Engine cranks, no spark

[mikecyc72usa]

Ok, so this is the short version. I got my car, got it to run some, then it would or wouldn't start. Totally random. Eventually it wouldn't start at all. So I replaced the rotor, cap, wires and plugs when I bought the car. Then I put a Pertronix system in, new coil. New battery, new ignition switch. The engine cranks great, but no spark at the distributor.

So, is there anything I've missed before I fire up the meter and hunt down an open circuit? Actually, it'll be a friend of mine doing the hunting, I'm stumped. Thanks, and it's a 1978 Spitfire.

 

[TR3driver]

Phew! I would have gotten out the meter a long time ago!

Just for luck, double-check that the rotor is actually inside the distributor and seated onto the shaft. I have a nasty habit of leaving it laying somewhere else.

I assume you realize that there is (or should be) a ballast resistor incorporated in the wiring harness; so you will need a coil that takes an external ballast, and the Pertronix needs to get it's power before the ballast resistor.

After you check with the meter and everything looks OK, try checking for spark right at the top of the coil. I've seen "brand new" rotors fail such that they short the spark to ground, with no visible defect.

 

[mikecyc72usa]

Well, I replaced all that since I was having trouble, and would have done it anyway. I do have a ballast resistor, and the power goes to the coil first. I'll double check the Pertronix rotor and make sure it's installed properly. My friend is an electrical engineer with a 78 Spitfire, too, so he's ready to help in exchange for some extra parts I have. I will have pics up soon.

This is my 10th Spitfire, and it seems to be the most troublesome. Go figure. Maybe this is why it has been sitting since 1993...

 

[Geo Hahn]

No spark should be one of the simplest failures to diagnose as there is a pretty well defined chain of events wherein one can check for power/ignition each step of the way.

If it were me (and clearly it is not) I would put the points back in and get it running with those before I used the Pertronix. That eliminates the one 'black box' in what you have described. But again, that's just me.

 

[mikecyc72usa]

Well, the original was electronic ignition, too. It was pretty fried. In fact, after the last time it ran, the module inside was slightly melted. Maybe I'll backdate my car to points...

 

[3798j]

I've got Pertronix firing a number of vehicles (not just Triumphs). Any time I had a "no spark" condition, it was either not enough voltage, or no ground. Here is some trouble shooting help: https://www.vintageperformance.com/retrorockets/low_voltage.htm
Here's hoping I'm helping.

 

[DougF]

Has the car ever run with the Pertronix? When setting it up, did you cross wires? Pertronics systems are very sensitive, any short or improper wiring can ruin the unit.

 

[mikecyc72usa]

Hit the car with the meter tonight. No power across coil. We jumped supply voltage to it, still no power across coil no matter what. If we jump the ground and power we get 7.8 volts across coil. If we add a direct ground volts go down to 7 when one probe is on coil the other at alternator. Did same test with old coil, also, only getting 5 volts across. It seems that a possibility is the distributor isn't grounded. Before a direct ground 0 volts were going across the coil, and test from negative to ground we got a 12 volt drop.

I guess my next step is to tear into the harness. Any thoughts? Thanks.

 

[TRED]

I had no spark issues myself and found the videos here
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=76076
very helpfull.

 

[TR3driver]

If we jump the ground and power we get 7.8 volts across coil.

Ok, this is where you lost me. If you jump power to ground, you should get a fire.

With the distributor side of the coil grounded (either through the Pertronix or a jumper directly to ground), a reduced voltage at the hot terminal is normal. Your wiring harness will have a ballast resistor incorporated in it, so when current is flowing through the coil, the voltage is reduced.

Of course the Pertronix needs to be installed so that it gets full 12v whenever the key is on, so it's red wire cannot be connected to the coil.

 

[mikecyc72usa]

I should have said we jumped power and ground around everything, trying to bypass various parts of the circuit, but no matter what we got no power at the distributor. Going to check the distributor ground today. My two friends work at Audi and have quite a bit of experience with older stuff, too. I can replace a harness, I just can't seem to understand how to troubleshoot it. Just the way my mind works. Go figure. To be continued...

 

[TR3driver]

IMO not likely the distributor isn't grounded; it's bolted to the engine block and if the block weren't grounded, the starter wouldn't work.

But it's quite possible that the Pertronix was not conducting when you were doing your checks. Just like points, it switches between conducting and not conducting as the engine turns. Or, the Pertronix module may not be grounded securely to the distributor.

Hmm, I'm not sure what the later 'electronic' distributors look like ... but on the point-type Lucas distributors, there is a short ground wire inside the distributor that has one end riveted to the movable point plate and the other under one of the screws that holds the fixed plate to the distributor body. You might look for something similar on your distributor; the Pertronix module must be securely grounded through it's mounting points, and since the two plates move relative to each other, you cannot rely on that joint to make good contact.

A good test at this point might be to disconnect the wire from the coil to the dizzy, and try jumpering the coil terminal to ground with the key on. That should show you 5-8 volts across the coil, and produce a (weak) spark when you remove the jumper from ground. If you get that, there is nothing wrong with the wiring harness.

 

[mikecyc72usa]

Cool, that's an easy test. I'll be going through everything with a fine tooth comb later. Maybe not today as I got some kind of stomach thing during the night. However, it lets me research. And plan. And thank you guys all for your help so far.

 

[dklawson]

You can also supply +12V directly to coil (+) and disconnect the "regular" wires on coil (-) (which go to the distributor). Connect a jumper wire to coil (-) and "tap" (not hold) this against a ground point with the ignition on. You should be able to make the coil fire using this method if the coil is good. Once you know the coil is working you can figure out what's wrong with the ignition module.

Randall's point about the ground wire inside the distributor is important. On the Lucas 25D and 45D series distributors there is a high-flex ground wire that must be in place between the breaker plate and dizzy housing. I assume this was also on the earlier DM2 models and on the electronic 45 series. When that wire fails coil power has to pass through the breaker plate bearings and this can cause intermittent running problems.

 

[poolboy]

If we jump the ground and power we get 7.8 volts across coil.

Ok, this is where you lost me. If you jump power to ground, you should get a fire.

With the distributor side of the coil grounded (either through the Pertronix or a jumper directly to ground), a reduced voltage at the hot terminal is normal. Your wiring harness will have a ballast resistor incorporated in it, so when current is flowing through the coil, the voltage is reduced.

Of course the Pertronix needs to be installed so that it gets full 12v whenever the key is on, so it's red wire cannot be connected to the coil.

This illustration has caused some confusion of sorts with the TR6 guys.
I think it's because the instructions are generic and not TR6 specific.
I think it applies more to ballasted ignitions that feed 6 volts to the coil.
Pertronix units can function if fed within a range of 7-14 volts.
The ballast resistor wires, at least the ones I know of, are supplying between 9 and 10 volts to the coil.
Bottom line is that the Pertronix can be hooked up in the conventional manner, directly to the + terminal of the coil, if your voltage reading is greater than 7 at the + terminal with the ignition key in the "ON" position.

 

[TR3driver]

Bottom line is that the Pertronix can be hooked up in the conventional manner, directly to the + terminal of the coil, if your voltage reading is greater than 7 at the + terminal with the ignition key in the "ON" position.

You may be right. But the Pertronix instructions say specifically not to do that. When the problem is that the unit doesn't work, I feel it's a good idea to be sure that your installation matches what the manufacturer recommends.

Of course it's quite up to you. But somehow, when someone says to me "I did it wrong and it didn't work", I don't feel too sympathetic

BTW, the above instructions should include at least "when the points are closed". When the points are open (or not working, or the wires are broken or all sorts of things), the voltage at the coil will read full battery voltage or darn near.

 

[3798j]

Bottom line is that the Pertronix can be hooked up in the conventional manner, directly to the + terminal of the coil, if your voltage reading is greater than 7 at the + terminal with the ignition key in the "ON" position.

This was my thinking when I did the install on my ballasted '64 Corvette. The engine would not fire. Running the red wire to switched battery voltage, it started immediately.

 

[poolboy]

Somewhere on the box that the Pertronix comes in it says that it can function in the 7-14 volt range. So my thinking is that 9 volts is a good as 13 for it to function as a switch. There's a link on this thread that says 8 volt minimum, but my memory is of the box.
https://www.vintageperformance.com/retrorockets/low_voltage.htm

 

[poolboy]

BTW, the above instructions should include at least "when the points are closed". When the points are open (or not working, or the wires are broken or all sorts of things), the voltage at the coil will read full battery voltage or darn near.

Randall, what if the - lead of the VOM were on the battery - terminal and the + of the VOM on the + of the coil terminal? Wouldn't that negate the position of the points ?

 

[TR3driver]

So my thinking is that 9 volts is a good as 13 for it to function as a switch.

Problem is, there's more to power than just voltage. It's expecting DC power, but what happens at the coil has at least as much AC as DC. IOW it bounces up and down a LOT. Expecting an amplifier to run on that isn't reasonable, IMO. (The Pertronix module basically amplifies the output of a sensitive Hall effect transistor in order to operate the coil.)