How can you test an ECU for a 1993 Civic ?

[some_other_dave]

I believe that the Main Relay (on earlier Civics, it was next to the driver's left knee on the side wall of the cockpit) powers the ECU. It is not uncommon for the solder joints on the relay's circuit board to crack and fail. You might consider pulling it out and inspecting or just plain re-soldering the pins.

-soD

[Cd]

I plan on taking my car into a shop possibly tomorrow and paying several hundred dollars to have them fix it, but If you guys can think of anything by reading this that stands out as needing to be checked, im all ears.

Don't waste your time though. There is a lot of reading and since its a random electrical problem, a lot could be replaced an the problem would still remain.


O.K. lets see if i can post a short summary of my symptoms and what i have done to my car to fix the problem :

SYMPTOMS :

Fuel pump fails to prime when i turn the key.

I can pull off the main relay from its harness and jump the connection. The fuel pump turns on and remains running when i turn the key.

( would it be possible to rig something up to where i could bypass the main relay and use a manual on off switch to turn the fuel pump on ? )

REPLACED OR TESTED PARTS :

* Battery is new and has new cables

* All fuses, both under dash and under hood fuses are good.

* Engine grounds look good - I even added a wire going from the engine to the body.

* Main Relay tests O.K. for continuity ( all points )
I have both my original and a new aftermarket - both check fine with a bench test.

* No trouble codes

* No stored trouble codes

* Ignition switch is good

* ignition switch key cylinder is good

* Installed new fuel pump

* Fuel pump works ( primes and remains running ) when i jump main relay and turn key.


* Amperage is lost somewhere between the Main Relay and the ECU apparently






Here is my post from several months ago when i thought i had a bad fuel pump.
It's a full five pages, but doesn't really relate to the current problem which is electrical.

http://ecomodder.com/forum/showthrea...ice-16146.html

Here is my post from the Civic Forums page . Lot's of good advice from one helpful guy on that site .

http://www.civicforums.com/forums/23...s-humid-3.html

Lots and lots of reading.

[Fosters80]

Its been a while since I had one of these, and I'm not able to get at my resources at the moment, but I seem to remember the 93 DX being prone to ECU failure. Try removing it and taking the cover off the ECU, there was a spot on the board that would be noticeably burnt. Also, and I apologize if you already mentioned this, if the CEL is on but no code is stored, it's bad.

There is no bench test that I am aware of. The dealer uses an inline breakout box to test the circuits in conjunction with the service manual.

Good luck!

[drmiller100]

why don't you just try a new main relay?

my kid had a 91 crx we just sold.. it had a similar problem. If you used a test light to test the wires, one of them glowed dimly, and then the relay worked correctly. swapping the main relay it still did the same thing.

I got pissed, and added a ground wire to that terminal in addition to whatever else it went to.

worked perfect ever since.

[hamsterpower]

civic dx ecu 93 | eBay

93 civic dx ecu from Ebay, many at $50. Avoid JDM ecus for 2 reasons- 100 octain fuels and no obd in some. If you are lucky and have a helpful dealer (I know, right...) they will sometimes do just the diagnostic and help you find the problem to fix elsewhere.

[Cd]

Originally Posted by hamsterpower

civic dx ecu 93 | eBay

93 civic dx ecu from Ebay, many at $50. Avoid JDM ecus for 2 reasons- 100 octain fuels and no obd in some. If you are lucky and have a helpful dealer (I know, right...) they will sometimes do just the diagnostic and help you find the problem to fix elsewhere.

Thanks ! I should have checked Ebay first. ( Dooop ! Why didn't I do that first ! )

I purchased the ECU you linked to. Hopefully it's a good one.

I went ahead and did some testing with my ECU. I slit the wiring that leads back to the fuel pump and ends up at the ECU. I slit the wires about an inch away from the ECU harness.

When I unplugged the Main Relay and jumped the Main Relay harness, the fuel pump kicked on but there was no current at the wiring to the ECU.

When i plugged the Main Relay back in, there was a full 12 Amps of current.
( both had 12 Amps ... or just shy of it due to a tired battery )

This would seem to indicate that the current makes it to the fuel pump if it is routed around the ECU by jumping it as i did right ?

I'm assuming this indicates a bad ECU ???

We shall see if this fixes the problem.

The board looks to be in perfect condition, but there is a small spot that looks suspicious. I have seen images of ECUs that short out at this exact area , so i was suspicious.

I plugged it back in and tested it - dead. Soldered the area and tested again - dead.

oh well.

[Cd]

By the way, the area in the above images looks burt, but i scraped at it and it appears to be something like glue.
They was a shiny silver bead of solder underneath.

[some_other_dave]

The "glue" could be stuff that used to be inside that silver/purple can. Some old electrical components can fail that way. (Not sure about early-90s vintage stuff, but...)

-soD

[drmiller100]

it is RARE an ecu actually goes bad.

it sure would be easy to hook a separate fuel pump relay to the ignition circuit.

[Cd]

Originally Posted by drmiller100

it is RARE an ecu actually goes bad.

it sure would be easy to hook a separate fuel pump relay to the ignition circuit.

OK - You have my attention . That sounds like something I should try for sure . How do I go about doing this ?


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BTW , I love your project car. You do amazing work. Really looking forward to seeing that car on the road.