Ignition problem - No spark '74 Fury

[cantflip]

I think it and *poof* it appears.

I was amused as well.... sorry.... got away from me...

 

[josehf34]

Very good... Hz still tells you there is a pulse... its a cheap quick test to narrow down no start dead module, not a very good module test... that would take a scope.

Since it runs try spraying water with a spray bottle all over the ignition components... watch for sparks and listen for snapping sounds. If voltage leaks you could have intermittent trouble based on weather conditions and condensation.

Before you dismantle anything and while running... do a few quick voltage drops:

DMM lead to coil + and other to battery +. recorded reading this drop should be .5volts or less IF you have a 12volt coil.

If you have a ballast resistor... Ballast switch side to battery + will be .5v and ballast coil side to coil + will be .5v the ballast itself will drop just under half of your voltage to allow 6volt factory coils to survive 12volt charging systems.

I don't want to start heroic measures to voltage drop the ground side of the coil. Because of the switching of the modules transistor it would take some doing to get meaningful results... just make sure all ground connections are in very good clean condition.

Do voltage drop the engine block with one lead and the battery - with the other... while cranking the engine with ignition disabled... if you drop more than .5volts clean up battery connections and ground connections at the block and retest... still too high you need a battery cable. Due to prior work and age ground cables get broken, corroded and left off during repairs. Typical symptom would be cranking speed or no crank... but once in a while the drop doesn't cause that problem but doesn't allow quite the right voltages elsewhere. It will ground through the engine mounts... just not very well.

the b+ at the starter and other lead at the battery while cranking will test positive cable .5v or less
the b+ at the alternator and other lead at battery b+ would test the alternator charging cable .5v or less
the case of the alternator and the battery - the test ground connection from alt to bat .5v or less

Voltage drops are the only accurate test for the condition of a wire or connection. If you do them enough to get comfortable you will be ahead of most of the folks who do this for a living. Where the starter attaches to the bell housing is its ground connection too... you would be surprised how often a little corrosion in there takes voltage away from the starter. With a schematic I can prove out the circuits of a car very quickly this way... always drop straight to the battery first, if you are .5v loss on the wire... stop testing it...it passed. when you lose too much voltage you have a poor connection or wire and need to start doing smaller tests between where you started and the battery until the problem is pinpointed. I have also used this test between rusty inner fenders and battery - to prove there wasn't enough metal connection for electricity to flow (add a ground strap)... the ground strap to the bulkhead goes to a transmission bell housing bolt and often gets forgotten at reassembly...

With lots of experience it usually takes longer to find a schematic and expose connectors than it does to get meaningful test results. The biggest trick is you can't open a circuit when doing a voltage drop so if you have a plastic connector you will need a needle or small paper clip to "backprobe" the connection. BE VERY CAREFUL NOT TO LET THE BACKPROBE SHORT TO ANYTHING ELSE.

Also double check your coil... if it says "12v" on it you may have the original ballast resistor still in the circuit and don't need it. See if you can find install directions for similar system... that may clear up your issue.

With no specs you could test your coils ohms and compare it to a replacement... not something I normally would approve of... if you can find a replacement on the shelf of a local parts store they should let you test it at the counter if its not sealed package. Bring your DMM and old part with you if you try this...gives the pretense of a sale, and temperature will greatly affect readings so don't get your too hot or cold. Similar coil with great differences on resistance might get me to buy the replacement and try it... its all guesswork at that point so don't get rid of the original and they wont take the replacement back.

Next time... go with a factory system. The old 4 and 5 pin systems were good and had tons of published diagnostics. A name brand aftermarket kit could work too... just watch reviews first and they should have diagnostic and installation help. Some A#$hole has shipping container of these with an investment of $5 or $10 per unit... no branding, no quality, no SEMA designation... forget it. Wife looked into a prototype toy for one of her clients as a promotional item... if you want to deal with 500,000... same price as 100 custom small run... all made in china.

From 3 weeks ago the car has been running fine without spark problems but today the problem came back. I repeated the pulse test and I still have 25Hz while cranking engine but without spark, I replaced the aftermarket ignition coil with the original and tired mopar one and the car started immediately so I think the problem is the ignition coil.

I don't know if the problem is fixed (I need to buy another ignition coil, the mopar is 42 years old ) but while I was driving the car sometimes it feels like the engine attempts to stall

About those tests... I sprayed water but didn't see any spark, the voltage drop between battery and ignition coil is 0.8V with ballast resistor bypassed (13.8V at ignition coil, 13.0V at battery with engine idling)

I'm going to search for the aftermarket ignition coil resistance specs and test it

 

[cantflip]

From 3 weeks ago the car has been running fine without spark problems but today the problem came back. I repeated the pulse test and I still have 25Hz while cranking engine but without spark, I replaced the aftermarket ignition coil with the original and tired mopar one and the car started immediately so I think the problem is the ignition coil.

I don't know if the problem is fixed (I need to buy another ignition coil, the mopar is 42 years old ) but while I was driving the car sometimes it feels like the engine attempts to stall

About those tests... I sprayed water but didn't see any spark, the voltage drop between battery and ignition coil is 0.8V with ballast resistor bypassed (13.8V at ignition coil, 13.0V at battery with engine idling)

I'm going to search for the aftermarket ignition coil resistance specs and test it

Excellent, at least your testing. sorry about the ongoing dilemma. In all honesty, unless there is a good reason for the upgrade, I prefer to stay stock. I do like eliminating points, but that's really more about laziness. Problem with finding specs is are they correct? Some cars had more than one factory coil available... PITA when all you want is to know if your number is good.

Best of luck to you with the coil, now wouldn't it suck if you simply have a bad connection on a wire... try wiggling the primary wires while running (not the plug wires) if it stumbles, maybe you can figure out which one is giving grief.