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

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.)

Reply to
hank
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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.

Reply to
johninKY

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.
Reply to
hank

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.

Reply to
Mike Deskevich

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