No spark on 340

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artfuldodger

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73 Duster with 340. Last month put in new resistor, ECU, Dizzy cap and wires. Started and ran fine, tried to start today and no spark to plugs. Test light grounded to body shows bright on positive side of coil in all key positions, but from positive batt to positive coil as a jumper test light goes out in key start position. Everything else seems ok, any ideas. I have a buyer and this is frustrating.
 
Lordie I'd sure like to break you guys of "dizzy."

Anyhow, no1 thing is start by making absolutely certain the ECU is grounded.

Take your light or meter, with key in "run"

Check ballast resistor, "key" side

Coil POS

and coil NEG

The "key side" of the ballast should be "same as battery"

The coil + should be a bunch less, perhaps 5V--9V but certainly not "battery"

Coil NEG should be very low, less than a couple of volts.

Don't discount that the coil wire can be bad

With the key in run, and a method to check spark, touch the bare side of the distributor connector--the end going to the firewall--to ground. One "snap" spark should be generated each time

Put your meter on low AC volts and crank the engine or spin the distributor. It should generate about 1V AC

Check under the cap, and the rotor, for dirt, debri, moisture, damage. Rotor "punch through."

Look at the reluctor and pickup, for debri, rust, and strike damage. Check for shaft wobble and bushing play

If you have a tach try disconnecting it
 
Maybe this helps, and maybe not

Here's a post I made about the simplest way I know to get across testing the ECU/ ignition parts

http://www.forabodiesonly.com/mopar/showpost.php?p=1970917976&postcount=6


You need a coil, the ECU and the distributor

Lay it out on the bench. Follow the diagram. Find the two distributor pickup terminals on the ECU. Hook them to the distributor

Hook the ECU case to battery NEG

Coil does NOT need grounded

Distributor does NOT need grounded.

Hook coil + to the power lead terminal on the ECU. Get a clip lead hooked there and let dangle. This is your battery "hot" when you are ready

Hook something from coil "case" to a probe for testing spark.

Hook up your power clip lead. Twist the distributor shaft while holding the test probe near the coil tower. The thing should make sparks

If not, unhook distributor. Take first one, then the other pickup clip leads, and "tap tap" ground them at the battery connection. Coil should make 1 spark each time you do so.

If not, try another coil. If that does not fix it replace the ECU

IF you hook it all up and it WORKS, then there is something AFU in the car harness. SUSPECT a bad ECU connector OR a bad DISTRIBUTOR connector
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This is all you need to test the basics of the ignition. You can easily test the ballast separate. A battery, the ECU, distributor and a coil, and of course some test leads

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Below, the basic diagram for a 4 pin ECU

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Below, the wire for testing spark. I use my 12V test light. No, LOL the spark won't blow up the bulb

166lmj7.jpg


Below, the ground connection. ALL you need is one wire from batt NEG to the ECU case

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Below, the two distributor connections. In the car these are polarity sensitive, but for testing does not matter

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Below, the coil NEG connection

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Below, battery PLUS connection, one wire to this terminal of ECU and jumpered over to + side of coil


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Below, all hooked up and ready to test (except for battery ground). Should produce sparks at least 3/8" and typically 1/2" long

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Below, distributor "one wire" test. I have removed the other distributor wire for simplicity. Take the bare connector end or this clip lead (the yellow) and with everything hooked up, ground it repeatedly. Each grounding should result in a spark (In this photo you need to hook up the ECU ground wire, I left it off for the photo)

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Thanks everyone, I have tried most of these things already. All of the ignition parts(except reluctor) have been replaced and I only started it twice last month. It fired right up but now no spark. With my test light grounded to body to + coil I have strong light even in key cranking position but when I use the test light as a jumper from battery to + coil it goes out in cranking mode. Everything has been checked 3 times for ground. When I put my test light as a jumper from batt to - coil and crank the starter the light does not flicker but stays constant, I was told that could be the ECU, could my ECU have gone out already after only 2 starts and sitting for a month. By the way the knowledge of everybody on these forums are second to none as I am a member of some others also. Thanks
 
^^This is unclear

"when I use the test light as a jumper from battery to + coil it goes out in cranking mode"

This should be normal. With the test lamp hooked to battery + and coil+ and the key to "start" you should have +12V at both of those points. Therefore no voltage to the lamp

What you need to do is as I said above:

1...Turn the key to RUN. Put your test light from ground to coil + Should light Actually should be "some dimmer" than full battery voltage

2....Put your test light from ground TO COIL NEGATIVE. Should light very dimly or not at all

IF THE light is bright in the above test, either the ECU is not grounded, is bad, or a wiring issue.

Don't discount the coil could be bad
 
67Dart273, this forum is lucky to have you. GREAT information. When I saw the title of the thread, I thought, "67Dart273 will be the first person to respond. I was close, you were second. Totally agree with the "Dizzy" thing.
 
LOL Thanks. But in fairness, I've "let the smoke out" of a few things. Sometimes, this involved much higher voltages than automobiles.
 
Thanks for all the info. I ended up disconnecting the Tach and the engine fired right up. Strange though, it ran last month with the tach just fine. anyway it is alive!
 
EASY!! LOL. Well check the tach wire routing, it may have abraided and shorted, or the tach developed an electriclal problem. "It happens" which is why I suggested it.
 
Dizzy :supz: lol

Glad you found out the issue. Are you running a aftermarket tach? Should only be one wire to trace
 
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