve had to be drilled out and an insert
installed. Also new AC Delco plugs and wires installed.
P0171 was initially thought to be an easy fix. Initial
inspection plainly showed a broken hard plastic vacuum line
to the PCV valve. I also ordered a fresh air inlet hose to
the rear rocker cover direct from GM, it was out of place as
they often get bumped around due to air filter replacement.
Fresh upper/lower intake gaskets were used (the metal
Fel-Pro replacements) and new bolts throughout. Sprayed the
intake and throttle body clean, ran the engine after
everything is done and P0171 still pops up.
Well at this point I decided to recheck my tracks. I did
note a cracked nozzle on the purge valve solenoid, another
one has been ordered and should be in sometime today. I also
replaced the o2 sensor on GP- car has about 90K miles. Upon
rechecking the scan tool, long term fuel trim is running
about 21%. The fault sets at idle, normal operating temp.
Long term fuel trim does come down to about 3-4% when I give
it some rpm's. I have checked all vacuum lines, sprayed
throttle body cleaner around the intake and hoses hoping to
locate a leak somewhere, all seems to be OK. I induced fuel
rich condition to recheck the o2 sensor, it did exactly as
it should, as well as watched the voltage cycle back and
forth as it should. I also checked fuel pressure at the
rail. KOEO, went to 59-60 psi. Running, stayed at 60 psi,
spiked to about 62 psi doing a snap test. I am about to
check the MAF sensor voltage and frequency.
Although the purge valve should be replaced and although I
would like to say its something easy like its the fuel
filter or fuel pump or some obscure vacuum leak under the
manifold somewhere, my tests are leading me to believe that
none of these things are gonna rectify the problem. I would
like some feedback to help me identify what could be going
on, and to see what have I missed. Thanks in advance.
Spradley Professional Auto Repair
Mechanicsburg, Pennsylvania, USA
42 Replies Received
42 Replies Received