Riddle me this, Mopar electrical experts.......

-
B

bizjetmech

Active Member
Joined
Nov 8, 2005
Messages
37
Reaction score
0
Location
Eastern Kansas
Car in question....1973 Dart Sport, Automatic

History.....dropped in my long awaited/saved-money-for replacement 340. Drove car over to shop for swap, no electrical issues whatsoever.

New engine in........cranks, lights off intermittently, or mostly not at all. Managed to get it running long enough to break in the cam (I hope). Seems to run okay if/when it lights. When cranking, shows low/no voltage at (+) post of coil. I can jump straight from the positive post of the battery to the positive post of the coil, and it will run some of the time.

Ignition switch was intermittent, subbed in another switch, seemed to work better. Disassembled column. put in new switch, now it doesn't start at all.

Ringing out wiring. I'm using a 1974 shop manual/wiring prints, if it matters......the closest I've been able to find at the swap meets around here. Am assuming they are basically the same, other than seatbelt interlock wiring.

Looking at page 8-156...Tracing path for 12 volts to get to the ignition switch. According to the print, wires "R6C 12 BK" (from ammeter) and "R6B 12 BK" splice together with wires "Q3 12 R", " Q3 12 R*", "L1 12 BK" and "J1 12 R". Is the junction of all of these wires on the back side of the firewall?

I'm assuming that "Q3 12 R" doesn't exist in a 1973 model car. Looks to me like I can check the "Start" wiring aft of the firewall (and ignition switch) by ringing for continuity between pins "P" and "Q" on CE 2, as long as....

-I turn the ignition switch to "crank/start"
-I don't turn on the lights and,
-I don't honk the horn

Then, ring thru "P" and "N" to check the wiring/switch in the "run" position.

Then.......it appears that the coil "grounds" thru the ECU. Theoretically, I should be able to get continuity between the (-) terminal of the coil, and a ground on the firewall/fender apron?

Then after that....I'll need a recommendation for a good automotive electrical shop near downtown Kansas City, Missouri. I've been dicking around with this problem off and on since June, and I'm no closer to figuring out WTF is going on than I was on June 30. Or, as much as I don't want to, pitch all the Chrysler stuff, and go with an MSD-6.
 
hold on , 67Dart273 , may have some medicine for you. i would say first things first, and check every connection at the bulkhead, and every single ground you have engine/body ETC.ETC.
 
The coil does not ground. The coil consists of a primary winding from the neg. coil terminal to the pos coil terminal, and the secondary is connected to the tower and one of the primary terminals, I think the neg. terminal.

So far as your wiring, can you post part of the diagram? Maybe take a screen shot and post it? Only diagrams I have access to are these for 73, and a 72 shop manual

http://www.mymopar.com/downloads/1973/73DartA.jpg

http://www.mymopar.com/downloads/1973/73DartB.jpg

I THINK what you are referring to above is sometimes called (in the shop manuals) as the "no1 splice" I usually call it the "in harness splice." It is taped up in the under-dash harness, you'll have to "feel" back from one of the ammeter wires and the big black going to the IGN switch to find it. THERE ARE a certain number of these that have failed. The NUMBER ONE issue with all these old girls is getting to be corrosion and heat related problems with the bulkhead connector.

READ this great article, which has a simplified illustration of the main charging/ ammeter circuit, and the in-harness splice:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

from here

http://www.madelectrical.com/electrical-tech.shtml

Be happy to answer more, but I don't have a diagram that matches yours. If yours is digital, (CD) please consider contacting AbodyJoe and consider posting to this thread, where several service manuals can be downloaded

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download
 
I'm in KCMO, and my homeboy Chris, an automotive god, is in KCMO as well. I turn to him when I can't figure it out (often, as my forte is motorcycles).

PM'd you with my number. Maybe we can hop in Chris's '75 Dart and see what's up.
 
I had a similiar when i dropped in my BB. All I can say is just look at the my mopar wiring diagram and go wire by wire. What was causing my battery to short our was the radio circuit and the firewall 3way pigtail connectors.
 
Make sure the battery ground cable goes to the block (paint removed from bolt location) AND goes to more than one body ground.
 
Run a grounding loop picking up an attachment screw on voltage regulator, orange box, case of alternator, and negative battery terminal. All three of these devices have to be at same potential, and won’t perform correctly if not grounded properly.

As 67Dart273 said; check for good ground connections at block, and head to fire wall. After grounding system is good to go, look for broken wire, bad connection at bulkhead connector including connector crimps, and under dash splices. Examine fusible link for damage.

I suspect that where you were working in engine compartment, the problem will be found there. Chances are good at some point a wire got pinched, or pulled a bit too hard during the engine swap.

One more place to check would be reluctor and magnetic pickup for proper gap, and resistance.
 
I had a similar problem with my 64 Valiant, engine dying,or not starting at all, but my headlights weren't going on and off. The ignition module wasn't tightened down well to the bulkhead (the mounting hole was wallowed out). I used a bigger screw and tightened it down and the problem went away. I took this to mean that the ignition module needs to be grounded at the firewall.
 
You can not have 12 volts to the coil in run position. 8 volts only or you will overheat the coil and it will shut off. !2 volts start. 8 volts run. Your ballast is not wired correctly. 74 harnesses are screwed up. I have seen several 74's with this proplem with miss matches harnesses. Wire your electronic ignition on its own. Do not use the green wire with the red tracer. Light blue / red 12 volts, Black / yellow neg coil, The other two dist. When key is on power should go through a ballast to the coil for 8 volts. When cranking you should have 12 volts dirrect to coil.
 
also it's possible that you have the two coil connector wires backwards. you can swap the wires it will run but will be real flakey.
 
the PO of my duster had the MSD coil wired backwards, as i later found out because my tach would only work on the postive side of the coil. i switched it, it ran for a while but eventually it gave out. as stated above the ballast HAS to be wired correctly or you will have an extremely weak spark at the cap. found this out the hard way
 
Oldmanmopar said:
You can not have 12 volts to the coil in run position. 8 volts only or you will overheat the coil and it will shut off. !2 volts start. 8 volts run. Your ballast is not wired correctly. 74 harnesses are screwed up. I have seen several 74's with this proplem with miss matches harnesses. Wire your electronic ignition on its own. Do not use the green wire with the red tracer. Light blue / red 12 volts, Black / yellow neg coil, The other two dist. When key is on power should go through a ballast to the coil for 8 volts. When cranking you should have 12 volts dirrect to coil.
Click to expand...

To further expand on this post, pay attention to the 4 terminal ballast.

First, you MUST use a 4 terminal ballast with the older, 5 pin ECU

You MAY use a newer 4 pin ECU with EITHER a 2 or 4 pin ballast

You CAN NOT tell a 4 or 5 pin ECU by looking, sometimes. Some 4 pin ECUs are actually 4 pin, but some have 5 physical pins. You must use an ohmeter to determine if the 5th pin is actually hooked up

PAY ATTENTION to the 4 pin ballast. You'll notice that it has an OPEN NOTCH at one end. Refer to your wiring diagrams and you will find this notch illustrated. The two resistors in the assembly are different resistances, I think one side is about 5 ohms, and the other is 1.5?

Referring to the two '73 diagrams I posted, look at them and follow the "dark blue" which goes to regulator IGN, alternator field, and the ignition resistor. This is the switched 12V "run" IGN buss coming through the bulkhead from the key. You need to probe this key in "run" but engine off, and be sure it is close to same as battery voltage. If not you have voltage drop in the ignition harness, probably the bulkhead connector or ignition switch or connector.

Here's how Mopar ignition start / run works

You have three separate circuits, IE several SEPARATE switches inside the ignition switch

ONE is the "run" circuit, in the diagrams I posted the "dark blue" and are hot ONLY with the key in "run." It is NOT hot in "start" or "accessory,"

TWO is the YELLOW which goes to the start relay. This activates the start relay in "start" IF the second push on terminal of the relay is grounded. On older "stick" cars this terminal is not there, is soldered to the relay case, and on those the relay case MUST be grounded

On cars with two relay "push on" terminals----on auto cars the second terminal goes down to the transmission neutral safety switch and must see a ground in park or neutral. ON "stick" cars with a clutch safety switch, that terminal sees a ground when the clutch pedal is depressed

THREE is the brown coil resistor bypass circuit. In the posted diagram for 73 this is shown as BROWN. It comes from yet another separate switch on the IGN switch and only goes one place---from the switch, through the bulkhead and electrically to the coil +, and this wire is hot ONLY in start.

So when cranking, you should have "same as battery" in "start." If much different, say down 1/2 volt or more, you have voltage drop in that circuit. Your number one suspect is the bulkhead connector, no2 is the IGN switch or connector.

You sound to me like you can do this, if you stay with it. Even though I'm familiar with these cars, it helps me to draw out a rendering of the bulkhead connector just as I'm looking at it from the firewall inside and out, label it with the factory markings, and label where stuff goes.

There is no reason you can't adapt a different year harness with a little work. As I posted above, the "MAD" link is good reading, it gives you a great perspective on the problems these cars develop in the bulkhead connector.

Simplified wiring using a 4 terminal ballast. Again, you can use either an older 5 pin or newer 4 pin ECU NOTICE the position of the notch in the drawing of the ballast

Ignition_System_5pin.jpg



Wiring diagram ONLY for a newer 4 pin ECU and 2 terminal ballast

Ignition_System_4pin.jpg
 
Never said I had 12 volts at the coil in "run". When it runs, it has about 8-9 volts.

Wiring on car is uncut, original 1973 harness for a five pin ECU. I've been running a four pin "orange box" also subbed in another brand new one, no difference. Wiring has been rung out, fusible links checked, and connections verified.......correct wire is on the positive terminal of the coil. Have used the stock/factory connectors (as built) with a dual ballast (have checked two, neither made a difference)

Both engine and instrument panel harnesses have been removed, tape removed, and inspected for opens/shorts. Have unpinned/removed all of the male/female pins from both sides of the firewall/bulkhead connectors (one at a time, then double checked the proper receptacle against the service manual), cleaned the pins where neccesary with a fine wire brush in a Dremel tool, and tightened the female connecters and the little retention tabs on both male and female pins to make sure they don't "push back" when the connectors are plugged in.

Checked the wiring between the bulkhead connector and ignition switch as noted above.....ringing thru "P" and "Q" shows continuity when ignition switch turned to "start/crank", rings "open" in other positions....."P" and "N" ring continuity when switch selected to "Run"........at this point, I've got to assume my start circuit is okay aft of the firewall connector.

As suggested above, I'm going to look at grounds. May add another bonding strap between engine and frame or firewall, just for grins. Also......I used a set of Mancini's chrome plated alternator brackets when remounting the alternator. It may be a reach, but I think I'll pull it off, and remove the chrome under the attach points.
 
I don't know where I picked up the voltage I assumed, l but in your first post, you say coil has "low or not volts" on cranking. This indicates a problem with the coil resistor bypass circuit. This is a separate terminal on the ignition switch that is hot only in start, and goes directly through the bulkhead to the coil side of the ballast resistor, in other words to the + side of the coil. It's ONLY purpose is to supply hot 12V to the coil during crank.

Normally, the "run" voltage goes cold during crank. To see if this is true, pull one of the leads off the starter relay so the starter cannot run. Turn the key to run, and check voltage at the KEY side of the ballast, not the coil side. Then, with the meter propped up where you can see it, twist the key to "start" and see if the "run" voltage goes away.
 
It's too much of a coincidence that the problem would appear right after the engine swap and not be something related. Since there has been other changes made since that time, you may have multiple problems now. It's going to take someone with a test light or meter and some electrical knowledge to trace it down. No power to the coil should be fairly forthright. Any decent auto electric shop should be able to find the problem in no time.
 
Update, if anyone is still following this thread......

As noted before, rang thru the ignition switch to check for continuity in "start" and "run". Just to clarify, the switch only showed continuity in crank/start ONLY when switch turned to start.......when switch released to "run", it showed continuity ONLY in the "run" position......basically, the switch and the circuit aft of the firewall works as designed.

Checked the grounds again. Removed the "plating" from both terminal ends of the engine grounding strap, and made sure that all contact areas of the alternator brackets were clean and grounded.

Now, for the fun part. Tried starting again with a meter hooked up to read voltage at the (+) post of the coil. When engine cranking, switch in "start", it now reads battery voltage.

Great!.....except.....it still doesn't have any indication of spark at the plugs.

Sooooooo...........as it just so happens, I located the original, almost 40 years old, 5-pin, potting-running-out-of-it, never been in the car/sitting in a box in my garage since 1991, numbers-matching 1973-vintage ECU, and had it with me. So, for grins, I sub this old effer in.......

And now, it starts. So does this mean that I need to forget about using modern, Chinese-made ECUs, and start collecting 40 year old, salvage yards ones?

Stay tuned........the engine runs, but it's running rough, and won't idle (yet). Haven't had a chance to play with the timing or carb adjustments yet. Or else I may have left a plug wire off. Won't stay running unless I modulate it with the gas pedal.
 
Sure we are. the consensus seems to be the high priced NAPA or Standard Blue Streak.

I went to a GM HEI module, have one used on in the car from an old HEI dist I had, and bought a new NAPA module for spare.

4 wires, no ballast, easy to hook up. I'm done arguing with Chinese Mopar ECUs
 
At the last SEMA / AAPEX show, I had a chinese company offer me "mopar" ignition modules for $3.45 each - that is US dollars, and the minimum was 100 pieces.

Of course he had "GM" 4 pin modules in his booth too.

B.
 
You must log in or register to reply here.
-

Back
Top