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Long vs short term fuel trim & hesitation?
Nissan Automobiles Nissan Automobiles Discussions (alt.autos.nissan)
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#11
 
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Re: Long vs short term fuel trim & hesitation? -
02-23-2007
, 08:22 PM
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"al" <abuo... (AT) msn (DOT) com> wrote in message news:1172109929.705338.176130 (AT) v45g2000cwv (DOT) googlegroups.com... On Feb 21, 5:20 pm, "JM" <j... (AT) ns (DOT) sympatico.ca.ns> wrote: Indeed, a rich mixture at idle can cause the hesitation. Check the behavior of the oxygen sensor at idle vice at speed e.g. 2000-2500 RPM. If the O2 sensor is getting tired it may switch rapidly, which is normal, at speed when it is hot but then switch slowly at idle when it is cooler. That slow switching rate in turn causes the mixture to be wrong at idle and results in a hesitation when you initially rev up the engine from idle. Good luck. Al Well, it is a new sensor, but I did notice that the sensor seems to be switching slowly at idle vs. at 2000 rpm or so. I seem to remember reading that the system is only designed to work above that speed anyway though, so maybe that's normal. Or maybe there's an issue with the O2 sensor heater causing the sensor to cool at idle speeds? One thing I forgot to mention that may fit with the rich mixture theory is the fact that the car seems to be slow to warm up, compared the '94 Altima I had before this one. In the winter I can be driving for 30 minutes or more before the needle reaches the normal point on the gauge, or before it even comes off the cold mark on really cold days (-20 C). The rad hose to the thermostat on these days is usually barely warm. I replaced the thermostat last summer, but saw no real change. Maybe this is normal though. Thanks for the input. |
The O2 sensor will drive the fuel mixture at idle and at higher RPMs
as long as the system is in closed loop. It should go into closed
loop soon after warmup. If it is not warming up, then you're right it
is likely running rich and thus causing the hesitation. I presume
you've checked the obvious things e.g. thermostat is the right
temperature, cooling fans don't come on too soon or too long etc. If
all that is OK, then maybe somehow coolant flow is getting past the
thermostat. If you can get hold of one of those infrared laser
pointing thermometers it might help to assess heat flow during
warmup. They're pretty cheap nowadays. You've in a very cold climate
where there's not much margin for error in coolant flow. I wish I
could be of more help but you're in for some detective work here.
Good luck. Al
#12
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"Codifus" <codifus (AT) optonline (DOT) net> wrote in message news:1u8Dh.33$RL4.5 (AT) newsfe12 (DOT) lga... You did the coolant temp sensor but have you cleaned your throttle body? It does wonders for low rpm smoothness if your TB is very coked up. I have cleaned the TB, not for a while now, probably not too much more than a year ago. The hesitation was present then, and didn't seem to improve after the cleaning, unfortunately. I did use throttle body specific cleaner. Thanks for your input though! Since you're in very cold area, why not try blocking the radiator like |
radiator to kill the airflow. Maybe the car wasn't designed optimally
for extreme cold, or however cold it is by you.
CD
#13
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Since you're in very cold area, why not try blocking the radiator like truckers do on their rigs? Put a big piece of cardboard in front of the radiator to kill the airflow. Maybe the car wasn't designed optimally for extreme cold, or however cold it is by you. |
time of year is probably around -6C so it's not super cold all the time, but
we have had a few mornings where it dropped to -20C and on those mornings
the car barely warmed up at all before I got to work, which is about a 20
minute drive, mostly city driving.
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