Howdy all.... acceleration with a 2002 Monte Carlo LS 3400.
Really piss poor accerleration in the 20 - 45 mph range... when I
press on the gas pedal, it just stumbles and sits there.
No codes are being set.
Where can I locate a chart of OBDII sensor settings / ranges for this
Map sensor is reading 13 in/hg to 29 in/hg.... will not pass 29
TPS adjusts well
Air Flow Temp was in a 62 - 78 degree range.
O2 sensor #1 ranges from low to about .800. O2 sensor #2 seems to
have a smaller range up to about .500 v.
The problem started after a visit to a service shop where they did an
wheel alignment and replaced the engine bypass hose. I did an
underhood inspection showed nothing except for the EGR hose being
disconnected. However the EGR valve showed strong suction and
engine stumbled when allowing air to flow into engine. Cleaned and
checked PCV valve, checked plastic hose for cracks and leaks..
Engine is fine at idle.. starts up quickly, idles fine at 500- 700
rpm. While in park using throttle I can accelerate up to about 3K
rpm. there is a definite stumble when rpms reach about 2500 -
3000... like something is kicking in and interfering with the engine.
It's not a misfire or stumble but seems more like something
controlling the engine might be dropping out and preventing the
engine from continuing to accelerate
Connected a timing light to all the wire.... spark seems strong when
increasing rpms, No misfires are being recorded.
However, when starting to drive... if I start slow, it moves okay
however at 20 - 30 mph, under normal pedal, it just sits there.
Timing will advance up to 40 degrees, MAP will max at 29 in/hg
TPS is open, rpms will move to 1500 or so, but the car will not
accelerate.. Increasing the rpms suddenly and the car will
accelerate rapidly, but slowly increasing the rpms, the car just
Now, by pulsating the gas pedal I can nurse the car up to 50 and
it trravels well at 60 and 70 (1500 rpm or so). But it just seems it
is not responding to steady acceleration.
Is there a chart showing acceptable ranges for the sensors.... I
can start here.
MAP was 13 in/hg to 29 in/hg seems maxed out at 29
Timing Advance went to as much as 40 degrees
Fuel Trim short and long were adjusting. between lean and rich
O2 #1 ranges between .100 and .800
O2 #2 ranges between 100 and .500
Engine Temps were within normal ranges from cool to a high of 203.
Air Flow Temps were with normal
All tests completed
I hate to bring it into the shop if it's something simple. And to be
honest, I don't trust that shop... the car worked well when it went
in for a wheel alignment. They replaced the bypass hose... and did
a 30 point inspection. Left the old hose clamps and hose in the
engine compartment. Found the EGR tube disconnected. So I
wonder what else they screwed up.
Any other suggestions as to where the problem might be ???
Thanks in advance for your help !!