How to troubleshoot the TCI ignition system

[bpeckm]

Being of the age where "real" cars and bikes have points, distributors, and carburetors, well... this was a learning experience.

But thanks to the MANY helpful hints, links and advice from fellow XS'ers, I have been able to figure out how to diagnose an intermittent ignition problem. So, I hope to consolidate the various bits of information gathered, and put it all in this thread.

First, some basic electrics: dc electrics can be thought of as a "loop"... electricity "flows" from one battery terminal to the other terminal (see pamcopete below). The battery is the storage unit, providing electricity when it is needed for starting, both the electric starter and the electricity for the ignition.

And thank you PAMCOPETE for the following:

bpeckm,

Great writeup on the TCI and basic ignition testing. I have one of those testers that you recommend and it's good to use it instead of just a spare plug laying on the engine.

Just a small correction:

Electricity flows from the negative of the source (IE: battery) to the positive. That's because electrons, as in electricity or electronics, are a negative charge.

The British used to install their batteries with a positive ground for this reason because we like to think of the current from the battery as coming from the the ungrounded terminal of the battery and returning to the grounded battery terminal via the frame of the vehicle. It's a little harder to think of the current coming from the negative terminal of the battery through the frame and returning through the wiring, but that is how it works.

The standardization of a negative ground for automobiles came about with the introduction of radios in automobiles. Radios then and now are designed with a negative ground due to the functionality of both tubes and transistors so the ground in the automobile was standardized to match the electronics in the radios.

Any testing of electrics will involve testing, in a bewildering array of options, how that electricity does its work. Basically, we are looking for (a) voltage, or (b) continuity. Using those two simple electric tests, we can do a helluvalotta troubleshooting!

I find these three tools to be the trick:

The red meter is a digital multimeter, sometimes called a VOM or a DVM or DM and probably a lot of other names. There are two scales that interest us: voltage, and resistance/continuity. Voltage indicates the presence of electricity, and is measured with the + and - probes. It is good practice to attach the (-) to the black (-) post of the battery: that way, your voltage reading is an accurate voltage in the "loop" back to the battery. A GOOD contact is always necessary, so don't be afraid to scritch and scratch whatever you are probing to make sure you have a good reading!

That little thingy with two thin red and black wires has proven to be quite trick: it is an LED (make sure your LED is for 12Vdc (volts direct current) nominal). The trick thing about LED's versus a "standard" bulb is that it reacts instantaneously to current, so when you hook it up to the pickup unit, for instanced, it will flash very quickly and let you know that the pickup is working.

The thing on the left is a spark tester. GET ONE!!! It will so-easily tell you whether you have spark, and this can eliminate a gazillion questions about whether we are trying to fix a spark problem or a carb problem. Since our TCI system uses the screw-thread type of spark plug, I had to modify this particular tester since it was designed for the fat-top spark plugs. I simply filed the blunt probe to the point where the spark plug cap would grab it. You screw the fat-top onto your bike's plug, and clip the tester on. EASY

This is what it looked like "before":

They cost about $6, so GET ONE!!

 

[bpeckm]

OK. So. first step: LOOK FOR SPARK

Use the spark plug tester. Just hook up one end to the spark plug, and plug the other end into the spark plug cap. Easy. Do it.

Now crank the bike, or kick it: even if it doesn't start, you will be able to see whether there is a spark, or not. If it is turning over and you don't see a little light flashing, then you have NO SPARK.

One thing to remember with TCI ignitions is that the coil can be damaged or ruined if you don't ground out the coil output, either using a grounded spark plug or whatever. This method is dead simple: no pulling/re-installing spark plugs, wondering whether you have a good ground, etc.

If you do see a spark, but it still doesn't start, then you can go on to test other things (like carburetors, timing issues etc)

 

[pamcopete]

bpeckm,

Great writeup on the TCI and basic ignition testing. I have one of those testers that you recommend and it's good to use it instead of just a spare plug laying on the engine.

 

[bpeckm]

I had an intermittent problem that ended up being in my TCI box, so I had to learn about this ignition system. In theory, it's pretty simple, and it's pretty simple to diagnose. Troubleshooting works best when you use a system to isolate the problem.

So we started by testing the spark....

Let's assume that you have NO SPARK, as tested above. The next easy thing to do is to test whether you are getting voltage at the COIL. The coil is pretty simple: it has 12vdc supplied to it by the red/white wire, and the path to ground is interrupted (as computed by the TCI) by the orange wire, and this interruption is what lets the coils build voltage to effect the spark. (If you are familiar with old-school points systems, as in the older XS's, the orange wire would be the one that goes to the points, but here it goes to the TCI.) Look at this picture below, and you will see where those two wires go into the coil.

You want to test for voltage at the red/white wire, which should have a nominal 12vdc when the ignition switch is "on". This red/white wire always has voltage when the ignition is "on", so if you if you have no voltage here, make sure that the ignition is "on", and the kill switch is on "run".

It is easy to test the voltage where the two wires plug into the coil: disconnect the red/white wire from the coil, put your + probe (red) into the loom-side red/white (make sure you have a GOOD ground!), and turn the ignition ON.

If your switches are all ON, you should see a nominal 12 volts. If it is below the battery voltage by more than a couple of tenths, you should clean switch contacts, plugs etcc.... these bikes are old and the wiring was well done from the factory, but clean connections are next to godliness in low-voltage electrical work!

 

[bpeckm]

If you have voltage at the red/white feeding power to the coil, as tested above, there is another simple test to be done to the coil, and this is to test the windings.

Inside that plastic coil thingy are miles and miles of thin copper wires that inductively create a much higher voltage: the voltage that "jumps" and makes the SPARK. If these miles of little wires are shorted out, or broken, the coil will not put out SPARK voltage. So, we test for continuity/resistance.

Basic primmer on continuity and resistance... the flow of dc through a wire (called current) has some resistance (the bigger the wire, the less resistance, and conversely)... think of a simple incandescent old-fashioned light bulb, which has so much resistance that it "glows" and gives off light. This resistance can be measured, and it is measured in "ohms". Books have been written about this, but let's keep it simple for our purposes!

One measures resistance with the ohm-meter (the "O" in the old VOM). The ohms scale on a digital VOM is self-adjusting, so just set the meter to ohms. I always test the meter when I switch to that range, as my meter has an audible tone when I touch the probes together (signalling NO resistance!).

To test the primary resistance: unplug the two leads, and touch the two leads to the two wires (red/white and orange, it doesn't matter which probe is where for resistance).... this should read about 2.5 ohms. If you get infinite resistance, there is a broken lead somewhere inside. If you get an audbile (no resistance) there is a short somewhere.
Edit; gggGary; To test secondary resistance: remove both plug caps from the plug wires (they are threaded into the plug wires) check that you can see shiny silver wires inside the insulation. connect your probes, one to each plug wire. measured resistance should be between 9K -13K ohms, ie 9,000 to 13,000 ohms. The spark plug caps should each measure 4K to 7K ohms. end edit. Check either plug wire to the steel coil core, should show infinity or no beep.
These tests are both go/no-go, and simple. To be sure, there are other problems that can occur with coils, but these two test will help isolate whether your problem might be in the coil.

I like to ground everything to everything, so there is a black ground wire from the wire loom to the frame here, as well as my big black wire from the battery to the engine, which is bolted to the frame (metal to metal!).....

 

[bpeckm]

The next test is to see if the signal is being generated. The above has established that there is voltage to the coil, now we determine whether the coil is "being told" when to fire...

Here we are going to test the resistance of the pickup coils... There are two tiny coils behind this black thing on the top of the area, and the TCI box uses these two signals to tell the coil when to fire... it is measuring and computing engine timing, spark advance and all of that stuff, and sends it to the coil through the orange wire. Below you can see three wires going into a black cover: black, grey and orange.

Again, a pretty simple test: unplug the three prong lead that comes up from that pickup... this wire snakes from the alternator/pickup area and goes up behind the primary chain sprocket. Look for the plug that has a black, grey and orange wire, and probe the engine/alternator side of that plug....

You are going to take two separate ohms/resistance readings: grey to black, and orange to black. My bike is an '80, so the proper spec is about 750 ohms. Both readings should be the approximately the same. If either is off-spec, the pickups are nfg.



I have also learned that there are is another simple test for that pickup. There can be a weak signal from the pickups' weak magnetic field...To test this, unplug the regulator/rectifier (big plug!), which will shut off and remove the alternator's magnetism, and then see if there is spark... if you fire with the regulator unplugged, you may have a weak pickup signal.

 

[bpeckm]

OK, so those are the easy "passive" tests... this next one is pretty interesting, too.... it tests the pickups under "live" conditions.

Plug the three-wire plug (grey, orange, blue) back together. I initially tried this with my digital VOM, but it would work better with an analog meter, and it works the treat with my LED, and can also be done with an oscilloscope. You are looking for an active "signal" from your ignition pickups....

Plug in your two "probes"... you can test it at the six-prong plug for the TCI, or at the orange wire at the coil. If you do it at the six-prong, put the neg probe into the black wire, and the pos plug into the orange wire.... this is the same orange wire that ends up at the coil.

Once it is hooked up, crank/start the engine. If your TCI is working properly, it is processing the pickup signal and sending it down the road to the coil.... my LED flashes rapidly when the engine starts, an analog meter would see the needle jumping, my digital VOM made funny little squiggles (which I interpreted to mean that it was getting a signal, but it was cycling so quickly that it could do a read-out), a 'scope would generate a wave form of on/off/on/off. These are all ways to see the signal that triggers the coil's output (SPARK!)

 

[bpeckm]

I have to give credit to many for steering me through my intermittent problem, which ended up being my TCI.

DOGBUNNY posted this, re an invaluable aid:

The easiest and most fool-proof way to test a TCI is to swap it for a KNOWN good TCI.
You can also try this manual:
link to manual
It's a pretty good trouble shooting guide made by Yamaha. It goes through a 4-cylinder trouble-shoot, but if you are an above average electrical guy as you say, then you should be able to figure it out. A couple of the wire colors in the guide are different, it helps if you have a color-coded wiring diagram of your year.

Much good information from gggGary (AND a known-good TCI, thank you!);

and thanks to XJWMX for advice on solder joint problems in the TCI;

The thread that got me inspired to write this up, which was my search for the problem, and may be of help as well: http://www.xs650.com/forum/showthread.php?t=23853

 

[bpeckm]

Below is the raw material from the very-useful link posted by DogBunny

 

[bpeckm]

Yeehaw... hope this helps!


I went from



to . . . . . . . . .

 

[gggGary]

Good write up, thanks for doing it and getting those troubleshooting steps "on the record"

 

[bpeckm]

gggGary: Thank YOU for all the advice you give to all of us here... and btw, if anybody sees anything wrong or has suggestions for something different, do let me know!

Happy New Year !

 

[XSLeo]

A good write up. It will help many figure out their problem. One thing I did find wrong was that you claim a signal is sent to the coil on the orange wire. This is wrong. The orange wire is a ground for the coil. The TCI grounds the orange wire so current flows through the coil. When the TCI gets the signals from the pickups to tell when to fire the coil it ungrounds the orange wire.
This is essentially the same as points. Power flows to the coil on the red/white wire, the orange is the wire to the points. As the ponts open and close they ground and unground the orange wire.
Leo

 

[gggGary]

Hey xjwmx you should get bpeckms TCI and do an inspection, repair, test. keep you hands from going crazy in the NDAK winter nights.

 

[bpeckm]

A good write up. It will help many figure out their problem. One thing I did find wrong was that you claim a signal is sent to the coil on the orange wire. This is wrong. The orange wire is a ground for the coil. The TCI grounds the orange wire so current flows through the coil. When the TCI gets the signals from the pickups to tell when to fire the coil it ungrounds the orange wire.
This is essentially the same as points. Power flows to the coil on the red/white wire, the orange is the wire to the points. As the ponts open and close they ground and unground the orange wire.
Leo

Thanks, yes, I did know that, but what I wrote is not clear, I will edit. Thanks for pointing it out!

(My old-motor background is with points/condensors, so the grounding function is pretty obvious there, and it follows that the orange wire "goes to the points".....!

 

[XSLeo]

I liked they way you used actual pics to show the test hookups. That will help alot of people.
One more thing, in the pic of your stator showing the pickups, the brushes are installed wrong. The fiber rectangle goes under the metal holders, not on top.
Leo

 

[bpeckm]

I liked they way you used actual pics to show the test hookups. That will help alot of people.
One more thing, in the pic of your stator showing the pickups, the brushes are installed wrong. The fiber rectangle goes under the metal holders, not on top.
Leo

Thanks, it works fine, but didn't look right, and I was putting it together with my imagination....

 

[bpeckm]

Got 'er running.... this on Vimeo

 

[gggGary]

Hey you want to ship me the bad TCI? I would like to mess with it. Maybe not on the front burner but still interesting.

 

[Lou]

I bought my 1980 TCI earlier this year and its always had a hesitation at speed, around 3K rpm. This string and others on the forum have been great in helping me troubleshoot the issue. As I was doing the tests detailed here by bpeckm, I noticed that my pickup coils described in response #6 were heavily corroded. I used some fine grit sandpaper to gently clean them up...appears to have worked! Went for a cruise yesterday and the hesitation was gone Still need to do some more test drives to make sure but fingers crossed!

Just one more thing for folks to check, perhaps especially in humid/wet locations or when dealing with a bike from a neglectful PO.