Hi everybody,

New to the forum, did some looking and found some good stuff, but was hoping to get some more info before I tear into troubleshooting again.

Here's what I've got:

1992 Civic dx 5 speed with 220,000 mi (more info if needed)

What happened:

Years ago, the car would occasionally fail to start. Engine would turn over, but couldn't hear the fuel pump. Suspected main relay. Bought a new one, but that didn't fix the problem. Checked voltages at the main relay harnass and found that I wasn't getting voltage from the ecu. Jumped out the main relay so that the fuel pump runs as long as the key is 'on'. This fixed the problem and enabled the car to run for quite a while. Based on this, I assumed that the ecu was bad, but, I never had the time to go back and really try to fix the problem - I drove the car infrequently and figured that I'd just leave well enough alone.

Recently, the car just stopped running. The engine light is on. Starter turns over and fuel pump still runs when the I turn the key. Checked that I have fuel coming to the injectors (I do). Tried to check to see if I have spark - I don't. Replaced the spark plugs and wires. Replaced the distributor cap and rotor. Tried jumping the diagnostic pins in the ecu - I get no flashing error codes - just a steady yellow check engine light.

Based on the past experience with the main relay, I still suspect the ecu. From reading some of the forum posts, I can tell that there are a lot of troubleshooting steps that I'm skipping. I'm posting here in the hopes that someone much more experienced than me will read this and can maybe give me a 1-2-3 checklist to help confirm or deny the possibility of a bad ecu before I go out and spend $200 or so on a new one. Or, if, after reading this, you think it sounds like an ecu, maybe a tip on where I can find one cheap?

Thanks a lot in advance - I can provide more specifics if it'll help... just trying to keep it simple.

 

If the CEL is ON, have you retrieved the code(s) (see link in my signature)? Edit: I missed that you mentioned an inability to retrieve a CEL. But is the CEL ON?

Without knowing the CEL code, my first guess is that the coil or igniter unit in the distributor is bad. Does the distributor connector have battery voltage when the ignition key is turned to ON(II)? Next test the coil (see diagram). Your local auto part store may also bench test the coil and igniter free of charge.

 

Basic no-spark checks:

Make sure the distributor rotor turns when you crank the engine. If not, the timing belt is stripped or broken. There may or may not be internal damage to the engine from the valves crashing.

If the distributor turns, leave the cap off and hold a grounded test wire near the coil output pin while cranking. You should get big strong sparks there. If you have sparks but they only jump a very short distance (less than 1/4 inch), the coil is bad.

If you don't have any sparks from the coil, take the plastic insulator plate out (will need to remove rotor first) and check that there is battery voltage on the small terminals of the coil with the key on. If not, troubleshoot car wiring. If you have primary voltage, distributor turns, yet no sparks, it could be the coil, igniter unit, or ECU.

The check engine light should come on and then go out when you turn the key on but don't start with the test wire off. With the test wire on, the check engine light will either blink out a trouble code, or come on and stay on steady if there are no codes stored. This is with the car stock. With your jury-rigged wiring around the main relay it could be different.

 

Thanks very much for your reply, RonJ.

One of the things that makes me suspect the ecu is that the check engine light does not flash anything at all when I apply the jumper as described in http://www.honda-tech.com/zerothread/1901557

It's just a steady, unblinking yellow. Would that be 'normal' behavior if the ecu is bad?

If the ecu isn't bad (and it's some other problem) shouldn't it flash something when I apply the jumper?

I'll put the Ignition Coil Test on my troubleshooting checklist. Would like to get a list of likely problems to check so that I can go out there and do as much as possible at one time. Any other ideas in case it isn't the ignition coil?

Thanks again!

 

By the way, the ECU does not provide power per se to the main relay but instead serves as ground for the main relay when power is supplied from both the battery and starter. So was the ECU not providing this ground or was power from the battery or starter absent?

 

The potential sign of a bad ECU is when the CEL is ON without the jumper wire inserted in the service connector and when no code is retrieved (steady ON) when the service connector is jumped. Is this the symptom?

 

mk378:

Thanks for your reply. When I checked for spark it was just at the plugs - I'll follow your suggestion to look at the distributor. I hope that the timing belt is still good - it was replaced maybe 40k miles ago by a garage (before I owned the car).

RonJ:

Hmmm - I don't know! It has been a long time. From what I can remember, the pins that I checked at the main relay that were supposed to have voltage didn't have any when checked against the body ground. So my jumper took power from another pin at the main relay connector.

It's been too long and I need to look at my service manual (and my horrible hackjob of a main relay) again to jog my memory.

Thanks to both of you for your replies.

 

RonJ:

Yes, exactly.

No service jumper=CEL on
Service jumper=CEL on (steady, no flashing)

How common are ecu problems? Since replacing the ecu is easy (just have to buy the thing), if it's a common problem, I'd lean toward gambling the cost of a new ecu in the hopes that it'll save me time in troubleshooting all of the other things that I should do by the book.

 

If correct, this information is inconsistent with a bad ECU and instead points to a blown fuse or bad wire in the main relay circuit.

 

This would be consistent with a bad ECU but does not prove it. Rule everything else out first. For example, as mk mentions, your rewiring of the main relay circuit must be returned to stock before jumping to this conclusion.