Cranks slow with the key, fast at the relay

[Kern Dog]

I’ve had this issue before with these old cars.
From inside the car, I turn the key and the starter spins over slow. When I take a screwdriver to the relay…

It cranks over as fast as you’d expect.
The battery is fully charged….

The car is a 72 Duster…

It isn’t anything wild. It was a slant six three on the column “Gold Duster” that my brother in law and I put together years ago. It has mostly sat parked since we got it here in 2007. The dash wiring is original but the engine side is a harness from some 73-76 V8 Duster or Dart. This was done to have factory electronic ignition.
The steering column did get a replacement ignition switch years ago. Otherwise, the wiring is at least 50 years old.
I’ve had this happen in other cars. Sometimes I’ve had them not even want to spin over when turning the key while again, full charge with the battery and normal starter speed when the relay is touched.
I’m going to slip another ignition switch plug into the dash harness to see if I can rule out that. Next would be potentially corroded bulkhead wiring terminals.
After that, what else do you suggest to try ?
Cheers…

 

[Kern Dog]

I tried a different ignition switch and it didn’t make a difference. It spun over at the same speed. It was enough to start the car though. The wiring terminals…

Here you can see the dash side plastic plug is broken on one edge.

The wires are remarkably clean looking though.

For now I just put a zip tie around the connection to keep it from slipping off.

 

[RustyRatRod]

I would bet on a dirty or loose connection somewhere. First thing I would try would be to remove and clean all the connections at the relay. Then make sure they are tight going back on.

 

[Kern Dog]

Forgive me....I didn't mention that I swapped in another starter relay and the symptoms persisted.
What is strange is that it isn't consistent. This does lead me to believe that the issue could come down to a loose or poor connection somewhere.

 

[Phreakish]

It has to be some loose or dirty connection. The solenoid is basically just another relay and it gets fired by the starter relay. A relay shouldn't really pass more current if a better connection is applied to the internal coil.
It could be that a quicker closing of the relay (caused by a cleaner signal by jumping the terminals) is closing the solenoid harder and creating a better connection sometimes? It's a reach, but is the only thing I can think of.
If so, then the starter or solenoid may be on borrowed time.
Testing the battery voltage when cranking and noting what it reads with a slow or fast crank might give some clues. A bad brush or bad connection should cause a difference in the load on the battery that should be fairly easy to spot.

 

[missing linc]

I suspect the bulkhead connector.

 

[Workingdog1]

I suspect the bulkhead connector.

Agreed, I've had some issues and bypassed bulkhead for ignition 1 and 2 and voila !

 

[RustyRatRod]

I suspect the bulkhead connector.

Could well be.

 

[Kern Dog]

Last week I had the car running where it is sitting in the picture. My nephew was in the car and smelled something, I saw the voltage regulator was smoking. I replaced the regulator, both battery cables and starter today. I started it up and saw no smoke anywhere. It ran fine, it just has that weird intermittent slow cranking issue.

I actually pulled the mini starter that I had in the car and put in a stock one. I love the sound of the stock starters but forgot how close the terminals are to the exhaust pipe. I have a 340 manifold on the drivers side with a 2 1/4" pipe on it. There is about 1/4" to 5/16" of room from the big lug to the exhaust pipe. I swapped in the old starter just to have that classic sound but I may switch back to the mini just for wire clearance.

 

[1WildRT]

Try grounding the terminal the brown wire connects to...
If no change try applying 12v to the terminal the yellow wire attaches to...

 

[Workingdog1]

Could well be.

And my good bud who's a few hours away sez sounds like time to rewire.

Who wants that cost, labor and headaches ?

I just need it to run, break down, blowup, wreck or cruise.

LMAO !

 

[Kern Dog]

I do have the terminal with the brown wire grounded since when I patched this car together, I didn't have the wiring that went to the neutral safety switch/backup lights.
I'll try running 12 volts to the yellow wire/terminal.

 

[Phreakish]

Last week I had the car running where it is sitting in the picture. My nephew was in the car and smelled something, I saw the voltage regulator was smoking. I replaced the regulator, both battery cables and starter today. I started it up and saw no smoke anywhere. It ran fine, it just has that weird intermittent slow cranking issue.

I actually pulled the mini starter that I had in the car and put in a stock one. I love the sound of the stock starters but forgot how close the terminals are to the exhaust pipe. I have a 340 manifold on the drivers side with a 2 1/4" pipe on it. There is about 1/4" to 5/16" of room from the big lug to the exhaust pipe. I swapped in the old starter just to have that classic sound but I may switch back to the mini just for wire clearance.

Do both starters do the slow dance sometimes?
I personally would trust an old OEM starter more than a "new" chinesium one.

 

[Kern Dog]

Both starters respond about the same. I've tested them out on the bench and they both spin just fine but then again, on the bench they are seeing no load.
The mini starters that I have here are OEM from later model Mopars. They are probably Japanese, I thought Denso was one of the suppliers.
All the cars and trucks out back have later model OEM mini starters.

 

[Bewy]

The problem is in the relay. In post #1, the s'driver is essentially shorting out the contacts inside the relay. Note that even with the contacts bridged, the current is still flows through the SAME wiring & connectors. So if it spins fast with the relay terminals bridged, then it cannot be these items causing the problem. The relay contacts maybe burnt from arcing or worn way. You can buy a 150 amp relay which comes as a black cube, only sligthly bigger than the popular Bosch 30 amp relay. This is what I use for the starter relay. 150 amps is waaaaaay more than the solenoid draws but it means the surface area of the contacts is greater, resulting in less arcing/wear.

 

[67Dart273]

Are you sure its not simply advanced timing, AKA trying to kick on the starter? Pull and ground the coil wire, then see if it still cranks the way you describe

 

[Kern Dog]

Are you sure its not simply advanced timing, AKA trying to kick on the starter? Pull and ground the coil wire, then see if it still cranks the way you describe

I have the timing set to 14 degrees BTDC.
The relays that I've tried are all "seasoned" parts that I've saved from years of parting out cars. Who knows...maybe the ones that I have tried are corroded inside?

 

[Dana67Dart]

Assuming all other things are good. When you short, with a screwdriver, the battery terminal to the starter solenoid terminal you eliminate the starter relay.

Nothing in the cars wiring would create a slow cranking situation EXCEPT a massive load like the headlights on or other large load.

The battery provides power to the ignition switch, from there it goes to the starter relay.
As long as there is enough power to engage the relay the relay will make the same connection the screwdriver does.

The proper way to test the relay would be to provide a switched 12v lead to the yellow wires terminal on the relay with the yellow wire removed and the key in the off position.

If the engine rotates as fast as with a screwdriver it's NOT the relay.


Next turn the key to run and do the same test, Take note of the cranking speeds

Next test for a massive load.

Get an amp meter and check the load from the battery with the key off, run, and with the yellow wire disconnected, start.

Note the amperages.

There should be no draw with the key off.
There might be a slight draw in run.
And with the yellow wire disconnected there should not be any significant change when in start.

You mentioned you changed the starter relay, was it a new relay?

A used relay might work but have worn contacts with high resistance.

The bulkhead connectors have nothing to do with the starter cir EXCEPT the yellow wire and the feed to the ignition switch.

But again... If the relay engaged there is enough power passing through the bulkhead connectors.

 

[Kern Dog]

Assuming all other things are good. When you short, with a screwdriver, the battery terminal to the starter solenoid terminal you eliminate the starter relay.

That is interesting. I never saw it that way but it makes sense.

You mentioned you changed the starter relay, was it a new relay?

A used relay might work but have worn contacts with high resistance.

New? Nah...I have a few used ones out in the shed that I keep for times like these. Maybe I need to buy a few new ones, huh?

The bulkhead connectors have nothing to do with the starter cir EXCEPT the yellow wire and the feed to the ignition switch.

I only suggested this because of the difference in cranking speeds from how it is right at the relay compared to the other side of the bulkhead.

But again... If the relay engaged there is enough power passing through the bulkhead connectors.

Thank you.

 

[halifaxhops]

Have to ask is the key on when you jump the relay? If not and it is fast check the timing it can possibly be to advanced.

 

[Kern Dog]

Yes, I've set the ignition key to RUN and crossed the terminals on the relay.

 

[Dana67Dart]

I only suggested this because of the difference in cranking speeds from how it is right at the relay compared to the other side of the bulkhead

I understand but the power to the starter is all under the hood.

Only the trigger for the relay goes through the bulkhead

 

[Bewy]

Everybody needs to re-read post #1. When he shorts the terminal on the relay [ brown wire coming from the ign sw ] to the terminal with the red wire [ red wire goes to starter sol ], the starter cranks fast.
Nothing to do with the wiring or...headlights being on. The relay is faulty.

 

[Dana67Dart]

Everybody needs to re-read post #1. When he shorts the terminal on the relay [ brown wire coming from the ign sw ] to the terminal with the red wire [ red wire goes to starter sol ], the starter cranks fast

Look again at the photo... the yellow is the only wire that comes from the ignition switch.

The brown wire goes from the starter relay TO the solenoid/ bendex on the starter, the red wire comes from the battery to the terminal on the starter relay and FEEDS the car through the bulkhead (and takes charge from the alternator to the battery) the starter motor gets it's power from a heavier wire directly from the battery to the solenoid/ bendex

By screwdriver jumping those two terminals the starter relay is removed from the circuit.

If he provides +12v to the yellow wire terminal, the relay acts like it does when the key is turned to start (minus the ballast bypass) and the relative IS in the circuit.

 

[Kern Dog]

Everybody needs to re-read post #1. When he shorts the terminal on the relay [ brown wire coming from the ign sw ] to the terminal with the red wire [ red wire goes to starter sol ], the starter cranks fast.
Nothing to do with the wiring or...headlights being on. The relay is faulty.

THIS makes sense. Thank you.
Electrical stuff has always been my weakest point.
I was under the incorrect impression that by crossing the terminals, I just bypassed the ignition switch and bulkhead wiring alone. It never occurred to me that this was also bypassing the entire function of the relay itself.
All these years when I've encountered the difference in cranking speeds, I blamed it on seasoned wiring when all along, it could be that I have simply had worn relays. I thought that they were go/no-go. It didn't seem possible that they could be anything but that.