[Gmecm] Tracker TBI

[Cowen]

Hello all, I have a mystery, with a Pontiac Asuna
Sunrunner (Chevy Tracker).  It started quite abruptly
in August....

My wife has the 1.6l TBI engine, and it fails
emissions with only high CO.  Looking at the graphs of
emissions over time, it spikes super high every time
the tester accelerates during the road test - then
it's fine  all other times.  That seems to indicate
running rich on Accel.

I also noticed last week we had a day down to -11
Celsius, and when I started it, it was so rich it ran
on 3 cylinders for 10 seconds - then it went to four,
as normal.  I'm guessing it was very rich in open
loop, then when the HO2S warmed up, it was fine.

It also has a mild "bog" coming off idle - just like
when it spikes the CO on acceleration in the emissions
test.

Finally, mileage is down from around 30 MPG to around
20 MPG.

So, that's what's wrong.  Seems to be running rich!!

My mom has the same car, year and even color!  So I've
switched known good parts from hers.  Hers still runs
great, my wife's doesn't.  Here's what I've done:

New Plugs.
Cleaned air filter.
Cleaner EGR.
Set the valves.
All engine compartment grounds have been sanded clean,
Nev-R-Sezed, reassembled.

Swapped the following from mom's good runner:
-cap, wires, rotor
-HO2 sensor
-TPS
-MAP


I also inspected the O-Rings on the injector(it was
immaculate), set the timing, the TB is very clean
inside, the compression is good and even, the coolant
level is up (those cars are very sensitive to that
we've found), can't find any vacuum leaks, PCV is
clean and sealing, charcoal cannister is clean and
dry.  I watched the fuel spray from the injector with
a strobe light - looked even and misty.  No dribbles
when I shut off the engine.  Vacuum line to the
pressure regulator is clear and solid.

So, I'm guessing it's rich in open loop.  What can
cause that to happen suddenly, in a totally stock
vehicle with no messing around??  Thanks for any
guesses!

Duncan


 
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