Basic ignition system and tci help??

Hi, I have just purchased an xj tci unit which i am trying to fit to a different engine. From other post's i have found wiring diagrams and pin diagrams that seem to show a constant 12v feed to both ignition coils??

Please could somone explain why this is, as i though only pulses of high voltage where sent to the coils from the TCI unit.

here is the diagram in question and i assume the red/white to be 12v positive.

This has realy got me stuck, thanks for taking a look.
Chris

 

As I understand it, the TCI switches the coil's earths instead of the lives. I'm not sure why this is, but it's how they appear to be in my diagrams too...

Also, the TCI is not the same as CDI in that it doesn't send a "spike" of voltage to the coils, it uses transistors to switch the coils on/off in much the same way as points would have done Also, I believe it cuts the earths off if the bike's left switched on/not running for a few seconds to stop the coils overheating as they would do with points so don't mistake this for a duff TCI during testing, I think it only holds the earth on for 2 seconds after power up if it sees no signal from the pickups.

Hope this is some help, and welcome! Good to see another UK owner & not a million miles away from me either! Please have a look at the brake/tyre threads linked in my signature by the way, we'd like to keep you alive & well if we can 8)

 

This is what I feared. Do you think that my CDI coils could be wired to work like this? ie like old-school coils. or are they different in some way. Thanks for sorting that out for me.

Ps my bike had the same problem with delaminated rear brake shoes, both had become completely detached and lodged in the hub. inconvenient for me but it could have been much worse if i was riding

 

I think you'd be better off using a coil rated for whatever TCI you're using to be honest as ones rated for a CDI system might have significantly different winding resistances & require much higher voltage to operate properly. People here have had good results with Dyna coils I believe, if you don't want to use originals.

What coils have you got at the moment? and what's the code on the TCI unit? (it should have a sticker with for example
"type TID14-37

58L-10" or similar)

And perhaps most importantly, what are you actually building here, because different TCIs have different advance curves/limits so will start & run pretty much any 4 stroke in line 4 you care to wire them into, but could cause serious issues if the timing is wrong.

Glad you found the brakes early on, it's a horrible thing to think about what a loose one could do! 8O

 

Coils that are designed for a CDI aren't going to work with a TCI.

In a CDI system the CDI builds up a high voltage charge that is released (discharged) to the coils. The coils then step up the voltage to fire the plug.

TCI coils are like in a point ignition system. The coils build up a magnetic field while the primary coil is powered. When the power is removed the field collapses inducing high voltage in the secondary winding.

The coil doesn't care whether you interrupt the (+) or (-). I suspect the TCI drops the (-) just because that's how it was done with ignition points.

In addition to the problem with the coils how would you trigger the TCI? You can't just assume the pick up from your CDI based engine will work with it.

 

+3. Bingo, bingo and more bingo.

My only comment is to agree in regard to the TCI dropping the ground because that's how it was done with points. Of course it is. Yamaha was famous for "parts room engineering." Just because some models got TCI when some still had points didn't mean they wanted to go and reinvent the wheel or anything. TCI was more or less a "drop in replacement" for the points and mechanical advance mechanisms that came before.

Listen to Carl, he knows what he's talking about.

 

A bit pedantic, but the reason the TCI drops the (-) is because NPN transistors have historically always been better and cheaper than PNP transistors. This fact makes it easier to build a good low side switch than it is to build a good high side switch.

Believe me, if it were easier and cheaper for them (and everyone else doing electronic ignition) to break the (+) side, then screw history... That's what they would do. But they don't.

Electronics just works better when referenced to ground.

 

I don't know anything about transistors, but should have guessed it was the less expensive solution (for some reason). When you're building in volume those pennies add up.

Thanks for the info.

 

The code is TID14-05, the thing im trying to make it run is a 70's outboard engine. A new cdi unit for the outboard would set me back £280 so im trying to use what i have to prove that with the new part, it will run.

I am going to swap out the CDI coil for a standard coil and pray that the hall effect sensor will trigger the TCI. If i could just get a spark id be happy and i could reassemble my xj

It has at least taught me many things about ignition systems and wiring diagrams. Thanks to you all for contributing to my horrendous bodge. Ill let you know how it works out for me tonight

 

Wow 8o I'd say if you insist on doing this, at the very least check the resistance values of the pickup coil to see that it's somewhere "in the ball park".

Obviously the simple answer is don't do it, but if you really must then please check your pickup first. Personally I'd just do a compression test on the outboard & see if the spark plug gets wet with fuel when you crank it over. If you have those two things & no horrid noises on cranking I'd just bite the bullet & buy the proper CDI. After all, if it's worth £280 to you it's worth £270-odd to the next guy with that type engine if you don't want it afterwards.

Just out of interest, do you have the old failed CDI? if you still have it & are going to just throw it out then maybe before spending out on a new unit you could post it to me instead and I'll open it up & see if it can't be resuscitated :wink: (I know *some* of what I'm talking about too Fitz, I'm just better at doing than putting into words lol)

 

I think you'll find cdi coils have around 1.7 ohms primary resistance
Your TCi is looking for 3 ohms.
Running a TCi with a cdi coil draws too much current and the TCi won't last long.
A cdi with a TCi coil might hurt the coil from too much voltage.
So whatever you do, don't do it very long.

 

The harness to the CDI should include leads from the charging coil in addition to the pick up coil. Hook those up to the TCI and you'll be a long term pedestrian.

Assuming you do get it to run you haven't narrowed it down to the CDI. You'll also have eliminated the coil and stator (charging coil) from your test. Basically, you'll have proved the pick up coil works (at list with a TCI).

You'd be ahead putting your effort into a proper diagnosis.

 

Yeah no kidding. And from the sound of things, the current course of action also includes a good possibility of damaging the TCI which it sounds like your bike might need.

Might want to step back and re-think this.