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Failed ECU....93 Leg OBD I ?

CEL flashing ECU fail OBD I Alt issue Bad ALT Carquest ALT

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23 replies to this topic

#1 Gloyale

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Posted 23 March 2013 - 12:57 PM

So I encountered a weird issue with a 93 Leg the other day.

 

First encounter.

 

Won't start, voltage kinda low, but engine cranks fine. (brand new battery and alt)  HAs the "hollow" cranking sound of a timing belt off a few teeth.  Reset belt, it was 1 tooth off, probably installed wrong, not slipped......not the problem.

 

Hmmm......I check electrical a bit.  Turn key on.  CEL lights for 1/2 sec. then goes out.  Will not go into test or read mode.

 

Swap Ig. relay, no change,  Clean connection of Fusible link supplying voltage to the IG. relay, no change.  Battery starts getting really low, so we hook up cables.

 

Let it charge for a while.  Try again, now CEL lights, almost steady....or at least more so.  But still is blinking on/off randomnly (not in test mode, not code flashes, I know what those are).

 

Try to start......struggles, but eventually catches, and starts.  Now before it started, the cranking sound went back to a normal cachuga-chuga and fired.  Shut it down and try to start again.....now cranks hollow won't start, no CEL again. I think ECU cuts out fuel and spark signal.

 

Try a few more times......Back to sounding good, CEL lights (but still is sketching out), Fires up good.  Has fired up each time since.

 

My question is, has anyone seen an ECU fail like this.  I've seen them fail to light the CEL at all, but never seen it trip out like this.  Going to try a new ECU in the car and see what we get today.  I'll take video of the CEL.

 

Just thought I'd ask the community.  Thanks.


Edited by Gloyale, 28 March 2013 - 12:05 PM.


#2 Fairtax4me

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Posted 23 March 2013 - 03:10 PM

Check ground connections for the ECU. You might also unplug the ECU connector(s) and reconnect in case there is a poor contact. Also unplug and clean the harness connectors on the bellhousing.

#3 Cougar

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Posted 23 March 2013 - 07:13 PM

Before calling the ECU bad I suggest you make sure all power connections into the ECU are ok. There may be a intermittent relay problem that supplies power to the ECU, like the ignition or main relay.



#4 Gloyale

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Posted 23 March 2013 - 09:53 PM

Update.  Swapped ECU today, same results. 

 

Today, I in a quieter location, I was able to hear the fuel pump cycle each time the light flashed off.  Seemed as if the ECU was reseting its self repeatedly, and doing the intial startup fuel cycle each time.

 

I checked all pins at the ECU and relay for proper voltage, all seems good.  I strip these harnesses for swaps all the time, so I know each wire and where they go and all check out good.

 

Dang, what else is tied into the ECU and IG. relay trigger????  THE YELLOW ALTERNATOR WIRE!!! 

 

I unplug the ALT connector (leaveing main wire bloted on) BAM!  Check engine light comes on once with key on, fuel pump cylces only once, and when it's started, it fires quicker and runs better. 

 

So now suspects are the brand new ALT, or on an off chance, the little blocking diode between the Green ECU/IG trigger wire, and the yellow IG. on wire to ALT.

 

Going to swap a known good alt in tommorow, and see if it does the same thing...if so, diode is likely culprit and I'll dig it out of the harnss and swap it. 

 

If it works with good ALT, then back to the store with reciept to get replacement/exchange.

 

I'm working on uploading video of the oddly flashing CEL. 



#5 Gloyale

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Posted 24 March 2013 - 02:36 AM

Video of the CEL flashing abnormally.  Fuel pump cycles in time with each "off" cycle of the light. sound didn't really work?

 



#6 Fairtax4me

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Posted 24 March 2013 - 10:50 AM

Oddness! Fits perfectly into the strange electrical problem category.

#7 mikaleda

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Posted 24 March 2013 - 11:19 AM

Did you check the main grounds to your ecu? Kinda looks like its not getting grounded good enough.

#8 Gloyale

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Posted 24 March 2013 - 06:39 PM

Did you check the main grounds to your ecu? Kinda looks like its not getting grounded good enough.

 

Yeah, I pulled, cleaned and reinstalled the groungding bolt on the intake (behind and under #4 fuel injector)

 

It's definately the ALT.  Or at least the alt cicuit. Unplugg it, all is normal, plug it in, the CEL flashes and the fuel pump cycles randomly, unplug it, backj to normal.


Edited by Gloyale, 28 March 2013 - 12:02 PM.


#9 Cougar

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Posted 24 March 2013 - 09:56 PM

It's a good thing a person with your savy got this problem Gloyle. This particular trouble could caused some other less skilled techs some real heart ache.

 

It sounds to me that the alternator may have been back feeding some AC voltage on the field lead. I suppose the AC could have been on the output instead, and pulling the rear connector disabled the alternator and cleared the problem. 



#10 johnceggleston

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Posted 25 March 2013 - 12:25 PM

where did you get the ALT?



#11 Gloyale

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Posted 28 March 2013 - 12:00 PM

Update.

 

Alts came from Carquest.  Reman  $135 dollars.

 

3 Alts tried from same source, all same results.

 

tried 2 known good alts from my stash, normal operation.

 

So beware........there is a batch of bad alts out there.  They will charge the car, but will trip out the ECU, and make starting difficult or cause no start at all because the ECU is trying to reset constantly while you are cranking til it finally catches and runs.

 

Cougar, I thought AC volts too, but it does it with key on/eng off.  So how coudl there be any A/C? I discovered disconnecting the BATTERY wire at the Alt stopped the issue too, so there is a connection from the big output post, and the IG. on yellow wire.   Faulty design of the aftermarket "sensing" circuit?

 

I am thinking more like a diode or a fault in the aftermarket



#12 Cougar

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Posted 28 March 2013 - 08:20 PM

You're right of course about the AC can't happen if the alternator isn't turning. I'm a little stumped on how to explain what happened in this case. Very good sluthing there Gloyale.



#13 coroboto

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Posted 29 March 2013 - 08:48 PM

I am researching on this site for my brothers 95legacy. He has this issue where the car will kill the engine at random times. The stereo stays on when the engine shuts off driving down the road... Does this sound like the faulty alternator? The car after warm will die at idle also but not when it is cold. Does anyone know of a post that shows how to ground out the OBDI sensor so the check engine light will flash codes (and what those flashes mean)?

#14 mikaleda

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Posted 29 March 2013 - 09:01 PM

I am researching on this site for my brothers 95legacy. He has this issue where the car will kill the engine at random times. The stereo stays on when the engine shuts off driving down the road... Does this sound like the faulty alternator? The car after warm will die at idle also but not when it is cold. Does anyone know of a post that shows how to ground out the OBDI sensor so the check engine light will flash codes (and what those flashes mean)?

Try using google to search this site, it works better than the search bar. Just type in :link ultimatesubaru.org after your keywords and it will give you results from this site, I know there is info on here about what your asking, just keep searching

Try searching coolant temp sensor ;)
Also new gen FAQ sticky has the info on the obd1 codes first page.

Edited by mikaleda, 29 March 2013 - 09:04 PM.


#15 coroboto

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Posted 29 March 2013 - 09:09 PM

Sweet! Thanks for the advice!

#16 Cougar

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Posted 29 March 2013 - 09:49 PM

I am researching on this site for my brothers 95legacy. He has this issue where the car will kill the engine at random times. The stereo stays on when the engine shuts off driving down the road... Does this sound like the faulty alternator? The car after warm will die at idle also but not when it is cold. Does anyone know of a post that shows how to ground out the OBDI sensor so the check engine light will flash codes (and what those flashes mean)?

Here is a link to a site that can help you.

 

http://www.troublecodes.net/Subaru/



#17 Fairtax4me

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Posted 29 March 2013 - 11:51 PM

I am researching on this site for my brothers 95legacy. He has this issue where the car will kill the engine at random times. The stereo stays on when the engine shuts off driving down the road... Does this sound like the faulty alternator? The car after warm will die at idle also but not when it is cold. Does anyone know of a post that shows how to ground out the OBDI sensor so the check engine light will flash codes (and what those flashes mean)?


95 is OBD2 and you need a scanner to read the codes. Most auto parts stores will read them for free.

Stalling while warm is usually sensor related. Crank or cam position sensor, or possibly a sticking Idle control valve. Have had a MAF sensor cause the engine to die at random while driving as well, but it also caused the same problem when the engine was cold.

Edited by Fairtax4me, 30 March 2013 - 12:22 AM.


#18 Olnick

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Posted 29 March 2013 - 11:58 PM

A '95 Legacy is OBD2 . . . or did I miss something here?



#19 ivans imports

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Posted 30 March 2013 - 10:31 AM

Loss of ig power supply check fuse box under hood conections black fuseabble link and ig fuses and links + battery power supply very mutch doubt ecu problem Check voltage at brown realy power supply see if it drops out when check engine light gos out



#20 mikaleda

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Posted 30 March 2013 - 10:41 AM

A '95 Legacy is OBD2 . . . or did I miss something here?


A few cars got obdII in 95-96 it wasn't until 97 that it became mainstream. An easy way to tell is if there is a diagnostic plug in the dash.

#21 Gloyale

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Posted 30 March 2013 - 12:31 PM

He has this issue where the car will kill the engine at random times. The stereo stays on when the engine shuts off driving down the road... Does this sound like the faulty alternator?

 

95 they changesd thte ALT circuit.  I don't think the yellow IG. wire is present on the 95-99 Alts.

 

To get codes from your car, look for the 2 Green connectors, and the 2 black connectors, under the dash.  OBD I or II will have these.  Black connectors= read memeory, Green connectors= Test mode........both toghether, = clear mode.



#22 Olnick

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Posted 30 March 2013 - 01:32 PM

A few cars got obdII in 95-96 it wasn't until 97 that it became mainstream. An easy way to tell is if there is a diagnostic plug in the dash.

 

Beginning in 1996 OBD II was mandatory on all cars sold in the US.  Subaru, along with some other manufacturers, adopted OBD II a year early, in 1995.  I've heard stories that some '95 Subarus didn't have it but I've never seen one personally.

 

You are right, though--the diagnostic plug on the dash is the simplest "proof."



#23 johnceggleston

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Posted 30 March 2013 - 01:47 PM

i think the 95 lego is obd2, but the 95 impreza is obd1.



#24 mikaleda

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Posted 31 March 2013 - 10:33 AM

Beginning in 1996 OBD II was mandatory on all cars sold in the US. Subaru, along with some other manufacturers, adopted OBD II a year early, in 1995. I've heard stories that some '95 Subarus didn't have it but I've never seen one personally.

You are right, though--the diagnostic plug on the dash is the simplest "proof."

I was just reapeating what I read n the book I got with my centech scanner, I'm not surprised that its off a year.

Edited by mikaleda, 31 March 2013 - 10:34 AM.





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