• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

No spark -- not sure why

Share this page

Hegg

Hegg

Jedi Hopeful
Offline
Trying to start up my LBC and it doesn't start. I tried to check for spark and I don't think I'm getting any. So...

(1) How do I *really* check for spark? I have a multi-meter and a bunch of LEDs I could rig up (did it on my Falcon) to see, but I'm not electrically-minded enough to know how/what/why and all that.

(2) If there is no spark, how do I diagnose where the missing spark is coming from?

By the way, I checked for no spark by taking the lead out of the coil and holding it close to see/hear a spark/tick. I also put my colortune in and turned out the lights to look for a spark.

Oh yeah, and the car's got a full tune-up, except a new coil. So everythang's pretty much new.

Thanks everyone!
 
Did the no spark condition happen right after the tune up?
What vehicle are we dealing with?
Points, or electronic ignition?
Did you check for power to the coil?
Stupid question, but did you re-install the rotor? (I left one off once! Needless to say, no spark.)
Need more information to make an educated guess.
A regular spark tester works well for checking spark, but a spark plug with the ground electrode bent to give about a 3/16" gap will work in a pinch. My favorite spark tester is actually a Briggs & Stratton tool, that has an adjustable gap, and an alligator clip to ground it to anywhere handy.
To determine why there is no spark is a simple logical process of elimination.
Jeff
 
Heh, I've done the "leave rotor off" too many times to count... /ubbthreads/images/graemlins/smile.gif

It's a points vehicle, and it's a whole engine installation, so there wasn't spark before "tune-up" more or less.... basically I'm saying that I don't think it applies because the whole motor and everything has been just put in.

How do I check for power to the coil? I hooked up my multi-meter to the + and - leads and stuff, but I don't know what numbers I *should* see. Battery is freshly charged and engine cranks with decent speed. I checked continuity between the negative coil lead all the way to the close side of points, and to the other side of the points when they were closed, and there was continuity as expected. I have no ideas how I could test to see if the rotor touches everything inside the cap as it should.

Thanks for the quick reply -- hope those answers help.
 
To test the rotor, you can always just put a little felt-tip ink on there, but I think you'll find that either the coil is shot, or the points were installed incorrectly (like what I did once which was stack two parts in reverse order, so the cicuit was broken,) or the wire from the coil to the distributor is out/ the lead isn't making contact.

While I'd guess it isn't great from the system, I've found that if you unplug the wire from the top of the coil and crank the engine, if it's good it will show a spark on top.
 
Select DC Volts on the meter, and turn the key on. You should see battery voltage at the input side of the coil, + lead to the coil, - lead to ground. (Assuming negative ground.)
Turn the key off. Set the meter for Ohms, and check across the points when they are open. You should read infinity, or OL on the meter with the points open. If you show a very low resistance value, or no resistance, the points are grounded, probably due to having the wire connected incorrectly. This is probably the most common cause of no spark after a tune up, or points change. Check the resistance across the two small terminals of the coil. If you have a ballast resistor, it should read about 1.5 Ohms. If there is no ballast resistor, about 3.5 Ohms.
Let us know what you find, and we'll go from there.
Jeff
 
Voltage across coil + and ground: 9.5 volts

Resistance across open points: Infinity

Resistance across + and - of coil: 2.5 Ohms

(I have no idea what a ballast resistor is)

Thanks a ton for the suggestions! Lemme know what I might try next.

Jeff (also /ubbthreads/images/graemlins/smile.gif)
 
Hello Jeff,
first disconnect the coil to distributor lead, (black\white cable. (If your car is negative earth this coil ternminal should be marked -ve) Check the coil voltage and it should read battery voltage approximately 12 volts. Connect your multimeter on ohms range to earth and the distributor wire and crank the engine, you should see the meter needle or reading (if digital) jump about as you crank, this shows the points are opening and closing and correctly connected. If OK so far, replace the lead onto the coil. Take the distributor cap and rotor arm off. Turn the engine until the points are closed then switch on the ignition, use a small screwdriver to gently open and close the points and if all is well you should see a small spark as they make and break. (This check actually is what I would do first if I had a 'no spark' fault, I don't bother getting the meter out.) If you have that spark the low tension side is probably OK. If you don't then it's a low tension fault; coil, points or condenser. If you have then look to the rotor, cap and leads. (By the way the rotor should not touch the plug lead terminals in the cap, there is a small gap)

See how you get on with that.

Alec
 
Alright, here's what I got. Doesn't quite make sense to me yet based on previous tests.

Coil voltage (+ to ground) is 12.15 volts. Sounds good.

When I check resistance between distributor wire and ground, I constantly get 0 resistance, even with engine cranking, which should mean that the points aren't even opening, right? I have the cap off and can physically observe that they are opening and -- using feeler guages -- can verify that they are opening to the specified gap.

With the ignition on, putting the - lead back on the coil causes sparks -- which should be expected. However, opening and closing the points with the ignition on does not show any sparks. I have two separate coils that I've tried this with (one is known to be good) and have the same results.

Should I start with the condensor? Seems like if I have a known good coil and I'm getting sparks at the coil, and I can check continuity across open/closed points successfully, the only remaining thing in there is the condensor. Maybe I don't have it screwed into the right pole?

Thanks again for the grand help.
 
Hello Jeff,
you may have a bad condenser, but I'd bet that the points are fitted incorrectly and the small lead that the coil connects to is the wrong side of the terminal, or the bottom insulating washer is missing. There should be an insulating washer at the bottom of the terminal, the moving point goes next, followed by the coil wire and condenser wire, another insulating washer then the plain washer and nut.

Have a look at that.

Alec
 
I checked the points and they appear to be fitted as you describe. I checked continuity between the parts of the points (specifically on opposite sides of where washers should be) and there is no continuity -- which I'd assume is good; otherwise the insulating washers wouldn't be there.

I also double-checked resistance between the negative coil lead (with the b/w wire attached) and the opposite side of the points. The resistance does go from 0 to infinity depending on whether the points are open or closed (as it should).

I still don't get a spark when opening/closing the points though. I do have 9.5 volts from the positive lead on the coil and the opposite side of the points when they are closed.

Thanks for everyone's suggestions. Maybe I am getting spark and just can't tell. I sure don't see it though if I am.

Should I swap out the condensor for the old one?
 
I take that back -- after re-reading what you typed and double-checking against my workshop manual, I think I do have something backward there. Checking it out and I'll reply later...
 
Hello Jeff,
As you say the the resistance goes from zero to infinity as the points open and close, this is correct. What I do not understand is how you can have a voltage reading at the points when they are closed? This is contrary to what i would expect given the first statement.
By the way not only will you see a small spark but it is audible also.

Alec
 
Sorry everyone, got called out of town for a bit. Now I'm back and testing again.

I've tried a bunch of things as mentioned, and here's my latest results. I'm thoroughly confused as to why this doesn't work now.

First, battery voltage is 12.7 ish. With the negative lead on the coil unplugged, voltage from coil + to ground is same as battery voltage. If the negative lead is plugged in, voltage is around 8.5 volts.

Next, with the ignition on, I unplug the wire to distributor and touch it to ground -- I get sparks (which is correct). I undo the internal wire that goes from the distributor wire to the moving points and touch to ground -- also getting sparks.

With the points open, I have 0 resistance from stationary points to ground, and I have infinite resistance from moving points to ground. Both sound correct.

I did have the distributor/condensor wires hooked up incorrectly at first, but they are correct now. They are touching the moving points, not the stationary points.

However, no matter what, I do not get spark across the points if I open/close with a screwdriver while ignition is on. I swapped out the condensor with the same result. I even took the condensor out and only connected the coil - wire and still no spark at the points. But I always get spark from the coil - wire touching to ground. I have 0 resistance across moving and stationary points when the points are closed, and infinite resistance when they are open.

I'm at a loss. Everything checks out! Why can't I get spark at my points? Anyone have some clarifications or further testing I could do?

Thanks VERY MUCH for everyone's help!
 
Yay! I got spark! Wooo hoooo!!!!

Not *exactly* sure why, but I think it was the nut that secured the coil/condensor wire to the points ground. I played around enough with it and now it's now shorting out to ground.

Thanks for everyone's help and suggestions -- they were very helpful. Now to see why it won't start... /ubbthreads/images/graemlins/laugh.gif

Hegg
 
Back
Top