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No start when hot and using key. #2697998
09/16/19 09:13 AM
09/16/19 09:13 AM
Joined: Jan 2003
Posts: 3,857
Connecticut
jeff968 Offline OP
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jeff968  Offline OP
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Hi, I'm still battling this issue and thought I would ask the Moparts gang for any thoughts. Here is the deal.

When my Challenger is cold it always starts.
When it gets warm and I shut it off and it sits for a while it won't start.
The car turns over but it is not getting any spark when the engine is turning over.
If I just leave the key forward (not under load) and jump it with a screwdriver on the start relay it starts.

So the "no spark" issue is only under load (key all the way forward, engine turning).

I had upgraded to Electronic ignition. I have a new ECM, ballast resistor, starter relay, plug wires, cap, and engine compartment wiring harness. I even replaced the bulkhead with all new connectors. The positive side of the coil shows it is getting power.

I'm thinking of replacing the distributor next.

Thanks for any suggestions.


1970 Dodge Challenger T/A

Re: No start when hot and using key. [Re: jeff968] #2698009
09/16/19 09:47 AM
09/16/19 09:47 AM
Joined: Mar 2006
Posts: 123
Maryland
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mrob Offline
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Have you checked the voltage at the coil when it's hot? Your problem sounds like it could be heat related. Voltage to coil is good when cold, but drops too low when hot. Voltage at coil should be no less than 6V when hot.

Re: No start when hot and using key. [Re: mrob] #2698011
09/16/19 09:51 AM
09/16/19 09:51 AM
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Andrewh Offline
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if it starts jumping the relay even when hot, then it isn't an ignition component.

I would be checking the key switch or bulkhead, or even the wire that supplies power on start vs run.

since you can start it jumping the relay, the run power wire is good. but turning the key the start power to the coil, which bypasses the ballast resister has some heat issue. you will have to trace it back till you find the dead spot.

Re: No start when hot and using key. [Re: Andrewh] #2698037
09/16/19 10:46 AM
09/16/19 10:46 AM
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Posts: 35,517
Lincoln Nebraska
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RapidRobert Offline
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What Andrew said, start at the ign switch/connector & clean the terminals.


live every 24 hour block of time like it's your last day on earth
Re: No start when hot and using key. [Re: RapidRobert] #2698046
09/16/19 11:15 AM
09/16/19 11:15 AM
Joined: Oct 2006
Posts: 6,604
Iowa
burdar Offline
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Iowa
Check for power on the brown wire coming out of the ignition switch. This should only have power during "start"(cranking). Once the engine starts and you let off the key, power transfers to the blue "run" wire. Check every connection(both sides) from the ignition switch to the engine compartment.

Re: No start when hot and using key. [Re: burdar] #2698082
09/16/19 12:43 PM
09/16/19 12:43 PM
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Posts: 3,857
Connecticut
jeff968 Offline OP
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Thanks! I will check these.

As I said earlier, I installed a brand new bulkhead and redid all the connectors. It still had the same issue.


1970 Dodge Challenger T/A

Re: No start when hot and using key. [Re: jeff968] #2698094
09/16/19 01:23 PM
09/16/19 01:23 PM
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Andrewh Offline
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is the key switch new too?

Re: No start when hot and using key. [Re: Andrewh] #2698105
09/16/19 01:51 PM
09/16/19 01:51 PM
Joined: Jan 2003
Posts: 3,857
Connecticut
jeff968 Offline OP
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jeff968  Offline OP
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I had the column done by SMS 12 years ago so no. But that said, I have a brand new ignition switch. When I plug that in it has the same problem. So I don't believe the ignition switch is the issue. Thx


1970 Dodge Challenger T/A

Re: No start when hot and using key. [Re: jeff968] #2698118
09/16/19 02:40 PM
09/16/19 02:40 PM
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Andrewh Offline
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from the wiring diagram I can't see what might be wrong that you haven't replaced, that would be heat related. but you will have to have a helper turn the key while you check different connectors along the path to see where it drops out.

Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.

Re: No start when hot and using key. [Re: Andrewh] #2698122
09/16/19 02:56 PM
09/16/19 02:56 PM
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Posts: 6,604
Iowa
burdar Offline
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Could possibly have internal corrosion in the brown wire that only acts up when it's hot. Might be the wire itself. As a test, you might be able to run a jumper wire from the ignition switch to where the brown wire terminates and see if it still acts up.(after you do your other tests)

Re: No start when hot and using key. [Re: Andrewh] #2698124
09/16/19 02:58 PM
09/16/19 02:58 PM
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Lincoln Nebraska
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RapidRobert Offline
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somewhere from the ign sw, brown wire (ign2) circuit out to the coil positive primary & or to the blue/yellow wire "power in" terminal at the ECU there is a part time open. EDIT & when you jump it at the relay & it fires (with key "on") you are immediately jumping it when it is still hot/not firing correct? (no cool down?)

Last edited by RapidRobert; 09/16/19 03:01 PM.

live every 24 hour block of time like it's your last day on earth
Re: No start when hot and using key. [Re: mrob] #2698169
09/16/19 05:25 PM
09/16/19 05:25 PM
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Andrewh Offline
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I have been thinking about this for a while and it had me stumped for a bit.

normally power is only applied to that circuit from the key in start.

however, once in run, it could back feed from the ballast back to the ignition.
now normally this isn't an issue because it could not complete the circuit since the ignition is in run, and even if it were not, there should be no path to ground since it is the hot side of the circuit.

But if one of your connectors is not right and has a partial ground going, enough to heat it up and make it act like a bimetalic, that might explain your symptoms.

While it might not be the switch itself, how does the connector look at the ignition? or at the column? how much of that is new?

If I am right, you don't even have to run the car, just set it in run for however long it would normally take to cause this to happen.
It is also possible to test in run and not bother with start, as you will see power up till the break from the back feed.

again just a guess, but the only one I can think of. one of the wires might also have an insulation problem, something with a wear in it so only 1 strand is touching the coulnm not enough to blow a fuse, or melt the line, (not even sure if it is fused).
since it only gets 12 volts on start and the backfeed would be the 5 or 8 volts to the coil.

Re: No start when hot and using key. [Re: Andrewh] #2698171
09/16/19 05:34 PM
09/16/19 05:34 PM
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Posts: 30,581
Grand Prairie,Texas
stumpy Online content
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Remember wiring contacts expand and contract with heat.

Re: No start when hot and using key. [Re: stumpy] #2698187
09/16/19 06:17 PM
09/16/19 06:17 PM
Joined: Jan 2003
Posts: 14,124
So Near, Yet So Far
topside Offline
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A couple things I've seen through the years that could match the OP's symptoms:

1. Starter relay - had one where one of the posts became loose; it would seem a warm thing (happened after driving) but was actually able to vibrate into not working.
Wiggle it, the car would start.
2. Wire passing into distributor - had a bare area and would ground (no spark) when everything was warm enough.

Weirdest sometimes-won't-start thing I ever came across was on an old Ford truck: someone had replaced the plug wires, but never put the terminals on the wires at the cap ends.
Just left the bare wire ends. Most of the time the truck would fire right up !


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