how to test ECU on Honda Civic '89

How can I check that the computer is working? Check engine light is on
while ignition is on and while cranking, but no flashing led on ecu.
I have no spark. all the distributor parts check out ok. Main relay too.
No pulse from ECU.
Fuse to ECU has no current draw on it. I pulled fuse and put an ammeter
across terminals, no current draw!
Anyone have a wiring diagram or a pinout of the ECU?
Thanks Roy

 

Try checking for voltage on the fuse (or the fuse socket, if that is
easier). I'd suspect loss of voltage first.

Mike

 

Yes. I have 12 volts to ground on hot side of fuse and no volts on load
side. ( with fuse pulled)
volts on both sides with fuse in.
I have checked all the simple stuff. I'm into the hard stuff now.
thats why I need a diagram or pinout at ecu.

should ecu flash anything on powerup ,or ignition on, even if ecu is good?
see earlier post "89 civic HB, no spark, not main relay or ignitor"
Roy

 

I don't have the pinout or wiring diagram, but I have a book on checking
codes for 1983-1995 import cars. (It was part of a $35 kit from Checker
Auto, which turns out to be a $30 book, a two dollar generic jumper tool and
a three dollar Toyota jumper tool.)

For the '89 Civic, it confirms you don't need a tool or to do anything
special to see the codes. It says: "Access ECU (located on passenger side
floorboard) by pulling back the carpet. Turn ignition on and observe LED on
ECU for codes. Codes blinked out by LED are separated by two second pause,
then repeated. For example, 2 blinks - two second pause - 2 blinks = code
2." The diagram shows the ECU at the passenger's toes, but it sounds like
you've already gotten that far. When you do get error codes, they are
cleared by removing fuse 30 for 10 seconds.

However, the chart doesn't list a code for "no problem - working okay." I
suppose you could unplug the crank angle sensor connector at the distributor
and you should see a code 8, but if you still don't what does that tell you?

The next thing might be to check each pin on the ECU connector for voltage
with the ignition off, and verify that it goes away when the fuse is pulled.
If you do have that, there should be at least one solid black wire on the
connector (the same connector if there is more than one) and it should ohm
to ground. It's really unusual for an ECU to fail like that unless it got
wet or voltage spiked somehow.

One more thing - are you sure that's the right fuse? 15 amps sounds like a
pretty hefty fuse for the ECU. In the '90-93 Accord it is a 7.5 amp fuse. (I
have a book for those models - in those models the power wire is a
white/yellow wire on pin D1; pin 1 of connector D.) The code book suggests
it is fuse #30 in yours.

Mike

 

Yes. I have 12 volts to ground on hot side of fuse and no volts on load

my
teenage son. I dont own it yet and it is not at my house. So it is not
easy to
work on at his house. I dont want to work TOO hard on "someone elses" car.
Digging thru wire bundles without a drawing would be too involved. He
hasnt
run it in about 6 months but was running when he parked it. He drove it to
work till he took over his wifes car when she got a new one.

The ecu is under passenger carpet. the led is visible thru window but I
have
never seen it flash.
I did remove connector to distributor and cranked car for about
30 seconds. no codes.
I even unplugged connectors to ecu and plugged them back in. Still no
flashes.
The fuse I refered to is under the hood. there are 5 or 6 fuses (15 to 30
amp)
and 3 relay looking devices rated 50 amps or so. They may be some sort of
breaker. It is labeled ECU 15 amp. I havent looked too hard at the fuse
block
under dash.

I tried the local honda dealer for a diagram, but was told to check back
tomorrow when the foreman was in. This dealer, the only one in town, is
known for being customer UNfriendly. So I dont hold out much hope.
Thats why Im trying the net. Always had good results from groups posts.
Roy

 

Ahh.... Somehow it sounds like you might be heading into the darkness if you
do purchase the car.

I checked with my son, who had an '89 Accord. His ECU got wet in a flood and
was damaged - replaced with one from a wrecking yard. He said he didn't
think it produced any codes when it was working normally.

Mike

 

According to the diagram you have three fuses for ECU operation. You
said you have found one faulty. The faulty (15A) fuse goes like this:

Battery--> 15A fuse --> (yel-wht)---> main relay --> (yel-blk)--->ECU

On slots A7 and A6 of ECU connector, look for a tiny printed
number. There should be battery voltage. If not, then power isn't
getting to them. If there is battery voltage then check A9 and A10
(ground.) You should see ground.

Simple way to verify that ECU is working is by observing that the
check engine light comes on then off normally. Cranking more than
30-sec is useless if their is no power to the ECU. [ 88-91 Civic
DX (carb) ]

 

According to the diagram you have three fuses for ECU operation. You
said you have found one faulty, even with the ignition on. The faulty (15A)
fuse goes like this:

Battery--> 15A fuse --> (yel-wht)---> main relay --> (yel-blk)--->ECU

On slots A7 and A6 of ECU connector (look for a tiny printed
number) should have battery voltage. If not, then power isn't
getting to them. If there are battery voltages then check A9 and A10
(ground.) You should see ground.

Simple way to verify that ECU is working is by observing that the
check engine light comes on then off normally. Cranking more than
30-sec is useless if their is no power to the ECU. [ 88-91 Civic
DX (carb) schematic from Chilton p. 6-90 or Helm]

 

Found the problem.

The dealer came thru with a wiring diagram for an '88 civic wagon. Close
enough.
Like Ricky said in his post there are multiple fuses to ecu.
In the under dash fuse block, fuse 14 (I forget what it was labeled but it
wasnt obvious) was missing. I guess the previous owner had removed it and
didnt replace it.
It is control power for the main relay AND feeds injectors and fuel pump.
without main relay pulling in, no power was passed to ecu( from fuse 2).
replaced 15 amp fuse and got spark. for a few seconds anyway.
then fuse blew again.

Ended up being a shorted fuel pump

Thanks for all who responded.
Roy