Hello, I bought a 2000 Civic LX that wouldn't start. Previous owner replaced fuel pump, distributor, main relay and ECU allegedly trying to get it to start. I brought it home and replaced the fuel filter and it started after a few cranks, drove it around the block. Next day i go to start it and it starts and then starts to cut out and then dies. Now fuel pump won't prime and can't connect my OBD2 Scanner to the ECU.

Main relay wasn't clicking when turning key, i replaced that. Now it is clicking but still no fuel pump priming and no CEL for 2 seconds when turning key to on like it is supposed to, only battery and oil lights on. I did all the checks from the service manual including checking visually all fuses and with a multimeter all relevant fuses. I got to the part of service manual where i need to check power to B1 and B9 ECU pins and voltage is less than 0.1V and drops to 0 with ignition on. When that connector is unplugged from the ECU i get battery voltage from that connector on the main relay to ground. I thought i had a short in wires from Main Relay to ECU B1/B9 so i unpinned it from ECU and jumped it straight from the Main Relay.

Does this point to ECU being bad and having a short or what am i missing?

Any help is appreciated, just wanting some other thoughts before I buy another ECU.

Thanks!
Brendan

 

If battery voltage returns to B1 and B9 when the ECU plug is removed from the ECU, then you either have a bad ECU or a bad ground for the ECU.

 

Awesome thanks for confirming. I checked ground pins and all have continuity to chassis so I will try replacing the ECU.

 

Ah, it's the fuel pump circuit in the ecu. It's a cheap fix if you can solder, or know someone.

https://www.homemadeturbo.com/engine-management-10/how-repair-obd1-honda-ecus-98549/
https://www.google.com/search?q=TA8903SN+honda+ecu

You need this chip: TA8903SN

https://www.ebay.com/sch/i.html?_nkw=TA8903SN

I have some on hand, if you feel like you want to do the repair, $10/each shipped anywhere in USA. Just message me.

All these ECUs are old, make sure the capacitors have been replaced too.

 

Good info, it's been a few years since I've done any circuit board soldering but I'm sure I could manage.

I already bought an ebay "tested good" used ECU but if I have any issues with it I will try resoldering the circuit since who knows what this used ecu has been through.

Thanks.

 

Used ecu came in, plugged it in and still nothing. Starting to doubt it the ECU, maybe I checked the grounds wrong?
Running out of ideas and patience on this car.

 

I tested grounds by checking continuity from back of ecu pins to chassis metal and all were OK. Is there a better way to check them?

 

I hope this helps! Sorry pages out of order

 

Thanks yeah this is what I used and I got to the point where B1 and B9 voltage is tested and there's no voltage when connector is plugged into the ECU but there's voltage when it's not plugged in. There's no short from relay to connector and relay is working.

 

Was cleaning grounds and checking connections to the under hood fuse block and found the culprits. Blu/white wire was taped together and came a part and black/white wire was holding on by a thread.

 

Great find. Well done. Thank you for the update... posting solutions really helps future searchers.