Causes of slow spark?

What could be a general cause for slow spark? When tested with a screwdriver, any given plug wire will fire once, maybe twice per second of cranking. Doesn't seem to change between slow-ish cranking (when battery starts to die), or faster cranking (jumping off of another car). Can go more in to detail but the basic story is this: the weather got cold, truck wouldn't start, plug wire and coil wire spark was slow and weak, changed LB dist to better vac advance dist, fixed coil wire spark but not plug wire, swapped from LB to GM HEI, plug wire spark is now mostly blue with some orange, just slow as previously described. Distributor timing is unknown at the moment, and probably out of wack, i've had it in positions where it hits well and wants to start, and spots in the opposite, still the same spark speed as before anything was touched.

Something else i'll add while i'm here, my old lean burn dist had 4 sections at the bottom where adjustments could be made, 90 degrees or so at a time, a local buddy of mine said that the vacuum can on the other dist should be pointing at cyl #2 or around that area, as apposed to where the lb dist was (can would have been pointed around cyl #8, if it had one), but the vac dist only has three of these 90 degree squares at the bottom, the missing area being the one i'd need for what general area he is talking about.

It does have a brand new coil, distributor and cap are clean, HEI is wired up correctly, plug wires are just a few months old (granted, they are duralast), plugs are good, and vac advance is hooked up to the correct carb port. It hasn't jumped time (tested cyl 1 at TDC). The most weird thing about this, is that when I had the vac dist in the ballpark where the LB one was, after letting it sit from cranking for a couple minutes, and cranking again with no pedal/ gas, it would almost fire right up, then go back to cranking. Happened consistently that way, regardless of smaller adjustments made to dist timing, and especially without giving the carb gas. Stumped and confused (lol), any help is greatly appreciated

Please define exactly "what you mean" by "HEI." Is this some aftermarket dist that looks like a GM original in-cap HEI? Or do you have some distributor hooked to an HEI module?

Do you still have a system with a coil wire? What does the spark look like there?

Measure power to the ignition system WHILE CRANKING and then measure battery voltage WHEN CRANKING and post them back

Until you talked about swapping things out, I was starting to think "problem with the distributor pickup/ reluctor" but if you changed the entire distributor..................then no

67Dart273 said:

Please define exactly "what you mean" by "HEI." Is this some aftermarket dist that looks like a GM original in-cap HEI? Or do you have some distributor hooked to an HEI module?

Do you still have a system with a coil wire? What does the spark look like there?

Measure power to the ignition system WHILE CRANKING and then measure battery voltage WHEN CRANKING and post them back

Until you talked about swapping things out, I was starting to think "problem with the distributor pickup/ reluctor" but if you changed the entire distributor..................then no

Click to expand...

Just to verify, factory chrysler dist, gm hei module, new oem coil. Dist is older than lb dist but is gapped correctly at the pickup coil and fired hotter to the coil than the lb did. Coil wire spark is blue as apposed to the blue/ orange from plug wires. No access to volt meter or anything of that nature, kind of tough to get one given that my daily is out of comission

Without a voltmeter you might jumper AKA "hot wire" direct from a battery source, such as the starter relay stud to the ignition module / coil.

Other thing you NEED to check is the distributor pickup connector.

Last, set up a test gap with the coil wire and crank it long enough to "catch a rythum". See if it seems like it is evenly sparking as the pickup would trigger it, IE steady, no large gaps in the rotation

I'm thinking either voltage supplyproblem, or a poor connection in the pickup wiring

Call me a DA, but
At a cranking speed of 300 rpm, this is 5 revolution per second, and a 4-stroker fires on every second revolution so.........2.5 sparks per second on any given wire sounds normal to me,at cranking speed
Am I missing something?

A couple things.
Flooded.plugs wet? Crankcase gas fouled?
Weakass battery.

I"m guessing this is a BB Mopar of some kind
If you have an electrical issue Del can fix you right up.
In the meantime, here's how you set your timing.
Put the #1 piston at TDC compression. Then back the crank up to 10* Advance. Then back it up another estimated 5* for a total of 15*; Accuracy is not important.
Next , put the Vcan anywhere that you can rotate it 1 to 2 inches before it hits something, when you go to advance it. Pull the coilwire out of the D and near-ground it. Turn the Ignition key to run. DO NOT CRANK IT. Back under the hood, advance the D until you get a single spark. Back up and repeat. And a third time. Snug the clamp. Turn the key off. Pop the cap, and with a Sharpie mark the D on the outside as to where the rotor tip is. Put the cap back on. That Sharpie mark better be right under,or very nearly under, a tower. Whatever tower it's under is now to be designated ;Number one plugwire. Make it so, and rewire as necessary the rest of the wires.......in the correct firing order, and in the correct direction. Lock the D down. Your base timing is now set at a place that is guaranteed to fire the engine.....if the cam-timing is good.. You can set the timing by lite after you get it running.
Now, as to the electrical; Del will fix you up;
just make sure your pick-up is wired for the correct polarity, as to in which direction the reluctor vane passes by it. SBMs rotate opposite from BBs. If you reverse the polarity after the start timing is set as above, you will have to redo it
After you get it running, you will have to reset the power-timing.

May the Force be with you

AJ/FormS said:

Call me a DA, but
At a cranking speed of 300 rpm, this is 5 revolution per second, and a 4-stroker fires on every second revolution so.........2.5 sparks per second on any given wire sounds normal to me,at cranking speed
Am I missing something?

Click to expand...

Last night in the cold it was firing almost exactly 1 spark per second

I remember when i had my 68 coronet parked on a sidestreet in dowtown winnipeg, no plug in for a block heater. If it would turn over,it would start. Choke setting was bang on though.

That being said, slow cranking is related to battery,cables and starter. Direct drive starter or gear reduction?
I preferred the bigger starter on my 318’s.

Tooljunkie said:

I remember when i had my 68 coronet parked on a sidestreet in dowtown winnipeg, no plug in for a block heater. If it would turn over,it would start. Choke setting was bang on though.

That being said, slow cranking is related to battery,cables and starter. Direct drive starter or gear reduction?
I preferred the bigger starter on my 318’s.

Click to expand...

Alternator belt has always had a way of telling me i have a kinda weak battery (lol), but it does the same jumped to another car and cranking fast

AJ/FormS said:

Call me a DA, but
At a cranking speed of 300 rpm, this is 5 revolution per second, and a 4-stroker fires on every second revolution so.........2.5 sparks per second on any given wire sounds normal to me,at cranking speed
Am I missing something?

Click to expand...

That's right and it's VERY difficult.........without using a lot of battery........to judge this on a "per plug" basis

Remember this horrid thing from J.C. Whitney? Friend of mine had one. 8 wires you wrapped one around the outside of each plug wire and the neon bulbs flashed with each cylinder LMAO WHAT A RADIO NOISE GENERATOR!!!

So, absolutely positive the distributor to module wires are correct?
Just for kicks try swapping them.

TrailBeast said:

So, absolutely positive the distributor to module wires are correct?
Just for kicks try swapping them.

Click to expand...

Positive, checked last night.

BigBlockMopar28 said:

Last night in the cold it was firing almost exactly 1 spark per second

Click to expand...

Well that would be 120rpm on the starter, so I'm with Inkjunkie," weakazz battery"
If you try to jump it with another car or a known good battery, The dead battery acts like a big old sponge, sucking the electrons out of the booster just as fast as it can, leaving very little for the starter.
IMO you have four options;

1) during boosting, momentarily disconnect the dead battery just during cranking,, reconnecting it after she fires up.
2) pull the battery out, bring it in and warm it up for 24 hours, Top up the electrolyte, as may be required and then charge it for three days at 5Ah, on an automatic charger, or
3) In the event that the engine still cranks too slowly, Clean all connections between the starter and the battery, including between the starter and the engine, and the cable clamps to the cables, if they are separable.. And if that fails to up the cranking speed, replace the starter.
4) Buy/install a new or known to be good,battery.

But I have a quick test
With a known to be good set of booster cables, and with clean tight battery cables, including the cables into the cable-ends,you can hook one side of the booster-cables directly between the battery negative and the starter case.Use the black ones. This bypasses all the grounds. Then try it.
If still slow, hook the other cable, a red one, directly to the starter power-lug. Unhook the black jumpercable off the battery neg, and do hook the red one to the positive post. Finally re-install the black booster clamp to the Battery neg. The starter should immediately begin to crank at full speed. If it doesn't, check the integrity of all your connections, and retest. Still no good? replace the starter.

This assumes the cylinders do not have a buncha gas in them.An engine with some gas in it, cranks differently than when it's dry. And there comes a point it won't crank at all because liquids are not compressible. When that happens, the rod can bend.

AJ/FormS said:

Well that would be 120rpm on the starter, so I'm with Inkjunkie," weakazz battery"
If you try to jump it with another car or a known good battery, The dead battery acts like a big old sponge, sucking the electrons out of the booster just as fast as it can, leaving very little for the starter.
IMO you have four options;

1) during boosting, momentarily disconnect the dead battery just during cranking,, reconnecting it after she fires up.
2) pull the battery out, bring it in and warm it up for 24 hours, Top up the electrolyte, as may be required and then charge it for three days at 5Ah, on an automatic charger, or
3) In the event that the engine still cranks too slowly, Clean all connections between the starter and the battery, including between the starter and the engine, and the cable clamps to the cables, if they are separable.. And if that fails to up the cranking speed, replace the starter.
4) Buy/install a new or known to be good,battery.

But I have a quick test
With a known to be good set of booster cables, and with clean tight battery cables, including the cables into the cable-ends,you can hook one side of the booster-cables directly between the battery negative and the starter case.Use the black ones. This bypasses all the grounds. Then try it.
If still slow, hook the other cable, a red one, directly to the starter power-lug. Unhook the black jumpercable off the battery neg, and do hook the red one to the positive post. Finally re-install the black booster clamp to the Battery neg. The starter should immediately begin to crank at full speed. If it doesn't, check the integrity of all your connections, and retest. Still no good? replace the starter.

This assumes the cylinders do not have a buncha gas in them.An engine with some gas in it, cranks differently than when it's dry. And there comes a point it won't crank at all because liquids are not compressible. When that happens, the rod can bend.

Click to expand...

Big thanks, ill give that a shot tomorrow, buddy also suggested testing to see if the actual ignition switch could be robbing power, by running a cable from the hot side of the battery to the hot side of the coil. As far as liquids and such, it had been flooded once pretty bad when this problem first happened, i do plan on changing the oil as soon as i get it to fire up, as it does smell like gas and the first flood was bad enough to foul the plugs.

In other news, decided to re test timing like i had last night just for re-assurance, cranked until the double yellow line on the crank dampener was just barely past the sight hole and cyl #1 was up, popped the cap off the dist where i had it set last night, and the rotor button was just barely past the #1 plug wire post, which to my understanding is close to where it should be? Tried some small adjustments CW and CCW after giving it some gas to fire, and it never hit once on any adjustment. Was cold again today and didnt have time to check for spark before the battery started to die

A weak battery along with a faulty starter? Starter drinking up all the available power. Current always takes the path of least resistance.

Cranking too long on a weak battry will smoke your starter too.
The slow speed allows too much current to flow through the windings for too long,and overheating and thrown solder alng with burned armature is a result.