QuestionI drive about 90 miles park, then the car will not start. Next day the car starts. Third day the car will not start!
I have had the coils replaced and that is not the problem.
When it will not start, the engine turns over and i smell gas but seems like no spark. What can it be? The garage thinks it may be the computer. They have guessed wrong so far!
AnswerFor this response, I'm assuming that this is a U.S. model accent with the 1.5L engine.
One of the things that's important to establish is whether there's fuel and spark when the condition occurs. This means in most cases that the diagnosing technician will need to be able to inspect the car while the condition is occurring.
Has anyone scanned the ECM (engine control module) for trouble codes? That would be my first step. If the computer has stored a code indicating a problem it has seen, that will be the first hint as to where to look for a problem that's not currently occurring.
We'll presume that the injectors are firing since you say you smell fuel. And we'll presume for the moment that you have no spark. To fire the injectors, the computer needs to see a signal from the crankshaft sensor. It's this same signal that the computer needs to see to fire the ignition coil, so we'll assume that the computer is seeing all the information it needs to fire the coil but the coil is not firing. That leaves us with two possible scenarios: either the coils are not receiving power when the key is turned on, or the computer is not firing the coils.
There's one power wire to the coil, so if the power circuit is bad, the car won't start. There are two coil control wires which go to the ECM. If one of these is bad, the car should still start but only run on two cylinders. Since the coil has been replaced, we'll presume that the coil and included condensor are good. Uh-oh. Here's a thought. I don't know how much of the coil assembly was replaced. The factory coil assembly comes with both coil packs and the condensor, but aftermarket parts often leave things out to save money. If the condensor wasn't replaced with the coil, it's possible it could be shorted and preventing the coil from firing.
If the computer is receiving the proper signals and is still not firing the coils, then the computer would be the defective part, but I find this dubious. I can say that not once have I needed to replace an accent ECM for any model year because it was defective. Hyundai has very, very few computer problems which require computer replacement.
I suspect, however, that we may have not yet verified there's no spark. And if you do have spark and fuel and the vehicle is still not starting, then that opens up possibilities which occur more frequently. In those cases, I've seen things like faulty air flow sensors and faulty coolant temperature sensors cause the air/fuel mixture to be so far off that it won't burn. Wiggling the connectors on the air flow sensor or the coolant temperature sensor will often make the readings change. Looking at the readings with a scan tool while wiggling the connectors can be instructive as to where the problem may be.
Whose idea was it to replace the coil? If it was the repair shop's idea, then you may wish to reevaluate whether they know enough about how your car's engine control system works to properly diagnose it. The coil assembly on your car has two ignition coils on it. One for cylinders 1&4 and the other for cylinders 2&3. If one of the coils failed, the car should still start and run (albeit not well) on two cylinders. This isn't to say it's not possible that the coil assembly could be the issue, just that it's unlikely. The power wire on the coil assembly itself could have broken or, as I mentioned above, the condensor could be shorted. The way I see it, the repair shop chose a low probability item to repair your vehicle (and seemingly didn't verify there was anything wrong with it) and is now suggesting another low probability item. Again, I'm not saying they're not right, but I'd be surprised if they were. If this shop isn't qualified to do driveability diagnosis and/or doesn't have access to a scan tool and the proper software to read the codes and data from your engine computer, you'll need to find a shop capable of doing that. Otherwise, you're probably in for a long line of guesses. Furthermore, it may be nearly impossible to find this problem unless it occurs while the repair facility has the vehicle.
