Voltage drop at the coil

[cordiagsr]

VOLT DROP AT THE COIL!!!!

Hi I own a Mitsubishi Cordia that has been in storage for some time. It wont start and when testing found Only 9V at the coil but after changing to new battery took it up to 11.6V I found the alarm was causing the volt drop so bypassed it and then had 12V at the coil. Then found that even the fuel pump when turned on did the same thing, anything lights, wipers etc would give a slight volt drop from 12.2V to around 11.6V at the coil. Car will not start not even try but as soon as I put 12V straight to the coil starts. would like to find the problem rather than run a new feed. My question is what voltage should you have at the coil when the car is running? Any ideas what might cause this volt drop?

Any info or help would be much appreciated

Mark

 

[TicklyT]

Some ignition circuits featurd a voltage dropping resistor in the coil circuit which was bypassed when the starter was cranking.

The coil normally worked on about 6 - 8 volts, so there was enough reserve to allow for the voltage drop when the battery was cranking the starter. The resistor stopped the coil overheating during normal running.

Check all battery connections, including both ends of the earth strap to the bodywork are nice and clean and shiny. A high resistance connection will seriously reduce the available battery voltage under load, and probably won't allow enough current to crank the starter. It probably won't do a lot for the alternator either.

 

[Burnerman]

A bit of a head scratcher......the old contact breaker systems often used a 6v coil, complete with a ballast resistor in the circuit. When trying to start the car, a full 12v was supplied to the coil to give it a boost, and when it was running the ballast resistor would cut in to prevent the coil from overheating. The ballast resistor could either be in the form of a complete length of cable, or in the form of a round carbon resistor fixed to the positive terminal.
Either way, ensure that the negative coil terminal is disconnected when taking voltage readings.
If your car has this system (points and condenser), replace the condenser.
John
PS If your car has electronic ignition, ignore all of this rubbish
J

 

[Belle427]

if its been stood a while then it could be a dodgy or corroded contact somewhere but where is anybodys guess