75 duster slant six weak spark

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C

Cooter

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Amongst the thousands of posts about weak/no spark, here is my problem. 75 duster slant six/automatic. A/C. It has spark, but its very weak and won't start/fire. I'll be perfectly clear with ALL of you, I'm no electronics wizard, I just plain don't understand it enough to troubleshoot under the hood. I can wire in a tachometer and install a Crane Fireball ignition (which is removed and disconnected since the Crane coil took a dump) so I reverted back to stock electronic ignition and factory coil (which ran before installing the Crane stuff) but I can't find broken stuff if it carries electricity.

Facts:
Outside temperature (11/13/14): near freezing Fahrenheit (and now snowing i might add). When the car stopped running it was around 65-70 degrees about a month ago.
The car is getting plenty of gas. You can see it and smell it inside the Holley 1945 carb.
The starter turns the motor over just fine. No hitches or skips in the starter.
Factory coil. Car has just over 70,000 original miles.
NGK plugs gapped to .035"
Brand new 4 blade ballast resistor (more on that in a minute)
Taylor 8mm plug wires about a year old (car is short tripped only, never taken out of town)
Cleaned up distributor cap (was the same one that was used on the Crane system). Brass lugs inside the holes
Reman Cardone brand distributor arrived last week and installed few days ago. (the old one had too much play in the shaft and seemed to ground out the reluctor gap, either way i wasn't getting a pulse as noted by the indicator on the Crane hi-6 box as it should have pulsed the LED indicator light while cranking. Plus you could feel the slight slop in the shaft bushings).

Odd things about the weak spark: I had removed the spark plug wire from cylinder 3 and put brand new NGK resistor plug on it and grounded this to the valve cover bolt (too lazy to remove the NGK spark plug installed in the engine; its faster this way). My son gets in the car and turns the switch to run, the spark plug gets a HUGE white spark right before he hits the starter and the engine cranks. When the starter turns the motor over, the spark reduces to a very small white dot (not a huge streak of lightning) on the tip of the spark plug.
On occasion, you'll hear the engine almost fire right when you turn the key from run to start but then it just cranks without firing. Its almost like the ignition system is hotter in run than in start.

Ballast resistor. Following the test listed here please note i have my resistor oriented the exact same way in the picture. The top ohm reading is 1.6 ohms and the bottom reading is 5.7 ohms. Does this matter that they are flip-flopped?

I did some basic testing of the circuits to the coil and heres what I have:
Brown wire to coil positive stud when key is turned to RUN: 2.05 Volts
Brown wire to coil positive stud when key is turned to Start/crank: 9.50 Volts
Ohm reading from positive stud on coil to center/top of coil (key turned off): 8.66 ohms (meter set to 20K ohms)
Ohm reading from positive stud on coil to negative stud on coil (key turned off): .002 (meter set to 2K ohms)
Battery voltage: 12.42 Volts

What this tells me is that there is a 2.92 voltage drop between the battery and the coil stud, however i've read anything under 10 and theres a problem, so I'm assuming SOME type of drop is normal?

67Dart273 had quoted that "Ignition "run" (IGN1) is ONLY present with key in run and NOT in start

The ONLY source of ignition voltage in "start" is the "bypass" circuit, or "IGN2". This is a brown wire, comes off the switch, goes through the bulkhead connector, and to the coil+ side of the ballast. So if the switch, the connector, or the bulkhead connector becomes corroded, you can lose that start voltage."

Is it likely the bulkhead connector causing all this despite the ballast having the top/bottom flipped and possibly the coil being bad? I have no idea what the ohm readings are trying to tell me, they are just numbers. Are they good/bad?
 
yes the resistance in run matters. Todays ignition modules will have only 4 contact posts under that connector. They operate on full 12 volts so they don't use the second part of dual resistors. Anyway... With the switch in run position the coil should receive about 9.5 volts. That is 12 volts going through the 1.5 resistor to get there.
In start the coil should get all the 12 volts.
 
Yes, the coil + voltage should be close to the battery voltage when cranking; it will liklely be < than 12v since the starter is loading the battery but your 9.5 volts seems a bit low. It could be:
1) the brown wire through the bukhead connector (IGN2) has a problem
2) the ignition switch
3) the power into the ignition switch.

Do all of your spark test WITHOUT the spark plug. Jumping an .035" gap in open air is meaningless; it takes lot more voltage to jump that plug gap in a compressed fuel/air mixture inside the cylinder, so looking at that small gap in open air does not mean it will do that in the engine. Pull the spark wire from the center tower of the distributor and place the end of that wire about 1/4" from metal and test in that fashion. A good stock system will jump that 1/4" gap in open air with a hot looking spark. (This will isolate the distributor cap and rotor out of the problem too.)

Your best test of the coil by itself is as follows and will establish if the coil is good or not:
- jumper the coil + by itself to battery +
- set up the coil spark wire as above with a 1/4: gap to metal
- jumper the coil - to ground for a moment to and unground and it will spark when ungrounded; make sure you are insulated from this jumper as you can get a jolt from it

You ought to recheck the resistance through the coil from coil + to coil -. Set the meter to the lowest scale (it may be 200 ohms) and recheck that resistance with all other connections to the coil removed. You ought to measure 1 to 2 ohms. (Make sure you connect the 2 meter leads together first, record that reading, and then subtract that from the coil + to - reading.) (The .002 reading is likely 2 ohms but make sure.)

Finally, did you set the reluctor gap in the new distributor to .008" with a non-steel gapping tool? (Brass strip or matchbook cover)
 
nm9stheham said:
- jumper the coil - to ground for a moment to and unground and it will spark when ungrounded; make sure you are insulated from this jumper as you can get a jolt from it

How exactly do you do this jumpering of said negative stud on the coil? Do you just unhook the neg stud wire and connect/unconnect back on the stud in a pattern like morse code and watch the end of the coil tower wire held 1/4" away from something grounded like the head? Or do you connect a secondary ground wire from the negative stud on coil (leaving the original factory negative wire hooked up) and ground that in a pattern? I don't follow here. And I'm assuming the car needs to be on "run" correct?

Finally, did you set the reluctor gap in the new distributor to .008" with a non-steel gapping tool? (Brass strip or matchbook cover)

Yes, I have a set of brass feelers. Set to .008, then test fit the .010 feeler and used very light force to remove the .010.

You ought to recheck the resistance through the coil from coil + to coil -. Set the meter to the lowest scale (it may be 200 ohms) and recheck that resistance with all other connections to the coil removed. You ought to measure 1 to 2 ohms. (Make sure you connect the 2 meter leads together first, record that reading, and then subtract that from the coil + to - reading.) (The .002 reading is likely 2 ohms but make sure.)
Click to expand...
I can re-check the ohms on coil again for you no problem.

How would I test the brown wire into the bulkhead? Tell me if this works:
Unhook brown wire connector which includes the red/green wire from the ballast resistor.
Find the flat white plastic connector inside the car along the steering column which has the brown wire in it.
Ohm test (correct?) that circuit to see if there is any resistance.

And this is where i freeze up.....how do i check the brown wire for a voltage drop between the flat white connector on the steering column and the ballast resistor connector? Do I compare whatever voltage i'm getting there with what the battery is putting out?
I would assume I should also test the brown wire coming from the ignition switch to the flat white connector and see what voltage its putting out....should be damn close to what the battery is putting out right?
 
For the coil test you can indeed do this with the coil + connected and the key in RUN; you will be testing the coil, ballast, and ignition system wiring so that method does not isolate the coil by itself. As for the grounding of the coil -, disconnect the existing wire from the coil -, and then use a jumper (what you call a 'secondary ground wire' ; i.e., another plain piece of wire), connect it to the coil - and ground the other end. Each time you ground and then unground the other end of that jumper, you should see a good spark. As noted, don't be hanging on to the jumper anywhere! (You can connect the end of the jumper to a screwdriver blade and touch the balde to groudn whiel you hold the handle...)

You can also test this while someone holds the key in START to check the coil operation off of IGN2; just disconnect the yellow wire from the start relay and it will not crank when the key is tunred to START.

Yes, you can ohm test the brown wire as you say; make sure any wire you test is completely disconnected at one end. But the latter part where you describe voltage testing along all point in the wire is adequate and tells you more. Put the - lead of the meter on the batttery - and keep it there as you move the + lead of the meter from point to point and write down the voltages. You can do this in START and along the blue wire in RUN.

BTW, do you think this has the original spark module? If so, that is a real 5 wire unit and needs both sides of the ballast resistor in place.

OH, yeah, have you cleaned the ground connection to the spark module reeeealy good and make sure you have perfect metal-to-metal contact between the chassis and the metal case of the spark module? A poor ground there will sure stop it from working; that is a basic 'do this first' type of step with these problems.
 
I decided to dive into the bulkhead connector. Mine had this tar lookin crap on top of the connectors in the engine bay which I had to scrape off so the connectors would come out. Minor PITA but I got them off. I found all connections were bright shiny brass, looks like the tar protected it over the years.

However, there was a thick black wire with a red tracer that someone had added a length of fusible link wire to (going into the connector). I'm not sure what this is but I'm assuming its one half of the ammeter/power circuit into the car. It appears someone had a corrosion/bad connection on this some years back so added 14 gauge fusible link to it. I need to get a replacement packard connector so I'm not able to test anything right now.

I can't imagine this fusible link would hurt anything right? I have plans to do the ammeter bypass soon, so perhaps I should just get rid of that fusible link (its not factory appearing, I.E. there are no big square plastic tabs that say "FUSIBLE LINK")????

Forgot to mention, its a 5 pin ECU, there are no mopar stampings on it. It has both sides of the ballast resistor in place.
I have sanded the body where the ECU mounts on drivers side inner fender, it should be getting a good ground but I haven't tested with a meter.
 
Does that black and red tracer wire splice into the main black or blue wire coming from the alternator as it routes to the bulkhead connector? If so, it and that fusible link is shown in the mymopar.com schematic for your year car. Look at the lower part of sheet A. (Download this if you have not done so already....)

It goes to a red wire on the inside and is the main power feed to the ignition switch in that year. In earlier years, the ignition switch power feed came from the welded splice in the dash harness, but it looks like Mopar fixed changed in 1975 to put the ignition switch power feed from the alternator power output; that reduces the load on the main alternaotr feed back into the ammeter. Soooo keep that in ! You have a 'sort of' Mad Electrical bypass in your '75.
 
UPDATE. The car starts and runs.

Got a packard 56 connector from NAPA (85 cents) for the brown coil + wire, cleaned the firewall connectors with brake cleaner (didn't have electrical cleaner) and got all that buttoned back up including filling the female connectors with dielectric grease.

I didn't check the coil ohms as suggested above. Not sure why I didn't.

Also cleaned the other packard connector on the passenger side inner fender (had some old stale grease on it but no corrosion that I could see). A quick buzz with a hand file till it was bright shiny brass and back together it went.

STILL wouldn't start, although it wanted to during cranking. Strangely as soon as I let go of the key, it would die which as we all know (or should know) is the ballast resistor. I had just purchased it a month ago and the car had not yet run on it so I assumed new=good. It even tested out within specs on the ohms but as stated above, the pins seemed flipped around. I even connected it upside down but still no dice. It was 12-15 dollars at AutoZone.

Scabbed the other ballast resistor I had on my 73 Duster out back. I'm so glad I left that on the firewall when I pulled the motor 10 years ago. Once I installed that, it started right up.

I'm going to get a new cap and rotor because it has a few single misfires when accelerating. Timing is 5 degrees BDC at idle. Plugs gapped at .035
Found that the black w/ green tracer to feed the negative coil post had some shitty connection done by previous owner. Seems to work for now, but will do it right when I can.
I also installed a brand new ground cable since I found the old one was starting to grow green under the insulation down by the engine block.
If I don't buy another Crane PS-91 coil, I'm going to HEI it as I've heard alot of good things about that conversion.

Thanks to all who helped with this. I understand a ton more about the ignition system, bulkhead connectors, and voltage drops now. Awesome.
 
Final update on this. Installed a new Crane Hi-6 Fireball ignition. Midrange miss is totally gone. I suspect either a bad factory ECU or ground on it.
 
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