Ignition coil check

So two weeks ago, I was having a non-start issue with my 81 xj650 and after posting to this forum, I learned I had mistakenly left the petcock in the prime position for a week, flooding the carbs and possibly the crankcase (given at least one of the carbs had stuck floats).

I've been assuming that was the cause of the no-start since the bike was running a week before when I bought it.

However, today I checked for spark and learned that 2 of the cylinders, 1 and 4 have no spark. Since those two both spark off the same ignition coil, I now suspect something might be wrong with that coil (even though at least one of them needs a new cap, if not a new wire).

So my questions:

How to test the ignition coil? Are there other tests I should be considering (connections into the coil?). Is there a manual or post explaining the process?


Does anybody have a part number or suggestion for a single new cap? Is it OK to replace just one, or should I consider new caps and wires?


Thanks for any suggestions!

 

You can test the primary side of the coil by measuring resistance across the orange/black, and grey/black wires out of the ignitor. They should read 2.7ohms +-10%

You can measure the secondary side by measuring the resistance across the number 1&4 high tension leads with caps removed. Should read 10kohm +-10% (or is it 20%

If those both check out, it may be a pickup coil issue. Which we'll get into if the need arises.

It's OK to replace just one, if the rest look to be in good condition. Replacing ALL of them is best, especially if their 30 years old

 

NGK LB05F for the outer pair (90 degree), or YB05F for the inner pair (120 degree).

 

Short of doing a few conclusive tests.

Swap the coils, if the problem moves with the coil, then thats the problem.

 

-Wires are molded with the coils, replacement requires surgery or splicing.

-If both plugs quit firing, it's highly unlikely that both caps failed at exactly the same time.

-The caps screw into/onto the wires, unscrewing the cap from the wire and lopping off 1/4"~3/8" or so will give the caps a new bite into the wires.

-The resistor cores inside the caps can come unscrewed all on their own, often what appears to be a faulty cap is nothing more than a cap with a loose resistor core. If you look inside you'll see screwdriver slots on either side of where the tip of the plug goes. Tighten gently if loose.

-Your problem could be the coil itself, the wiring to it, or the pickup (trigger) coil; or even TCI-related.

You need a manual. The Haynes is OK, a factory manual is better; but you need a book.

 

By the way, ignition troubleshooting procedure is here: http://xjbikes.com/Forums/viewtopic/t=2 ... oting.html

 

Thanks for the responses. Will try Fitz' suggestions to see if the caps are actually OK. If one starts working, then that could help me eliminate the ignition coil or the wiring to that unit. If that doesn't help, then I'll start these tests.

SQLGuys ignition troubleshooting guide is excellent--thanks for posting and directing me too it.

I have a downloaded .pdf of the Haynes manual, which sometimes is really helpful, and other times, a little under explained.

 

Are these ohm measurement/specs the same for a 82 550 Maxim?

I just got the bike a couple weeks ago and am going through everything, and I think it has a random miss. It runs great sometimes, and other times it has a miss.

Just wanting to check things out.

rash

 

This site says that they're pretty close (2.7Ohms, and 11K Ohms): http://xj550.sweb.cz/tech.htm

 

I'm in the midst of troubleshooting the ignition system using this guide:

http://xjbikes.com/Forums/viewtopic/t=2 ... oting.html

On step 5a. "Switch the Orange and Grey wires from the pickups".

I can't tell whether the wires into the wiring harness are crimped into connectors that can slide in and out of the harness. Or do I need to uncrimp the wires themselves from the harness? If they have connectors, they're not coming undone with increasing pressure from needlenose plyers. I'm worried if I pull too hard, I may break the wires or damage the harness.

Anybody have any tricks or methods for separating the wires from the harness? Thanks!

 

The contacts have a tang at the back of them that locks them into the connector body. They can be removed by sliding a thin steel pin into the notch above the contact to press the tang down, then pulling out the contact.

Or you can use jumpers to run from the connector to the TCI contacts.

 

SQL is correct, he usually is really good with electrical stuff but I'll warn you that you only get a couple of "removal cycles" with those tangs in the plastic connectors. Seems like after "2", it's gonna be a crapshoot if they go back in nice and snug. sliding your test lead into the back of the connector at the correct location and using the test lead as a jumper is a better bet for preserving the connector.

jeff

 

Thanks to you both. jumpers from the plastic connector to the TCI seems like the solution with the lowest impact...

 

UPDATE: Troubleshooting reveals a bad pickup coil. It took soldering custom jumpers that would fit the terminals on the TCI unit, but that did it. Many thanks to SQL for the thorough troubleshooting guide.

I suppose the next step is to order another pickup coil assembly.