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1956 lack of spark

Started by caddyorganist, May 30, 2023, 08:19:28 PM

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caddyorganist

I'm trying to figure out why my 56 SDV has no spark. I've read through the forum and can't seem to get a clear answer on where the negative ground strap connects, assuming that could be part of the problem. The one from the battery negative post is bolted to the frame and then there's one that runs from that bolt to the bell housing at the starter.

We've replaced the ballast resister/condenser block on the firewall because the old one was junk. We've tested it and it's showing the correct voltage. Also replaced the coil and it appears to be fine.

It cranks and we have interior lights, but no spark. I was told that a bad ground strap could be the issue.

Matt G.
1956 Sedan de Ville
2017 XT5

Dave Shepherd

Got 12v to the coil positive terminal on cranking? Points good, proper gap? Rotor ok?. All basic ignition checks.

caddyorganist

Quote from: Dave Shepherd on May 30, 2023, 08:23:57 PMGot 12v to the coil positive terminal on cranking? Points good, proper gap? Rotor ok?. All basic ignition checks.

How do you test that on the coil? I want to make sure our process matches lol. It looks like we're getting 9v.
1956 Sedan de Ville
2017 XT5

Dave Shepherd

Should have 12v during cranking, but it still would have spark at 9v. Check spark across the points, cranking, check the gap of course. Do you have spark out of the coil wire to ground?

J. Gomez

Quote from: caddyorganist on May 30, 2023, 08:37:18 PMHow do you test that on the coil? I want to make sure our process matches lol. It looks like we're getting 9v.

Matt,

You will need to refer to the Service Manual wiring diagram to follow the ignition wiring layout.

1-   When cranking you will get a solid +12V from the starter solenoid "yellow" wire up to the + side of the coil. This is needed to get the max spark from the coil.
2-   Once the engine starts the ballast resistor should drop the voltage (around 9V) up to the coil "black" wire, the "pink" wire from the ignition switch has the +12v and is connected to the ballast resistor.
NOTE: Both the "yellow" and "black" wire should be at the same connector on the ballast resistor.

As for your other question, there is only one ground strap from the – side of the battery which as you posted is attached on the top of the chassis (just below the battery tray) and up to the bell housing where the starter is bolted.

There are two small ground straps on both side of the heads (rear) attached to the firewall covers.

Good luck..!
J. Gomez
CLC #23082

signart

Ther are two places that you can check for spark. Where are you checking for spark?
Art D. Woody

TJ Hopland

Grounds like between engine and body and battery are fairly easy to troubleshoot.  One way is with jumper cables, use them to add grounds and see if it makes any difference.

A 'ground strap' people could be talking about could be the one inside the distributor.

Don't overlook basic things like is the distributor actually turning?

StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Lexi

Attached find the 1956 Cadillac chassis wiring schematic. Hope this helps. Clay/Lexi

bcroe

#8
I might start by clipping a 12V test light directly
to the coil low voltage terminals.  Cranking it
should flash on and off, to show power is at
least getting to the coil. 

I have seen points oxidise over and make no
contact if left alone too long.  I fix them
by putting them in series with a 120VAC 150W
lamp.  good luck, Bruce (all HEI) Roe

caddyorganist

Thanks for the advice. Finally got a chance to spend some time with the car again today. Several asked questions so I'll try to cover them all here.

We set the multimeter to 9v and tested at the yellow wire that goes to the positive of the coil. During cranking we were only getting 0.11-0.13v.

There appears to be no spark from the coil wire to the ground.

We ran a negative jumper cable from the negative post on the battery to the bell housing bolt. Still no spark at the coil.

The rotor looks fine and the distributor is turning.

Doubt we're getting spark across the points.

We have power at the resistor and going to coil yellow wire on positive side.

Thanks again for the advice!
1956 Sedan de Ville
2017 XT5

cadman59

So you found the cause of the no-spark condition at starting: you should have the full 12 volt at the yellow wire while cranking.

Check the yellow wire at the starter motor.
Feiko Kuiper - Netherlands (Europe)

1959 Cadillac Series SixtyTwo 6-Window Sedan
https://instagram.com/feikokuiper

James Landi

Mr. Gerhard--- you've got a digtal multimeter that's reading a "ghost" of a power connection.  As has been stated above, and for emphasis sake, you've NO POWER to your coil, and cranking the starter over and over again will eventually destroy the starter. We can GUESS why your ignition key, associated and wires are not delivering power,  If you have no experience with electricity, then you need to find someone who does to help you. If I were helping you, I'd connect a wire from the positive side of the battery to the ballast resistor,and then have a "Jumper Wire" that would "bridge" the resistor, so that when you began cranking the starter, I'd bridge that resistor, thus applying full power during cranking ONLY. When we performed this imagined scenario, your engine would likely begin to show signs of life... that is if the two other preconditions for engine function were met.  SO in summary, you need spark, adequate compression, and fuel.  Hope this helps, James

V63

For testing purposes, just 'hot wire' the coil with full 12 volts.

caddyorganist

#13
Tested with a 12v test light. Yellow wire from ballast resistor to primary winding on coil has power. Secondary winding and the wire from the coil to the distributor have no power. Does that mean bad coil? The light flashed very slowly.

We changed the battery in the multimeter and got the following:
Secondary winding from center post of coil to the positive stud on the coil is 9.26. Meter is on 20k ohms. Primary winding from the positive small post to the negative small post on the coil is 1.6. Meter is on 200 ohms.

Can the points and condenser in the distributor prevent the coil from having spark even though we have power going into the coil?
1956 Sedan de Ville
2017 XT5

badpoints

Yes it is the points switching that generates the high voltage for the spark. Have you changed your points? Badpoints are very common, should of been the first thing you changed after confirming that you have voltage.

caddyorganist

Quote from: badpoints on June 14, 2023, 02:58:00 PMYes it is the points switching that generates the high voltage for the spark. Have you changed your points? Badpoints are very common, should of been the first thing you changed after confirming that you have voltage.

That's our next step. Wanted to make sure there wasn't anything else before we did that.
1956 Sedan de Ville
2017 XT5

caddyorganist

Update. Still no spark. Replaced points and condenser as well as distributor cap and rotor. We know we have power to the ballast resister on the firewall. We know we have power to the coil. We're not getting power out of the coil. We tried disconnecting the condenser on the coil and that made no difference. The coil checked out when we tested it; however we ran a jumper wire from the red wire at the ballast resistor to the top positive post on the coil and no spark. Bad coil?

We also have continuity at the points. We backed it off a half turn as suggested and still have continuity.
1956 Sedan de Ville
2017 XT5

dn010

#17
Perhaps you will give this thread a read:

https://forums.cadillaclasalleclub.org/index.php?topic=105576.0

There is a very good check list in there on page three I believe. Not to spoil the ending, but it turned out to be the replacement points in that thread. I gathered that he had someone cranking the engine with the distributor cap off to view the points and saw the problem.
-----Dan Benedek
'57 Cadillac Sedan Deville 6239DX
'81 DMC DeLorean

caddyorganist

Quote from: dn010 on June 23, 2023, 04:18:28 PMPerhaps you will give this thread a read:

https://forums.cadillaclasalleclub.org/index.php?topic=105576.0

There is a very good check list in there on page three I believe. Not to spoil the ending, but it turned out to be the replacement points in that thread. I gathered that he had someone cranking the engine with the distributor cap off to view the points and saw the problem.

Thanks, I'll check that thread out.
1956 Sedan de Ville
2017 XT5

Chopper1942

It's this simple.  KOEO do you have 9V at coil +?  If so, at the coil, take off the wire to the distributor and connect a jumper to the coil.  With KOEO, ground the jumper wire.  Remove the jumper wire from the ground. You should have a nice fat spark that jumpps at least 1/2" from the high voltage coil wire that goes to the dist.  If there is no spark, the coil is bad.  If there is spark, hook up the dist wire at the coil.  Turn the motor until the points are closed.  KOEO open the points with a screwdriver.  Should have spark from the high tension lead of the coil.  If not, connect a jumper wire to the point mounting bracket and then to a good engine ground. KOEO open the points, if you now have spark, the points and/or distributor is not grounded to the engine.  Check the small wire in the distributor to make sure it is not broken or corroded where it mounts to the dist housing.