View Full Version : Pertronix Distributor

01-14-2017, 06:04 PM
Still tweaking the engine for best performance. As you know, I have a FAST EZ EFI system. I swapped my OE distributor with a Pertronix and that made a noticeable improvement. This has a GM style adavance so is a lot easier to tune. I've been working with FAST on their help forum for the correct settings. However still running rough under load, and mpg is less than 13.

I opened up the distributor cap and found that the carbon button was worn to nothing. So I replaced the cap and rotor. No difference at all.

I analyzed using an oscilloscope and identical clamp type probes. One on the coil wire and the second on a plug wire. Here's a picture of representative results. It looks like I'm losing a lot of energy through the distributor cap. I did this with all eight plug wires and all results were similar.

Yellow is the coil wire and blue is a spark plug wire.

01-14-2017, 06:07 PM
This afternoon I cut a large window in the old cap and used that to measure clearance between the cap and rotor electrodes. I get about 0.039 to 0.048. This is larger than my plug gap.

Joe Johnston
01-14-2017, 08:20 PM
Even though that gap seems large in the cap you cut up, you need to compare the diameter distance between the contacts across the cap from the cut up cap to the new cap you are running. Its not quite apples to apples as you have two different caps.

Also you should try to get a good guestimate of the length of the 2 rotors by measuring from the center mark made by the carbon center post to the end.

I would assume the differences to be slight, but y'all know how that goes and you are trying to track down something important. Easy to check and perhaps another dead end, but it would be a known dead end! Perhaps a different combination of brands would make the gap tighter??

01-15-2017, 10:14 AM
The old and new cap and rotor are all pertonix. Should be identical. Also I don't have deep calipers to measure the new cap. I figured this would give the most accurate results.

Joe Johnston
01-15-2017, 10:58 AM
I agree, dimensions should be identical across the same brand. Still would be interesting to even fit a wood strip across and compare how it fits to an old Ford cap.

That gap seems really big to me too. I've never liked aluminum contacts either in a cap, but that is just me. Keep checking - you'll find the problem.

01-15-2017, 01:35 PM
I'm going to take the dremel to the old cap and make the contact closer, see how that works.

01-15-2017, 02:48 PM
This afternoon I cut a large window in the old cap and used that to measure clearance between the cap and rotor electrodes. I get about 0.039 to 0.048. This is larger than my plug gap.

But the spark doesn't have to fight compression, possible fuel wash, heat etc inside the distributor cap so I don't think that gap is unreasonable. (I have run motors with 40 thou plug gap)

01-15-2017, 03:31 PM
Good point, but how do you explain the oscilloscope graphs?

01-15-2017, 03:59 PM
I'm on par with Tom's explanations.
As far as the graphs, did you try swapping oscilloscope leads? Do they give exact same results?

If you're worried about .03" gap, solder a wire extension onto the brass rotor (or peen it closer). My bet is, it won't make a bit of difference.

Did you ever have a plug that wouldn't fire? Sometimes pulling the boot off the plug 1/2" will wake it up again. To rationalize, I think the collapsing field in the coil builds to a higher voltage before it can jump across the gap. That's why more modern vehicles incorporate a resistor-plug. - Dave

01-15-2017, 09:38 PM
Yes swapped the leads from the coil, same results. Also tried every plug.

I decided to experiment a bit and apply the dremel to the rotor contact. The first picture is my first grind and the second is my final, after several trial and error fits. I brought the clearance from 0.040 or larger down to 0.018.

Too late to fire her up, I'll try to find time tomorrow and get a new scope reading.

01-16-2017, 10:33 AM
With reduced clearance, no improvement. In fact more erratic.

01-24-2017, 09:04 AM
After my issue last week I ordered a new Pertonix "Second Strike" box and Flame Thrower II coil. The Pertronix box is lighter than the FAST box I'm replacing and does not seem to be as robust. But now distributor, Ignitor II module, coil and box are all the same manufacturer who lists them as working together.

I took about a 15 mile test run including speeds up to about 70. Misty rain, now the car's dirty. This seems to run somewhat smoother. Stopped twice to adjust the second strike and it seems to be smoothest with the second strike turned off. Still not perfect though.

Scope on the system shows occasional spikes on the coil wire (channel one) which coincide with the plug wire (channel 2). Random, about every third or fourth cycle. Channel 2 pattern not as consistent as with the FAST box, "bouncing down" from the coil wire spikes.

I put the battery voltage on Channel 3 and it won't read as a DC source, so set it to AC. This shows a series of pulses, like an AC wave form with the negative cut off. Interesting thing is that I see spikes from it that coincide with the coil wire spikes. So much for the battery acting as a filter.

The alternator is a Tuff Stuff with the regulator integral in the unit. Some call this a one-wire. It gives me a consistent 14.4 volts on a digital multimeter.

I purchased a 150 amp voltage filter, a NewMar 150A, and will install between the alternator and the battery. Hopefully this will smooth out the electrical and solve the problem.

01-24-2017, 03:00 PM
An automobile's electrical system is EXTREMELY noisy, as you found out. The battery does act as a filter but not nearly as fast as a capacitor (even though we are happy with a battery's response for starting and charging). If it were possible to disconnected the battery while the engine is running, you would see far more noise.

So, capacitors work great. Did you ever see a circuit board with a whole bunch of little caps all connected in parallel? That's because little caps work much faster than one huge cap.

I'm not suggesting you run out and buy a couple thousand .22-uf caps and tie them all together, but that is the value we use on your points, on your mechanical voltage regulator and on the original generator. All those caps are mounted close to the spike source for maximum efficiency, otherwise your radio antenna will pick up the frequency and amplify the noise over your speaker. They seemingly do nothing so most of us simply let them be. The only one that ever gets replaced is the 'points condenser'.

That filter you bought... mount it closer to the alternator and distributor than the battery. Shorter wires are faster than long wires. - Dave

01-24-2017, 08:08 PM
According to my genius son this is a "huge LC filter", which is an inductor and capacitor, or low pass filter. I read about it on wikipedia and I get the basic jist.

My alternator, battery and 100 amp breaker between them are all on the passenger side. I plan to mount this on the radiator support just below the breaker. I might even use a short bus bar to connect the filter to the breaker.

Either that or the shortest #4 cable on record. :p

01-24-2017, 11:54 PM
Steve, what is the function of an inductor? What is the function of a capacitor? Then, when you put them in series? Or, in parallel?

We use LC in speaker crossovers but they deal in frequencies of 20kHz. This is a car with frequencies far lower.

A capacitor opposes a change in voltage.
An inductor opposes a change in current.

Together in series, they form a tank circuit that oscillates when matched. That's why your ignition circuit works. If your coil OR your condenser crap out, no spark.
In parallel, they cancel each other, producing a resistive circuit.

I can understand putting a capacitor somewhere around your engine but not by the battery.

Did you ever use HID headlamps? They require a cap, mounted close to each lamp or the light flickers. I'm sure you've seen that at night, where strong, annoying flickering headlights are shining from a car.

BTW, short copper wires can carry far more current. I have used a #14 copper wire as a 100-amp fuse, but it was 2" long. - Dave

01-25-2017, 12:13 AM
As said earlier, I merely get the basic jist. I can see why the circuit would oscillate (wikipedia has a "gif" demonstrating its operation) but how does it filter? I'm guessing that it stores the peaks and uses that to fill in the valleys.

I plan on reading the manufacturer's instructions when I get the unit and following them to the letter.

The same manufacturer makes 10 and 25 amp units. I was thinking of using the 25 and just using it to filter the ignition two fat wires to the ignition box, but for an extra few bucks I can filter the entire alternator output.

What I should have done (or still can do) is unplug the alternator from the circuit and see if that improves my scope readings.

01-29-2017, 05:57 PM
I installed the filter but it's snowing and they salted the roads here so no test drive. I've attached a picture of the install plus an interesting scope graph.

The filter is behind the battery. I have an 18" long cable (max length allowed by the filter manufacturer) from the alternator to the filter. On the BAT side I have a battery cable, my starter hot lead, a cable to my 100 amp main breaker and then the ignition box hot lead.

Channel 1 is the alternator output. Ch 2 is the battery positive terminal. This is at idle with no accessories running. Big difference between the two.

Channel 3 is my coil secondary. The CAO dial on the ignition box is set to 2, which creates a second spark at 4 crankshaft degrees after the initial. Pertronix recommends that as your initial setting and go up or down from there.

Channel 4 is my #8 spark plug wire. It's a lot more consistent than it was before. This points to a solution, but I won't be able to tell for a few months until spring and we have a few good rains to wash the salt off.

01-31-2017, 10:14 AM
A question for you Dave. A while back you advised me to put a fuse between my alternator and battery. By installing this filter I've bypassed my main 100 amp breaker that I had been using for that. My new wiring diagram is below.

I need to keep the #6 cable from the alternator to the filter 18" long or less. In order to fuse this, I was thinking of building a fusible link, a short length of #10 within that connection. So the first 4" or so of my 18" long cable, connected to the alternator, would be a #10 wire. Do you think this will be an acceptable solution?

02-01-2017, 08:17 AM
Decided to mount an AMG type 100 amp fuse block between the alternator and filter. On order from Amazon. I spent an extra ten bucks and bought a fuse holder by Blue Sea Systems. It looks a lot more attractive then the cheap plastic units sold by Bussman or Littlefuse.

02-01-2017, 04:32 PM
Steve, I didn't see your post yesterday.
I think you are missing the main goal here. The purpose of the fuse is to protect against a faulty alternator resulting in a burned wire and possibly a fire. Alternators use solid state components that can go bad at any time, especially when nobody is around.

If a diode or SCR shorts, it will draw as much current to ground as your battery will supply, as fast as possible.

If you place the fuse between your battery and alternator, when this happens, the fuse will blow and your alternator will be isolated BUT your car should still start and run off the battery.

So... the first order is to fuse the alternator. Any wiring after the fuse should not interrupt power from the battery to the starter solenoid (and ignition circuit). It's like a tee, or a parallel branch.

This was and still is my suggestion:
...I can understand putting a capacitor somewhere around your engine but not by the battery...
This is because the source of your noise is your alternator and ignition circuit, both of which are mounted to your engine. Batteries never produce noise. Questions?

02-01-2017, 06:00 PM
Dave, here's my revised wiring diagram.

We're deep into winter up here so a test drive isn't possible for a while. But based on the new scope readings and the fact that the engine starts up easier I think the combination of the All Petronix ignition with this alternator filter have solved this pesky little problem.

02-01-2017, 06:03 PM
Picture of the filter.

02-02-2017, 04:21 AM
Yeah, that center ground lug is important. THAT is your capacitor. The huge posts have an inductor coil between them, inside. So, connect the center ground lug to your alternator case, not your battery.

You show a 'starter' with two wires. Is this a GM starter motor or one with a separate solenoid?

Finally, I see a 100-amp breaker. Is it self-resetting?
If your ignition wires go through the self-resetting breaker, get them off. If that breaker opens your engine will stop. It's one thing to protect the fuse box and all associated branch circuits BUT keep your ignition circuit by itself, as Ford did. - Dave

02-02-2017, 09:31 AM
Right now the filter is grounded with a #6 to a common bolt (to the chassis) with the alternator ground and main engine ground. The car is at my cabin, so I'm going by recollection now, but I think the alternator ground is a #10. I'll check that, as it may explain the less than smooth scope readings while the alternator is under load (32 amp cooling fan). If so, good catch.

The starter is a performance type with a separate #10 wire that triggers an integral solenoid. There is no longer a Ford type solenoid mounted on the chassis. I did this on purpose to make the car harder to steal.

The 100 amp breaker is not self-resetting. The OE ignition circuit is powered by this breaker and I intend to keep it that way. I use that as a battery cut-off along with the ground connector on the battery. I can trigger that and the tell-tale isn't obvious, another theft preventative.

Right now both my EFI and ignition box main power and ground are direct to the battery, un-fused, or engine grounds, as required by the manufacturers. The reason that I was given is that the battery is the filter. Apparently that didn't work so well. If the car runs well with this filter I'd like to move those wires into my main power panel with their own fuses.

02-02-2017, 11:40 AM
...The 100 amp breaker is not self-resetting. The OE ignition circuit is powered by this breaker and I intend to keep it that way...Suit yourself. I gave my suggestion but it's your car.

Most cars do use the battery as a filter with no ill affects and never a second thought.

If you want real theft protection, shut off your FUEL. Thieves will have electrical knowledge but they will not plumb because that takes far too long. - Dave

02-08-2017, 10:02 PM
Tweaked it a bit over the weekend. The instructions for the filter insisted that the ground strap to the alternator be a #6 less than 18" long. I went to several stores to find a #6 connector that had a screw hole small enough for my alternator ground connector. Hopefully this smooths out the engine over the entire RPM range.

The ground required by the alternator itself is only a #10. I still have that going to the chassis.

02-08-2017, 10:13 PM
If you want real theft protection, shut off your FUEL. Thieves will have electrical knowledge but they will not plumb because that takes far too long. - Dave

Good idea, and all I have to do is take out one fuse in my trunk panel to cut off power to my fuel pump relay. But I think a thief with electrical knowledge will have a challenge here. Where my starter solenoid used to be is a 100amp circuit breaker. That feeds a custom electrical panel and they'll have to figure that out to jump start the car.

02-11-2017, 03:09 PM
I think I found the last of several gremlins causing my rough running problem. I've marked the damper with a paint stripe not just at zero degrees but at every 90 degrees. This lets me use my timing light on each wire to verify correct timing for all eight cylinders. When I looked at plugs 7 and 8, I'd get random misses. I cleaned off most of the anti-seize from the plug threads and sealing surface, and the problem went away. I never used to use that stuff until lately, when several guys told me that I should. Even though I've never had a plug seize, even in an aluminum head, I used it anyway. It's supposed to be conductive.

02-11-2017, 08:17 PM
The TYPE of anti-seize you use makes a difference. In fairness, most people don't know that many types exist.

Mine is N-1000, made by Fel-Pro but it is copper and graphite-based and good up to 1,800 degrees F. It has a copper color, not an aluminum color and it is highly conductive. I use it on everything including wheel lug nuts and yes, spark plugs. It's also designed for stainless applications. I apply a very thin coat to spark plug threads, then I run them in and back out, then another very thin coat on top of the one I had. That ensures enough is spread over both male and female threads.

I've been using this on Edelbrock aluminum heads (and OEM cast iron) since 1990 and have never had a thread problem.

I see that Loctite 51147 is also a copper-based anti-seize but I have no experience with it. There is also a graphite-based anti-seize offered by Fel-Pro for electrical conductivity. - Dave

02-11-2017, 08:42 PM
I've had a jar of the stuff for years, I think it's a Permatex product. I bought it for brake fasteners. Silver in color.

02-12-2017, 12:41 AM
I use KopperKote (sp?) on everything I don't want siezed, it works a treat.

02-12-2017, 01:12 AM
I use KopperKote (sp?) on everything I don't want siezed, it works a treat.Tom, be extremely careful using Kopr-Kote, and NOT on zinc plated bolts (which most of mine are). Read their site:

02-12-2017, 03:03 AM
Tom, be extremely careful using Kopr-Kote, and NOT on zinc plated bolts (which most of mine are). Read their site:

No worries Dave, I'm not rich enough to afford zinc plated nuts & bolts!
My main use of it is on anything that is part of an exhaust system.

06-05-2017, 11:05 PM
Last night I went through the Pertronix electrical tests, found and repaired two problems.

The resistance between the distributor base plate and battery ground was about 3 Ohms, and they recommend a maximum of 0.2. I traced it to the battery cable. It wasn't the connectors but the actual cable itself. So I purchased a new $8 cable.

The voltage at the coil under load was just over 8 volts, and Pertronix likes at least 10. As you know, there are two wires from the ignition switch to the engine bay. One powers the coil through a resistor wire to maintain about 6 volts. The other goes to the starter solenoid and gives the coil full battery voltage while cranking. I had simply used the second wire to power the coil. It turns out that it is a smaller gauge, I had to add on some length, and it had a good amount of resistance itself. So I ran a new 12 gauge wire from the switch directly to the coil, and now I get 10.4 volts.

The engine ran better but still not perfect. I tried using a second strike setting on the pertronix box but that made it worse.

One problem that has started to develop, so must be related, is that the car bogs down once or twice after about the first mile or so. It just loses spark for a split second.

I'm thinking that the problem may be because I don't have full 12 volts at the coil. The resistance is probably in the key switch. I'm thinking that the easiest way to get 12 volts is to use a relay, but I don't like the idea of having a fuse or relay in that circuit. If I have time tomorrow I'll power the coil from the battery and take a test drive.

06-06-2017, 03:17 AM
I went the relay way.
And used the original coil wire to activate the relay - it's not voltage dependent.

06-06-2017, 01:45 PM
I powered the coil directly off the battery and no improvement. Powered from the ignition switch with the engine running I get 13.5 volts at the coil vs. 13.9 volts at the battery itself.

06-06-2017, 01:53 PM
I get about 1.0 Ohm resistance between the battery negative and the distributor case. This is lower than the 3.0 with the old cable but not as good as the 0.1 that I got after I put the new cable in two days ago. It would be easy for me to run a #12 wire ground from the distributor body to the battery but I think I'm chasing a ghost here.

06-07-2017, 09:23 AM
EMI may be the culprit here. I am running MSD Street Fire wires and when I tried a set of OEM style Motorcraft wires, performance was a lot worse. I'm going to try a set of MSD superconductor wires, that claim to have very good EMI suppression.

06-20-2017, 10:07 PM
BINGO. The MSD superconductor wires did the trick. I can actually use my Second Strike unit now too.

The other thing I did that probably had an impact was to shield the distributor trigger wires and the ignition box input wires by twisting the pairs, then covering with tinned copper weave jackets. The jackets are grounded at one end only, together to the chassis.