Fried ECU

[davepak]

3 hours ago, idosubaru said:

This is weird - I have an XT Turbo I converted to non turbo and it had fuel problems.

so I ran a direct switched power wire as el_freddo said.  During my longest run with it - about 40 miles it shorted and started smoking. Made it home but never found the culprit or fixed it and still have the car. 

XT Turbo, converted to nonturbo, fuel pump powering issue - That’s uncanny similarity to yours.  

coincidence?  

Or could there be something  different between the turbo and non? Seems unlikely  though.

I don’t have good internet access but Ill try to look up my old posts and see if I ever mentioned it hear  

 

I find uncanny coincidences very rare and needed to be respected. And then it makes me think that we might be finding something after many years affecting these type of cars. This car has never really worked as far as I've known it. It was abandoned and it "started" but it was barely brought home by a lousy shady mechanic (previous owner) I thought I'd be able to make it work as I had 2 subarus, one carbureted and one SPFi, both were unbreakable. 

But now, after reading all the FSM, I think about the following systems: Anti Knock System, Turbo pressure switch, anti knock sensor, MAF, coolant thermosensor, the TURBO itself, ECU, etc. They should all work together and despite an old school ECU computer, it worked based on signals, or inputs from potentiometers, enough for binary decisions: more fuel, less air, advance of the spark, retarding it..etc. Perhaps this affected your XT back in the day, I'm leaning on something the ECU is doing to the pump, limiting the voltage supply. (ECU is new certified remanufactured in Canada). This voltage "punishment" is a decision the ECU must be doing on some "unknown" basis to us, highly likely because there is a reading that the ECU is not getting. (or getting)

It makes me believe then, that if I was to install a switched relay feeding 12 volts to the pump, ignoring the ECU, I might get the same smoking, shorting issues you had on that 40 miles run.. The ECU could detect the pump's absence and kill the engine's operation altogether. I know this ECU is NOT THAT advanced like modern cars to do that, but it was MORE advanced than the DL's carbureted ECU or even the GL's SPFI one. 

Say...:  Ignition pulse, fuel pump's priming, spark and starting, operating temperature, fuel/air mixture ratio, pressure boost from the TURBO, knoking detection and spark retarding/advancing as needed, atmospheric pressure's influence in the fuel/air mixture and subsequent compensation, reading from the O2 sensor and the coolant thermosensor for more compensations, fuel pressure demands when with load, climbing and at altitutes above 5000 feet (where I live)...

I think is a recipe for a terrible engine operation with this car where there is a missing link (or several) in the chain

The gearbox is working super smoothly, kick downs, overdrives, D-2-1, reverse, all fine by the way, as I had the chance to ram the gas yesterday

 

[davepak]

6 hours ago, el_freddo said:

Running a switchable and fused wire to the fuel pump would be a good test. 

If that proves successful, I would keep those new wires and put a new relay in that’s activated by the ECU ground wire. Pull the positive voltage from a known good source, or if it’s 5v, find and use the corresponding ECU positive wire. See if that setup works. 

Sounds like you’re onto a good thing there though! 

Cheers 

Bennie

I'm trying to avoid this route, as checking on what @idosubaru said when he did that, it seems that the ECU might act up even more. I noticed a potential drop in voltage when the car reaches operating temperature, cannot confirm it to a 100%m but 1 h ago this is what happened. There was 11.90 volts to the pump (still not 12v), no whining, 42 psi or so steady, no significant voltage drop at the pump.

After a while, voltage dropped to 10.34 volts, the pump was whining in a "wave" with oscillating pressure between 36-42 psi, no significant voltage drop either, but the engine had reached operating temperature and the fans where working.

Scratching my head...

[davepak]

On 1/21/2021 at 5:02 PM, el_freddo said:

Reversed fuel lines is a good suggestion. 

Quick way to check is to disconnect the fuel hose from the filter in the engine bay, put a container under each hose and prime the fuel lines. 

Which ever container has fuel in it is the direction the fuel is flowing from. It should be coming from the filter  

Cheers 

Bennie

Yeah, I checked them, they are fine, no obstructions, proper ventilation at the fuel separator and the fuel tank's cap too.

[davepak]

On 1/22/2021 at 3:41 PM, el_freddo said:

Also, any play in the distributor shaft? 

Cheers 

Bennie

Zero play, and its a new distributor 

[idosubaru]

16 hours ago, davepak said:

**have seen voltage as low as 8.32 and as fine as 12.03 volts. Why?

 

 

4 hours ago, davepak said:

I had a suspicion of a voltage drop particularly on the negative (ground) side to the pump. Especially because the ECU uses a grounding signal to operate the pump. However, the voltage drop is not significant and in fact corresponds to less than a volt on each lead.

 

Less than one volt - but the previous post said 8.32?  I'll go ahead and assume the most recent post is accurate and you dont' suspect a voltage issue.  

[idosubaru]

4 hours ago, davepak said:

 This car has never really worked as far as I've known it. It was abandoned

 

mine had a blown turbo and engine when i got it - so it had sat for an unknown length of time and has low miles (suggesting it sat for awhile).  another coincidence. 

It's a been a few years since I even tried to look at mine but I do recall like 3 differences when comparing the FSM (Subaru) wiring diagrams from the turbo to the non turbo. 

Also - I even swapped 4 cylinder ECU into an XT6 (6 cylinder XT) and the thing started and ran...terribly and not drivable - but it ran.  So yeah the wiring is "just close" enough on these to do something, but I wonder if something isnt' quite lined up.  

 

4 hours ago, davepak said:

I'm trying to avoid this route, as checking on what @idosubaru

*** wait - unfortunately it was 8-10 years ago and I don't recall but it might have been due to my wiring and temporary set up rather than causing an issue with the vehicle.  i had run the wire right through the center console (probably so the switch was close to the parking brake maybe?) and it got hot right there...which was fortunate i knew about it right away but burning carpet is deadly poisonous so a little sketchy!  anyway - i don't know if that was my mistake or doing that messed with the circuit?

if the ECU is supposed to always have power - then it shouldn't matter too much.  so maybe it's still an option? 

Maybe you could try an entirely dedicated circuit - ground one wire to the vehicle and just connect a fused 12 volts straight from the battery.  Then you wouldn't have to worry about damaging the ECU.  Don't even plug it in or connect and just leave the ECU dangling....though it might need a reference signal or that circuit completed, dunno?  

[idosubaru]

I'll try to dig up the FSM and see if I made any notes on those circuit differences. 

One was like a pressure sensor or something...probably for the turbo..again from memory??  they weren't big ticket items - all the main things were the same. 

One difference for mine was that it was a 1987.5 turbo - which was an oddball in a couple ways and is often called "the unicorn", though mostly for aesthetic reasons. 

[idosubaru]

Check this out - a guy investigating EA82 turbo and nonturbo ECU differences, though they aren't XT specific but he mentions some very interesting stuff - although keep in mind he's from australia and they're models differ slightly in offerings - they get stuff for a few years after it's discontinued here, etc.  but otherwise it's all the same:

Quote

 have opened the case on both ecu's and they look identical as far as component placement goes (the only difference is that the turbo one has a second circuit board mounted about half an inch above the other one.

I assume this is the knock sensing part.

 

I have found that i do not need a boost sensor unless i have the instrument cluster with the boost light. There is no input on the 87+ ecu for this sensor, unlike the 84-86 ecus that used 2 boost sensors, 1 to turn on the boost fuel maps and one for the boost light.

There's the "second board" - what does that do and if the wiring harness pins are there in the body - what are they seeing - nothing because it doesn't exist or somethign else? 

He mentions the additional 84-86 turbo sensors - one impacting fuel maps??  maybe that's freaking things out? 

 

 

[idosubaru]

Are you ready to sell me this thing yet?   It's probably my favorite XT color!!!!  HAHAHA

[subaru1988]

5 hours ago, davepak said:

I did a voltage drop test: 0.86  and 0.64 volts in both positive and negative leads of the fuel pump. Also, a super smooth engine's operation and a responsive "driveway" test, it lurched forward nice and strong.

 

This XT issue is beyond my current Subaru pay grade  , but that being said, it's my general understanding the total voltage drop on positive and negative sides of an electrical fuel pump should be less than a total of 1.0V (.5 for posit side +.5 for negative side). Your numbers show a total voltage drop of 1.5V when you add both together. If a SUbaru is different for some reason, I'm sure someone will correct me, and my apologies.

One would think .36 in that one circuit wouldn't be much, but maybe that seemingly small amount is translating to a voltage loss that is causing issues above idle.

I respect you really getting into the weeds with this, and not just throwing parts at it. What you're doing is real troubleshooting; plus it's cheaper in the end when you figure it out

Edited January 28, 2021 by subaru1988

[davepak]

"Today's updates" 

Alright let's get started... Fine  the car actually starts.

Upon reasoning on voltage issues, I removed the back seat and traced the wires to and from the fuel pump. There is a special wire that has an internal mesh to it. My dad used to be a tecnician in telecommunications in the late 70s and 80s , so he said: "hey that's a wire that comes with a pulsing signal and the mesh is a protection against noise. The FSM has that wiring and that mesh is meant to come from the ECU together with the grounding signal to the negative lead. They are next to each other. NOW HERE there was something, someone had worked on this part of the car, the shielded-meshed wire had been cut to expose that mesh and the person who did this did not know its purpose, SO, he or she spliced the grounding wire (not the mesh) and took an extra wire to attach it to the chassis as a means of ground. This was ALMOST right in essence, but not at all actually. The fuel pump recives a positive lead from the fuel pump relay, and the negative lead is actuated as a pulse by the ECU as a means of completing the circuit and let the pump run. This is an archaic way of "fuel pump control" So this car HAD some issues with this before. Once this was found, and corrected I tested voltage and operation of the pump and did not notice many changes. However, as per my dad's explanation, the mesh acts as noise reduction due to the electromagnetic "noise" created by the car's various systems, but it is not meant to be a ground to chassis but rather a noise waste discharge controlled via the commanded pulse from the ECU's "permitted grounding/earthing signals." This was a big eureka moment, I tested the wires resistance and all checked out fine, only the attempt by the previous person was mistaken, as he did not know that that mesh was a noise suppresor/protectant, and the negative lead did not have to be touching ground/chassis.

So, about the voltage issues.

I had mentioned previously that I noticed a voltage drop when the car was at operating temperature, but here the key was: radiator fans kick in! I had removed the faulty-beyond -repair- fan clutch and placed a second fan, now this works together with the AC auxiliary fan. Super. But, power consuming much! When they do come on, the voltage drops badly, from 11.80 v or so down to as low as 9 volts or so to the pump. And from 12.20v to 11.20v or so at the alternator. This is on idlling..

I unplugged one of the fans and the voltage drop was less..So the fans create a high current and voltage demand leaving the alternator struggling. Here something else happens: Im keeping the car in the garage at idle mainly, where it relies a lot on the fans to keep the water cooled, there is no actual running where the wind will help cool the engine, the running will make the alternator generate more power. Odd, isn't it? Too many things working in a recipe for disaster.

At one point, with all these findings, the pump was at say 11.60 volts (meh..not that bad right?) and the engine purrs nicely, I know this, I know it has power, torque, all of it, so I tested it and it was true, it is amazing how elegant it sounds, as it has an automatic transmission, it's almost surreal. I decided to take a break, recharge the battery and enjoy a ride on my motorbike. I came back and tested it, yes it sounded great..for a moment, then sputters, a "sudden death" thing where it dies at 2000 a rpm or anything and just boggs all the way down. So what did I do Unicorn?? I moved it in the driveway uphill and .... dead, dead dead. Zero pressure to the pump. Plugged in the jump tester/wire, pump primes and primes...ZERO pressure to the pump. The car is in a nose-up attitude. It wont budge! I switch to neutral, roll the car back, it gets horizontal.. I key it in and it starts like nothing. No what? And I said that aloud too!

Im a darn good technician, but this is like detecting a minuscule tumor in a giant body, with no records available and all kinds of possible culprits.

I could say that fuel pup operation and voltage fluctuation are due to a slightly discharged battery and the power demands of thw 2 fans on idle. With all this, *I think* I can put it back together and..... sell it for parts? Im doubting it will run propertly, perhaps the tank is badly clogged, perhaps the knock sensor is wrecking havoc with altitude issues, maybe the turbo pressure switch yells at the ECU..maybe maybe..

Pictures:

First and second, cleaning a grounding point under the carpet. I thought "hey why not", and "who knows", no changes, just something well done.

Third picture shows the fuel pump wires under the back seat, there is a yellow wire spliced-cut into the negative lead coming from the ECU, courtesy of a previous troubleshooter, that same wire has a mesh exposed higher up, courtesy of the same guy, it is here where I tested that mesh connected to that negative lead to the pump, not to chassis. 

Fourth the last pic shows how that wire was cut to be inspected by that same someone..

Fifth, just a visual explanation of that mess 

 

 

 

 

 

Edited February 2, 2021 by davepak
Content added

[davepak]

6 hours ago, idosubaru said:

Are you ready to sell me this thing yet?   It's probably my favorite XT color!!!!  HAHAHA

Hahaha, I would, but shipping it back to the US?? I don't think is worth it. 

Oh, that is a custom color, it was Subaru Burgundy when stock,  I painted it once in that color, and again in the current color, (hush hush it's a Mazda "purple" color **smirk**) 

[davepak]

6 hours ago, subaru1988 said:

This XT issue is beyond my current Subaru pay grade  , but that being said, it's my general understanding the total voltage drop on positive and negative sides of an electrical fuel pump should be less than a total of 1.0V (.5 for posit side +.5 for negative side). Your numbers show a total voltage drop of 1.5V when you add both together. If a SUbaru is different for some reason, I'm sure someone will correct me, and my apologies.

One would think .36 in that one circuit wouldn't be much, but maybe that seemingly small amount is translating to a voltage loss that is causing issues above idle.

I respect you really getting into the weeds with this, and not just throwing parts at it. What you're doing is real troubleshooting; plus it's cheaper in the end when you figure it out

Thanks a lot for the words of support! I have realized that the 2 fans I have now for the car are consuming a lot of power, reducing the available power to the fuel pump. At least there was no voltage drop due to anything else

[davepak]

6 hours ago, idosubaru said:

Check this out - a guy investigating EA82 turbo and nonturbo ECU differences, though they aren't XT specific but he mentions some very interesting stuff - although keep in mind he's from australia and they're models differ slightly in offerings - they get stuff for a few years after it's discontinued here, etc.  but otherwise it's all the same:

There's the "second board" - what does that do and if the wiring harness pins are there in the body - what are they seeing - nothing because it doesn't exist or somethign else? 

He mentions the additional 84-86 turbo sensors - one impacting fuel maps??  maybe that's freaking things out? 

 

 

Ive checked this one out, maybe that knock sensor unit has somehing else to do with the bad performance of this unicorn..

[davepak]

6 hours ago, idosubaru said:

I'll try to dig up the FSM and see if I made any notes on those circuit differences. 

One was like a pressure sensor or something...probably for the turbo..again from memory??  they weren't big ticket items - all the main things were the same. 

One difference for mine was that it was a 1987.5 turbo - which was an oddball in a couple ways and is often called "the unicorn", though mostly for aesthetic reasons. 

Pressure switch for TURBO and vacuum switch for naturally aspirated.. Why Subaru, why? 

[davepak]

6 hours ago, idosubaru said:

mine had a blown turbo and engine when i got it - so it had sat for an unknown length of time and has low miles (suggesting it sat for awhile).  another coincidence. 

It's a been a few years since I even tried to look at mine but I do recall like 3 differences when comparing the FSM (Subaru) wiring diagrams from the turbo to the non turbo. 

Also - I even swapped 4 cylinder ECU into an XT6 (6 cylinder XT) and the thing started and ran...terribly and not drivable - but it ran.  So yeah the wiring is "just close" enough on these to do something, but I wonder if something isnt' quite lined up.  

 

*** wait - unfortunately it was 8-10 years ago and I don't recall but it might have been due to my wiring and temporary set up rather than causing an issue with the vehicle.  i had run the wire right through the center console (probably so the switch was close to the parking brake maybe?) and it got hot right there...which was fortunate i knew about it right away but burning carpet is deadly poisonous so a little sketchy!  anyway - i don't know if that was my mistake or doing that messed with the circuit?

if the ECU is supposed to always have power - then it shouldn't matter too much.  so maybe it's still an option? 

Maybe you could try an entirely dedicated circuit - ground one wire to the vehicle and just connect a fused 12 volts straight from the battery.  Then you wouldn't have to worry about damaging the ECU.  Don't even plug it in or connect and just leave the ECU dangling....though it might need a reference signal or that circuit completed, dunno?  

My dad reckoned that a problem with the wiring might have been the culprit back then. This car sat for a while while!  It has about 100 000 miles..like really? this car did not roll! Most likely the TURBO died and from there all died. Too many sensors giving readings to  the ECU, too many no no no, the ECU is overwhelmed. Performance really drops, way to many compensations..nah..really a recipe for disaster..

[davepak]

On 1/15/2021 at 10:00 PM, idosubaru said:

In addition to the pump - Maybe the fuel pressure regulator as well. Doesn’t it have a vacuum hose - pull the hose and see if it’s wet inside.  

I think SPFI and MPFI pumps are interchangeable if not identical. Like 30+ psi.  

The carbbed engine pumps are much lower fuel pressure.

Ive gone through 3-4 EA used pumps trying to get a good one.  They don’t seem to be aging well when unused, so if it sat for any period of time...and maybe even if it didn’t, it’s suspect. 

This is an area I haven't worked much on, but I had bought an aftermarket fuel pump and an adjustable pressure regulator, the plan is to fit both of them and see if this solves this hesitation problem. 

What I've noticed is that the car is working smooth and at some point when hitting the gas it sputters and it "drowns" so I have to stop the car, keep the gas until it picks up again, as if it had a carbbed engine and there was dirt that needed to be passed through.. @idosubaruyou mentioned to check if the vacuum hose was wet.. Meaning "fuel wet" where the pressure regulator might be faulty? 

 

Edited February 2, 2021 by davepak
content cleared

[davepak]

Just now, davepak said:

This is an area I haven't worked much on, but I had bought an aftermarket fuel pump and an adjustable pressure regulator, the plan is to fit both of them and see if this solves this hesitation problem. 

What I've noticed is that the car is working smooth and at some point when hitting the gas it sputters and it "drowns" so I have to stop the car, keep the gas until it picks up again, as if it had a carbbed engine and there was dirt that needed to be passed through.. @idosubaruyou mentioned to check if the vacuum hose was wet.. Meaning "fuel wet" where the pressure regulator might be faulty? 

Hard to see, but this is the infamous ECU, and the wiring to the fuel pump. If you can... notice the  (- - - - - - - - - - - - - - - - - - -) type of line that signifies the mesh from the shielded wire that goes to the negative lead of the fuel pump together with the actual grounding control wire just next to it.

[Rampage]

With the negative pump wire being shielded with the wire mesh makes me wonder if the ECU is using PWM (pulse width modulation) to control the ground for the pump. The positive should be steady voltage from the relay. By varying the negative pump wire to ground it will vary the speed of the fuel pump motor thereby controlling fuel pressure.

If they used a simple voltage regulator on the negative it would not have to be shielded.

It would take a scope to see which type it is.

Ask your dad about PWM.

ECU Input signals to control that, TPS and fuel pressure sensor comes to mind. Hopefully someone knows.

[idosubaru]

10 hours ago, davepak said:

, it is amazing how elegant it sounds, as it has an automatic transmission, it's almost surreal. I decided to take a break, recharge the battery and enjoy a ride on my motorbike. I came back and tested it, yes it sounded great..for a moment, then sputters, a "sudden death" thing where it dies at 2000 a rpm or anything and just boggs all the way down. So what did I do Unicorn?? I moved it in the driveway uphill and .... dead, dead dead. Zero pressure to the pump.

If the fuel tank is clogged or fuel has debris floating in it - could that shift around as the car is angled/elevated/driven?  probably not but?  Oddly I’ve seen people have rusty tanks or have them replaced/redone but I’ve never seen them discuss what symptoms they have.

The stock pumps have socks on the intake side to prevent debris from getting into the pump. 

The do they run with the knock sensor disconnected?  Disconnect it, and see what happens? Although I think you’ve already addressed that. 

[idosubaru]

Time to just throw a carb intake on it and wash your hands of this mess?

[el_freddo]

2 minutes ago, idosubaru said:

Time to just throw a carb intake on it and wash your hands of this mess?

Need to swap heads for that. The NA MPFI runs the same dual port heads as the MPFI turbo. 

Cheers 

Bennie

[davepak]

3 hours ago, Rampage said:

With the negative pump wire being shielded with the wire mesh makes me wonder if the ECU is using PWM (pulse width modulation) to control the ground for the pump. The positive should be steady voltage from the relay. By varying the negative pump wire to ground it will vary the speed of the fuel pump motor thereby controlling fuel pressure.

If they used a simple voltage regulator on the negative it would not have to be shielded.

It would take a scope to see which type it is.

Ask your dad about PWM.

ECU Input signals to control that, TPS and fuel pressure sensor comes to mind. Hopefully someone knows.

Definetely is PWM. I can see the fuel pumps change in voltage when revving up the engine, which comes from the ECU that way it can send more fuel when needed, but we are talking a small changes in voltage, however I can see those fluctuations, the shielded mes/shielded wire is intended to absorb and discharge electromagnetic noise, and this is done by the ECU

. The reduced voltage at the pump is related to the battery and the alternator struggling to meet the demands of both radiator fans I installed.This car used a fan clutch and an auxiliary fan.. Clearly not intended for 2 fans. Thing is, I couldnt get the fan clutch any more, I actually tried to repair it by injecting thick silicone 5000 into it, it looked like it worked, but it didnt. So I resorted to fit another fan. For practical purposes, I can have it with one fan only and adapt a switch for the second one if needed. When driving, the incoming wind and the higher rpms work together to demand less use of the electric fan.

TPS definetely plays a role here. together with the MAF and O2 sensor, all these are working ( I tested them) and the O2 is new.

[davepak]

23 minutes ago, idosubaru said:

Time to just throw a carb intake on it and wash your hands of this mess?

@idosubaru how many times I have thought of that, but as @el_freddo said, I'd need to swap the heads for that. they come with two openings for the individual injectors. . Oh did I mention that the last injector I haven't replaced is now leaking a bit?  No chance  to have it changed..this car is reaching its end here

 

I think about getting a BRAT maybe..in a distant future.. I just dont like the wagons, they look too "family and kids" type. Ive always liked the coupes, even the sedans. But they are so hard to find... I had 2 wagons years ago!

Edited January 29, 2021 by davepak
content added

[idosubaru]

EA81 wagons are nifty.  After that I’m done with wagons except newer ones.