How to diagnose the CDI

[gjohnson]

I am pretty sure a bad CDI is causing my starting issues with my 1982 GS450L, how would I go about testing this before dropping $150 on a new CDI?

 

[BassCliff]

Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. gjohnson,

From the collection on my little website:

Igniter/Signal Generator/Coil Test
Igniter Repair/Testing (2MB PDF)

There are more troubleshooting tips in the Electrical Odd and Ends page.

Acutally, I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

 

[Steve]

Since there is no "CDI" on the bike, it's real easy to troubleshoot.

But, as BassCliff has pointed out, there are places where you can go to check your ignitor.

.

 

[gjohnson]

Since there is no "CDI" on the bike, it's real easy to troubleshoot.

But, as BassCliff has pointed out, there are places where you can go to check your ignitor.

.

You sir are absolutely correct lol, I was shopping ebay and they are all referred to as CDI units..

Thanks for the quick replies, i'll be doing some testing tonight it looks like.

 

[Steve]

..., I was shopping ebay and they are all referred to as CDI units. ...

You are shopping eBay and trusting their descriptions?

Next, you will be telling us about the wonderful quality of Craig's List ads.

.

 

[koolaid_kid]

Since there is no "CDI" on the bike, it's real easy to troubleshoot.

But, as BassCliff has pointed out, there are places where you can go to check your ignitor.

.

I am glad you said that. I saw an ad just the other day where the bike came with a new CDI unit. :-s

 

[Curly]

Hello, resurrecting this thread since it has such a helpful title for future problems.

I have what I think to be a fairly rare bike, an '85 700. So you can imagine my excitement when I found instructions on how to test my exact CDI box.

I'm having a problem where only the 1&4 coil is working. I have tested the coils and signal generator. Both signal generators are reading 155 ohms, primary coils are reading 3.6 ohms, and secondary coils are reading 35,000 ohms. For what ever reason, I'm reading 11.8v (battery has been abused quite a bit while testing this problem) on all four coil terminals. AKA: Both orange, the white, and the black.

When I turn the key on and kill switch on, I am jumping terminal 1&2 and then 3&4 with all the plugs grounded to the head. I get absolutely nothing. I tried jumping the blue and green wire, with the same results. Yet when I push the starter, 1&4 work great, and it'll actually run on 2 cylinders surprisingly well. I can plug the 2&3 coil into the 1&4 wires and it works fine with the starter.

Who's got some ideas for me?

P.S. Are those tests supposed to be done with the signal generator plugged into the CDI box, or disconnected?

 

[tom203]

Turn on ignition and kill switch-this sends 12 v positive down orange wire to coils. When the ignitor grounds out the black and white wires ( first one, then the other) going to other coil terminals , the spark plugs connected to that coil will fire. You can manually do this grounding at each coil to check spark by using a jumper lead quickly touched to a good ground.
Since you switched coil positions, your coils both seem good, but you might have a poor connection from ignitor to coil, or your ignitor is bad.

The signal generator ohm test should be done disconnected from ignitor. Your ohm reading seems reasonable. Doublecheck all connections.

 

[Matchless]

The most basic of basic tests on many bikes with pickup coils and a battery powered igniter can be done as follows:

Pull all the spark plugs and plug them into the plug caps and lay them on the motor so that the outers are grounded.

Remove the pickup cover and with the ignition switched on, swipe a bit of metal, allan key or screwdriver tip past the metal core of the pickup coils and you should have the plugs kicking out a spark. #1 & #4 should spark simultaneously and the same for #2 & #3.
If all is OK, hit the starter button and see if the spark still looks good.

If you think the spark looks weak, use a ignition spark tester which checks if a spark can jump for 6 - 8 mm or a modified spark plug with gap bent open.

This is especially useful if your battery is a bit down, as you do not have to use the starter. Hitting the starter is just a test to see if you still get a healthy spark while at the same handing the starter a lot of current, which could drop the battery voltage quite low on a weak battery.

 

[Curly]

Ok I'll test by grounding the coils to check the connection between the ignitor and coil, and then by jumping the rotor to the each of the signal generators. Well see if that works, thanks.

 

[Curly]

Ok, here's the update. The test of grounding out the rotor to the two signal "points" produced zero results. Grounding out the white and black/yellow wires at the CDI box made 1&4 coil spark, but nothing on the 2&3 again. Switching signal wires from 1&4 to 2&3 initally didn't produce a spark, but after putting the 1&4 spark plugs in, it was working, so something is up with the 2&3 spark plugs. Does this mean my $400 CDI box is bad?

These are my voltage readings at the coils:
1&4:
orange-12v
white-0v
2&3:
orange-12v
black/yellow-.25v

 

[Matchless]

Ok, here's the update. The test of grounding out the rotor to the two signal "points" produced zero results. Grounding out the white and black/yellow wires at the CDI box made 1&4 coil spark, but nothing on the 2&3 again. Switching signal wires from 1&4 to 2&3 initally didn't produce a spark, but after putting the 1&4 spark plugs in, it was working, so something is up with the 2&3 spark plugs. Does this mean my $400 CDI box is bad?

These are my voltage readings at the coils:
1&4:
orange-12v
white-0v
2&3:
orange-12v
black/yellow-.25v

Not sure what you meant by "grounding out the rotor at the two signal points"
You should actually move/pass a bit of iron (screwdriver, allan key etc.) past the front of the pickup, simulating what happens when the iron rotor passes it on every revolution. It is supposed to generate a magnetic pulse that triggers the igniter with ignition on, the coils are powered, generating a spark at your plugs.
There is no grounding out.

If you have proven two plugs to be faulty, then you have found your problem, replace them with new ones and test again. By the way your bike does not have a CDI, it is called an Igniter.

Note added: I have found some Igniters with dry joints (bad solder connections) on the output transistors in the past which gave rise to some very intermittent problems. Its usually visible. Rather first prove the igniter faulty before going that way.

 

[Curly]

Right, igniter, sorry. I get what you mean now by moving an iron something past the pickup.

About the plugs though. I realize two are apparently bad, and they will be replaced. But when putting the two good plugs in a known good coil and trying to fire them with the orange/black coil wires, I'm not getting anything. Switch the black wire for the white wire and I get spark. This is the black with orange stripe wire that's reading .25 volts.

 

[Curly]

Ok here's another little hint: I'm getting infinite resistance when testing from ground to the white wire, which is the good circuit. However I'm getting 5ohms when testing the black/yellow wire. So it seems like I have a short some where, I'll be tearing into my harness later. Its all been extended when I remounted all my electronics under the seat, however I've unwrapped both ends of the extension and theyre all still perfectly wrapped in shrink wrap.

I also got the screwdriver trick to work with my signal pickup, thanks for the clarification on that. Obviously it only worked on coil 1&4 though.

 

[Matchless]

Ok here's another little hint: I'm getting infinite resistance when testing from ground to the white wire, which is the good circuit. However I'm getting 5ohms when testing the black/yellow wire. So it seems like I have a short some where, I'll be tearing into my harness later. Its all been extended when I remounted all my electronics under the seat, however I've unwrapped both ends of the extension and theyre all still perfectly wrapped in shrink wrap.

I also got the screwdriver trick to work with my signal pickup, thanks for the clarification on that. Obviously it only worked on coil 1&4 though.

OK, screwdriver trick help saves the battery and at the same time proves the pickup as well.

Next test would be to unplug the igniter and check if the black/yellow wire is clear, no resistance and shows continuity. If so you are back at your ignitor. Examine the plug first especially the Black/yellow wire. Or pull the Black/Yellow wire out of the Ignitor plug and at the coil and just run a short direct wire of your own and see if it sparks. I am assuming you do not have a coil relay modification fitted?

If your own bypass wire does not work it could be the igniter that is faulty.
Inside the igniter there are two transistors that output the spark pulse to each coil individually. The one to the Black/Yellow wire could be faulty and can be replaced if required.

 

[Curly]

Actually it's all a moot point. I redid my gauges, including the wiring for power I accidentally used the black/yellow wire and it was grounding out the 2&3 coil circuit. Unplugged that and it's working fine now, sorry for all the trouble. I'll use the grey wire now, which I believe is for parking lights.

 

[Matchless]

Actually it's all a moot point. I redid my gauges, including the wiring for power I accidentally used the black/yellow wire and it was grounding out the 2&3 coil circuit. Unplugged that and it's working fine now, sorry for all the trouble. I'll use the grey wire now, which I believe is for parking lights.

These things happen, but the main thing is you got it sorted and did not have to buy something you did not need! Glad you are sorted.

 

[tom203]

These things happen, but the main thing is you got it sorted and did not have to buy something you did not need! Glad you are sorted.

Well, I learned alot following this saga. Thanks, Mr. Matchless! I had been wondering if the pole piece passing the signal coil interrupted a small current flowing from ignitor or if it instead caused a pulse in the coil .

 

[Curly]

It technically only sends a pulse to the ignitor. The spark pulse is entirely in the coil, with only 12v triggers being sent from the signal generator and then a timed trigger going to the coil. Remember it changes with rpm.

 

[Matchless]

As Curly said, a small pulse is generated by the pickup which then goes to the igniter where it is amplified and from there a stronger pulse is sent to the coil to generate the spark. Earlier bikes had a mechanical advance which would advance the timing at the pickups. Later bikes have the advance built into the igniter where it is advanced electronically.