No secondary coil resistance? Could it be?

My 1985 xj700 wont run (ah yes… the age old story). It did 2 months ago when I test rode it… all be it for just a few minutes.

But that is not why I write this.

As it stands now, it will start after MANY attempts, when I get the current battery good and charged. Unfortunately, after a few min of running (and will only run with choke engaged), it will cut out and not start again.

I'm not looking for a fix to the "big picture" just yet as I know it could be 1000 different things (and multiple ones at that!)…

Since bringing it home a few weeks ago, I repaired the fuel leak coming from both the petcock and fuel level sender with new o-rings, seals, and other hardware from Len @ xj4ever.com… Awesome to deal with by the way!

Petcock has been rebuilt and in working order as well, so I know the fuel is leaving the gas tank.

New plugs are in too. I definitely need a battery, and I know how important a STRONG battery is to the entire equation here… it is on my list of things to get.

but… I figured I'd look at other things while I wait to buy a battery and eliminate that as part of my problem.

Now that history is out of the way, I'll get to my specific issue.

In checking the "health" of my ignition coils, I'm getting a primary number of 4.2 ohms (spec is 2.7) and NOTHING when attempting to check secondary coil resistance.

I'm pretty sure I'm using the Multi-Tester correctly.

To get the primary coil reading I am putting both leads from tester into the coil lead slots (dial on tester set to 200).

To get the secondary (take the 1&4 cyl coil for instance), I'm putting the red/positive from tester to red/white wire on coil lead and black lead from tester to the #1(plug) wire… making sure i'm making contact with the metal inside the boot (dial set to 20k).

Question #1.) Is 4.2 ohms too far out of spec? The book says +/- 10 percent is ok... but the math here is bad...

Question #2.) What am I doing wrong with secondary resistance? Is is possible to get NO activity on the screen of the tester? When I touch the two probes together, I do get activity, so the meter appears to be working correctly. It seems to be reading my (weak) battery correctly as well… Am I reading the diagram/directions wrong from the service manual?

Again, could the coil(s) be THAT dead... It does run when it feels like it!

 

You should test from one HT lead to the other (caps removed)

 

the manual you are using is wrong. here is the proper way to test your coils.

CN

 

CN,

Thank you... Will try it the way your diagram suggests and see if I get any activity. The diagram I'm using (and have posted in this thread) is from the Yamaha XJ700N/NC service manual. I have read in other threads about being cautious of BAD information that sometimes appears in the manufacturer manuals... I guess this is one of those times...

I was floating around YouTube. and I found this video:

It is exactly what I experienced. Checking the secondary with only 1 HT lead and the other in the connector of course.

Will report back.

Again, thanks...

 

that's weird because there is no electrical connection between the primary wiring and the secondary wiring inside the coils.

CN

 

Ok, tried it the way your diagram suggests (as well as what wizard said) with a tester probe in each of the HT leads. The screen starts out with a "1" on it (as it did before). Then I do get a reading for just a "blip" of time, then returns to the "1." I can't seem to get the reading to stay on the screen for more than a moment. Each time I press the probes in, the number that appears momentarily is anywhere from 10.xx to 20.xx.

I'm curious about what Wizard said about "caps removed." Do the hard, plastic 90 degree "boots" that connect to the spark plugs come apart? They look pretty solid on the end of each HT lead.

 

the caps do come off the wires. you can unscrew them from the wire. if your xj is air cooled, the caps are good for an additional 5k ohms of resistance per cap. if it is water cooled, they are good for an additional 10k ohms each. it would be best to remove them and test them individually as well. to make sure you are getting a good connection in the boot, put a spark plug in and touch your probe to the center electrode. you should also have non-resistor plugs.

CN

 

Update!

I unscrewed the caps and got a solid display on the meter that stayed there for as long as I held the probes in place. For the 1&4 coil: 12.09k for the 2&3 coil: 12.26k.

Then I put the caps back on, pulled the 1&4 plugs from the engine and tested to the center electrode as CN suggested. It responded as it did before with just the caps… a brief "blip" of a number, then gone… I did notice the numbers that appeared briefly, were higher (with cap resistance)… makes sense…

Still, the reading would not hold on the screen.

Given the caps were not part of the initial test (where i got a good display), is it safe to assume that the actual numbers, adding the 5k per cap when testing a single coil, adds a total of 10k resistance, therefore putting the coil WAY out of spec?

Does the math really look like: 12.09k (reading) + 5k (first cap) + 5k (other cap) = 22.09k ???

It appears the caps are the "break" in the chain here…

The plugs are brand new from Len.

Bought: HCP1294SET4 Original BP8ES NGK SPARK PLUG, stock NON-RESISTIVE plug

Two days ago, after putting the new plugs in, I had the bike running (roughly) in the driveway. Again… it was only for a few min as previously posted. When I just pulled the 1&4 plugs for this test, #1 plug showed some use… #4 looked as clean as the day it went in. #1 is not pulling his weight around here!

What are your thoughts now that I have some solid numbers from the meter, be it caps on or off? Deep 6 the coils?

New battery coming soon. I feel pulling the plug and grounding to see what kind of stark I get with a weak battery is not a good indication…

Thanks for everything.

 

Clip 1/4 inch off of the end of the coil wires, reinstall the caps, and see how she runs. Also chek the caps separately. The resistor can degrade over time.

 

Yes, that is correct.

Yes, that is correct, too. Your coil secondary (output) circuits are well within spec.


K-moe's advice to check the cap resistance (separate from the coils) is good advice, too.