How to test the ignition coils

[Anonymous]

All four plugs on my bike have a very weak spark and the bike won't start. I have very limited knowledge of electrics - I know how to test the battery and check that it's charging OK but that's about it. I want to test the coils but don't know how. What tests should I run with a multimeter and what readings should I get? I really need the basics like which probe to put where to obtain each reading.

Thanks

Roger

[earlfor]

Re: How to test the ignition coils

Ahhhh, an easy one. :-)

To check the primary side of the coil, set your multimeter to the 200 ohm setting. Disconnect the wires on the positive and negative terminals on the left coil. (remove gas tank first eh eh ) Hold the red and black leads of the multimeter on the + and - coil terminals. The reading should be between 2 and 5 ohms. It will probably be slightly over 3 ohms. Anything between 2 and 5 is OK. (repeat for the right coil)

To check the secondary side, you measure resistance through the spark plug caps. Remove the plug caps from the spark plugs on cylinders 1 and 4 (that is the left coil) Set the multimeter to 200K ohms. Put one meter test lead into the metal contact inside the plug cap on plug wire 1 and the other lead of the meter inside the plug cap on plug wire 4. The reading should be between 30-40K ohms.

You might want to also check for voltage level going to the + wires on each coil. Set the meter to 20 volts DC and check to see what voltage you have at the battery terminals. Then turn on the ignition and check the voltage available at the orange and white + wires that connect to your coil + terminal. Meter red lead to orange/white positive wire and meter black lead to ground on the bike's frame. I have about a 1/4 volt drop between voltage at the battery terminals and what is available at the positive orange/white input lead to the coils. If you have a large voltage drop, it would probably be a good idea to check connectors and grounds for corrosion. The coils could be fine, but if voltage input to them is too low, they will not produce a good spark at the plugs.

Earl

All four plugs on my bike have a very weak spark and the bike won't start. I have very limited knowledge of electrics - I know how to test the battery and check that it's charging OK but that's about it. I want to test the coils but don't know how. What tests should I run with a multimeter and what readings should I get? I really need the basics like which probe to put where to obtain each reading.

Thanks

Roger

[Anonymous]

Thanks- and a question about the igniter unit

Thank you - that's just what I needed.

While I'm at it, have I got this right? If the igniter unit is faulty, that could also explain a weak spark? If I've understood my Clymer manual right, the igniter unit amplifies stuff from the signal generator and triggers the coils so, if I disconnect the igniter, I should still get a weak spark at the plugs.???

I've run the igniter test set out in the Clymer manual. I connected the positive terminal of a 1.5v battery to the blue igniter unit wire and the negative terminal to the green. With plugs 3 and 4 removed and grounded on the engine and the ignition on, neither plug sparked. According to the manual, that means the igniter unit needs to be replaced. However, as I've never run this test on a bike that's working properly, I'm not sure enough of what I'm doing to be sure I've got this right and to rush out and order a new igniter unit.

Roger

[earlfor]

Re: Thanks- and a question about the igniter unit

I just realized I made a typo in my previous post, for checking the resistance between the plug caps, I said "set the meter to 20K ohms"
That should have been set the meter to 200K ohms.

Earl

[quote="TEMS"]Thank you - that's just what I needed.

[earlfor]

Re: Thanks- and a question about the igniter unit

To check the signal generator, measure the resistance between the leads.
On my bike the colors are yellow, blue, black and green. The colors may be different on your bike. The resistance between pairs should be between 100 and 300 ohms.

To check the ignitor box with a multimeter, set the meter to the X 1 ohm scale. Connect the meter + lead to the black terminal of the ignitor box.
Touch the meter - lead to the green terminal of the ignitor box. When the - lead of the meter is disconnected, the number 2 and 3 sparkplugs should spark.

Connect the meter + lead to the yellow terminal of the ignitor box. Touch the - meter lead to the blue terminal of the ignitor box. When the - negative lead is disconnected, the number 1 and 4 sparkplugs should spark.

My usual method is to check the resistances on the four wires of the signal generator. If those are between 100-300 ohms. I remove and ground the plugs on the engine and turn it over with the starter, if there is no spark, then its pretty safe to assume the ignitor box is faulty. (assuming its connected and powered up) :-)

Earl

Thank you - that's just what I needed.

While I'm at it, have I got this right? If the igniter unit is faulty, that could also explain a weak spark? If I've understood my Clymer manual right, the igniter unit amplifies stuff from the signal generator and triggers the coils so, if I disconnect the igniter, I should still get a weak spark at the plugs.???

I've run the igniter test set out in the Clymer manual. I connected the positive terminal of a 1.5v battery to the blue igniter unit wire and the negative terminal to the green. With plugs 3 and 4 removed and grounded on the engine and the ignition on, neither plug sparked. According to the manual, that means the igniter unit needs to be replaced. However, as I've never run this test on a bike that's working properly, I'm not sure enough of what I'm doing to be sure I've got this right and to rush out and order a new igniter unit.

Roger

[Anonymous]

OK, I think I've got 3 problems. I'm not sure if they're all separate or if they're related.
The resistance in the coils is 4.5 ohms so that's OK.

With the multimeter set at 200k ohms, the resistance through spark plug caps 1 and 4 is 21.9 ohms - quite a bit lower than you say it should be. What does that suggest?

The battery reads 12.33 volts. The voltage at the positive terminal of the left and right coil is only 10.47 and 10.54 respectively. As you suggest, I'll have to look for bad connections.

I've still only tested the ignitor with a 1.5 battery as I described earlier. The manual says to set the multimeter to R1 and you say to set it to x1. My multimeter has only the following: 200, 2000, 20k, 200k and 2000k. I assume the one I need is 200 but, as I'm not sure I didn't try it.

Thanks again
Roger

[earlfor]

[quote="TEMS"]
With the multimeter set at 200k ohms, the resistance through spark plug caps 1 and 4 is 21.9 ohms - quite a bit lower than you say it should be. What does that suggest?

********* What is the resistance between 2 and 3? Most probably the caps need replacing. NGK makes "screw on" replacement caps and they cost about $4 each at your local dealer. They are made in various resistances. You want the 5k caps.*******



The battery reads 12.33 volts. The voltage at the positive terminal of the left and right coil is only 10.47 and 10.54 respectively. As you suggest, I'll have to look for bad connections.
*******While youre in there, also check for any brittle or stiff wires too********


I've still only tested the ignitor with a 1.5 battery as I described earlier. The manual says to set the multimeter to R1 and you say to set it to x1. My multimeter has only the following: 200, 2000, 20k, 200k and 2000k. I assume the one I need is 200 but, as I'm not sure I didn't try it.
************I've never seen a meter without an x1 scale.
You cant hurt the ignitor box by using the 200 scale though. You dont connect a 1.5v battery to the ignitor box to measure resistance. The ignition is off and the box is unpowered.***********



What values did you get on the pickups?

Earl

[Anonymous]

Earl,
Sorry, what do you mean by the 'pickups'?

I'm still puzzled about the igniter unit. The Clymer manual says to remove spark plugs 3 and 4 and ground them on the cylinder head. With the ignition turned on, it says to connect the positive multimeter probe to the blue wire and the negative to the green. As the negative lead is connected, the No. 3 plug should fire and, as the negative is disconnected, the No. 4 plug should fire. That doesn't sound right to me but it is what the manual says. It also says that a 1.5 volt power source such as a dry cell battery can also be used for this test. As I understood it, this test was to simulate a pulse from the signal generator - not to check resistance.

I've now tried the test with the multimeter set at 200. Neither spark plug fired. If I could try the same test on a bike that I knew was working correctly then I'd be more inclined to believe the results. I've just seen the price of a new igniter unit and I really hope I don't need one. My next step is to try to find the reason for the drop in voltage at the coils.

Glad you mentioned new spark plug caps - I'd already got some more on order, though without really knowing why it was a good idea. I didn't think to check the resistance between 2 and 3 (doh - that would have required initiative!).

Roger

[earlfor]

*****I'll just intersperse my comments...easier that way.

Earl,
Sorry, what do you mean by the 'pickups'? ******* I'm sorry, I tend to lapse into my habit of calling the signal generator on the crankshaft end, the pickups.......yes, I know thats incorrect :-) ********

I'm still puzzled about the igniter unit. The Clymer manual says to remove spark plugs 3 and 4 and ground them on the cylinder head. With the ignition turned on, it says to connect the positive multimeter probe to the blue wire and the negative to the green. As the negative lead is connected, the No. 3 plug should fire and, as the negative is disconnected, the No. 4 plug should fire. That doesn't sound right to me but it is what the manual says. It also says that a 1.5 volt power source such as a dry cell battery can also be used for this test. As I understood it, this test was to simulate a pulse from the signal generator - not to check resistance.
******** The above proceedure doesnt make sense to me either. However, as you say, the purpose of the test is to simulate a pulse from the signal generator and cause the plugs to fire. That is not the purpose of the resistance test I listed for you. The purpose of the resistance test is to determine if the transistors in the ignitor box are within specified limits. If the circuits inside the ignitor box are within specs, then the box has to work properly.

There is an easy way to sort this out. The signal generator (on the crankshaft) has four wires coming from it that end in a square, four prong plug. Look at the left side signal generator and note what color the two wires going to it are. Set you meter as I said earlier and place the red test lead on one wire of the set and the black lead on the other wire of the set. Is the resistance within specs? Then check the right side signal generator pair of wires. If both sides are with the specs I gave, then there is no problem with the signal generator. (if you make this test at the four prong plug end and the results are within limits, then there can be no short or wiring problem on the signal generator side either.)

We now have two possibilities left. Either the ignitor box is not working, or the coils are not working. As you said, you have low voltage to the coils and you have too low a resistance reading on the secondaries. If the coils are not working, you can not expect even a perfect ignitor box to cause a plug to fire. You need to fix the coil problem before you will be able to do a firing test with the ignitor box.

A BTW here: yes, you can retrofit a points ignition if the ignitor box does prove to be faulty. I know the boxes are expensive. In fact, a complete, new Dyna 2000 ignition system costs less than a new replacement stock ignitor box.

Take care of the coils and verify the working of the signal generator first.
Then we can move on.

Hang in there, :-)

Earl




I've now tried the test with the multimeter set at 200. Neither spark plug fired. If I could try the same test on a bike that I knew was working correctly then I'd be more inclined to believe the results. I've just seen the price of a new igniter unit and I really hope I don't need one. My next step is to try to find the reason for the drop in voltage at the coils.

Glad you mentioned new spark plug caps - I'd already got some more on order, though without really knowing why it was a good idea. I didn't think to check the resistance between 2 and 3 (doh - that would have required initiative!).

Roger

[Anonymous]

Thanks again. Unfortunately, this is going to have to wait until the weekend - my bike is under cover outside so I'm limited to daylight hours at weekends.

Roger