No pulse to the 1-4 Coil; Only to the 2-3 coil

The bike is a 1984 XJ750, and I'm based in London, UK.

I'm a bit sad because I don't want to part this bike, but it's getting more expensive every day. Today it's the ignition.

The bike has been in storage for a few months, so this was the first run.

I did a voltage check on the coil power wires. There is a pulse going into the 2-3 coil but not the 1-4.

My guess is that the ignition unit is malfunctioning. Is it possible it is something else? Maybe a pickup for the second coil? Fuse?

I was messing around under the headlight with the wires, but I can't imagine it is something to do with those wires.

:?

 

Won't be a fuse. Check out this diagnostic guide:

http://xjbikes.com/Forums/viewtopic/p=274100.html

 

It could be the pickup coils, you need to read them before they enter the TCI. SQL's suggestion is a great start to narrowing down your woes.
Good luck and keep us appraised of your progress please.

 

Before you get too far along searching for an Open or a Short, ... look to see that the Pigtail for the Pickup's hasn't been pinched by the Shifter Case beneath the Wire Protector at the top-front of the Case.

 

+1^^Rick, I know I've seen that happen before. WHY don't I remember these things readily like you guys?!

 

Thanks to SQLGuys writeup, I'm closer to the solution.

So looks like it is the pickups (or somewhere between the TCI and the pickups). I want to get the cover off -- but I don't have an impact driver, or even a decent screwdriver to whack with a hammer to loosen those screws.

At least it's not the TCI.

Rick, I will investigate the wires a bit more. Maybe you are right about the pinching.

 

A nice new #3 Philips will usually work well on those screws... assuming they haven't already been too torn up by a #2 Philips.

Good luck.

Cheers,
Paul

 

Off to the shop in the morning to get a number 3 phillips with a metal head then.
The local DIY guy should almost know me by name now. He sees me every morning for a new tool or part (fixing some things in the house too).
The joys of leaving your well stocked tool box in another country.

 

I have misdiagnosed.

It is (I think) the TCI

Voltage to one coil (orange) goes up to 12 or so, then down.
Voltage to second coil goes up, but only to around 1 volt or so.

This was discovered after messing around with the Pickups for much too long and not being able to figure out the results. The hangover didnt help.

I will need to look over the TCI repair posts now.

 

Read the diagnostic guide I posted earlier. What you describe sounds more likely to be a bad coil or a bad connection to the coil from the fuse box.

If the TCI is continuously grounding the coil (i.e. its output driver is shorted) you can verify that with a meter: disconnect the 2-pin plug at the coil and measure from the Orange or Grey wire to chassis. You should see very high resistance. This should be pretty close on both the working and non-working channels. If you read a few Ohms or less, then you are correct that the TCI is bad. Such a shorted driver would usually also make the coil pretty hot and may ruin the coil.

BTW, everywhere I said coil above, I was talking about the ignition coils, not the pickup coils.

 

When I have a tight screw and I don't want to strip it I use a pair of vice grips on the handle of the screw driver. Push down hard and use the vice grips for leverage. Works great.

 

Can't believe what it was. Just can't believe it.

THE REV LIMITER WIRE WAS GROUNDED

So I cut it (the yellow / black wire into the TCI). Now I have full spark. There are no words to explain how dumb that feels.

 

You should feel proud that you solved that mystery. The problems are almost always simple it's finding them that can be difficult.

 

Interesting. The US models don't have a rev limiter on the 750's and no Yellow/Black to the TCI... but, then, I know that the French market also has different (power restricted) models of current bikes. Maybe this was related.

Thanks for letting us know what the solution was.