Engine Tries to Start When I Let Off Ign Switch

[wishihadahemi]

it's a friends BB Duster with a MSD distributor and box. he just moved the battery to the trunk. it cranks fine, but will not start and run one thing it does is pops off a cylinder as he releases the key to the "Run" position. if he puts jumper cables on it from another car , it fires right up like it should.i have not seen the car (in another state), but he feels he has everything tight, cleaned paint off for ground cables.
whats with the engine trying to run when the key is released?
i've had that on my cars in the past, and i think i tightened up the reluctor gap and that was the fix for me.

 

[moparlover]

there are wiring diagrams on mymopar (google mymopar wiring diagram service manuals you will find that page)

but essentially, when the key is in START it's a duplicate/parallel circuit of when it's in RUN

in START it bypasses the ballast resistor while lighting up the starter relay and turning the ignition on
in RUN (normal operation) it does not turn the relay on (leaves starter off) goes through the ballast resistor to make your coil live longer.

the IGN switch has both circuits running through it. if it has bad contacts/shorts/tarnish etc then one or the other might not be working properly.

but those wiring diagrams I talked about will show you which color wires are which, etc and when the key is in start or in run you can use a meter to see if the right wires have juice

http://www.mymopar.com/index.php?pid=31

 

[67Dart273]

The above, but I'd guess that in the battery move he re-wired/ disturbed something. Without knowing more about what he changed, not possible to say

Did he use a 4 post (DPST) disconnect? If he wired the small posts in series with his ignition switch, he may have separated the brown (bypass wire) from the dark blue (ignition run wire)

 

[TrailBeast]

The voltage is too low when cranking to fire it, because of too much to draw through the new battery cable.
What guage cable did he use to make the trip to the trunk?
(most likely too small)

He may very well need to run a dedicated ground cable to the front also.

 

[crackedback]

As mentioned above, I bet you only have the run ignition wire connected to the small red MSD box wire.

Probe the small red wire connection from MSD box with a test light or voltmeter. See if it goes dead when cranking. If so, you found your issue.