Junkyard ignition - TCI replacement

mrriggs

XS650 Junkie
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I was playing around with a Mitsubishi J120 ignition module that I pulled off of a Mazda MPV minivan and I think it's the BEST factory ignition module I've ever seen. It has a smart built-in dwell control and clamps primary current at 7 amps, just like a Ford TFI. It was originally triggered directly from the ECU but the input threshold is magnetic sensor friendly (only requires 2.2 volts to trigger it). The best part is that it is a tiny little box that is easily mounted and wired.

My cousin picked up a basket case XS650. It had a TCI rotor/stator/pickup and that was all he had. I brought over that ignition module, a battery and a dual output coil, hooked it up with some alligator clips, and the thing fired right up and ran strong. The voltage output of the TCI crank sensor is a perfect match for the J120 module. With a slow kick, you will get no spark. With a healthy kick, the crank sensor puts out enough voltage to trigger the module and make a spark. That means that you can hook the module directly to the "advanced" leg of the crank sensor and the engine will start reliably and run well.
 
I like this Mr riggs, pictures?
A quick wiring diagram?
When I started looking I found this;
http://xs650temp.proboards.com/thread/7899/19-junkyard-electronic-ignition
Who'da thunk LOL
Brand new for $17?
Mitsubishi J120.jpg

Did you get an idea of the advance? it might allow a vacuum advance?
Found this.

mitsu j120 wiring diagram.gif
 
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The above linked 650garage thread probably has all the info you need though that seems to mainly deal with cam fired ignition using the mechanical advance. I'm about 1/2 way through that thread so far............ The biggie here is using the TCI ignition pick ups but I'm unclear about how it deals with advance. Does the module have an advance curve built in???
Back to speed reading that thread.
 
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I think automotive ignition parts are a great way to go for these bikes, because they are "heavy duty" quality. The Toyota pick-up appears to be the reluctor type and should be the usual Toyota high quality.

Agreed. I love that Riggs is always out there trying new things for the ignition and charging system. True pioneer if you ask me.
 
I didn't bring a camera to my cousin's place where we were doing the work and the parts are still over there.

The J120 module is not the same as the picture above. At some point the cross reference list got screwed up and now that in-the-distributor module pops up when you search for J120. This module mounts outside of the distributor and is a square shape, only about two or three inches in size, has two mounting tabs and a weather tight wire connector.

The applicable part numbers are;

Mitsubishi:
J120
J007T01072

Mazda:
B6S7-18-251

Ford:
F02Z-1ZA297-B

Motorcraft:
DYE-620

AC Delco:
E1954A

Standard:
LX245

Don't buy a McParts store knockoff. The real module says Mitsubishi J120 right on it. From what I've gathered, these Mitsubishi modules are extremely reliable. From the Pick-N-Pulls around here you can get them, with the pigtail to hook it up, for about $30. These were used mainly on early 90's Mazdas. There is also a J118 module that appears to be the same thing with a different electrical connector that was used in the late 80's. I haven't tested a J118 module yet to see if it functions the same as the J120.
 
Wiring is pretty straight forward. The pins are all labeled; C, G, B, IGt, and IGf. As you can probably guess, C is coil, G is ground, B is battery. The IGt pin is the trigger. IGf is a feedback signal that went to the ECU so it could detect misfire. The IGf pin is not used in this application.

Applying >2.2 volts to the IGt pin "arms" it, it fires the coil when the voltage on pin IGt drops below 2 volts. If you apply a signal shorter than what is ideal for dwell then the module will start the dwell on it's own before it receives the "arm" signal. That makes this a perfect module for a crank triggered ignition. If you apply a signal longer than the ideal dwell time then it will charge the coil based on the longer time. So this module is not well suited to conversions that use breaker points for a trigger (use a Ford TFI for that).

The TCI crank sensor is actually two separate crank sensors. One sends a "retarded" signal for starting and low speed, the other is an "advanced" signal for going down the road. On my cousin's bike there were three wires; gray, orange and black. Both sensors use the black wire for return, the advanced sensor is tied to the gray wire, the retarded sensor is orange. I didn't get a chance to hook up my scope and check polarity. I did do a quick screw driver test with an analog volt meter that said that black was positive, however that may not be valid since the sensor is triggered by a flying magnet and not a reluctor.

The module does not have any advance function built-in. We wired the black sensor wire to the IGt pin and grounded the gray wire so that the ignition would be "locked out" at full advance. This works because the crank sensor won't put out enough voltage to trigger the module until the engine is spinning fast enough to prevent kickback.

That is for a kick-only bike. To use the electric starter you would probably need to wire both pickups to a relay that switches the IGt pin to the retarded sensor when the start button is pressed. It may also be necessary to apply a bias voltage to the sensor when starting. His bike didn't come with a starter motor so I can't test this.
 
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Retard for starting, relay powered by the yellow alternator wire? probably leave the retarded pick up on all the time add the advanced one on power from yellow. aren't there harley electonics with adjustable advance curves?
 
The trouble with triggering it off of the yellow wire is that the ignition will retard when the alternator cuts out. Which may be more often than you think.

Before the PMA, I was running my bike batteryless on the stock alternator. It would cut out at high RPM due to the brushes "dancing" on the slip rings. This isn't noticeable when running a battery because the battery will step in and power the ignition when the alternator cuts out. The yellow wire, however, is isolated from the battery. If the advance is triggered by the yellow wire then it will retard the timing every time the alternator hiccups. That could lead you on a wild goose chase trying to track down a funky surge or flat spot.

I experimented with different advance curves on my bike and determined that it runs the best with the timing locked out. It's smoother, quieter, runs cooler, and has better take off. As far as I'm concerned, the advanceless TCI crank trigger setup is ideal. No need to waste time and effort adding an advance curve to make it run worse.
 
As far as I'm concerned, the advanceless TCI crank trigger setup is ideal. No need to waste time and effort adding an advance curve to make it run worse.
In that case what about disabling the advance on other systems and forgetting about advance? Weights and spring gizmos seem to be causing enough grief around here.
 
As long as you can start the engine, go for it. That's the only drawback to having the timing locked out. If you use the electric starter and/or have points/Pamco ignition and a battery then you are kind of stuck needing a retard.

With kick start and a VRS triggered ignition it is not necessary to retard the timing for starting. You can adjust the bias or reluctor gap so that the ignition won't fire until the crankshaft [and you] have built up enough inertia to overcome the burning fuel mixture.
 
Please explain again, maybe simpler, why one system will start and run at full advance and one won't. I'm not getting it yet.

When the spark comes before TDC the piston is pushing against a burning fuel mixture as it comes up on the compression stroke. The earlier the spark, the harder the piston has to push.

An electric starter simply doesn't have enough power to overcome the burning fuel mixture when the timing is fully advanced.

The kick starter alone can't overcome a fully advanced ignition. That is what leads to the dreaded kick back. But if you can get the crankshaft spinning before initiating a spark then the combination of the crankshaft inertia and the kick starter will power through it.

The trouble with points/Pamco is that they will generate a spark no matter how slow you turn the engine over. So you are just starting in on your kick, the engine is barely spinning, and you get a spark that hurls the upcoming piston back down the cylinder. Through a series of gears and levers that piston is connected to your foot. Now you are walking with a limp.

The advantage of a variable reluctance sensor (VRS) triggered ignition is that the peak voltage of a VRS is directly related to speed. The faster the speed, the higher the voltage. When you turn the engine slowly the VRS doesn't generate enough voltage to trigger the ignition module. The trick is to tailor the VRS output so that it won't trigger the ignition on a weak kick or the start of a kick. You only want a spark during a strong swift kick. We lucked out on this TCI/Mitsubishi setup. It is right on the money, no fiddling required.
 
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