My 1991 Miata with the Tec3 engine management system is not starting. The engine cranks and shows oil pressure, but there is no response from the tachometer.
The diagnostics on the Tec3 computer show the most probably cause to be a break in the line from the computer to the magnetic crank sensor, or a faulty/misaligned sensor.
I checked the wiring and all looks good. The sensor appears to be in the exact same place relative to the crank pulley as before and the spacing is within specs, so I am guessing that the magnetic sensor itself gave out.
Is there any easy way to test this sensor without just replacing the part and hoping for the best? I am still waiting to hear back from the company.
It can be tested with an Oscilliscope, or If a Timing light shows that the timing is correct, it's most likely working. Also, some of the more expensive (sensitive pickup) timing lights may show that the sensor is producing timing pulses. The Tec3 may inhibit ignition pulses if the battery voltage at the unit drops too low during cranking(and for other things it doesn't like). It sounds like the Tec3 doesn't see the pulses. I don't know if it uses a cam sensor as some of the later stock systems do.
I don't have an oscilloscope or easy access to one, and they look pricey.
Is there a way to tell if the timing is correct when the car won't start?
My friend has a high-dollar light, I will try that, though a new sensor is already on the way. I love replacing parts and hoping for the best, at least this one is less than $100.00. :-)
It uses a trigger wheel that is mounted to the crankshaft, not sure about much else. I would know a lot more about it if I had put it together myself.....or taken the time to research it.
I did swap a nearly-new battery in to make sure it wasn't the voltage dropping too low. The results stayed the same.
"Is there a way to tell if the timing is correct when the car won't start"
Lets go for it-- Pull #1 plug and stick a dowel rod or something similar in the plug hole. When the timing mark(s) shows ~0 advance, the #1 pistion should be at the top, remember that you don't know if this is the top for the power stroke, so you don't know if this is the ignition stroke or not, unless you pull the valve cover and look at the valve positions. The reason for doing this is to check a possibility that the Crank Pully has moved from the correct position. (You know things were disassembled to install the timing wheel, and Mazda recently released a service note concerning this issue.) Next, place the timing light pickup on the #1 plug lead (after you reinstalled the plug and connected the plug wire-- Never allow the ignition to fire with a disconnected plug lead, since it can cause a coil failure. If you are lucky, the timing light will fire when the engine is cranking with the starter. You should see flashes at different positions on the timing marks. One of the flashes should be about 0 to about 10deg. the other?? (Stock ignition is wasted spark) With only two stock coils and the Tec3, you still have wasted spark ignition.
The low level trigger capability is needed if you want to use the timing light to see if a trigger pulse is present at the coil. I have a light I bought from Summit (#5586) that is sensitive enough to trigger on the coil primary pulse. Actually, an LED and a series resistor should show the primary pulse, and if the resistor limits the LED current to ~ 20-30ma, the additional load should not cause a problem. (word of warning--I haven't tried this personally on a Miata, since I have a timing light).
I don't know what you use for a pickup-- the stock pickup has a mark that (if memory serves), should be close to the trailing edge of the stock timing wheel tit when the #1 pistion is ~ at the top of the cylinder, and the timing marks show about 10deg of advance.
My ignition system is one of the coil over systems, and there is no access to the plug leads with the coils in place, so the only way I can check timing is to use the primary (trigger) coil lead, or lay the clamp on sensor next to the coil.
OK, I have to admit that you have lost me. Never ashamed of that, I would much rather learn from someone with experience than assume that I know what I am doing.
I am guessing that I should manually crank the engine with a wrench until the piston is at the top before checking the timing marks? I would like to check the crank pulley position before wiring in the new sensor if possible. The crank pulley looks to be solidly mounted, but it could save $75.00 if that is the problem and it can be corrected easily.
The Tec3 is hooked up to two Direct Fire Units with two spark wire terminals each. One of the tests that is recommended is to remove the two plug wires and see if a spark arcs across the two terminals while cranking.
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I wasn't even aware that the Tec3 could be hooked to stock coils, but I guess it could. Like I said, this is not something that I know a lot about. Lots of learning.
I am pretty sure that I have also lost the loaded MAP setup that the previous owner made, and the backups also seem to have gone missing, so I will have some more fun learning how to get it to run as well as possible. This is something that I should have been doing anyway. No reason to have that level of control and not use it.
I have a lot of research to do on timing in general. Thanks for the advice, it will be a good starting point. For now, I am going to replace the sensor and pray. If that doesn't do it, it is probably off to the shop it goes.
Generally, with most "stock" ignition coils, esp. the 30-40kv versions, it's not a good idea to operate them without a plug and wire connected. It's OK to ground the shell of an out of cylinder plug to the engine to satisfy the requirement. (Or two plugs if appropriate) The reason? Simply that the open circuit voltage across a stock coil can be much higher than the normal 30-40kv, and cause the coil insulation to "break down".
Some aftermarket "racing" coils have had built in protection from an open secondary circuit. In the old days this was done with a spark gap in a glass tube inside the molded coil. With aftermarket coils, who knows, other than those who have the complete specs.
RE: Timing Marks Mazda put out a fairly recent service note covering virtually all the 1.8 engines. Seems that the original factory manual instructions were inadequate, in that reassembly to the instructions might result in the timing plate & pulley assembly becoming loose, and even chewing up the front of the crankshaft-- similar to an older problem with the 1.6L "short nose" crankshafts.
At least that much I understand, I have always known to ground the plug wire. The direct fire units look pretty cool, big warnings not to touch them. :-) If I get it back up and running, I will have to try it, (testing them, not touching them), just to watch that pretty spark arc across the terminals.
No ideas what they are doing for protection on this. More research....
Oh joy, indeed! The part should be here Monday or Tuesday and I will find out for certain. This is the 3/8 inch chisel point magnetic sensor. I was told by the Tec3 dealer that these fail fairly frequently and that a lot of people are moving up to the 1/2 inch sensor, which requires modifying the sensor mount.
This one lasted 4 years and over 35,000 miles. I won't own the car for even half that long, so I ordered a direct replacement. Grinding metal or replacing two allen-head bolts, not a hard decision.
Will keep you updated. If it is a chewed-up crankshaft and not the sensor, then this just became a parts car for certain.
If I get another Miata, it will not be boosted, with the possible exception of a Mazdaspeed.
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