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symptoms of dead or dying ecu / ecm - 1984 ea81t


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88 replies to this topic

#26 naru

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Posted 01 October 2013 - 10:50 AM

another member mentioned checking the plugs at the ecu/ecm, how would that be done? car running or not? ohms or volts? 

Either ohms or volts.

Voltage measurements on an operating circuit can be more enlightening.Ohms are OK

 

For ohms:

Pull the ECU plug.

One lead on battery negative,the other on the relevent ground pin.

Resistance should be very low.Maybe 0.1 ohm or so.

You can use the yellow and red "check connectors" near the ECU instead of pulling the plug,but,I would not bother.

 

For volts:

Key on.Car running would be desirable.

One lead on battery negative,the other at each check connector ground pin or backprobing the ECU plug.

Voltage should not be more than a tenth or two.I would quickly check for AC voltage while the leads are hooked up.

 

Check power on pin 24 or the check connector similarly.

 

Check for good pin engagement while the plug is off.



#27 lastchance

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Posted 01 October 2013 - 11:46 AM

Either ohms or volts.

Voltage measurements on an operating circuit can be more enlightening.Ohms are OK

 

For ohms:

Pull the ECU plug.

One lead on battery negative,the other on the relevent ground pin.

Resistance should be very low.Maybe 0.1 ohm or so.

You can use the yellow and red "check connectors" near the ECU instead of pulling the plug,but,I would not bother.

 

For volts:

Key on.Car running would be desirable.

One lead on battery negative,the other at each check connector ground pin or backprobing the ECU plug.

Voltage should not be more than a tenth or two.I would quickly check for AC voltage while the leads are hooked up.

 

Check power on pin 24 or the check connector similarly.

 

Check for good pin engagement while the plug is off.

 

thanks for the info, i appreciate it.

 

for ohms:


you mentioned -

I would pull the ECU plugs and verify proper grounding between ground pins 5,27,31,32,33 and battery negative.Proper connection too.

5 is the control ground.

Same for power on pin 24.

that's what you're referencing here, right? one lead to battery negative and the other probing each pin, most notably the ones you mentioned above? 

 

for volts:

 

you said - 

 One lead on battery negative,the other at each check connector ground pin or backprobing the ECU plug.

Voltage should not be more than a tenth or two.I would quickly check for AC voltage while the leads are hooked up.

backprobing? is that checking power to the pins with the plug plugged into the ECU, on the "out" side of the plug? 

 

checking voltage at the "check connector ground pin", do you mean the green "T" connector  or something else?

 

thanks again, man, i really appreciate you being patient/awesome.



#28 naru

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Posted 01 October 2013 - 12:27 PM

Yes,one on each ground pin.Other on negative.

Backprobing is what you said.

 

Check connectors are multi pole red and yellow open connectors right beside the green one.

They provide non-intrusive access to the ECU wiring (and other stuff).

Look for a 9 pin yellow,6&9 pin reds.Ground wires are black/red.Power is white/black

 

One more 5 pole brown check connector near the airflow meter Ground is black.



#29 lastchance

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Posted 01 October 2013 - 01:37 PM

Yes,one on each ground pin.Other on negative.

Backprobing is what you said.

 

Check connectors are multi pole red and yellow open connectors right beside the green one.

They provide non-intrusive access to the ECU wiring (and other stuff).

Look for a 9 pin yellow,6&9 pin reds.Ground wires are black/red.Power is white/black

 

One more 5 pole brown check connector near the airflow meter Ground is black.

awesome man, thanks a ton. 

 

i'll report back.



#30 naru

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Posted 01 October 2013 - 03:40 PM

I mispoke.

Make sure the ECU is unplugged w/measuring ground resistances whether you measure at the plug or check connector.



#31 lastchance

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Posted 01 October 2013 - 03:41 PM

got it man, thanks for the clarification. i'm all over it this afternoon.



#32 lastchance

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Posted 01 October 2013 - 08:33 PM

well, i poked and prodded every connector i could find for continuity, definitely found some trouble spots in both ECU plugs plus on the red 9 pin check connector. i also noticed 2 big translucent yellow plugs way back up against the firewall that i poked around in, found an issue or two there, also. 

 

my problem now is figuring out what to do, i have the '83 FSM but not the one that covers the ea81t, so i've got all this continuity data but no pinout to link it up with. bummer.

 

i didn't check for voltage but will in the morning, it was getting dark. 



#33 lastchance

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Posted 01 October 2013 - 08:38 PM

oh, i guess i should note that on the ECM plug towards the front (the one with the female plug, male ends are on the ecm) i was getting a reading of 70.0+ ohms of resistance on the black/red wire (top row, 8th from left) - grounding issue, i assume. 

 

the other plug, closer to the driver, had two pins with poor continuity - 2nd row, far right (18.4 ohms) and the bottom row, third from left - 7.6 ohms. 



#34 turbosubarubrat

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Posted 01 October 2013 - 09:58 PM

Probably not the main problem but the MAF sensor could be dirty so MAF sensor cleaner could help out a lot since that contols the air/fluel mixture. The sensor is where the air cleaner is at, if i remember right you have to take the boot off right next to it and spray at the sensor inside the air cleaner box. I kind of fill your pain with this since i just had to take the dash with the wiring harness out of one of my 83 turbo wagons and do some rewiring to it since the digi-dash shorted out when the previous owner drove it which caught on fire. The tachometer, ecm, plastic pieces  were replaced and some rewiring was done by him but it wasn't running which is why i have it now. Hopefully i get it running this coming saterday or sunday since i've done a bunch of wiring to it by replacing melted plugs, fixxing melted wires, and replacing bad electical components like the ignition ignition plug wires.



#35 lastchance

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Posted 02 October 2013 - 10:59 AM

Probably not the main problem but the MAF sensor could be dirty so MAF sensor cleaner could help out a lot since that contols the air/fluel mixture. The sensor is where the air cleaner is at, if i remember right you have to take the boot off right next to it and spray at the sensor inside the air cleaner box. I kind of fill your pain with this since i just had to take the dash with the wiring harness out of one of my 83 turbo wagons and do some rewiring to it since the digi-dash shorted out when the previous owner drove it which caught on fire. The tachometer, ecm, plastic pieces  were replaced and some rewiring was done by him but it wasn't running which is why i have it now. Hopefully i get it running this coming saterday or sunday since i've done a bunch of wiring to it by replacing melted plugs, fixxing melted wires, and replacing bad electical components like the ignition ignition plug wires.

 

oh, bummer! i'll be sure to get that thing clean, it's something easy i can do while i'm diagnosing these wiring issues. thanks!



#36 naru

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Posted 02 October 2013 - 11:44 AM

9516a4f2.jpg

#37 ivans imports

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Posted 02 October 2013 - 11:49 AM

any luck ?



#38 lastchance

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Posted 02 October 2013 - 07:57 PM

thanks naru!!!

 

i'm working these wiring issues out right now, i noticed my ignition switch wiring was all hacked up from an alarm install by a friend of a friend - sorting that too.

 

i also noticed the air flow meter connector was hacked up and showing crazy high resistance so i'm working that out too.

 

getting somewhere!!! 



#39 lastchance

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Posted 03 October 2013 - 08:51 AM

preliminary findings:

 

15 pin plug - 

 

high resistance on 23 and 29 (AAV and user warning lamp ECS) 18.4 ohms and 7.6 ohms

 

20 pin plug - 

 

high resistance on 18 and 19 (altitude signal and fuel pump relay) 70 ohms (YIKES) and 6.5 ohms

 

all the other pins were showing 0.4 ohms or lower, most at 0.2 or 0.3, that's normal, right?



#40 ivans imports

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Posted 03 October 2013 - 09:41 AM

Well if nothing else your geting smarter on working on it will be very good at it by the time you find the problem



#41 lastchance

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Posted 03 October 2013 - 09:44 AM

Well if nothing else your geting smarter on working on it will be very good at it by the time you find the problem

exactly. this makes me much more confident. 



#42 lastchance

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Posted 04 October 2013 - 08:33 AM

i worked on uninstalling the alarm that's been in the car for over 10 years, cleaned up the ignition wiring, tightened up some other areas, fixed the hack job AFM wiring, retested and am showing much, much, much lower resistance across the coordinating circuits.

 

i should have the ECM on monday to throw in there, we'll see if that fixes the o2 trouble code light, otherwise i'll be slogging through these other continuity issues.

 

on a side note - i started the car after a few hours of cleaning up the wiring and the car ran perfect. haha, weird.



#43 lastchance

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Posted 07 October 2013 - 06:21 PM

a strange turn of events...

 

got an ECM in the mail today, plugged it in and while it'll give me trouble codes (are these stored from the last car the ECM was in?) the car won't start, it just cranks but doesn't turn over. :( 

 

to make sure i hadn't messed something up in the wiring while down there i plugged in the old ECM and the car starts right up, no problems (except the trouble light stays on). 

 

WTH?



#44 naru

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Posted 08 October 2013 - 10:35 AM

What are the new codes?
They will be yours,not from the previous car.

My theory,is that the original ECU was in some kind of CPU limp mode that ignored most of the sensor inputs.New ECU is not,and is looking for missing sensor info.

Was the new ECU a confirmed runner?
Maybe it has a failed fuel pump drive like mine.It will give codes all day long,but,will not drive the fuel pump relay.

#45 lastchance

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Posted 09 October 2013 - 08:59 AM

the ECM came from an established/trusted member but i'll ask him to make sure he knows it came from a running car.

 

i got codes 11, 12 (of course, i know the gig with these two) and also 33, 41 (coolant temp sensor and atmospheric pressure sensor or circuit) 

 

when testing for resistance on the ECM plugs i was getting the following:

15 pin plug - 

 

high resistance on 23 and 29 (AAV and user warning lamp ECS) 18.4 ohms and 7.6 ohms

 

20 pin plug - 

 

high resistance on 18 and 19 (altitude signal and fuel pump relay) 70 ohms (YIKES) and 6.5 ohms

 

could that fuel pump relay with high(ish) resistance be similar to what you mentioned? 

 

the "altitude signal" that showed high resistance, is that the same as the ECM trouble code for atmospheric pressure sensor?

 

thanks again for your help.



#46 ivans imports

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Posted 09 October 2013 - 09:16 AM

new ecu bad ? or wrong year



#47 lastchance

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Posted 09 October 2013 - 09:26 AM

new ecu bad ? or wrong year

 

the part numbers are the same, i verified before i had him send the ecm. 

 

don't know if the new one is bad, the car was definitely dumping fuel/flooding. :/ 



#48 naru

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Posted 09 October 2013 - 11:40 AM

It is not clear to me how you are taking those measurements.
One lead on the unplugged ECU harness and the other on battery negative or.....?

With one lead on harness #23 and the other on negative you are measuring the resistance of the AAV coil in series w/the fuel pump.

Proper way to check resistance for this one is to have the second lead on the blue/green wire at the unplugged AAV connector instead of battery negative.

I would concentrate on finding the cause of codes 33 and 41.
I would measure resistance between harness pin 3 and ground to see what is going on w/the CTS and related wiring.

The atmospheric pressure sensor does indeed generate the altitude signal.
It simply tells the knock control computer to advance ignition timing 5 degrees w/above 1400 metres.
Here is where it gets interesting.
84 ECUs mount the sensor internaly,83s have a sensor mounted external to the ECU.
ECU pinout above is for an 84.I`m not sure how different 83s are.
I`m not sure if an 84 ECU would be compatible w/an 83 car.
However,if your car ran well w/the same part# ECU previously,you should be OK.
I can`t see this code keeping your car from running.5 degree timing error,perhaps.
According to my info 83s are 46089 7110,84s are 46089 7210 or 7320

#49 ivans imports

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Posted 10 October 2013 - 08:31 AM

The light on ecu if i remember right is a o2 moniter light when diagnostic wires are not conected so it does what the o2 does if the light is staying on mabe o2 is shorted out should be of and on slightly flashing



#50 lastchance

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Posted 14 October 2013 - 11:03 AM

It is not clear to me how you are taking those measurements.
One lead on the unplugged ECU harness and the other on battery negative or.....?

With one lead on harness #23 and the other on negative you are measuring the resistance of the AAV coil in series w/the fuel pump.

Proper way to check resistance for this one is to have the second lead on the blue/green wire at the unplugged AAV connector instead of battery negative.

I would concentrate on finding the cause of codes 33 and 41.
I would measure resistance between harness pin 3 and ground to see what is going on w/the CTS and related wiring.

The atmospheric pressure sensor does indeed generate the altitude signal.
It simply tells the knock control computer to advance ignition timing 5 degrees w/above 1400 metres.
Here is where it gets interesting.
84 ECUs mount the sensor internaly,83s have a sensor mounted external to the ECU.
ECU pinout above is for an 84.I`m not sure how different 83s are.
I`m not sure if an 84 ECU would be compatible w/an 83 car.
However,if your car ran well w/the same part# ECU previously,you should be OK.
I can`t see this code keeping your car from running.5 degree timing error,perhaps.
According to my info 83s are 46089 7110,84s are 46089 7210 or 7320

 

this is how i was testing, just as you mentioned with - One lead on the unplugged ECU harness and the other on battery negative

 

i'll check for resistance the way you mentioned (at least to test the AAV, etc.)

 

i'm worried this ECM came from an 83 model car, thus giving me the non-start issue and smell of flooding. i'll check with the guy i'm borrowing it from to see if he knows. 






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