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How to repair a damaged ECU for EA82 (if the fuel pump doesn't run)

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This how-to at least applies to the ECUs of the EA82 engines with MPFI (Turbo and non-Turbo) when the fuel pump doesn't run and the fuel pump, the relay and the cables are OK. But of course I give no warranty that it will solve your problem!

You should only work on electronic devices if you know what you are doing! And please check every other possible malfunction before working on the ECU

 

To describe the back story in some words: I purchased a very cheap 1993 Loyale in summer 2006 which has a damaged ECU because the previous owner somehow managed to confuse the two battery poles. So the the ECU seemed to work but the engine didn't start. After getting the car home with another ECU, I made some research in June 2007 to fix up this damaged ECU. Look at this thread how things proceed: http://www.ultimatesubaru.org/forum/showthread.php?t=76466. It seems that the circuit for powering on the fuel pump is some weak point of the electronic design and seems to fail quite often.

 

If your engine won't start anymore, you can easily check if it's related to the fuel pump: Just put the two green test connectors together and switch on the ignition. The ECU is now in some kind of test mode and it switches the fuel pump continuously on and off in a short intervall. You should easily hear the pump kicking in and out. If you don't hear it, then your start problems are most likely related to the fuel pump (if the starter kicks in at all when you try it). So there are mainly four possibilities:

1. The fuel pump itself is broken

2. The fuel pump relay is broken

3. The electric circuits for the fuel pump are somehow damaged

4. The electronic inside the ECU is damaged.

 

So, if you test or replace the first three points and the fuel pump still doesn't work, then it's most likely a damaged ECU. You can check it by replacing it with a known good one, if the fuel pump then runs, it's the ECU. And this is most likely repairable since the electronic design is from the 80ies and therefore it's very simple and you can fix most things with basic electronic and soldering knowledge.

 

1. You have to open the ECU by removing the eight screws, which most likely are very tight.

 

2. Search for the transistor Q701 (look at the picture above, it's the one with the red circle). Q701 is a preamplifier for Q702 which controls the fuel pump.

 

repair.png

 

3. Check if the transistor Q701 is working. If you know how to do it, just do it, if you don't know, search someone who knows or search the internet for instructions. It's not really difficult if you have a electric meter and some electronic knowledge.

 

4. If the transistor is damaged, replace it. Since this NPN transistor is original a NEC 2SC2719 and this one isn't any more in production, you should use another type with the same ot better technical datas (look at this datasheet for informations about 2SC2719: http://www.datasheetarchive.com/datasheet.php?article=3746501) as replacement. A BD139 will work great and because this is a very common type, it's very cheap (about 50 US Cent in Germany). It's produced by many companies, e.g. TI, STM, Siemens, Motorola, Fairchild and others. Look here for some datasheets of BD139: http://www.alldatasheet.com/view.jsp?Searchword=BD139

 

If the transistor Q701 seems to work, then you could check Q702, but I guess this one won't be damaged that easily. If it's indeed damaged, replace it with a proper type (not BD139!!). If Q701 and Q702 aren't damaged at all, you could have a look at the other electronic components of the fuel pump circuit or just replace the ECU.

 

5. After replacing the transistor, put everything back together and make a test if the fuel pump now works (the green connectors, remember?). If it kicks in and out, disconnect the green connectors and try starting the engine!

 

Congratuluations if it's running now!!!

 

If it's not running, then there is another malfunction, but at least the fuel pump now works again...

 

I attached a ZIP file with all datasheets and the picture.

ECU repair.zip

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