68 Fury Starting issue- help!

Custom 880

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Hello all, I have a 68 Fury III Convert, 383 auto. Motor and trans have a fresh (mild, highway car) rebuild. She fires right up when she is "cold". Never a problem or hesitation. But when she is "warm" the engine will not crank. No clicking and battery is fully charged. All accessories function properly when the key is turned. The starter is not engaging. Only happens after driving her and she will not start again unless she sits for many hours, usually overnight.
Have a fresh battery, connections, starter, firewall relay, NSS. NSS is the "old" one but we have the 3 prong and connected to the center prong.
Suggestions?
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HWYCRZR

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NSS?
That acronym is not ringing a bell.

Does it crank warm if you jump the starter relay?
Key on, in park, jump the two terminals. Do not jump or cross wires beyond that. Black wires are not grounds.

If it still doesn’t turn over, it is something between the relay and into your starter (heat adds resistance)
If it turns over that way then get the service manual out and look through the starting circuit.
Heat issues with electrical usually means a bad connection or dirty circuits somewhere in the line. I many cases a bulkhead wire harness bad connection causes some heat and resistance issues.
 

Davea Lux

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Check the wiring to your starter relay, the spade connectors are famous for getting to a loose fit over time and not making good contact. Also check to be sure the relay is properly grounded. If you have replaced the relay with one of the Chinese knock offs, those units are famous for sticking. Next time it won't start, try rapping the relay with the handle of a screwdriver, that will usually unstick it. The other area that sometimes causes problems is the neutral safety switch, the contacts inside sometimes get corroded and do not complete the circuit to the starter solenoid, as yours is new, check to be sure the center wire is tightly connected.

Dave
 

Davea Lux

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NSS?
That acronym is not ringing a bell.

Does it crank warm if you jump the starter relay?
Key on, in park, jump the two terminals.
If it still doesn’t turn over, it is something between the relay and into your starter (heat adds resistance)
If it turns over that way then get the service manual out and look through the starting circuit.
Heat issues with electrical usually means a bad connection or dirty circuits somewhere in the line. I many cases a bulkhead wire harness bad connection causes some heat and resistance issues.

Neutral Safety Switch.

Dave
 

Davea Lux

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Hello all, I have a 68 Fury III Convert, 383 auto. Motor and trans have a fresh (mild, highway car) rebuild. She fires right up when she is "cold". Never a problem or hesitation. But when she is "warm" the engine will not crank. No clicking and battery is fully charged. All accessories function properly when the key is turned. The starter is not engaging. Only happens after driving her and she will not start again unless she sits for many hours, usually overnight.
Have a fresh battery, connections, starter, firewall relay, NSS. NSS is the "old" one but we have the 3 prong and connected to the center prong.
Suggestions? View attachment 302333

If you changed the neutral safety switch to a 3 prong unit, you also need to change the shifter comb inside the transmission to get the more modern switch to properly mate with the comb. As the car starts cold that probably is not the problem but something to think about. Or did you just change to a 3 prong plug?

Dave
 

Custom 880

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Thank you HWYCRZR and Dave's Lux for your replies!
I will work on that this evening and see what happens with the jumper.
The transmission was built with the new NSS in mind.
The concept of heat causes resistance is very helpful.
Thank you both, I appreciate your time.
 

HWYCRZR

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Dave answered most everything
About Things that activate your starter relay. Changing the NSS May add a complication, but if it starts cold it shouldn’t cause problems hot.

Here is a quick verbal wire schematic of the start system. Based on ‘68 Polara 383
Brown wire on relay goes to your neutral start switch. If that doesn’t create a good ground, due to being not sensing that it is in neutral or park, it will not let the relay activate. The yellow wire my original wire (the 68 Polara schematic says gray) goes through bulkhead connector T. (Bottom pack). These are labeled on the inside under dash. This wire goes to starter switch. On the starter switch the red 12 gauge wire is battery power, hot all the time. When the key is turned on the black wire gets power to feed your accessories. If your radio works and heater fan blows when key is on, you have power through your switch. For this case ignore the dark blue wire with tracer and brown wire.
When you turn your key to crank (against spring) you allow power to go through the yellow wire to the starter relay, if your neutral safety switch is working properly, it should complete the circuit to excite the relay feeding power (heavy brown wire may look black) to the starter solenoid. This excites the solenoid completing the circuit allowing your starter to turn.
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RGORHAM29

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Hello all, I have a 68 Fury III Convert, 383 auto. Motor and trans have a fresh (mild, highway car) rebuild. She fires right up when she is "cold". Never a problem or hesitation. But when she is "warm" the engine will not crank. No clicking and battery is fully charged. All accessories function properly when the key is turned. The starter is not engaging. Only happens after driving her and she will not start again unless she sits for many hours, usually overnight.
Have a fresh battery, connections, starter, firewall relay, NSS. NSS is the "old" one but we have the 3 prong and connected to the center prong.
Suggestions? View attachment 302333

Beautiful car!
 
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