Quick Question Coil issue or more? (Mopar but not A-body)

-
MonkeyMadness

MonkeyMadness

FABO Gold Member
FABO Gold Member
Joined
Jun 13, 2016
Messages
1,414
Reaction score
1,939
Location
Yorba Linda California
I have a 73 D100 with a 318 Daily driver ran fine then parked for a week. Tried starting it this week and no go. Turns out no spark at the plug, so I stat at the plugs and work my way back. I go through plugs, wires, rotor and cap, Elc pickup air gap is on the money @ .008 everything checks out good. Unplug the Coil to cap lead and turn over the motor arcing the lead off my valve cover and get a weak spark.
I've heard of coils going bad but I have never dealt with one. Do they usually just break or fad out?

Thanks
j
 
What’s the voltage to the coil? Blue wire. Could be a coil. They can do strange things like quit all at once, go intermittent, and get weak.

if You have spark and timing hadn’t changed and it’s not running next in line is fuel.
 
4mulas said:
What’s the voltage to the coil? Blue wire. Could be a coil. They can do strange things like quit all at once, go intermittent, and get weak.

if You have spark and timing hadn’t changed and it’s not running next in line is fuel.
Click to expand...
I'll check voltage at the coil tonight. Fuel, line, pump and filter and carb are good that was the first thing I checked before pulling a plug and not getting any spark.
 
MonkeyMadness said:
I'll check voltage at the coil tonight. Fuel, line, pump and filter and carb are good that was the first thing I checked before pulling a plug and not getting any spark.
Click to expand...
So do you have weak spark or NO sparks.

if no spark check for voltage to the coil. if There’s voltage to the coil id change the coil. If still no spark the pick up is probably no good.

if there’s no voltage to the coil check your ballast resistor

choose the path of least resistance first.
 
If it's an untouched engine, possible nylon timing gear worn down and chain skipped, check compression.
 
Weak spark could be the coil if the voltage to it is correct. It could also be the ignition module. I believe it's a 5 pin one that year. Try using a 4 pin replacement. Also, make sure the module is properly grounded and the cannon plug is clean and tight on the module pins.
 
1...Clip your meter to coil + and to ground. Turn key to run and read. It should NOT read full battery, but rather, 6-10V or so. This shows that the coil is drawing current, and is dropping voltage through the resistor

2...Now Turn key to start and read meter while cranking. It should now read really close to whatever cranking battery voltage is. You can double check by moving meter to battery +, crank, and read. If battery pulls down to 11.5 at the batter, cranking, then coil + when cranking should be close to that

With key in run, "rig" a test gap direct to coil tower. Remove dist. pickup connector and tap the bare side to ground. The engine bay end, not the dist end!! Each time should result in one nice hot blue snap

3...ECU MUST MUST be grounded. If reading (1) in "run" is high, close to full battery, check if box is grounded. Put your meter on block ground, and to ECU metal case. If it shows any voltage, it is NOT grounded.

If you suspect coil, you can disconnect either wire, and check continuity.

Examine pickup/ reluctor for rust, damage, debri.

Vigoursly work all connectors in/ out, the dist, the ECU, and connectors on ballast. The dist connector is especially vulnerable, as it has no real current. Examine it with a light for corrosion, and "work" it in/ out several times to "feel" for tightness and to scrub the terminals

You can get some idea of the distributor pickup IF the "tap" test above produces a spark, but witht the dist connected, it does not, by connecting the dist connector to your meter and cranking engine, and with meter on low AC volts (AC, not DC) the meter should produce about 1V AC
 
Last edited:
If the coil & ECU have the correct voltage while you are cranking, then the problem is the coil or ECU. Assuming any plug/connectors in the circuit have been checked for corrosion, proper connection.

Coils can measure ok [ resistance ] & still be faulty. Substitute is the only way to check for sure & same with ECU.
 
^^He is forgetting the wiring, connections, and the distributor.^^ This is why it is important to attempt to troubleshoot instead of just throwing money and parts at it.
 
So I've double checked everything and narrowed it down to the distributor pickup. The ballast, and 5 pin ECU are testing out fine. Coil, rotor and cap, wires and plugs are all tested fine as well. I got soo fedup with this I bought an HEI and a new coil to swap out.

But then I found a video and the guy talks about the exact issue I'm having.
- If you turn the key to run (ign1) then back off with the coil lead next to a ground you'll get a charged spark "which is normal" but if you don't get a constant spark when cranking its a pickup failure. And this is exactly the issue I'm having at the moment.
(see video here; 7:50 is explanations of issue I have found )


So I have ordered a replacement pickup and reluctor wheel and will try this tonight.... fingers crossed... lol
 
Welp went through the full ignition system and and after replacing the distributor pickup I was getting a good strong spark from both the coil lead and the spark plug! Problem Solved! yea right...
moparlvr166 said:
If it's an untouched engine, possible nylon timing gear worn down and chain skipped, check compression.
Click to expand...
^^^ yep this, cam is out of phase from the crank it must have jumped a tooth or two. ugh

Not too big of an issue, I'm already in the process of building another motor for the truck anyway But hey the ignitions is working awesome now!

Thank you all for the feedback and help!
 
You must log in or register to reply here.
-

Back
Top