What does the ECU control in a 1988 GL turbo engine? Details?

[hank]

I've just had to replace the ECU in a 1988 GL -- everything else
checked OK but the actual ECU, in the end, and it was that or see the
car junked since it wasn't within my reach to intervene. So I funded
the work to get the car.

It's running better than it has in years, since the ECU swap --
apparently the chip did have a bad internal ground signal fault.

So -- what's it doing?

(I bought this from an old friend. He says the engine sounds and
drives better than it has in years -- apparently it's had this ECU
problem intermittently for a long time -- He'd had it worked on by a
shade-tree mechanic who didn't think the ECU mattered so had been
ignoring it except to somehow make the light go off long enough for a
California smog check station to approve the vehicle -- it did and does
pass smog.)

I know I've spent more money on it than it's worth -- it was far away
from me at the time, and being worked on by a reputable shop, so aside
from the (ouch!) price of a new ECU from Subaru it didn't cost all that
much to get it California legal.

But -- now what is the ECU doing? -- I'm hoping that from here on I'll
be able to keep it running well.)

 

[johninKY]

Timing, injectors, ignition spark etc. Just find and take a look at the
list of trouble codes for this engine. The ECU monitors/controls about 30
different functions. Some are emmision related but the rest are "engine
running" functions.

 

[hank]

Thanks, I did get that far and beyond.

I'm going to try to clarify here, in case someone who's worked on this
actual specific piece of hardware comes across the question (eventually
-- one nice thing about Usenet, it stays around).

I've looked at the very short list of trouble codes. Note this is not
the new system most people are familiar with -- that's why I'm hoping
for a response from someone familiar with this specific setup.

I'm aware generally of what an ECU might/could/possibly be doing. Some
do a lot.

This one doesn't.

The trouble codes -- for this particular 1988 SPFI turbo engine --
don't distinguish between SENSOR problems (something's wrong) and
SETTINGS (something it should be adjusting or changing isn't working).

1988 was a very early year for these; on this Subaru there is only one
fuel injector, for instance.

 

[Mike Deskevich]

I can't say for sure what the Subaru ECU is doing. But I have done a
lot of reading about my '89 toyota ECU, which is of the same era.
Here's what my ECU does (in general).

It reads input from these sensors:

AFM: air flow meeter - this tells it how much air is coming in the
intake
O2S: oxygen sensor - this tells it how much oxygen is left in the
exhaust - gives it an idea of how rich/lean the mixture is
CPS: crank position sensor - this tells it where in the revolution the
crank is
Knock sensor - tells it if the engine is knocking
TPS: throttle position sensor - this tells it what you're thinking (how
fast you want to go)
Brake light sensor - this also tell it what you're thinking (if you
want to be stopping)
there are probably a couple other that i'm not thinking of right now.

By doing some math with these inputs, the ECU then tells the injectors
when (in relation to the CPS) and how long to fire. I have 4
injectors (you said you have 1) but my computer is so old, it can't
manage 4 injectors, so it actually fires the 4 all at once - it's
really no better than having the old TBI style like you have.

All the spark timing is done by mechanical means, and there's no
adjustment on valve timing.

So if you had a bad computer, or faulty ground, or somthing like that.
It's definately possible that the injector was being fired at the wrong
time, or not often enough, or anything like that. That's enough to
make the engine run rough and fail emissions.

If you want to know more about what your computer is doing, I suggest
getting a factory service manual. That will tell you in detail what
this specific computer is doing. Anything else is just a guess.