No spark when cranking

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cuda_conv

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Ok so this is a problem I have been trying to fix for over a year now and I finally stumbled onto some additional information.

1974 Swinger /6 with 5 pin ECU. I have checked wiring, cleaned/sanded/star washered the ECU and Voltage Regulator. I have replaced, ECU, Dizzy, Voltage regulator, alternator.

What is the minimum voltage needed on pin 1 of the ECU?

Blue wire voltage on the 4 pin ballist resistor is:
11+ volts in Run position.
5.5 volts in Start position. No Spark.

What can be pulling down the voltage on the Blue wire so drastically?

If I pull the Blue wire off of the Alt. or disconnect the voltage regulator I have 8 to 9 volts to the ECU and I have spark the car will start correctly.

Thanks
Ron
 
First let's figure out what you mean by pin one.

Here's a simplified diagram

Ignition_System_5pin.jpg
 
Actually let me just estimate a few

First, notice the upside down "U" on the bottom of the ballast. This orients it as the two halves are different resistances

A.....Far top right "existing wire" is the "ignition run" or IGN 1 coming from ignition. With key in run, this should be very close to battery voltage. THIS WIRE GOES DEAD in crank

B...Clip your meter to the coil + Crank the engine USING THE KEY that is important and read while cranking. You should see close to "same as" battery CRANKING voltage, and in no case below 10, better 10.5 and higher

(This circuit is not properly shown. That voltage, known as IGN2, brown, the "bypass" circuit hooks to the coil + side of the ballast and would be at bottom right)

C...Follow down from the bottom left ballast connector. This side of the ballast, and that wire, are ONLY used in 5 pin ECUs. This is fed "backwards" through the resistor during crank

The circuit path is.........

IGN2 coming through the bottom right of the ballast. Goes up through the right side --- crosses over through the jumper at top --- and back down the wire to the ECU.

I would guess this wire sees as little as 6V during cranking if everything else is normal

================================================

Generally..........

Turn the key to run and check voltage at + and - of coil. Plus side is anywhere from 6V up to maybe 10-11, neg side should be very low, perhaps 1 volt or less

IF THE positive side of the coil is much higher, this might be an open coil, bad ECU, or ECU NOT GROUNDED

Pull loose and work all connectors in / out several times, especially the dist. connector

Inspect the cap / rotor for grease, moisture, rotor punch through, etc. Check for debri and rust, and strike damage to the pickup and reluctor. Check for dist. side play. If you have brass .008" (inches) feeler, set the reluctor gap.

Hook the dist. connector to your meter on low AC volts. Crank the engine. The dist. should generate about 1V AC

Turn key to run, ground first one, then the other wire at the dist. connector leading to the ECU. One or the other (forget which) should generate a spark each time you short and open it to ground.
 
Here's a better diagram. Unfortunately the two are drawn differently

attachment.php
 
What could draw system voltage down so low in start that you can't get a spark ?
How about the starter ?

Ignition one / blue wire.. In the later models they branched that wire to whatever crap they added ( electric choke assist for example ).
What some don't realize is ignition two / brown wire is on the ballast resistor just like the others. That resistor will pass current in either direction so any time one wire is hot all the wires at hot to some degree ( pardon the pun ) in both start and run.
 
Since the 4 pin ballast has different resistance on the 2 sides, I have to wonder if the brown and green wires to the ballast in the 2nd diagram are swapped in this car.....
 
I am getting +10.5 volts on the coil. New coil and ballast resister.

The blue/trace wire on the top pin (1) supplies power.
I will have to take you word on the "Existing Wire" going DEAD on crank. It has always been my understanding that this is the power pin needed for the ECU to operate.

If you jump +12 volts to the blue wire the engine will not turn off until this voltage is removed.

If I unplug the blue wire from the Choke Control Switch, I get +6.5 volts on the blue wire and the car will start properly in the start position.

I will check the Choke Control Switch and the Choke Heating Element tomorrow.

Thanks for the suggestions.

Ron
 
Review your shop manual. You can prove this yourself. The ignition switches over the years have IGN1 and IGN2. 1 is "run" 2 is "bypass" in start

I dont remember when Ma quit doing this, but on many many years, the IGN1 line goes dead with the key twisted to "start." The only ignition power for starting is "IGN 2"
 
-Sounds like a short/drain on the Ig1 circuit; since it runs with any one of three items disconnected( two of which are new). Or as previously stated, the starter is sucking up all the juice. Or a defective battery/battery to starter circuit.
-If only 11 volts at the blue wire when Ig sw in run position(per post 1); is that within 1/2 volt of battery? If yes then battery needs charging. If no, and bat voltage is 12.5 or better(still in run), then where did the missing volts go? Trace it out.
 
If I understand what 67Dart273 is saying is that:
In Start position the ignition switch no longer provides 12 volts to the blue wire.
In Start position the ignition switch provides 12 volts to the ballast resistor (brown wire).
I have read it both ways on different forums. IGN1 should always have 12volts in START or IGN1 should be DEAD in Start.

This means that the brown wire would be supplying voltage to the Blue wire circuit through the ballast resistor.

Since the only way this car will start is when you go from Start to Run, I have gone through 2 starters and 1 battery. I have also replaced the ignition switch which is a real pain.

Either way there is still a minimum voltage level that is required for the ECU to work correctly.

What is the minimum voltage level for the ECU?

From: http://chargerr.com/Ignition/Ignition.htm

mopar_5pin_ign.jpg
 
in start you get full voltage to the coil
in run you only get half

that's the purpose of the ballast resistor. if you run full voltage during run constantly it would wear out the electronics/coil/etc (was worse on points) so they run half voltage and it was plenty of spark for run. during start they wanted 100% to help it start easier
 
^^To put this another way...^^

All US manufacturers did the same thing. All of them COULD have used a coil which operates off 12-14V directly with no resistor

But if they had done so, then when cranking, the spark would be WEAKER because of the drain from the starter.

So they all used a lower voltage coil, running on (nominal) 8-11V through a resistor, and incorporated a bypass circuit for start

IN GM, AMC, and Ford, this is the extra contact on the starter solenoid. In Mopars, it was built into the ign switch.

Part of the reason for this was the advent of higher compression engines, which require more spark. "Back in" the 6V days, engines were very low compression. They didn't need as much spark to fire

(Far's I'm concerned, going from 6V to 12V was a mistake. They SHOULD have just gone right to 24V)
 
Well the Choke switch and the choke thermostat check Ok so there must be something else pulling down the voltage in the Blue circuit.

The Blue wire does indeed go "DEAD" in start just as 67Dart273 said.

This is such a poor design and goes against everything taught about designing electrical circuits. You should never rely on voltage from another circuit (Brown in this case) to supply needed voltage to critical devices IE the ECU.

It is just down right stupid to take the normal 12 volts (Blue) running voltage and replace it with just ~6.9 volts during start. Especially when Chrysler decided that the coil needs 12 volts instead of the normal ~6.9 volts during start.

There must be something under the dash that is pulling down the Blue IGN2 voltage.

I think I am going to just put in a 12volt relay connected to the Yellow wire to give me the needed voltage for the Blue circuit or just rip out this crap and install a GM HEI setup.

Opinions?

Thanks
 
OK Refer to the most recent drawing above. This drawing does show the connection through the ballast resistor.
If the wire shown in red does in fact have 12 volts in start, the wire shown in blue should have voltage, although reduced by the resistor.
I wont argue that the switch removed from the cars harness and tested for connections would show blue dead in start. The cars harness creates the connecting loop through the ballast resistor. This goes both ways too. Proof ? ... Switch connected and in run position, check the wire they marked red all the way back to the switch ( actually a brown wire ). You will find voltage there.
The above probably doesn't help to solve your problem anyway.
I'm no longer as familiar with the later model wiring. I no longer own one and my memory fails.
If I'm not mistaken there are actually 2 blue wire circuits at play here. One is a solid medium blue. The other is darker blue with a white tracer. If that is true the 2 could be or should be separate. I really just don't know. I'll say good luck with it and leave it at that.
 
cuda_conv said:
or just rip out this crap and install a GM HEI setup. Opinions? Thanks
Click to expand...

First, this DID all work on thousands of cars Second, "sometime" later, Ma redesigned the ECU and went to a 4 wire design, which eliminated the need for the dual ballast. YOU CAN NOT ID a 4 wire vice 5 wire by looking. Many "4 wire" ECUs have 5 physical pins, so you must "ohm" the plug and see if the pin shows continuity anywhere

So far as GM, that is EXACTLY what I did. Many use the later GM modules, which allow electronic retard control. I simply used a 4 pin. I didn't even use a heat sink. I simply screwed it to a flat area on the firewall Notice the Mopar distributor connector. This is important The HEI has a small projection for indexing. You can either break it off to mount flat, or drill a matching clearance hole on your heat sink

The main reason I went HEI is because of modern Chineseation of replacement parts. In terms of "down at the present day store" I know of no brand name, including NAPA / Echlin / Blue Streak, or anybody else, that truly makes quality Mopar boxes. Since there are scads more GM HEI around, they are cheaper and easier to get, if not better.

Also, notice you no longer need a ballast. EVEN IF you use the factory coil, you get a bit more spark out of it. The final icing is that if you leave the key in "run" as in when testing, the GM does not draw coil current when at rest

attachment.php
Also, I rattled together this little box to fire up used engines, and then realized it makes a perfect "throw in the trunk" emergency ignition
hwlcfa.jpg
 
Since this is a '74.... Gotta ask, has all the seat belt interlock crap been removed? It only existed to kill the ignition when you were trying to start the car without buckling up. There are sensors under the front seats that need to be unplugged. They look like a brake light switch with a short pigtail going into the carpet. Pull the pigtails but leave the control box under the hood alone. If you unplug that the starter won't work. Unplugged the seat sensors on my '74 Charger before I drove it off the dealer's lot. The Service Manager put a bug in my ear...
 
grumpuscreature said:
Since this is a '74.... Gotta ask, has all the seat belt interlock crap been removed? It only existed to kill the ignition ...
Click to expand...

This is a bit misleading, because it is not per se in the ignition circuit. It's in the CRANKING circuit. This is easy to fix. Just look under the hood for the manual reset, about the size of a horn relay. There are two yellowish wires, one yellow black. You just wire those permanently together

This device originally breaks the wire to the starter relay

http://www.forabodiesonly.com/mopar/showthread.php?t=205307

http://www.forabodiesonly.com/mopar/showthread.php?t=168214
 
cuda_conv said:
... I think I am going to just put in a 12volt relay connected to the Yellow wire to give me the needed voltage for the Blue circuit or just rip out this crap and install a GM HEI setup. Opinions? ...
Click to expand...
Since you don't care about keeping it factory, I say go HEI. You already have an e-distributor. I did that in my 64 Valiant slant. I actuate a relay (in a 95-99 Jeep relay/fuse box) by IGN1+IGN2 and run "12 V IGN out" to a terminal block on the passenger inner fender beside the HEI module. Get an 8-pin HEI module from a 85-95 GM V-8 truck (car to 93). It is inside their "small cap" distributor. Also take the GM "external coil" and the cable that connects it to the HEI module (plug & play). Snip the input wires (red +12V, wht tach) as long as you can and the distributor pickup connector & wire. Cost me ~$15 at PickNPull. Or buy same parts from TrailBeast here for $150. I also took the knock sensor & module from the GM (for use w/ Holley Commander 950). The 8-pin module is better wiring and will allow spark timing control down the road. Read on megasquirt site for more info. Don't use your yellow "crank" wire to actuate the relay. To answer your earlier question, coil+ should run 8-10 V (I think) when using the ballast resistor & Mopar ECU. All new ECU's don't need or use the 5 ohm resistor (electronics has improved since 1970's). If a replacement ECU has a 5th pin, it is usually a dummy (so dummy customers don't fuss).
 
67Dart273 said:
This is a bit misleading, because it is not per se in the ignition circuit. It's in the CRANKING circuit. This is easy to fix. Just look under the hood for the manual reset, about the size of a horn relay. There are two yellowish wires, one yellow black. You just wire those permanently together

This device originally breaks the wire to the starter relay

http://www.forabodiesonly.com/mopar/showthread.php?t=205307

http://www.forabodiesonly.com/mopar/showthread.php?t=168214
Click to expand...

So how come my Charger would crank all day but never fire if you didn't buckle the belt after sitting down but before you turned the key? Think maybe B bodies were different? I know the control box was not like the ones pictured and was mounted on the firewall between the heater fan motor and the cowl/fender brace. Now ya got me curious...
 
I'll have to look, but I do know the reset box was right in series with relay. Maybe I forgot, maybe there's additonal stuff in the box.

I "believe" there's a video and pdf over at MyMopar on this:

http://www.mymopar.com/index.php?pid=31

in the "Master Tech" stuff:

http://www.mymopar.com/index.php?pid=117

The top one

http://www.mymopar.com/index.php?pid=431

There's a pdf normally, maybe it was removed

Here's a video

[ame="http://www.youtube.com/watch?v=3xXtmlSHtIQ"]Chrysler Master Tech - 1974, Volume 74-1 Seat Belt Starter Interlock - YouTube[/ame]
 
Re post 13; Thats what i did. A relay insures voltage. used a weatherproofed one. Bought a spare about 2002. Never needed it. I bound the start and run circuits together and dioded the backfeed to the starter.Kinda GMish, but it worked for me.
 
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