Subaru Impreza, hard to start, check engine light on

[mountaindog]

I have a 95 Subaru Impreza.

In the last 6 weeks the check engine light goes on and off. At cold
startup it is always on. In the last week it has been on permanently.
With the key in the on position the system runs the fan at all times
cold or hot and it continues to run when the engine starts even when it
is cold, like 30 degrees and stays on when the temp is up to normal.
When connecting the diag system under the dash to get the the check
engine flash codes it seems to be pointing at almost every sensor in the
car.

11 crank
13 cam
21 temp
23 O2
33 speed

After the engine is up to operating temp it runs fine but, the check
engine light stays on and so does the fan.

It takes 10 to 20 attempts to get it started. Each time it will turn
over a few more times until if fumbles around enough to keep running,
then it smooths out and runs fine. No power loss, it seems to run fine
and then will restart fine. It seems as though the system can't tell
the engine temp so it does not know how to manage the fuel at cold
startup. As the engine warms up the temp gage seems to show valid readings.

------
Questions.

Is the temp sending unit used for the dash gage and the EMU?

Where is the temp sensor on this engine and is there
more then one? I know where the other sensors are buy I don't
know where the temp sensor is.

Is there any particular sensor to replace to just do a test. I have two
of these cars so I can swap parts looking for the problem. As usual the
dealer will not tell me anything.

 

[Remco]

I had the same problem on my daughter's Subaru last year. Look if you
can start the car with the ECM reset connector on -- look on the web,
as there are several sites that will show you how to do this.

If it then starts, it is most likely the thermosensor. It is sitting
near where the coolant comes in op top of the engine. Let me know if
you need help locating it.

Hope this helps,
Remco

 

[Bob Bailin]

A bad crank or cam sensor would cause hard starting,
and a bad temp sensor that's always indicating hot would
result in the fan running all the time.

The one thing they have in common is an engine ground.
Check the ground wires to the engine to make sure they're
not rusted out at the connectors. And check the battery
cable connections for corrosion build-up which you can
scrape away with a flat-blade screwdriver. This will
clear the codes from the ECU, so that you can see which
trouble codes come up first next time you start the car.
And make sure the battery isn't undercharged (13 volts
when the car is off).

Bob

 

[Remco]

That's a good point, Bob.
I forgot to mention that the fans are running even with the engine
cold, if the thermosensor is bad. That is a surefire way to tell if the
sensor is bad.

 

[mountaindog]

I connected the EMU reset and diag connecters together (under the dash),
one brown set and one green set. Yesterday the car started right up and
it was cold outside, 19 degrees yesterday here in Utah at 8000 feet.
The next day I unplugged the connectors and the problem is back.

My wife and I each drive Imprezas hers, the one with problem is a 95 and
my car is a 94. For a test I unpluged what seems to be the Temp sending
unit on top of the engine, near the alternatory on the 94. I was
expecting a check engine light but this did not happen and the car
started just fine and the fan did not run. After doing this the temp
gage is no longer working. So I am still wondering if there are 2 temp
sensors on the car. One for the gage and one for EMU. Why would I not
get a check engine light when I unplug this sensor?

 

[Remco]

Right - there is one temp sensor for the dash, one for the computer.
Are both your fans on when it is failing?

I am pretty sure I made pictures of the repair - let me know if you
want me to dig them up. It is in a little bit of a weird spot; not hard
to get to, but hard to find.

Remco

 

[Remco]

I dug out a couple of pictures of where the thermosensor is located on
a 95 Impreza:
http://www.weidema.com/remco/pix/ImprezaThermoSensor1.JPG
http://www.weidema.com/remco/pix/ImprezaThermoSensor2.JPG

You won't have to drain a lot of coolant, but do drain some of it
because it will make a mess if you don't. The draincock is on the
bottom of the radiator, along the back, towords the passenger side. It
looks like it has plastic "mickey ears". Be careful turning it because
they tend to snap, being plastic (don't ask me how I know

On picture 1 drop down along one of the rubber tubes next to the arrow.
You'll see that tube in picture 2 and the socket to the sensor as well
(it was brown on mine). You'll need a deep metric socket (I forgot the
size) on an extender because you can't access the thing with a socket.
You can work it in using the approximate angle of the arrow in picture
1. You won't have to remove anything (besides of course the
thermosensor) but the extender will just clear what is around it.

Don't be tempted to use teflon on the threads -- it doesn't need it
and, from what the dealer told me, will actually screw things up. Also
be sure to include the brass washer under the sensor.

After you've done the repair, reset the computer with that green/black
connector -- just replacing the sensor is not enough as the ECM will
still think it has overheated.

Hope that helps. Let me know how you make out.

Remco