My mazda mx5 starts sometimes and then it doesnt
This sounds like a pretty common problem with a lot of cars - my guess is that your solenoid for your starter motor or maybe even the starter motor itself is faulty.
A simple test to verify that you have a starter motor/solenoid problem is to turn on your headlights before attempting to start your car. When it starts sucessfully, your headlights should dim briefly. When you try to start it and achieve little more than a clicking noise, you'll notice the headlights aren't dimming because the starter motor isn't drawing an additional load from the battery.
Now - to diagnose your problem and fix it:
1. Check your battery voltage with a multimeter - you should have 12.5V or so across the terminals - any less than about 11.8 and you should think about a new battery whilst you're at it. However, as it seems to start fine sometimes, I'm going to assume this is not the problem
2. Check that you're getting power from the ignition switch to the solenoid. The light-dimming check should help you out on this one, however, we'll make doubly sure. Locate your starter motor and the solenoid (the solenoid will be wired to the starter motor - the circuit is basically battery, ignition key switch, solenoid and starter motor). Disconnect the ignition cable from the solenoid (this is the heavier cable) and put a multimeter from it to ground (somewhere metal on the chassis). Get someone to turn the key to ON and check for 12V at the ignition cable. (Always put the car in neutral and the parking brake on etc...). If you don't get 12V here you've got an intermittent connectivity problem and need to trace your wiring back to your ignition switch and from there to the battery and try to find a poor connection or potential short. Judging by the 'clicking' sound, I don't think this is your problem either.
3. Now we want to test the starter motor to ensure it's OK (I think it will be and you'll find the problem is the solenoid). To do this, we need a large screwdriver with an nicely insulated handle. On the SOLENOID, you'll find to large electrical post connectors. Short across these with the screwdriver - be careful to only touch the handle or you're going to think someone has just kicked you in the groin...You should get some serious sparks and hear your starter motor whirring (don't let it run too long or you'll flatten your battery and possibly damage the starter motor). If your starter motor makes any nasty grinding kinds of noises, you need to replace or rebuild it. If it doesn't move, you need to replace it (or get it rebuilt).
4. If none of the other problem have suggested a component at fault, you probably have a faulty or 'sticky' solenoid. To check this, find which of the two heavy post connectors is connected to the starter motor. Place one probe of the multimeter in this wire and ground the other (metal on the chassis). Have someone turn the key (neutral and parking brake) and check the voltage. You should read 12V and hear a 'clunk' from the solenoid (this is the solenoid activating and sending power to the starter motor). If you're getting a low voltage and not hearing a clunk your solenoid is probably on it's way out and needs to be replaced. A quick fix that often works is to have your helper try to start the car and give the solenoid a bit of a tap with a rubber mallet. This might jar the mechanism loose and give the electromagnet a chance to pull it into the connecting position and power your starter motor.
Hope this helps and please don't hesitate to contact me for further assistance as I'm sure I haven't been able to cover everything in this...
Mar 01, 2009 |
2000 Mazda MX-5 Miata