Thread: Hot engine won't start

Originally Posted by dennisS1

If you change the coil remember it needs to have a inbuilt resistor. the only ones I know of are the Bosch HT40s they come in both types, chances are the staff at Auto ****** wont know what you are talking about.

You need to ask for a 12V coil, designed to operate with no ballast resistor. The other version, a 12V coil designed to operate with a ballast resistor, is actually a 9V coil. The voltage is dropped to suit, accross a ballast resistor. The benefit of this is that during cranking, the ballast resistor is by-passed, providing 12V to the 9V coil. The result is a stronger spark while cranking. This compensates for the voltage drop in the battery due to the cranking current. Early Land Rovers do not have a provision for this in their circuit, so will deliver 12V (14V when running) constantly to the coil. This will result in a stronger spark, but will burn out the coil and points.

Aaron.

I'm a bit confused here ( not hard to do ! ) . From what Dennis said , 12V coils now come with a resistor inbuilt inside them ? ..I've never heard of that.

You can get high performance coils .. these have higher HT voltage output than normal .. I think I've seen them at SC auto...bright Orange .

I agree about the SU pump... there shouldn't be any problem with vapourising.. even on the hottest day.

I have never heard of, nor experienced, any coil with a built in resistor. The whole idea of the resistor is so that you can short it out to get a temporary boost in performance while cranking. This would not be possible if the resistor were internal.

Aaron.

Its really old school stuff from the days when you used to have to crank start.

hasnt been in common usage since about (WAG) the 70's

Originally Posted by Blknight.aus

Its really old school stuff from the days when you used to have to crank start.

hasnt been in common usage since about (WAG) the 70's

Actually I think the coil ballast resistor is a hangover from 6v systems, which needed every possible help to start, especially in cold climates. Never was used to any extent except by Americans.

John

Originally Posted by JDNSW

Actually I think the coil ballast resistor is a hangover from 6v systems, which needed every possible help to start, especially in cold climates. Never was used to any extent except by Americans.

John

Yes . I had a 1941 Ford truck with the 4.5 volt coil .. it was a proper rotten thing as it always played up... the resistor would heat up to the point of becoming a current limiter .. it was a special wire wound on a ceramic former .. the resistor was in circuit permanently . I dropped the voltage reg. output down a bit and it did improve slightly ..but would still play up.. the coil sat right on top of the ' divers bell' distributor.. right down in the heat wave spot, near the radiator . It would always start .. even with a almost dead flat battery ... but after the resistor heated up.. pain .
Mike

my bad, I was talking about the internally resisted coil not an externally ballasted jobbie.

I have never worked out why the hell it was done but my best guess is it has something to do with current limiting which might have extended spark plug/lead/points life.

Originally Posted by Aaron IIA

coil designed to operate with a ballast resistor, is actually a 9V coil. The voltage is dropped to suit, accross a ballast resistor. The benefit of this is that during cranking, the ballast resistor is by-passed, providing 12V to the 9V coil. The result is a stronger spark while cranking. This compensates for the voltage drop in the battery due to the cranking current.

A lot of "modern" (1980's and 1990's) cars that I look at have a ballasted coil set up. I know from recent experience that Mitsubishi and Suziki definitely do.

Aaron.