"A. S." <adakota4x4@hotmail.com> wrote:
: Truck:
: 1997 Dakota 3.9 V6 Auto 152K miles
: Problem:
: Truck starts and runs fine, but 2 or 3 miles down the road it begins to
: sputter and lose power. It almosts acts as if it's not getting gas and
: wants to die. Turning the truck off and restarting fixes the problem and
: then the truck can be driven 50+ more miles without problem (this has
: happened 3 or 4 times now).
: The check engine light comes on sometimes but will go off by itself. I've
: checked the codes and get the following: 12, 21, 55. I've know that the 12
: and 55 are common and the 21 is related to the o2 sensor.
: The catalytic converter recently began rattling. About a week after the
: rattle began, the check engine light came on and the troubles began. The
: cat. and muffler have since been replaced, but the problems continue.
: Nothing else has been replaced (o2 sensors are both original).
: No change in fuel mileage or performace other than the symptoms mentioned
: above.
: Questions:
: 1. Can a bad o2 sensor cause these symptoms (stutter, no power, kill
: engine)?
Its possible, I'm no expert but you never know with the computer
controlled vehicles. If the O2 sensor was really flaking out, I would
have expected the computer to flag it and subsequently ignore it, but
if the sensor is failing in such a way that it doesn't short out or
go beyond the pre-programmed limits in the computer that would cause it
to be flagged as bad, then I suppose its possible.
: 2. Code 21 relates to both sensors.....which one is more prone to dieing?
It would be the upstream O2 sensor, the one before the cat. Essentially,
the sensor before the cat is used to control the air/fuel ratio, and the
sensor behind the cat (downstream sensor) is just used to monitor the
health of the cat. Some folks say that the downstream sensor is also used
to control engine parameters. They may be right, but if there is any
effect, I would hazard to say it is minimal, based on what I have read
in FSMs and such. I would concentrate on the upstream sensor first.
Something you can try is to simply unplug the upstream O2 sensor.
The sensor isn't used until the engine has warmed up anyway, and your
problems may be occuring when the truck switches from open loop (not
using the O2 sensor) to closed loop (the O2 sensor is used to control
your air/fuel ratio). If you disconnect the O2 sensor, the computer will
probably throw a code 21 detecting an open condition, but it will
recognize that the O2 sensor is not there and it will stay in open
loop mode. If the truck does not have the stumbling/dying problem with
the O2 sensor unplugged, then chances are excellent that just putting a
new O2 sensor in there will fix the problem. BTW, 152K miles is about
three times the expected life expectancy for these sensors, so I wouldn't
doubt that it has gone bad. You've got your money's worth out of that
one. :-) If it turns out that you need to replace the sensor, after all
those miles you might have some fun removing it though; soak it in PB
Blaster for a while. (Starting a few days beforehand if possible.)
: 3. Is it normal for the check engine light to come on and off by itself (I
: always thought it needed to be cleared once on)?
Yes, the computer will perform diagnostics at certain intervals, and if
the condition that caused the light to come on is tested and seems OK, the
computer will turn off the check engine light.
: 4. Could I have a fuel problem that just happened to show up with a bad o2
: sensor but won't trip a specific code?
Anything is possible, but the fact that you can re-start the truck
and it will run fine afterwards is a bit weird, and makes it seem like
that might be unlikely.
The fact that the problem always occurs 2-3 miles down the road
is telling - that's about the right time for the computer to be
switching from open to closed loop. If I were a betting man,
I'd put my money on the upstream O2 sensor.
--
-Jon-
.- Jon Steiger --- jon@dakota-truck.net or jon@jonsteiger.com -.
| 67 Dodge Coronet, 70 Plymouth Barracuda, 76 Peugeot TSA |
| 78 Dodge B100, 90 Dodge Dakota Convertible, 92 Dodge Ram 4x4 |
| 96 Dodge Dakota, 96 Suzuki Intruder 1400, 96 Kolb FireFly |
| 99 Jeep Cherokee 4x4, 01 Dodge Ram 3500 CTD |
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