Hello everyone!

I'm hoping someone here might be able to give me some ideas on what might be causing a strange intermittent no-start issue with my friend's beloved Civic.

The problem is intermittent, but in a predictable way. The car can be counted on to start exactly once, and then its a crapshoot -- it won't start more often than not until it sits for at least several hours.

I've used a spark tester and it does seem to be getting spark, and the mechanic we brought it to (generally a very good mechanic) said that he tested the fuel pump, tried changing the distributor, the ecu, and the main relay. After we brought it back from the mechanic we changed the ignition switch, which was absolutely bad, but it didn't fix the problem. It seems like some inscrutable electrical gremlin, but I figured I'd check in with the experts here before we gave up.

Any ideas?

 

Why are you posting rather than your friend who owns the car?

Post the CEL codes.

Is it a no-crank problem or a cranks-but-won't-start problem?

 

If it's a crank but no start situation check these things:

First check the ground lug with 4 small wires on the thermostat housing (where the lower radiator hose meets the engine). These wires ground the whole ECU system.

When it won't start turn the key on but don't crank. The check engine light should go on for 2 seconds then go out. While the light is on the fuel pump should run, then stop when it goes out. If the light stays on and the pump does not run this is usually a bad main relay or ground but if you are sure those are good it could be the ECU itself being balky to boot up. ECU failure is rare but it does happen-- don't replace ECU without ruling everything else out first though.

Pull the brake handle up and watch the brake light on the dash as you turn the key on and crank. It should stay on. The light gets its power from the same circuit that runs the ECU and ignition. If it goes out that could be a bad ignition switch. Also the battery light should be on when key is on but engine not running.

 

Replace the engine coolant temp sensor it's gone bad. The ECU thinks the engine is always cold and is giving too much fuel trim when the engine is warm and the warm engine won't start with too much fuel.

 

Thanks for the great diagnostic tips, they have been VERY helpful and I think it may be fixed.

To answer the first reply, it is a crank-but-no-start problem and I am posting because I have more mechanical knowledge than the owner, so I'm better equipped to ask questions and understand answers, even if I am not a Civic owner myself. I'd have posted the CEL codes but I am afraid I don't have a reader.

In any case, I followed mk378's diagnostic procedure, and the fuel pump did run. I wasn't concerned about the ECU because the owner's regular mechanic had already swapped with a known good unit during diagnosis. Also the brake and battery lights behaved normally, which I did expect because I've already replaced the ignition switch with a new one (which fixed other problems, but not this one).

delsolintegra's suggestion to swap the engine coolent temp sensor, I think, turned out to be our salvation. As soon as I read it the explanation made perfect sense in light of the symptoms. I decided to take a flyer on it since the part was cheap; $30 bucks and 10 mins worth of work later, and so far it seems back to normal. Still crossing my fingers since it was at least somewhat intermittent and it has only been a day, but it starts MUCH more readily after driving now and I am optimistic that it is fixed.

Seriously, thanks a million!

 

Glad it worked. You will notice overall better performance and throttle response. It will feel like a new car. Exact fuel trim is important in a small engine. Thanks for the thank you. Good feedback on this site is rare.

 

Reader not needed.

https://honda-tech.com/honda-civic-d...lists-1901557/

...though the problem may be behind you now.

 

Even if it is fixed, this is good information to have. Thanks!