Jim Grant's Tech Tips
‘87 Nissan
Pulsar, Idle Problems
Q: I have an ‘87 Nissan Pulsar. The car’s
idle is very rough, so I brought it to a Nissan dealer. They had it all
day and couldn’t find anything wrong with it, but the trouble was still
there. Sometimes it runs good and then it gets rough again with some black
smoke coming out the exhaust. I took it to another mechanic and he said
that it needed a TPS sensor. He replaced it and it was all right for a
while but then the idling problem returned. I brought it back to him and
he replaced the fuel filter. Once again, it ran okay for a while but we
are right back to the rough idle.
A: The
black smoke out the exhaust would be a good indicator that the engine
is receiving too much fuel. To truly determine if the engine is receiving
too much fuel the exhaust can be sampled with an exhaust analyzer or by
checking the voltage values of the oxygen sensor that is mounted in the
exhaust. The vehicle’s computer uses information from the oxygen sensor
to aid in adjusting fuel delivery. The same information can be used by
a technician to determine if the engine is getting too much fuel. I’ve
seen problems with fuel injectors in vehicles like yours. It isn’t that
the injectors are not working, it’s that they don’t close tight allowing
extra fuel to enter the engine. This is most noticeable at idle speeds
and will cause black smoke out the exhaust. The proper equipment and diagnostic
procedure will pin down the cause for your problem.
|
