Fried ECU

[davepak]

Hi guys, I've recently discovered my XT's ECU was fried inside, I took it apart and saw the burnt electronics. For a long time, it had a lot of sputtering and hesitation. My suspicion is that it developed a short circuit.  When trying to start it, it would blow the fusible link, I traced all I could until hesitantly checked the ECU, it looked bad inside with signs that a massive short circuit took place. But I can't avoid wonder if something else could have had a short which burnt the ECU..

Top left corner is all burnt. (On the image) 

Question, do I need to replace the ECU with the exact same type as it originally came with? Are there any issues regarding whether it is Automatic or manual transmission, turbo or non turbo?. I have a real unicorn  here, it's a 1986 XT 3AT converted to a non turbo with non turbo

pistons... Any thoughts, as always very much appreciated! 

davepak 

Edited December 4, 2020 by davepak
grammar check

[idosubaru]

I'm mostly familiar with 88-91's which are different but I think any non-turbo 85-87 ECU should work for yours.

3AT isn't electronic so auto/manual should be interchangeable just like later 88-91's. 

88-91 XT ECU's are all interchangeable, auto/manual, FWD/4WD doesn't matter.  But there are no turbo's during those years.  I would get a non-turbo like your current ECU.  If you happen to find a turbo ECU and want to try it then ask here specifically or look at the wiring diagrams.  The 1987.5 turbo is very close in wiring to the 88 non turbo and does "run and drive" mostly on a non turbo ECU. 

I converted a project 1987.5 XT Turbo that didn't run to non-turbo and plugged in a non-turbo ECU and it ran and drove. It didn't drive well and I never got to diagnose if the running issues were pre existing mechanical issues of an old project car that hadn't run in years, or the ECU swap.  The wiring diagrams were different but very close. 
 

[idosubaru]

I can't see the burn portion but if it's not bad and you have electronic friends it could be repaired.  There are also companies around that used to repair ECU's....though it's probably far more $$$ than a used one. 

[davepak]

Thanks @idosubaru!

What I have done is sourced the exact same ECU which is on its way, probably a week to get to me. In the mean time I'm working on peripheral jobs like brakes, upholstery, radiator fans, shock absorbers etc. This car is now a non turbo regular EA82 with a MPFI system. I guess I'll have fingers crossed when plugging in the new ECU. As I wonder if the ECU will be "wondering" where the Turbo is. The actual picture does not show much of the damage, as I thought of a repair by myself.. But on the other side of the circuit board it looked pretty bad, you can see the pictures.. I'll update soon! 

Edited December 3, 2020 by davepak

[1 Lucky Texan]

if it was limited to just 2-3 traces and the components seem OK, might be worth trying some 22ga or w'ever wires patched in. It could work - at first.  However, one has to wonder, with that severe a surge, what's the remaining lifespan of some of the components that have been 'stressed'.

[davepak]

I agree with you @1 Lucky Texan, first call of action was to try and repair it. But it doesn't look good. The only question now is whether I have to modify a pin in the upcoming ECU to "cancel" the Turbo signal /pulse? I'm guessing the ECU doesn't "read" the turbo or does it? 

[naru2]

86&87 XTs use the same ECU whether MPI or turbo according to the parts book-22611-AA073

[naru2]

2 hours ago, davepak said:

Thanks @idosubaru!

What I have done is sourced the exact same ECU which is on its way, probably a week to get to me. In the mean time I'm working on peripheral jobs like brakes, upholstery, radiator fans, shock absorbers etc. This car is now a non turbo regular EA82 with a MPFI system. I guess I'll have fingers crossed when plugging in the new ECU. As I wonder if the ECU will be "wondering" where the Turbo is. The actual picture does not show much of the damage, as I thought of a repair by myself.. But on the other side of the circuit board it looked pretty bad, you can see the pictures.. I'll update soon! 

Looks like the power transistor on the heat sink (another NEC D1590?) shorted out.Could be an easy fix

C401 looks overheated too.

I would make sure the injector harness is not shorted to ground before plugging in another ECU.

Edited December 3, 2020 by naru2

[idosubaru]

3 hours ago, davepak said:

I guess I'll have fingers crossed when plugging in the new ECU. As I wonder if the ECU will be "wondering" where the Turbo is.

 

That underbelly pic looks nasty.

Why are you worried though?

If that previous ECU worked, then the same replacement ECU will work. 

If the previous ECU didn’t work, then the replacement won’t. Or we have the wrong info and are discussing the wrong questions.

If this ECU fried the first time it was started then I’d test the alt and double check every wire that was cut or customized in anyway. And let us know more details - what non stock parts - has it ever run?

Edited December 4, 2020 by idosubaru

[davepak]

Thanks gents for the info and inputs!

Well, it was originally an EA82T but when I got the car the turbo was broken beyond repair. I had the engine rebuilt and used the regular pistons, therefore making it a regular EA82 naturally aspirated. This car has been really abused and badly maintained. I've tried to take it to its best possible shape.. My worry about the ECU not working was based on a possible error should the ECU didn't "see a turbo input" but reviewing the posts.. I understood this shouldn't be a problem. The ECU will read the air flow from the MAF and act accordingly. 

I suspect a wiring issue with the starter motor or the ignition circuit which could have fried the ECU, although the car had been suffering from hesitation and sputtering consistent with a faulty ECU, perhaps showing end of life service signs. This, because I managed to fail-proof peripherals like spark, distribution, fuel pump, thermosensor and a plethora of other possible suspects. 

So.. Either a short somewhere fried the ECU or the ECU failed (moist maybe, or age).. 

The updates will continue! The new ECU it's on its way, meanwhile I'm washing all the seats, servicing the rear calipers and shock absorbers 

Dave

 

Edited February 2, 2021 by davepak
content cleared

[idosubaru]

10 hours ago, davepak said:

Thanks gents for the info and inputs!

Well, it was originally an EA82T but when I got the car the turbo was broken beyond repair.

I suspect a wiring issue with the starter motor or the ignition circuit which could have fried the ECU, although the car had been suffering from hesitation and sputtering consistent with a faulty ECU, perhaps showing end of life service signs.

 

Great, this is good to know.  This could be much more than just a burnt ECU.  So it sounds like the car never run properly ever since the conversion?  Is that true?  So you'll want to try to narrow down if the ECU just failed due to age or something caused it to fail.  Sorry to drag this out - this would all take like 34 seconds if we were hanging out over lunch...

1. check alternator

2. Is there any custom wiring - cuts, splices, changes to the wiring? 

3. Yes these older electronic components can fail due to age, it happens. 

These old Subaru's are simple and robust - a good engine with an untouched stock (never cut or messed with) wiring harness should run just fine. 

The older circuit boards are prone to occasional failures - so if you alternator is not over charging and the wiring isn't cut/spliced/messed with - it's probably the ECU. 

I would just want to address questions 1 & 2 above to make sure you don't fry the next ECU. 

 

[idosubaru]

10 hours ago, davepak said:

Thanks gents for the info and inputs!

Well, it was originally an EA82T but when I got the car the turbo was broken beyond repair.

 

I have the same thing a 1987.5 XT Turbo I got with puked turbo and engine. I dropped a non turbo engine in it and plugged in a non turbo ECU, no wiring or changes otherwise.  It drove, but I never got it running properly and never figured out if it was mechanical (rusty fuel tank) or the ECU isn't compatible. 

You've got nice OEM rear axles in those pictures - don't replace them for junk aftermarket!  Reboot those axles and never throw them away, they'll last the life of the car.  

[davepak]

Hey @idosubaruyou're right, I'm going to run some tests on the alternator and check the wirings. Last night I checked the wiring diagrams from the manual to follow the power sources and potential threats to the ECU. The alternator is one of those. On another thought, I wonder if the knock/detonation sensor might have had something to do with your car in the past. As it's a part of the turbo system. I can say that the car actually ran better after the engine rebuilt and removing the turbo. But it wasn't for long, the sputtering started and I thought typically fuel pump issues. But now I've got better info to check for the culprit. Then again, maybe the ECU just gave up. Or as mentioned before, maybe the injector harness.. 

On the axles.. Yes, they're solid. I managed to put a boot on the LHS one before it lost the grease so they're safe. Three days ago I installed new outer CV joints from German quality and OEM specs. Can't wait to try it on the road! 

[idosubaru]

7 minutes ago, davepak said:

Hey @idosubaruyou're right, I'm going to run some tests on the alternator and check the wirings. Last night I checked the wiring diagrams from the manual to follow the power sources and potential threats to the ECU. The alternator is one of those. On another thought, I wonder if the knock/detonation sensor might have had something to do with your car in the past. As it's a part of the turbo system. I can say that the car actually ran better after the engine rebuilt and removing the turbo. But it wasn't for long, the sputtering started and I thought typically fuel pump issues. But now I've got better info to check for the culprit. Then again, maybe the ECU just gave up. Or as mentioned before, maybe the injector harness.. 

On the axles.. Yes, they're solid. I managed to put a boot on the LHS one before it lost the grease so they're safe. Three days ago I installed new outer CV joints from German quality and OEM specs. Can't wait to try it on the road! 

An overcharging alternator fried my 88 XT6 TCU a year or two ago, so this is fresh on my mind.  Car ran and drove fine but alt was overcharging and took out the TCU and I think a couple other oddities happened that made me check the alternator.

I've rebooted clicking CV's with no grease - Subaru OEM axles are beast. 

knock sensor is a good guess, I have seen those cause issues without tripping a check engine light before.  

[davepak]

My dad  told me he realized that he noticed the negative terminal of the battery loose ( I was abroad at that time) so that is one possible suspect of the electricity issues. He was tracing back those possible issues while I was away. He told me as well that he could not test the alternator since the car didn't start, this means as you mentioned that the alternator needs to be rule out for faults. Once the ECU arrives, after checking wirings, I'd attempt to start the car with the alternator disconnected and test the outputs from it, whether overcharging or any other potential fault.

I know the effects of a bad thermosensor on the engine's performance. It wreaks havoc as the ECU receives wrong info on the engine's temperature. Also the PCV, EGR, O2 sensor among others. Oh I had both front CV joints clicking, I actually repacked them with grease but.. they were really bad, loose as marbles , I put new joints, boots, bearings, they look mint now !

Thanks as always for the tips and advice!

davepak

[Step-a-toe]

Trace all wires from the three plugs that plug to ecu to see if any concern found ?

[davepak]

I'm waiting for the new ECU, the alternator is next in line for troubleshooting. I've also repaired the combination headlight switch. The high beam push button wasn't working. 

[davepak]

Next new problem.. The control wing with the headlight switches 

So I found the switches and push-buttons aren't working well.. 

If anybody has any idea if this can be fixed.. 

[davepak]

**UPDATE**

I've fixed the control wing's headlight combination switch by bridging a faulty connection with a tinned copper wire and removing the push button function of the High Beam, leaving a pull and push action instead. 

 

ECU: The new ECU arrived and after hooking it up the car wouldn't start. I traced a problem on 2 injectors. After removing the harness for injectors 1 and 2, the car started although roughly as running on 2 cylinders. I got 2 injectors and fixed the issue only to find now injector #3 flooding and not working! As I disconnected #3 & #4, the car started immediately but again on 2 cylinders! This Soobie is a treat! I'll get another injector tomorrow and hopefully it'll fire up once and for all! 

[idosubaru]

XT headlight switches are tricky. I’ve had a bunch apart and there are various issues. Just have to get in there and address as best as you can.  The high beams same see if you can adress issues, lube or create a work around.

I had one XT where a previous owner had drilled a hole and inserted a wire attached to the internal switch mechanism you could Move to toggle high and low beams  

Wow.  Good job on the fuel injector mess.  That’s not easy to guess or track down. 

[davepak]

This is the headlight switch section that was faulty, I soldered a piece of wire to actually allow connectivity between the two needed points for the actual operation of the High/Low beam. 

The orange arrows point at the exact section where the conductivity was lost hindering the operation of the High /Low beam. 

@idosubaru The second plan of action was just that, to attach a pair of soldered wires and place a push button somewhere to actuate those lights. In fact,  a few years ago I placed an entire custom wiring with a fuse and a relay to operate the high/low beams with a switch totally separate since I couldn't fix the combination switch then. This repair was a home run! As now all the original wirings are in place and the switch works to a 90% 

Edited December 14, 2020 by davepak
content added

[idosubaru]

3 hours ago, davepak said:

This is the headlight switch section that was faulty, I soldered a piece of wire to actually allow connectivity between the two needed points for the actual operation of the High/Low beam. 

The orange arrows point at the exact section where the conductivity was lost hindering the operation of the High /Low beam. 

 

Great work and thanks for the pictures, very helpful!  

[davepak]

Thanks @idosubaru that combination swith was tricky but it worked.

**Update** I am totally mystified with the XT, beginning to think it is haunted or possessed or something..

So I changed the ECU to a known working one, I replaced 3 seemingly faulty injectors as they would leak as soon as the fuel pump would prime and during starting. Here is the thing, the car would not start, and by chance, I unplugged the connectors to injectors 1 and 2 and the car started awfully. I reconnected them, crank but no start. I then removed injector connector #3 and the car started, on 3 cyclinders. It even got some idle. Checking all connectors, I found harness #3 had the following: 12v on the battery source and 0v on the ECU pin. Ha! I said to myself, here we've got something. I checked continuity on that ECU pin source and it seemed fine up until the engine harness. So I attached a test harness providing the known 12v battery source and a "bridge" all the way to the ECU. No effect. Here I admit there might be an issue, maybe im testing the wrong pin. However, on the test it didnt start. Here is more: on reconnecting things, I then realized that it is now cylinder #4 the one NOT cooperating!?  so I reattached harness for #3 and disconnected harness #4 ....and... the car started ! Running on 3 cylinders and maintaining some "steady" idle..

So the car would not start on 4 cylinders. No fuses or fusible links blown. No relay failures, ECU works, there is spark, there is fuel and fuel pump action, rotor, cables and sparks are ok. But the cylinder pair #3 and #4 have something going on. Where the ECU only "allows" one cylinder to work. As I said this is really mystifying

It seems as if the problem "shifts" from one injector harness to the other. That would fit a fairy tale, but not a machine with (+) positive and (-) negative.

Question: Is the ECU and the MPFI one and the same inside the same enclosure? Or is there an MPFI controller somewhere tucked under the blower motor that needs to be checked up?

 

Shouting out for help, whether someone has faced such a strange thing 

  

[idosubaru]

Nah just an ECU.  No other separate controller.

What check engine codes are showing?

If you clear which code(s) come back first?

What does the ECU use to time the injector firing?

Could the distributor pick up - is that the Hall effect sensor style - be dirty and fuzzy and sending wonky signals?

I guess I’m just wasting time guessing  but I think I’d install another distributor or test it if possible  

The distributor is the only sensor directly related to initiating engine timing and firing I believe.

Can you test the knock sensor, do you have an FSM or Specs for it and does yours have one?  All 88+ XTs have one 

 

Edited December 15, 2020 by idosubaru

[Rampage]

1 hour ago, davepak said:

But the cylinder pair #3 and #4 have something going on. Where the ECU only "allows" one cylinder to work. As I said this is really mystifying

This is only a guess without a schematic of the ECU. Each fuel Injector should have one transistor to control it, so there would be 4 identical (Darlington) transistors (usually NPN type). The control chip sends a pulse to the Base of each transistor to turn it on (like a switch) and cause current flow from the Collector (+) to Emitter (-). The Emitters of the two transistors in the photo are grounded through a current limiting resistor. The big resistor that fried. The Collector of each transistor will connect through the socket to a wire going to its injector coil. The other pin of the injector coil connects to 12v. In the burned section is one of those transistors so there should be 3 more with the same part number.

Again, I'm guessing, but the photo shows the common thing between two injectors would be the supply voltage and the grounding resistor for the two transistors.

If you can, follow the traces from each transistor Collector (the center pin that sticks out from the other two) to the connector socket pin and see what color wire is on the plug. It will match the color on an injector plug.

Also check the ground wires on the connector. You can see the two Emitters are connected together and go to the big resistor. The other end of that resistor might to to a pin on the plug for a ground.

 

1 hour ago, davepak said:

Question: Is the ECU and the MPFI one and the same inside the same enclosure?

Different name for the same unit. ECU, ECM, MPFI, SPFI.

Edited December 15, 2020 by Rampage