how to test cdi?

i think i have a dead short in my cdi box. i keep blowing ignition fuse. i notced when i disconnect the 4 prong plug the short goes away. when i tested the two terminals close to the 5 prong plug they are connected inside the cdi . not sure if they are supposed to be that way or not. pricey part just to guess at it. i have done some searching can't seem to find anything. i am working on a 85 xj700n air cooled.

 

With the plug pulled check for continuity on the wires going back into the loom.
The only sure test for the TCI is to switch it with a known good one.

 

those two wires going back into the loom don't have continuity. when tested at the the connector. when tested at other in they do. i think i have pretty much ruled out a pinched wire. i went and tested continuity all the wires also test to see if any where shorted to ground. no where that weren't supposed to be.

 

are there any other xj that i can get a cdi from that would work?

 

Has this bike run properly before? is this something that just started happening? Any history

With acknowledgements to Chacal:

There are three main problems that TCI units succumb to after years of reliable service:

1) bad solder joints on some of the internal components (known as "cold solder joints") result in the component pieces coming loose from the circuit board, and thus they can no longer perform their function reliably (or at all).

2) component failure......a blow-up transistor, a burned circuit trace, etc. This situation can develop if you have a short-circuit in your electrical system, or hook up your battery or jumper cables incorrectly, etc. TCI units do not like "big blue sparks" in the electrical system (except at the spark plugs, of course!).

3) dirty external terminal connections.

Bad solder joints can be repaired by someone who is skilled at that sort of diagnosis and repair, and even individual circuit components can be replaced, but it's tough to find someone in the modern world of "pitch-and-plug" skill-sets who actually has the skill and patience to do this type of work. Yamaha gave absolutely "zero" electrical specifications for checking the condition of the TCI units, besides the afore-mentioned "check everything else first" type of diagnosis.

But you can perform a simple set of tests to determine whether your TCI unit is good or not, without having a second, known good unit to install in place of the suspect unit. Although these instructions were written for XS owners, the exact same thoughts apply to the TCI units on the XJ-series of bikes:

home.ptd.net/~theragos...0faq's.htm


Remember that the Red wire with the white tracer stripe should always be hot with the key on. The TCI unit grounds the gray and orange wires from the ignition coils. The ignition coils fire when the TCI interrupts the ground.

The tricky part is the TCI un-grounds the gray and orange if there is no signal from the pick up coils for a few seconds. This is to protect the coils from overheating if the key is on and the engine isn't running. So unless you check the Red/white wire to gray (or orange) really quickly, you might get false readings or a mis-diagnosis of the true nature of the problem.



All of the XJ-series TCI units are of the "4RO" style as described in the above article.

And if the above isn't enough, if you feel the need to get medieval with your TCI unit, well, then it doesn't get much better than this:

www.jetav8r.com/Vision...onFAQ.html

 

i have a nother post going titled ignition fuse blowing. if you read it it will tell you what i did to the bike to start this problem. yes it ran great till the battery got weak. then i tried to charge it. charger fell off postive. sometime while i was sleeping. and fired the ground running from the batt to the coil. so i replaced the wiring harness from the headlight back to the tailights pretty much replaced the whole thing. i just didn't want to replace the cdi on a guess. when i get home i will check with what you have told me. seemd like i cause a big blue spark that the tci doesn't like. so most likely this is the problem. i hate being broke. if i could i would just buy one and give it a shot.

do you think i killed it?

thanks for the info.
i will keep plugin along. little cussing is good for the soil. lol

 

could i use a cdi or tci out of another bike. i know the numbers are supposed to be the same number but does it matter. they all seem to have the same clips. they seem to be alot cheaper.

 

XJ's have TCI's and yes it makes a difference. Look through XJ4Ever catalog in the upper right corner to find if any other TCI's will work.