Toyota MR2 Message Board - View Single Post

mr2greasemonkey · 05-15-2007, 10:20 PM

No start diagnosis:

If you have access to a VAT machine then you can simple perform and amp/voltage draw test on the battery. 300+ amps is excessive, and anything lower than 9.6 volts mean you should recharge the battery and re-test.

If you dont happen to have a VAT machine in your garage, use your multimeter to check voltage when cranking. Dont hold the starter in the crank position for more than 15 seconds, you could burn up your stator windings. You just want to see if there is actually a voltage "drop", or the system is trying to use the battery. As before, anything below 9.6 is considered weak source voltage.

But you say, hey my dash lights work and my idiot lights come on. The radio seems to work but it still doesn't crank over the engine.

Now that you've confirmed the source power (battery) is in proper working condition we move on to the starting circuit. Battery terminals must be clean and properly fastened. Even slight corrosion between the post and the terminal will be enough to keep the electronics from working properly. Battery post cleaners are cheap, pick one up and keep it handy.

Check for power at the starter, the big wire on the side of the starter. It is source power all the time, unless you forget to hook it up. Test light is quick and easy for checking. If you suspect a bad wire you can do a voltage drop test with your multimeter by checking voltage from the wire at the batter and then again at the starter. The difference in voltage, is what is called the "drop". It should be very minimal, less than .25 volts , most of the time it reads the same.

The next wire to check is the ignition start terminal, the connector located right next to the big power wire. That is power that comes from the ignition switch (key switch). Someone will need to turn the key in the crank position while you unplug the connector and check it with the test light. It should light the test light every time the key is in the crank position. If it does not, then your problem lies in the ignition start circuit; key in crank position power, clutch switch/or park/neutral position switch, starter relay, or ground. Now the simplest thing to do is find your starter relay and make sure it has power, key power , ground and load. Unplug the relay, it should have power at one terminal, power at another when the key is in the crank position, a good ground at one terminal, and the load side should be the same as the wire that goes to the starter. Now before you put a wire across the relay to bypass the starter ( will need the electrical diagram or else you smoke fuses ) you could also use a remote starter (also cheap tool you can buy) and hook it right up to the starter to see if it actually works. The remote starter is basically a switch with long wires terminated with clips so you can pull power and apply it directly to the ignition terminal on the starter to see if it actually engages and spins. I suggest making sure the vehicle is in neutral/park with parking brake set, or the rear wheels are off the ground. Nothing like standing next to your car and hittin the button just to see it take off on you, heeh. If you have igntion crank power then that means the ignition switch works and the clutch or park neutral switch works. If you dont have power than check your fuses ( the BGB or a decent repair manula will come in handy ). If you suspect a bad ground from the relay you can always use a jumper wire to ground ( radio shack is gonna be your best friend, heh.). Or as mentioned before, if you know how to read a wiring diagram then you can jumper the relay connector and completely bypass the relay.

Now keep in mind so far all we've really checked is power through the system. You must have a dedicated engine ground. That big black wire that runs from your tranny or block straight to the body. The starter pulls lots of amperage and a thin wire will not be enough. Make sure grounds are clean and properly secured.

This is a little long winded so i may have missed something so please ask questions. But that should be enough to figure out how to make the starter work.

More to come...

05-15-2007, 10:20 PM	#2 (permalink)
mr2greasemonkey Once again....yups Join Date: Sep 2005 Location: Portland, OR Posts: 1,440 Thanks: 4 Thanked 54 Times in 39 Posts iTrader Rating: (0/0% )	I try to star the car and nothing happens? No start diagnosis: If you have access to a VAT machine then you can simple perform and amp/voltage draw test on the battery. 300+ amps is excessive, and anything lower than 9.6 volts mean you should recharge the battery and re-test. If you dont happen to have a VAT machine in your garage, use your multimeter to check voltage when cranking. Dont hold the starter in the crank position for more than 15 seconds, you could burn up your stator windings. You just want to see if there is actually a voltage "drop", or the system is trying to use the battery. As before, anything below 9.6 is considered weak source voltage. But you say, hey my dash lights work and my idiot lights come on. The radio seems to work but it still doesn't crank over the engine. Now that you've confirmed the source power (battery) is in proper working condition we move on to the starting circuit. Battery terminals must be clean and properly fastened. Even slight corrosion between the post and the terminal will be enough to keep the electronics from working properly. Battery post cleaners are cheap, pick one up and keep it handy. Check for power at the starter, the big wire on the side of the starter. It is source power all the time, unless you forget to hook it up. Test light is quick and easy for checking. If you suspect a bad wire you can do a voltage drop test with your multimeter by checking voltage from the wire at the batter and then again at the starter. The difference in voltage, is what is called the "drop". It should be very minimal, less than .25 volts , most of the time it reads the same. The next wire to check is the ignition start terminal, the connector located right next to the big power wire. That is power that comes from the ignition switch (key switch). Someone will need to turn the key in the crank position while you unplug the connector and check it with the test light. It should light the test light every time the key is in the crank position. If it does not, then your problem lies in the ignition start circuit; key in crank position power, clutch switch/or park/neutral position switch, starter relay, or ground. Now the simplest thing to do is find your starter relay and make sure it has power, key power , ground and load. Unplug the relay, it should have power at one terminal, power at another when the key is in the crank position, a good ground at one terminal, and the load side should be the same as the wire that goes to the starter. Now before you put a wire across the relay to bypass the starter ( will need the electrical diagram or else you smoke fuses ) you could also use a remote starter (also cheap tool you can buy) and hook it right up to the starter to see if it actually works. The remote starter is basically a switch with long wires terminated with clips so you can pull power and apply it directly to the ignition terminal on the starter to see if it actually engages and spins. I suggest making sure the vehicle is in neutral/park with parking brake set, or the rear wheels are off the ground. Nothing like standing next to your car and hittin the button just to see it take off on you, heeh. If you have igntion crank power then that means the ignition switch works and the clutch or park neutral switch works. If you dont have power than check your fuses ( the BGB or a decent repair manula will come in handy ). If you suspect a bad ground from the relay you can always use a jumper wire to ground ( radio shack is gonna be your best friend, heh.). Or as mentioned before, if you know how to read a wiring diagram then you can jumper the relay connector and completely bypass the relay. Now keep in mind so far all we've really checked is power through the system. You must have a dedicated engine ground. That big black wire that runs from your tranny or block straight to the body. The starter pulls lots of amperage and a thin wire will not be enough. Make sure grounds are clean and properly secured. This is a little long winded so i may have missed something so please ask questions. But that should be enough to figure out how to make the starter work. More to come...