Start and Ignition Problems on 71 Demon

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Gibber

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From a simple job of changing out plug wires and a electronic distributor with a non working vacuum advance on my 340 Demon I have managed to pooch things up to the point of no spark at the coil. I inadvertently switched plug wires and so went thru the drill of finding TDC on number 1 cylinder and redoing the plug wires, but had no spark at the coil, so I swapped the distributor back and still no spark. Car ran fine before I messed with it.

On top of that now I think the ignition switch has quit as in the start position I get no voltage at the yellow wire on the starter relay. Only way to crank it is the old screwdriver trick...any ideas from the experts?

Thanks in advance,

Mark
 
I don't remember, 71 didn't have any seat belt interlocks, did it?

I'd get into the ign switch connector where it comes down the column. You might need to remove the 2 screws and trim under the column.

You have a shop manual, wiring diagram?

Usable diagrams here:

http://www.mymopar.com/downloads/1971/71DartA.JPG

http://www.mymopar.com/downloads/1971/71DartB.JPG

which came from here

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

Look at diagram "B" and find the ignition switch connector

I do not believe these are in order on the connector, probably same as the '72 connector

Yellow goes directly from the IGN sw through the bulkhead to the start relay, UNLESS the thing has a seat belt interlock and is hot ONLY in "start"

Brown goes directly from the IGN sw through the bulkhead to the coil + side of the ballast resistor, and is hot ONLY in start. The yellow and brown are isolated from each other

The dark blue goes from the IGN switch and is UN fused, and feeds the warning lights and gauges (cluster voltage limiter.) It "tees" off and goes through the bulkhead, and feeds the alternator field, the regulator "I" terminal, and the ignition system. It is hot ONLY in run NOT in start

So check those three at the ign switch connector, chase them through the bulkhead. Probably a good idea to pull the bulkhead connector sections apart and inspect them

Do the gauges/ oil warning light work?
 

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Thanks, no seat belt interlock. I will check it out..appreciate the help...the gauges all work fine...

Mark
 
With the ignition on, you should measure at least 7 V at coil+, rel. to Batt-. If not, measure upstream - ballast resistor (both sides), bulkhead connector, ignition switch (both sides), until you find where voltage disappears.
 
Latest update, fixed my no start problem with a good cleaning of the contacts on the bulkhead connector. Yellow wire from starter relay to bulkhead was only getting intermittent contact. Thank gawd it was not the ignition switch.

Car cranks, have spark at coil and even have spark at a couple of the plug wires I pulled off, but the car still will not fire....could I have screwed up the ignition timing so badly when I replaced (mixed up) the plug wires that it won't even fire at all? I thought I went thru all the steps to find #1 cylinder at TDC and go from there, but maybe I'm still way off...Puzzling, but I am making progress....thanks in advance!
 
Do you have a GOOD HOT spark? Take a grounded probe, remove the coil wire and hold the probe at the top of the coil tower. Crank the engine USING THE KEY, and NOT jumping the start relay.

You should have a NICE fat hot spark there, 3/8--1/2" long

Just what DID you do to determine TDC?

If you are sure the timing marks are correct..................

Pull the no1 plug, stick your finger in, and bump the engine over until you start to feel compression. You might have to do this 2 --3 times until you learn "what to expect."

As you START to feel compression, turn your attention to the timing marks. Do NOT stop the engine on TDC, but rather BEFORE TDC, IE wherever you think you want your intitial timing, say, 10* BTC

No look the dist over. Rotor should be at or in neighborhood of no1 wire If not, move the wires around until this is so.

Now, I always make a small file mark on the top rim of the dist. case immediately below the no1 tower so I can see what's goin' on

Retard the distributor (CW for SB) and slowly bring it back CCW (advanced)

IF you have points, advance until the points just open

IF you have breakerless, center the reluctor tip on the pickup coil

This should be "close enough" that the engine just fires right up, no fuss!!
 
Shall check all of the above tomorrow and report back...thanks...

Mark
 
After further testing, spark at coil is weak and intermittent, cranking engine over gets a small spark at coil every 5 sec of cranking or so....any ideas? Tried changing the coil out, no change...and measured voltage with key in run, battery voltage at both sides of ballast resistor (12.25 VDC or so), and positive and neg side of coil show .682 VDC...measured it several times....not 6.82....I'm stumped...

Thanks,

Mark
 
Gibber said:
After further testing, spark at coil is weak and intermittent, cranking engine over gets a small spark at coil every 5 sec of cranking or so....any ideas? Tried changing the coil out, no change...

Mark
Click to expand...

just a thought, but verify the ballast connectors are where they are supposed to be. i once had a locating pin on a ballast connector that was broken off and the connector was upside down and giving me a weak and intermittent spark. it wouldnt hurt to try a different ballast resistor. seems a lot of folks having problems with them,,, you could also try a different EI box. i know this falls into the category of "throwing parts at it" but if it was running before , it has to be something simple, maybe you just bumped something loose
 
I'll make sure the connections are tight, and I do have a spare ECU box and ballast resistor...I'll replace them one at a time and see if I can make any headway. Thanks..
 
ONE Your "run" voltage sounds OK. Voltage at coil NEG is meaningless

You must understand TWO things:

IF you crank the engine by jumpering the start relay, you may have a weak spark because the system is getting LOW voltage through the ballast

If you crank the engine USING THE KEY AND the ballast bypass (brown) circuit is bad, you won't get good starting voltage, either

You need to hook your meter to coil POS, crank the engine USING THE KEY and see what you have. You should have "close to battery" when cranking, and in no case less than 10.5 volts

If this is low, a temporary workaround for troubleshooting is to run a clip lead from coil POS to battery, such as the start relay stud. Don't run the car this way more than a minute or two, just use this as a troubleshooting aid

TWO How did you check the spark? Use the coil wire? Instead, use a grounded probe (clip lead and screwdriver) and hold it near the top of the coil. Crank the engine USING THE KEY

THREE Have you checked the gap in the distributor? Inspected the reluctor and pickup for rust/ debri/ corners knocked off? AND pull the dist connector in/ out several times to "scrub" the connection clean. Do the same thing with the ECU connector, and the resistor. Get a "feel" do the terminals seem tight?

FOUR Failed / failing components

After you have done the above, Something may be failing. This stuff does not "just quick" sometimes it "gets weak"

Bad coil

Replace reluctor / pickup, they're cheap

If none of the above replace the ECU

CONSIDER rigging yourself up a GM HEI if nothing else for emergencies and troubleshooting. MOUNT the module on a scrap of aluminum and device a "handy" way of mounting it, such as a bolt hole in the corner of the aluminum, or a great big alligator clamp to just "clamp it to ground

Get a 2 wire trailer plug and use 1/2 of it for the dist. connector:

http://www.wholesalemarine.com/mm5/graphics/00000001/S-D-426880-1_med.jpg

Wire nice clip leads to the other two HEI module terminals, red for hot, black or white for coil neg

So you have your "emergency HEI" all mounted up, and in the trunk, and your ignition quits, what WILL you do?

1 Unplug the ECU connector

2 Mount your HEI to ground. Hook up the distributor connector

3 Hook the red (hot) wire to coil + and hook the last (white, etc) to coil NEG

4 If desired, take a clip lead and bypass the coil resistor.

Only thing left is the coil, see if you have spark again, driver 'er home.
 

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Outstanding, thanks for the info, since the starter relay is working now, I'll check everything as you suggested with the ignition switch.

Mark
 
You could try applying 12 V from the battery directly to coil+. Use a jumper wire of 16 awg or larger and good alligator clips (or a ring terminal). If it runs well then, the problem is erratic wiring from the ballast to the coil, or the ballast itself. You need a timing light to see if it is firing at the right time (when it does fire). Used ones are real cheap since not used on newer cars.
 
Problem fixed, bad wire terminal on the neg side of coil and loose connection at brown wire side of ballast resistor. Fixed those and it fired right up...thanks for all your help everyone...

Mark
 
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