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Before Replacing Your Starter Motor...
by David Lane
dlane@peabody.jhu.edu
Funny how cars always pick an inconvenient time to refuse to start. It's always just when you want to go somewhere.
How does it know?
We all understand about the rotary engine's classic flooding problem, and the solution is well documented elsewhere. Less well understood are the kind of problems which keep the car from cranking when you turn the key. All you get is a "click" from underneath the car, or perhaps the whole electrical system goes dead. One of my favorites is a really nasty grinding noise. Sometimes turning the key on and off a few times resolves the trouble -- at least for awhile. Most people figure the starter motor is bad, and they replace it, only to discover that the trouble persists.
This article will help you trouble-shoot the electrical system which supports the starter motor. To help you make sense of it, I need to explain how the system works. Then, we can look at typical problem areas. These problems are most often associated with age, so it makes sense that they will show up with the earlier cars first. My own car is an '85 GSL-SE, but I understand that most Rx-7s are the same (or at least similar).
The usual disclaimers apply: I am not a mechanic and I make no pretense about being an expert. However, I have experienced these problems on my car, and I want to share what I have learned.
At the end of the article I will give you some tricks to pep up your electrical system. I will also discuss the "grinding noise" problem in that section.
HOW IT WORKS
The starter is wired directly to the positive battery cable. Switching the starter motor on and off is accomplished by an electromagnet called the starter solenoid. Turning the key activates the solenoid, which does two things. First it slides a gear (connected to the starter motor) in place to mesh with a matching set of teeth around the engine flywheel. Then it moves a metal "contact plate" to complete the electrical circuit between the battery and the starter motor. This circuit requires clean electrical connections between the starter motor, both battery cables, and the engine. Hopefully, the starter motor starts to spin and the engine cranks. When the ignition key is released, the solenoid returns to its original position, breaking the electrical circuit, and removing the gear from the flywheel.
As usual, Mazda has their own way of naming things. The gear connected to the starter motor is called the "pinion" gear in the shop manual -- probably to complement the "ring" gear which circles the flywheel. This is technically correct, but most mechanics refer to the gear on the starter motor as the "Bendix" gear, after the man who invented the engagement mechanism. In the shop manual, the solenoid is referred to variously as the "magnetic switch," or "magnet switch."
Troubleshooting the starting functions of the car is best done in three phases. First the battery and its connections must be checked. Then, depending on your particular problem, you can look at either the large battery cables that power the starter motor, or the smaller circuit which activates the solenoid.
THE BATTERY
Since it is central to the entire operation, the first thing to check is the battery. An ailing battery can give you differing symptoms depending on what is wrong with it. Slow cranking and dim lights, are typical of a battery that isn't up to snuff. A nearly dead battery can give you no cranking at all -- just a clicking sound. You can also check the voltage meter on your car with the key on and the engine off. You should see around 12 volts. With the engine idling, but no electrical accessories on, you can see as high as 13.8 volts.
If you suspect that your battery is not doing its job, the best way to test it is "under load," simulating what the battery must do when the starter motor is cranking the engine. It takes a special machine to do that, so take the battery to a shop that specializes in batteries, or a good garage. Be advised that a battery can put out acceptable voltage at rest, and still not perform properly under load.
As part of checking the battery, pay particular attention to the terminals -- the clamps that hold the cables to the battery posts. Strange as it may seem, it only takes a thin film of corrosion to block or severely inhibit flow of electricity to and from the battery.
Here is how to clean the terminals. Working with these connections can be hazardous if you are not careful, so heed the warnings as we go along.
- Remove both battery cables from the battery.
- Check to be sure the terminal is attached tightly to the cable itself.
- Use sandpaper or a commercial battery terminal cleaner to clean the terminals and the battery posts. You must see bright metal on the mating surfaces.
- Apply a thin coating of petroleum jelly to the battery post, or use a commercial corrosion inhibiting product.
- Replace the connectors on the battery posts.
The posts are slightly conical, so if the terminal is still loose after being tightened all the way, loosen it up again, spread it a little with a screwdriver, and maybe tap it lightly so that it clamps down more toward the base of the post.
PROBLEMS ASSOCIATED WITH BATTERY CABLES
When a battery cable goes bad, or a connection gets dirty, the effect is like an electrical traffic jam. The cables can't pass electricity fast enough to power the starter motor. Thus, when you turn the key, you hear a loud click from the solenoid, but there is not enough current to crank the engine.
The first task is to clean all connections associated with the cables. For safety, remove both cables at the battery before proceeding. Otherwise, you risk handling live cables, and the results can be a shower of sparks. Put the front of the car up on jack stands, or a ramp. Do not rely on a jack alone if you are under the car.
The first connection to check is the positive battery cable, where it terminates at the solenoid (located on the starter motor). The battery cable is the one on the left, covered with a rubber boot. Remove the cable and sand the connecting surface until it is bright. Replace the cable. While you are working in that area, you will notice a smaller wire terminating with a clip connector on the solenoid. This carries electricity from the ignition circuit, activating the solenoid when you turn the key. Might as well pull it off and clean up the post. You can also squeeze the female end attached to the wire if it no longer makes a tight connection.
While you are looking at the aft end of the solenoid, consider that the two large terminal posts are the ones connected by the metal plate when the solenoid is activated. If you look carefully, and have enough light, you will be able to see that the large post on the right has a wire attached to it which runs into the starter motor. Now let's go to the negative battery cable -- the ground strap.
The ground strap is part of every electrical circuit in the car, so if it is internally corroded, or if the connections are dirty, everything will be affected to one extent or another. This includes lights, starting, and other things we don't usually think of, such as engine management computers and the various relays and small solenoids which serve switching and control functions. Some of these systems are mounted to the body. Others are mounted to the engine, so the ground strap is connected to both. As you can tell by the thickness of the wire going to the starter solenoid, powering the starter motor requires more electrical flow than any other electrical function, so any weakness in the ground strap is likely to show up there first.
The ground strap is connected to the engine. Mid-way down the cable is the connection to the body -- typically part way down the driver's side shock tower. Remove the connections, sand until bright (including the mating surface in the shock tower), and replace. Third generations cars have another ground strap from the exhaust to the body. While a fault at this connection will not cause a starting problem, some owners have reported problems if this cable is not clean and solid.
Replace the connections at the battery, and try to start the car.
If this doesn't fix the problem, the next step is to test for internal corrosion in the cables. There is some possibility that the cables are corroded, but in the process of cleaning the terminals, you have caused enough internal friction to rub away some of the corrosion. In this case, the car might start, but exhibit the same problem at a later time. When the cables crud up internally, it is hidden underneath the insulation. Also, you can't test for corrosion with a volt meter because even a badly corroded cable will provide plenty of voltage to produce a reasonable reading. The best approach is to substitute a jumper cable (the ones you might use to jump start the car with a dead battery) for the cable you want to test. Here is how:
To test the ground strap, first disconnect the ground strap at the battery to expose the negative battery post. Connect one end of your jumper to a clean, unpainted place on the engine. Connect the other end to the negative battery post. Try to start the car. If you have no luck with that, remove the jumper cable from the engine and connect it to the body via an unpainted bolt or other piece of unpainted metal. Try to start the car again. If the car starts in either case, you need a new ground strap. You can get something close at a local parts store, or get the genuine Mazda part from Mazdatrix or your usual source of parts. It saves time to use a Mazda part because it has provisions for the body and engine connections. If the car doesn't respond to substituting a jumper cable for the ground strap, move on to the positive battery cable.
Testing the positive battery cable is a little more tricky. We want to avoid sparks, so the first thing to do is to remove the positive battery cable at the battery. Next, clamp one end of your jumper cable to the left hand post at the solenoid (where the stock cable is connected). Be very sure the clamp is ONLY touching the terminal post (including the stuff connected to it) and NOT anything else. Nothing on the body, nothing on the engine, nothing on the starter motor. Any contact with a ground such as those mentioned will result in a shower of sparks when you connect the jumper cable at the battery. To double check that you have a clean connection at the starter, bring the other end of the cable near the positive battery terminal and quickly brush it across. If you get no reaction, it is safe to clip it to the battery terminal. If you get sparks, recheck the connection at the solenoid. Once the jumper is in place, try to start the car. If the car starts, replace both battery cables (the negative cable, if not bad already, will go bad soon).
If the car still won't crank and you still get the click from the solenoid when you turn the key on, the problem is probably within the solenoid or the starter motor itself. You can check the solenoid with a test light or volt meter by clipping one connector to a ground on the engine or body, and the other to the right hand terminal on the solenoid (the one with the wire leading inside the starter motor). All connections of the battery cables are normal for this test. Turn the key to start. If the solenoid is good, you should see twelve volts or so on the meter. If you are using a test light, it should illuminate. If the solenoid seems good, it may be time to pull the starter motor and have it checked.
PROBLEMS ASSOCIATED WITH THE SOLENOID ACTIVATION CIRCUIT
If you turn the key and nothing happens -- not even a loud "click" from under the car, and if you have properly checked the battery and cables, you may not be getting power to the solenoid. Here is how that circuit works -- at least on a 1st generation car. Later models are probably similar in concept, but I have not researched it.
As usual, we start from the positive terminal of the battery. In addition to the thick wire which goes to the starter, there is another wire that supplies power for virtually everything else. This wire goes to the fuse box under the hood. First generation cars don't have a fuse box in the traditional sense, relying instead on what Mazda calls "fusible links." These are actually little U-shaped wires, loosely covered with cloth, and designed to burn through in the event a short circuit draws too much electricity through them. The box of fusible links is mounted to the front of the driver's side strut tower. Since later generations of Rx-7s have a proper fuse box, they are less troublesome in this regard.
The fusible link marked "Main" is in the electrical path going to the dash board and ignition key. When you turn the key to "start" electricity is sent to the starter solenoid via the small clip-on connector located between the two large connecting terminals.
If turning the key to "start" results in the dash lights going out, you probably have a problem with the fusible links. Disconnect the positive battery terminal at the battery. I suggest removing the box of fusible links and cleaning all connections while you are there. Pay particular attention to the clip connections on the fusible links themselves. Remove, clean, and tighten the connection where the battery power comes in. Do not throw away a broken fusible link. You can get an in-line fuse holder from an auto parts store, but the size of the clip connector is not easy to find. You may have to solder the connector from the old fusible link on to the new fuse holder. A fuse holder is not a bad idea for the "main" circuit since fusible links (while not known to be particularly troublesome) are out in the open, and vulnerable to clumsy hands. Don't ask how I know.
If turning the key to "start" does not effect the dash warning lights, you will want to verify that the solenoid has power coming to it to activate the electromagnet. First, clean and tighten the clip-on connector at the solenoid. Next, check to see if it is getting power by putting a meter or circuit light between the wire and ground (an unpainted part on the engine or body). Turning the key to "start" should light the light, or register 12+ volts on the meter.
If the solenoid IS getting power, but not activating (no click) you may have a bad solenoid. The shop manual says you can check for continuity between the right hand post and the body of the solenoid. They illustrate this with the solenoid separated from the starter and off the car. At least remove the positive battery cable at the battery end. Remove all three cables from the solenoid terminals. Set your meter for resistance, or use a continuity checker. Check for continuity between the right hand post and the body of the solenoid. If you get no continuity, the solenoid is bad. Although the shop manual says to "replace the switch," I would not be surprised if you had to buy the whole starter/solenoid assembly. Just a hunch.
If the solenoid is NOT getting power, you may have a mechanical or electrical problem with the ignition switch itself.
HOW TO PEP UP YOUR ELECTRICAL SYSTEM
A respected Rx-7 mechanic says that no car leaves his shop without the following simple modifications done to the electrical system. All are done with 8 or 10 gauge wire. You can secure the wire to the battery terminals using the terminal clamps, or you can get clamps which have provisions for extra wiring -- as you might find with a complex auto sound system.
Run two new ground wires. One goes from the engine to the negative battery terminal. The other goes from a bolt or bare-spot on the chassis to the negative battery terminal. The additional ground paths will provide a little cushion for the stock wiring which is marginal when new. This has been known to solve low voltage problems at the cigarette lighter -- the kind that gives you low voltage warnings on cell phones or Valentine One radar detectors. The V-1 detectors will show a false "laser alert" if you try to power it with low voltage.
Run one new wire between the alternator output (the wire secured by a nut) and the positive terminal of the battery. This parallels the stock wire and makes it "easier" for the alternator to recharge the battery. With both these modifications, you should see at least 13.8 volts at on your dashboard volt meter when at idle (but without other electrical loads).
THE GRINDING NOISE
At the beginning of this article, I spoke of a grinding noise you get sometimes when you try to start the car. Most often, you can just turn the key off and try again. Sometimes it takes several attempts to get the car to crank. Grinding occurs when the gear teeth of the starter motor and the flywheel ring gear fail to engage. The starter motor powers up and the gears grind against each other. Over time, this erodes the matching surfaces (bevels) on both gears, making the engagement process progressively more difficult. While there may be a mechanical reason for the problem, in many cases something is marginal in the electrical system. For instance, it may be that the solenoid is not getting enough power to solidly place the bendix gear in mesh with the ring gear. In that case, cleaning up the circuit supporting the solenoid will help. Another possibility is that there is a problem with the ground strap, making the circuit sluggish. In that case, working with the ground strap as previously described (or replacing it) will help. Certainly, installing the suggested supplemental wiring will have a positive effect, as it increases the available ground path. If the car usually cranks normally, and occasionally grinds, I would troubleshoot this particular problem in the following order (taking care to use the precautions mentioned in the earlier text).
- Clean and tighten the clip lead to the solenoid.
- Clean and tighten the Main fusible link (1st gens).
- Install the supplemental wiring
- Replace ground strap.
I actually replaced a starter motor because of the grinding problem, but it did not go away. As I worked through the above items (trying to solve another problem) the grinding became progressively more rare.
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