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symptoms of dead or dying ecu / ecm - 1984 ea81t

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the trouble code light on the front of my 1984 turbo wagon's ecu/ecm stays on, could the computer be failing and/or has failed? 
 
i've done a hard reset by disconnecting the battery and leaving it overnight that way, no change. 
 
the car can be running or with the key in the ON position, the green t-connector connected or not - it doesn't make a difference, the red light on the front of the ecu just stays on. 
 
car runs like crap, idles poorly and has an inconsistent misfire under load. 
 
 
 
 
 

 

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There is a ground on the passenger side of the engine where the intake bolts on. It is for the ECU and tends to corrode. Remove the bolt and ground and clean both along with the intake surface where the bolt goes through. Should get you all cleared up.

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I still have 2 of that ecu left

 

There is a ground on the passenger side of the engine where the intake bolts on. It is for the ECU and tends to corrode. Remove the bolt and ground and clean both along with the intake surface where the bolt goes through. Should get you all cleared up.

 

oh, cool... i'll see if that does the trick, had no idea!

 

at least pulling codes will help me identify what the issue is with the car running like complete crap, i don't think a bad ground connection would be the cause for the car running poorly, do you? 

 

I still have 2 of that ecu left

thanks man, i have a line on a few others if need be.

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oh, cool... i'll see if that does the trick, had no idea!

 

at least pulling codes will help me identify what the issue is with the car running like complete crap, i don't think a bad ground connection would be the cause for the car running poorly, do you? 

 

thanks man, i have a line on a few others if need be.

 

Anything is possible with bad electrical grounds.

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I found a ground above two relays, passenger side engine bay, towards the front of the car from the shock mount/hat... two wires going to it, both black. i pulled and cleaned the connections really well, inspected them well, and reinstalled. 

 

still a no-go. 

 

trouble light blinked code 11, then code 12, then went back to being stuck on. 

 

is there anything else i look for before i buy another ecu to drop in? 

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Nope... The ground I am referring to is where the intake bolts to the head on the passenger side. It is actually on one of the intake mounting bolts. Look again. This ground is most likely causing all your 'false' codes. Once you clean it, you should be fine.

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Nope... The ground I am referring to is where the intake bolts to the head on the passenger side. It is actually on one of the intake mounting bolts. Look again. This ground is most likely causing all your 'false' codes. Once you clean it, you should be fine.

 

ohhhhh, gotcha. 

 

i've been down in that area a lot lately, noticed some oil buildup/blow-by under the intake, good call. 

 

i'll dig around this afternoon, hopefully i can find the one you're talking about. hahaha!

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The single most important wire on that harness is the small shielded one that gos to - side of coil this is tach signal to ecu tell it what to do

 

oh, that wire is definitely frayed/ugly/beaten up. that's probably the culprit right there. 

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I found that ground, cleaned it up really well and have my fingers crossed.

 

I also noticed the - side wires on the coil were all beat up, barely making contact with the coil post.

 

Between those two things I'm hoping that will do the trick.

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negative. 

 

replaced the contacts/loop connectors on the - side of the coil. no change.

 

the ECU's trouble code light is also still stuck on. 

 

does anyone have a diagram of all the grounding locations for an ea81t by any chance?

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On my car and in the 84 FSM,ECU control ground is at the centre of the intake about 2 inches in front of the "B" in TURBO.

ECU drive is grounded thru the body ground connection near the battery and the ground post buried "under" the fusebox,AFAIK.

 

I doubt a bad ground is causing the light to stay on,but,worth checking.

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.

 

I recently had trouble w/a loose ECU plug.

Barely ran,had an airflow meter code and 30 volts AC! at the battery.All because of a loose plug.

 

The oil buildup/blow-by under the intake thing,makes it sound like you have a vacuum/boost leak as well.

You may want to check the air relief valve assy.

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On my car and in the 84 FSM,ECU control ground is at the centre of the intake about 2 inches in front of the "B" in TURBO.

ECU drive is grounded thru the body ground connection near the battery and the ground post buried "under" the fusebox,AFAIK.

 

I doubt a bad ground is causing the light to stay on,but,worth checking.

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.

 

I recently had trouble w/a loose ECU plug.

Barely ran,had an airflow meter code and 30 volts AC! at the battery.All because of a loose plug.

 

The oil buildup/blow-by under the intake thing,makes it sound like you have a vacuum/boost leak as well.

You may want to check the air relief valve assy.

 

yeah, that first ground you mentioned is the one i pulled and cleaned really well. 

 

i replaced the battery cables with some big ol 2 or 4 gauge ones just a few months ago (it hasn't been driven since) so i know i'm good there. 

 

testing the ECU plugs seems like a good next step, is that done with my multimeter set to OHMS for resistance or is that a test done for voltage? 

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alright, battery is all charged, grounds are cleaned/checked, started the car up and after sitting for a solid 3-4 months it idle perfectly for 5 minutes. 

 

check engine light is still stuck on, though.

 

:( 

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yeah, that first ground you mentioned is the one i pulled and cleaned really well. 

 

i replaced the battery cables with some big ol 2 or 4 gauge ones just a few months ago (it hasn't been driven since) so i know i'm good there. 

 

testing the ECU plugs seems like a good next step, is that done with my multimeter set to OHMS for resistance or is that a test done for voltage? 

 

So you made a change to the electrical system, didn't drive the car afterwards and then the car wouldn't start?  I would go back and look at your battery cable installation and be sure you got all your connections correct and didn't disturb anything else in the process.

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So you made a change to the electrical system, didn't drive the car afterwards and then the car wouldn't start?  I would go back and look at your battery cable installation and be sure you got all your connections correct and didn't disturb anything else in the process.

 

got it... i had starter issues for a while, then upgraded to a bosch (new) starter and bigger cables, fixed the problem with starting but seemed to start this ECM trouble light issue.

 

hmmmmmmmmmm.......

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nope. :(

 

everything looks fine (ground cable to engine, cables to starter, etc.) there. 

 

i wonder if it's time that i suck it up and buy a new ECU/ECM. 

 

does anyone have one they'd let me borrow? i'll pay for shipping if someone wants to send me one to test in my car.  :P

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I'll send you one for cost of shipping to try, if it fixes it you can pay the remainder of what we had agreed on for the ecu.

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I'll send you one for cost of shipping to try, if it fixes it you can pay the remainder of what we had agreed on for the ecu.

 

perfect, that sounds good man, i appreciate it. 

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Especially when older Connectors with poor mechanical or Electrical connections as well as Earth connections are responsible for the majority of so called ECU issues.

 

Self Diagnosis and operation of any Electrical or Electronic control system relies on signals operating within set voltage levels,Corrosion and poor Earth's resulting in Voltage drops will trigger fault codes and poor running.

 

We also have to contend with bad connectivity on the actual circuit boards known as a Dry joint when soldered, then of course components themselves can fail as an assembly or simply something like a Diode, Resistor or other Electronic part within the Module itself.

 

All Diagnosis rely's on testing for either Bad or non existent  Earth's and correct voltage supply or outputs.

 

Hence why some of the more clued up board members correctly state did the problem occur after you did something that may have disturbed the status of the System ,It does not even have to be something you did but can be as simple as some wires you disturbed in the process of doing something else.

 

Get a Multi Meter and learn how to check not just Voltages but using the Ohm Meter aspect of the Meter as well as that is how you measure resistance,As an example any length of wire should read no more than 1/2 an Ohm resistance for trouble free operation.

Simple checking requires connecting the Positive and Negative connectors of the Meter when set to the Ohm Meter range and reading any length of wiring or connector for resistance readings, Many Components are also checked with the Ohm meter such as Air temp and Water Temp Sensors, Ignition Coils and Pickup Coils, Injectors etc so a Multi Meter is a cheap and vital part of any self maintenance Owners Tool kit.

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From what I have read,some Nissan ECUs(also hitachi made) will hold the ECU light on steady to indicate that they are in "ECU limp mode"(as opposed to garden variety sensor failure limp mode).Maybe ours are similar.

 

As a last resort,I would open it up to resolder everything I could,hoping trouble is due to a poor connection.

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Especially when older Connectors with poor mechanical or Electrical connections as well as Earth connections are responsible for the majority of so called ECU issues.

 

Self Diagnosis and operation of any Electrical or Electronic control system relies on signals operating within set voltage levels,Corrosion and poor Earth's resulting in Voltage drops will trigger fault codes and poor running.

 

We also have to contend with bad connectivity on the actual circuit boards known as a Dry joint when soldered, then of course components themselves can fail as an assembly or simply something like a Diode, Resistor or other Electronic part within the Module itself.

 

All Diagnosis rely's on testing for either Bad or non existent  Earth's and correct voltage supply or outputs.

 

Hence why some of the more clued up board members correctly state did the problem occur after you did something that may have disturbed the status of the System ,It does not even have to be something you did but can be as simple as some wires you disturbed in the process of doing something else.

 

Get a Multi Meter and learn how to check not just Voltages but using the Ohm Meter aspect of the Meter as well as that is how you measure resistance,As an example any length of wire should read no more than 1/2 an Ohm resistance for trouble free operation.

Simple checking requires connecting the Positive and Negative connectors of the Meter when set to the Ohm Meter range and reading any length of wiring or connector for resistance readings, Many Components are also checked with the Ohm meter such as Air temp and Water Temp Sensors, Ignition Coils and Pickup Coils, Injectors etc so a Multi Meter is a cheap and vital part of any self maintenance Owners Tool kit.

thanks for the reply, home electrical is my thing but car electrical seems so much more confusing. i have a multimeter and know how to use it, understand electrical theory but struggle when i'm poking and prodding around under the hood. 

 

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

 

thanks!

 

From what I have read,some Nissan ECUs(also hitachi made) will hold the ECU light on steady to indicate that they are in "ECU limp mode"(as opposed to garden variety sensor failure limp mode).Maybe ours are similar.

 

As a last resort,I would open it up to resolder everything I could,hoping trouble is due to a poor connection.

that's what i've been thinking and the reason i'm hunting down a backup ecm to test. i cracked the case a few weeks ago and checked out the connections, everything looked fine but who knows? 

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