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Guest Message by DevFuse

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Any protocol for testing an ECU formally?

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9 replies to this topic

#1 Hank Roberts

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Posted 07 April 2005 - 10:57 PM

Is there a place I can send an ECU (pulled out of a 1988 GL) to have it checked?

I know computers and computerized controls -- but never had a car new enough to have a computer in it til, um, yesterday.

And from what I know of computers and cars -- who was the genius who thought of combining them? -- to properly test a piece of computer gear you plug it into a test board that measures all the outputs and provides all the inputs, step by step, a few hundred times , and eventually you isolate whatever's out of spec.

Anyone do that? Or is this all throwaway stuff now?

#2 TheSubaruJunkie



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Posted 07 April 2005 - 11:00 PM

Goto the junkyard and get a new ECU. Small enough to fit in a pocket.

Problem solved.


#3 85Sub4WD


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Posted 07 April 2005 - 11:54 PM

Realistically, the cost of buying a new/rebuilt ECU is low enough it is not worth screwing around with your old one. - Most work, or don't - Had one run rich on me (threw in a spare, problem solved) - generally speaking, they aren't worth messing with

Yes, they can be plugged in and tested - but they're not worth it

#4 Hank Roberts

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Posted 08 April 2005 - 11:44 AM

Where is a place I can send an ECU for testing? I understand this is a debatable thread, I don't want to debate it here, I'm looking for information in this thread.

#5 85Sub4WD


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Posted 08 April 2005 - 12:03 PM

I know the CarQuest near me has the equipment, but they are a distrubution center - so your local one may not be able to do it - I am not sure if they can check older Soob ECU's though - probably have American, and big three Japanese - check NAPA, and the dealership may even have it - however, I know the scan equipment for these ECU's was not common, even in their day

Another thing to consiter is the firmware of the ECU's evolved over time - while they are interchangeable to the point that they will work between model years, I would opt for a later, rather than earlier model ECU if I have to replace it - reflashing it is something we ALL wish we could do (I know it is possible on earlier ones), but that would cost big $

Good Luck!

#6 Hank Roberts

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Posted 08 April 2005 - 12:48 PM

Thanks, I'll hunt around in Berkeley area for some place that might do it. The old ECU removed from this 1988 GL is the size of a hardback book -- I'm guessing the PROM chip was not separate at that point, and maybe it's got some power relays inside this big metal box.

Here's why I'm not just diving in and part-swapping til the problem goes away -- I've had bad carpal tunnel (failed surgery, got it too late to fix the nerve damage done by decades of keyboard/mouse work), I can't do much fine work myself --- so I try to understand things even when it costs more, rather than just pay other people to swap parts and tell me it's fixed.

#7 rallyruss


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Posted 08 April 2005 - 01:40 PM

I used to work at a parts store. on a verry rare ocasion we would send out a ECU for testing. it can be done. they are not verry acurate in my opinion and it usually costs close to the price of what a reman ECU would. thus those of us in the industry learn to determine when an ecu IS BAD bad looking at what it does on the car. under real conditions with all powers and grounds checked at the ecm first. also all outputs must be good (soilnoids ect. hint hint) as they are drivin by a transistor in the ECU and are checked fo voltage drops in order to set codes for thiese items.
In my 10+ years of fixing cars I have only had one ECM actually need replacement.
from our conversation I have an idea of what you are chasing. It needs to be looked at ON the car under normal conditions. Its usually somthing simple. a bad connection, bad solinoid, who knows.
so if you meet some resistance about how/where to get an ecu tested please understand its not common to have one fail, really uncommon to send one out for testing.
now you have noted that it had a new(reman) ECM installed right? they fired the shot gun at the ECM so they are responsible to find the real cause of your problem now too. egr solinoid?

most troubleshooting charts in factory books end up at change ECM. we learn that we must have missed somthing if you got there. I hate those stupid charts though. you can waste hours trying to find out what common sense and past experience could have told you in no time at all with the proper test equipment.

so as to answer the question. folowing the trouble tree in a factory book is the answer you are looking for.

#8 Hank Roberts

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Posted 08 April 2005 - 03:08 PM

>trouble tree

Now we're talking.

Can you tell me for the 1988 GL turbo, what reference book has this? I see people selling them (a four volume set, sometimes).

I may have to provide it to the mechanic that worked on the car.

And the way I approach things, that's what I'd like to have for myself anyhow.

#9 calebz


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Posted 08 April 2005 - 05:32 PM

There was a scanned copy of the 89 FSM (engine and associated wiring sections only) floating around here. I'll see if I can dig it up. Its the same as the 88.

One more time. Don't overthink this. The ECU needs to be in the car. From there the next step is to pull the codes. If you are having a CEL with no operational difficulties, you are probably looking at something like an EGR solenoid or Purge solenoid. Both being common failures, easy to diagnose with quick code pulling and a DVOM and easy fixes.

I have seen one of these cars with a failed ECU. It just happened to be mine. And when it happened, it was a total failure. You know the kind, burning electronic smell, followed by a complete spark and fuel system failure.

I can't stress enough how much this resembles tail chasing at this point.

Step 1 - Find a new mechanic
Step 2 - Pull the codes
Step 3 - Report back

Addional note: If in fact your car is a turbo and not SPFI, the D-check connectors are not under the hood they will be located under the dash between the ECU and the fuse box.

#10 Hank Roberts

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Posted 08 April 2005 - 09:43 PM

Good advice.

I'd been thinking I ought to get the shop that worked on it to at least look again in case anything they'd put in was blown or done wrong -- they wouldn't be responsible if someone else had gotten into it first, of course.

One thing might be confusing this, I'm checking --

The car has had an engine swap, a used Japanese engine that has about 60k miles on it, put in a couple of years ago -- so I'm asking the guy I got it from if he's sure the _engine_ is still a 1988!

The car's a 1988 GL SPFI turbo. Definitely still single point fuel injection.

The test leads are under the hood, I've found both the green pair and the white pair. Odd, they were pushed way down under a wire bundle, doesn't even look like they've been plugged in to each other.

I haven't tried connecting either of them -- apparently don't need to, which puzzles me. I can read the ECU by looking up under the steering wheel -- I don't even need to drop the panel, though I did the first time to make sure what I was seeing -- just move a bit of foam to the side with my finger in the gap above the panel and I can see the red light on the ECU, it's blinking 3 slow, 4 fast, repeating -- the code is clearly a 34 -- it's showing as soon as I put the key in and turn it to the run position without starting the car.

About the under-hood connectors -- they have right next to them a tan-colored multi-connector plug and a black multi-connector plug (which don't mate up to each other) -- which puzzles me and makes me wonder if this could be a different year engine.

Too rainy and cold to do more today in the yard; tomorrow I'll go back to trying to make sure I know what the EG solenoid actually is! and see if I can measure resistance across it. Remember, I've now owned a Subaru for a total of about 24 hours.

But this time tomorrow, I'll have owned a Subaru for twice as long!

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