96 Nissan Pathfinder - Missing/Hesitation/Bad Idle
 

Howdy folks. 96 Nissan Pathfinder. 3.3L V6 2WD. 151K on the odom. Three
weeks ago started getting a real bad surging/poor acceleration problem. At
a stop, the engine would idle poorly, and on acceleration, would be very
sluggish, and then suddenly accelerate as if nothing was wrong.

So, this is what I ended up changing:

Fuel pump, all fuel lines (rubber), fuel filter, under hood fuel hoses, fuel
pressure regulator. New Plenum gasket. New Throttle Position Sensor. All
new vacuum lines under hood that I could reach or replace. New spark plugs.
New rotor. Cap and wires have less than 5K on them. Both front O2 Sensors
(Denso).

So the surging/poor acceleration is gone. But here is the problem that
remains. When the engine is cold, it starts and runs perfect. As it warms
up, everything is ok. After about 10-15 mins of driving I start getting a
bad miss between 40 and 50 mph, real evident on cruise control. The engine
appears to be "hesitating". Here is the kicker. Disconnecting both front
O2 sensors makes the problem go away. Both sensors are brand new Denso, OEM
style replacements.

I can run all day with the O2 sensors unplugged (at the under hood wiring
harness) and the engine runs perfect. Plug them back and I get:

Cold engine: Good running engine
Hot engine: Missing, stuttering, hesitation.

What is the problem? Dirty fuel injectors? I have never cleaned the
injectors. Bad O2 grounds?

Help!

"Not Anyone We Know" > wrote in message
nk.net...
> Howdy folks. 96 Nissan Pathfinder. 3.3L V6 2WD. 151K on the odom.
Three

>
> So the surging/poor acceleration is gone. But here is the problem that
> remains. When the engine is cold, it starts and runs perfect. As it
warms
> up, everything is ok. After about 10-15 mins of driving I start getting a
> bad miss between 40 and 50 mph, real evident on cruise control. The
engine
> appears to be "hesitating". Here is the kicker. Disconnecting both front
> O2 sensors makes the problem go away. Both sensors are brand new Denso,
OEM
> style replacements.
>
> I can run all day with the O2 sensors unplugged (at the under hood wiring
> harness) and the engine runs perfect. Plug them back and I get:
>
> Cold engine: Good running engine
> Hot engine: Missing, stuttering, hesitation.
>
> What is the problem?

You probably have a vacuum leak. When the O2 sensors are unplugged the
computer sees a major fault and runs it rich. I would guess if you went
through
an emissions check it would be exceeding HC.

When it's hot the O2 sensors allow the computer to lean it down, and due
to your vacuum leak it's getting way too lean.

Ted