78 ignition coil problem

[manoa matt]

This is a continuation of my previous post about "Help won't run smoothly under 1200 rpm.

Well since the previous post, I've completely gone thru the electrical system. I knew my problem stemed from an ignition fault. Now every thing is wired as it should be for a 78. I identified one of the circuits under the intake manifold. The larger one near the front is the ignition mode relay thermo switch[(blue wire and (pink wire and gray/red wire)].

At first I had it wired for dual points, with the green and green/black wires. I was getting 12v at the starting points(green wire)with the ignition switch on, and 12v at the + side of the coil(blue wire) but no spark from the coil. All the ignition components are new except for the coil which tests good. I made shure the points condenser, and the points are grounded with wires to the fender wall ground pod(recently cleaned). The coil also has a condenser for radio frequency interference. The dwell angle and timing are set right on. Still no spark from the coil. I bought a new Bosch blue coil, still no spark.

As soon as I set it up for single points. (eliminate green wire and green/black wire from points. Install new wire from - side of coil to points). It starts right up and runs well. I finally got it to run at around 900 rpm. This is the best it has run in in a long time. But there is still an erratic miss. If you look at the coil closely you can see a spark jump from the base of the tower to the nearest terminal. If I wrap everything with electrical tape it gets better, no visible spark but I know its still having an influence because its still missing erratically. This is all with my old coil, if I use the Bosch blue coil, no spark at all.

I cleaned up the old coil, there are no visible cracks in the plastic near the tower base. Despite it looking like heck, it actually has a higher output than the Bosch coil. The only markings on it are (12v heavy duty) no maker name. I've tried both resistor and non-resistor type spark plugs and no noticable difference. I also tried an external coil resistor, no luck there. The wires are Beck/Arnley mag-core.

I'm OK with running it on single points, but how do I get the spark to stop jumping from the coil tower. I've seen dialectic epoxy to repair old hard to find ignition coils. Has anyone experienced this before?

Matt

[So Cal Mark]

spark will follow the easiest path to ground; so if there is less resistance from the tower to the post than through the coil wire, rotor etc, the spark will continue to arc to the post. You need to find the high resistance and eliminate it. Get out the ohm meter and check coil wire, rotor, cap, plug wires

[verycoldfiat]

one thing to try is the die electric grease in the coil boot. also they sell a spray that coats the ignition for off road racing stuff. i'll look up the name. you just spray it on and it comletely waterproofs the ignition. but i would suspect you have a tiny hole in the coil boot.

[manoa matt]

Well, I got out the volt/ohm meter and checked everything, nothing unusual, as everything is new. I had a light coating of die-electric grease in the tower, but I put more in and some on the two coil terminals. I made a tower boot extension from an old hose. The flashover got worse.

I took the coil out again and found "use with external ballast resistor" I hooked it all back up and used some alligator clips to introduce the resistor into the circuit once the car was started. Before I get 12v at the coil + terminal, once the resitor is introduced I get 6.8v at the coil + terminal and the car immediatly dies. Fiat factory service manual gives specks on origional coil, but no indication of resistor in any diagrams.

The brand new Bosch blue coil still won't produce a spark.

Coil research: Older type oil filled coils (existing coil) have better internal flashover protection, while newer epoxy filled coils (Bosch) have better vibration protection. There are alot of coils out there that are listed as replacements. Many of them require an external ballast resitor, but very few come with it. Trying to get specks like primary and secondary resistance is like getting blood frome a stone.

I tried a coil from a 79 electronic ignition, the resistance readings were similar to my existing coil. It worked, but ran rough.

Here is what I'm going to try:

1: Rewire back to dual points and try existing coil with and without resistor.
2. Same as # 1, but with Bosch coil.
3. Buy a new resistor so voltage at coil + terminal is around 8v-9v.
4. Try distributor and coil from 79 ignition (tests good)
5. Buy new oil filled coil with resitor included (Beck/Arnley # 178-8025)

Another Possibility: Worn Distributor cam lobe. My points are set at a perfect 55 degree dwell, but the points gap is .019 to .021. Possibly the gap is to wide for a spark to jump. If someone has a good points type distributor, I need two measurements, milimeters or inches is not important, but accuracy is.
1. flat spot to flat spot on opposite side
2. high point to high point on opposite side.

Any suggestions or comments will be appreciated

Matt

[racydave]

Matt, Check the sparking coil for a hair line crack inside or out. Try your old coil wire. Do you have a good second ground wire from eng to body? You can find balast resistors, Chrysler used to use them. Ask the Mfg (of coil) for their specs on balast, and ohm readings, they probably have a web site. Maybee you should thourally inspect every inch and connection in the wiring harness esp at ign switch connector. On the points adj, you really need a dwell meter to do properly, it can tell you alot about the dist. always adj timing after points adj. you have done alot already, hope this is of some help?

[So Cal Mark]

what is the ohm reading of the coil wire?

[manoa matt]

The wire set came with 2 coil wires one long and one short. The plug wires all have the same resistance, can't remember off top of head right now. The long wire has a resistance almost double what the short wire has. I have been running the shorter wire. I'll repost the ohms when I get home.

matt

[So Cal Mark]

you're approaching the arcing problem from the wrong end; the arcing is from the secondary circuit and you're working on the primary circuit with your resistors. Find the high resistance in the secondary circuit and you'll cure the arcing

[manoa matt]

Mark,

New wire set is Beck/Arnley premium high temp mag core silicone

Old wire set is Bosch 7mm high temp silicone

All readings are taken on 20K ohm scale of digital multimeter

all 4 new plug wires: 0.65

new coil to dist wire (long): 1.64

new coil to dist wire (short): 0.89

old coil to dist wire (bosch): 1.12

old plug wires (Bosch): 0.66 to 0.75 depending on length.

Going away for the weekend, won't be able to do any testing till Sun night.

Matt

[So Cal Mark]

I'd test the resistance of the rotor from the tip to the center and check the center button on the dist cap also

[manoa matt]

The new rotor tests same as old rotor: 0 resistance
The new dist cap test same as old dist cap at all points: 0 resistance.

No performance diff between old and new, both still produce flashover.

I did however get my dual points to work. I had the wiring reversed on the two sensors under the intake manifold.

Sensor at front (looks slightly larger) is water temp sensor has two blue/red wires

Sensor at back is ignition mode thermo switch has blue wire and grey/red wire.

Funny how so many people were wondering what the wiring to the two sensors under the intake manifold were, but no one was having ignition trouble, guess they switched to single points or electronic ignition.

Still probing and testing, will keep updated, thanks for the advise.

Matt

[So Cal Mark]

your new coil wire resistance seems high, since you're on the 20k scale, that reading would be 16,400 ohms

[manoa matt]

New wire set has two coil wires. I've been using the shorter wire (.89) Its the same length as the old coil wire which has a reading of (1.12).

I labeled everything before taking stuff apart, but I never really looked at the coil while it was running, before I took the car apart. It wasn't running perfect, but I attributed that to worn points, and a bad exhaust valve guide oil seal, and various other minor defered maintenance issues from PO. It could have experienced the coil flashover before I took everything apart, I just didn't notice.

Periodically I take out the rotor and use fine steel wool to shine up the area where the carbon button is. When I open it back up, after running it for a while, the area is kind of black in color. Its not carbon tracks, cause it doesn't wipe off. Its more like the brass is tarnished.

Does the button make contact with this surface? Or is there an air gap that the spark has to jump? Button being spring loaded would seem that it is to allow for difference in height tolerance, so contact is always made with sufficient pressure. Both rotors are same height when installed.

Matt

[manoa matt]

On the way home yesterday I picked up another ballast resistor. The first one I was using gave 6.8v at coil + terminal and was not enough power.

The new one gives 9v at the coil + terminal. I wrapped the tower base and the terminals with electrical tape and now the car idles fine with no flashover. I got it to idle pretty low with no erratic missing, which was a problem before.

Now that it idles slower, the idle mixture screw could be turned with noticable effects. I think I have everything properly adjusted now, man that feels great.

I'm going to run with this set up for a little while and see how it performs. If I take the electrical tape off it will flashover at the coil. Unfortunatly the electrical tape seems to be the only thing that stops the flashover. It may be time for a new oil filled coil. Forget that Bosch blue coil.

I'm halfway done with the suspension/steering. I just have to do the passenger side and get an alignment then I'm back on the road.

thanks everyone

Matt

[manoa matt]

Mark,

The light bulb just went off in my head. You said the problem was a high resistance in the secondary circuit.

Let me know what you think of this:

Origional coils: Marelli BES 200A
primary resistance: 2.59-2.81 ohms
secondary resistance: 6,750 - 8,250 ohms

Martinetti G37SU
primary resistance: 2.6 - 2.95 ohms
secondary resistance: 7,000 - 8,000 ohms


The coil I'm currently running: Unknown maker 12v
primary resitance: 2.7 ohms
secondary resistance: 9.8 ohms

Given the specs for the origional coil, my secondary resistance is too high.
After alot of research I think that this is the coil that is the closest to the origional specs:

http://store.summitracing.com/partdetai ... toview=sku

Matt