Really Need Some Help and a Spark

If anyone has any idea what I am up against here it would be of great help... I had an issue a couple weeks ago where my coil for 1/4 burnt up.... twice. After reading on here and testing and probing every wire on this machine I came to the conclusion that the TCI was bad (actually pretty certain it was since noting was coming out of one of the channels.. Well I got on Ebay and spent a ridiculoos amount of money to purchase a 41 year old TCI to replace a 41 year old TCI, sounds brilliant. So fast forward through a l0t of cursing, a very sore back, hours of reading, and a fortnight of headscratching and I am basically at point where if I do it quick enough no one will see me push the bike in the river. I have no spark.... none, zero. I had one this morning but I believe that one was late getting up and had to jet to catch up with the rest... I have checked, double check, read the manual, OHm read and voltmetered anything that wasnt moving within a 5 ft radius, cleaned every ground, checked all connections and as far as I know, this bike just doesnrt like me and decided to quit. I have power, power to the solenoid, to the starter, my pick ups are reading the correct resistance, the TCI putting a signal out on both channels, the relay works the pig tail frtom the relay to the coils has power. The plug wires have the correct resistance......The only thing that may be weird, welll actually is and I just realized it typing that this is probably a problem. The power from the TCi channels reads the same on the red out and the orange and grey. When I test at the coil there is power when I ground to frame but nothing when I test positve and negative on the coil itself


Obviously the model would be helpful.... Thanks Dan

1981 XJ650 Maxim

 

Which model?

 

Oh damn..... lol. 1981 XJ650

 

IMHO it would be good to try a known good TCI. It is possible that the “new” one is not so good either.

and you’ve tested the pickup coil,right?

hopefully someone has one you can try

also, there are dark wizards who can work on TCI units, so don’t throw anything away

 

i just tested the resistance at the TCI. Im not sure if it means anything or not but i swapped out the plug wires and was able to get a weak spark a couple times.. Very faint, very orange, but there.. Also shouldf have mentioned that when I was able to get a spark earlier it was blue and decently strong but it was when I released the start button.

 

Releasing the start button means more electricity for the TCI. Is that why you are getting a blue spark? When cranking the engine if the battery voltage drops below 10 volts you won't get a spark. Try another battery and test yours. Put multimeter leads on the battery set at 20 volts and crank the engine voltage must stay above 10. Might help worth checking it.

 

Sounds to me like the TCI is not doing its job. Then when you let off the starter and the current goes away it sparks

 

Its literally a brand new battery

 

Unlikely it is the battery then. What happens if you try and bump start the bike so all the current is going to the ignition system. If it runs on all four trying that then the TCI is fine. You can also jump it off a car battery if you want. Even with a new battery if you are cranking the engine a lot it may not have enough to trigger the transistors in the TCI.

 

You might try this the TCI back can be removed the circuit board maybe corroded . Spray it down with contact cleaner , I had one once that was pretty corroded , another item sometimes it may need to have the circuit board ressoldered . Don't give up you can fix this!!! Cheers

 

Here is the TCI repair thread. Lets you see into what can go wrong as Jetfixer stated.

https://www.xjcd.org/TCI_repair

 

Since no one will respond on this I'll put it here..
https://www.xjbikes.com/forums/threads/aftermarket-ignition.45931/page-3#post-671259

 

Likely shorted output transistor in TCI but could also be TCI internal protect circuit is not working

That would be normal, the exception being when the ignition is first turned on (kill switch on) and power is applied to the TCI. At this point one of the channels will go low (channel can be dependent on position of reluctor) for about 3 seconds, and then back to 12V. This is to protect the coils and the TCI as a constant on condition will overheat the parts.

That is also normal and like above the exception is when the ignition is first turned on and one of the channels is conducting then the coil primary (positive to negative) will measure near 12V. If the TCI channel is not conducting then there is no voltage drop across the coil primary so the positive and negative are at the same potential

Low voltage can cause a weak spark as suggested by other comments, and is particularly noted when there is a weak battery involved as the voltage to the coils is significantly reduced. Since you have a new battery just be sure it is charged fully, and try checking the voltage at the TCI R/W wire before cranking and when cranking. It is normal for the before cranking voltage to be below battery voltage because of drops in the switches, connectors, and wiring.

I have no experience with the aftermarket ignitions

 

Thank you for the wealth of info. I’ve made the executive decision that it is the TCI so now I have parts for one… yay . And I’m still getting used to how this site works so I’m not sure it posted correctly but my other question is on the HEI conversion. So not necessarily aftermarket more of a forced modification at this point. I just need a complete wiring diagram or explanation of what each pin on the modules do and how to compensate for the loss timing advance. I can figure out the rest. Or pretend to real good.


ADD ON: maybe I’m just completely misunderstood how these TCI work, maybe not. But what I’ve gathered is the timing is basically controlled by the resistors. As the RPM increase the voltage increases which moves onto the the next resistor and changes the timing accordingly… is there not a way to wire the appropriate resistors into the GM setups? Before you laugh at me disgracefully, please keep in mind that I really have no idea what the f&@# I’m talking about. I’m just verbally vomiting bits and pieces from what’s left of my brain (trust me, my 20s were scary rough) take on the last two weeks of soaking myself in XJ forum knowledge.

 

I meant amps

 

So the TCI timing is done within a special ASIC chip in the TCI (Application Specific IC). The chip is neither available to buy or was a datasheet ever released on it so inquiring minds could understand how the black box works. Anyways, there are millions of miles of good time XJ fun running with a TCI, so I can't see the reason to reinvent the wheel when they are readily available. I sent a PM and can help check out the TCI, TCI's that you have if you would like