LSVTEC96HB

Ok, I got a 100% stock '89 Civic LX sedan that has been sitting for 4 years because it quit running and the previous owner gave up and parked it.
So on to the list of things I've already tried in no particular order

put in a new coil/igniter (parts store not ebay)
swapped new coil/igniter into a new distributor housing
swapped new distributor cap, old one looked clean, rotor looks pretty new and clean
swapped spark plugs with some from a running car, existing NGK plugs looked ok
checked engine grounds
swapped main relay (a resoldered one)
unplugged and replugged all connectors to engine harness
checked fuses and found ECU fuse blown
replaced fuse and it blew as soon as the key was turned on
unplugged ECU and replaced fuse, turned ignition on, fuse was ok. plugged ECU back in, fuse blew

checked plug wires, they look good, not originals

Unplugged engine harness with original ECU and fuse stays ok, plug in engine harness and fuse blows.
unplugged all sensors and plugs on engine harness, ECU fuse still blows when harness is grounded
Swapped engine harness, fuse still blows.
Unplugged main relay, ECU fuse still blows
Unplugged atmospheric pressure sensor, fuse still blows when ECU is connected.


swapped ECU, new ecu doesn't blow fuse but still no spark. (new ecu is from a '91, not an '89)

would a '91 LX be so different from an '89 that it wouldn't fire the engine? I think the ecus are largely the same except for the PA sensor is built in to the later ones, right?

What am I forgetting? I need to get this car running.

DCFIVER

Well youre gonna have to get a wiring diagram and do some real troubleshooting instead of parts swapping.

With that said,the only part you haven't replaced related to spark is the crank/tdc sensor.

LSVTEC96HB

QUOTE=DCFIVER;49814216]Well youre gonna have to get a wiring diagram and do some real troubleshooting instead of parts swapping. [/QUOTE]

I am using the Honda factory service manual not a chiltons or Haynes manual so I have extensive and accurate wiring schematics.
I swapped parts because I had them on hand, and yes, I know it is easier to do that than troubleshoot. I was simply hoping I had missed something obvious before I spend a lot of time tracing down wiring.

I replaced the entire distributor housing, which contains the crank sensor.

I expected to find some shady wiring somewhere in the car causing a short circuit but there isn't any. Even the original radio harness is still intact and by the looks of it, none of the wiring has been hacked. I traced the wiring back to the ECU. Everything looks normal, nothing is shorted to ground. The ECU fuse supplies power to the yellow/white wire, which goes straight to the main relay. when the ignition is switched on, the main relay then sends power to the ECU along the yellow/black wires. Everything to that point is good. Once the ECU is plugged in, it blows the ECU fuse so it must be sending power to something that is overloading the circuit, causing the fuse to blow. I know it is not a sensor, because I had the engine harness out of the car, with only the ground connected (which supplies ground to the ECU and main relay) and it still blows the fuse, so that rules out a shorted sensor.

I have also unplugged the 2 smaller harnesses from the ECU and left only the main one plugged in so I have narrowed the wiring issue down to something coming through the main plug. There is only one wire that comes out of the main ECU connector that does not connect to a fuel injector or sensor and that is the yellow wire which goes to the lock-up solenoid valve. I unplugged that and it still blows the fuse. I pulled the harness from the firewall going into the engine on the driver's side to check for any cut or frayed wiring, and it all looks good. I am not sure what other circuits to trace and I am quickly running out of ideas. Anyone else care to weigh in on this?
I'm about to just do a B swap and a wire tuck haha

DCFIVER

Doesnt mean its good. Did you test it?
You said you put in a new ECU and that fixed the fuse blowing problem. Is it fixed or not?

lostforawhile

first disconnect the noise capacitor between the coil and the body, if it shorts it will short the coil positive to ground and blow fuses, the next thing is disconnect the small blue wire going to tach,ecu, ecu, etc, use a spark gap tester, a few bucks at the parts store, to see if you have spark while cranking, the dizzy will produce spark regardless of the ecu, if that tach wire shorts, or one of the things it's attached to short, the coil will never fire, as it will be a continuous ground at the coil negative terminal, have you even verified there is 12 volts at the coil primary side?

LSVTEC96HB

Update on this thread. I had 2 bad ECUs. I swapped in a third ECU that I bought from pull a part and that fixed it. I was thrown off because those 2 are the first ever bad Honda ECUs I have encountered since I started working on Hondas in 1996 and to have 2 in a row seemed so unlikely I was looking elsewhere. I also figured out what caused the ecu to fail in the first place. The positive battery terminal had been replaced with a cheapie and the wire worked loose. The alternator was putting out 20+ volts without the battery connected and fried stuff. I have since replaced the alternator and now everything is working properly. I hope this helps someone!

lostforawhile

look on ebay or online and look for the SDC heads up voltage monitor, single LED gives you a warning for all kinds of voltage conditions, not only under voltage, but it warns of over voltage, easy to hook up, and I put one in everything I own, the idiot light is worthless

Jonnyfly

I am having a similar problem with my 92 Accord EX coup. The engine cranks, the headlights work, turn signals work, I'm just not getting any spark to the plugs which are brand new, high end plugs. I bought new spark plug wires but the ones on there look good and are also high end. I'm thinking it might be the ECU Because I had a second battery in the trunk for my sound system and alarm but I didn't put a resistor between them. Interestingly my car ran better with the second battery. lights where brighter and it had better, more responsive ignition. Maybe I should have just installed some capacitors in the trunk. I do a lot of camping and I like having the extra power. I learned that you never want to put anything but a gel battery inside the cab because of the acidic fumes that are emitted by an non gel battery. Just a word of caution. All my fuses are good, so I'm rather stumped. I could buy a used ECU off of ebay but it always makes me nervous to buy used electrical equipment, especially from out of state. Any suggestions would be much appreciated. I'm a newby and didn't even think I was mechanically inclined until I bought the Haynes manual for the CB7.