Misfiring Dodge.???

Interesting point FV1609, ( Negative Spark )

my low tension wires are Red & Black & they go from the coil to a small box in the dizzy, can you please explain how to connect it up to the coil to get a negative spark & ill check that its wired that way round tomorrow,

All the best, 2door.....

I'm afraid I know nothing about the electrics in a Dodge, whether it is an insulated or earth return system, if it is earthed whether that is positive or negative, or whether it has been changed & whether the LT connections have been swapped or whether a proper coil has been fitted wound for the appropriate earth polarity.

The practical point is to establish the polarity of the spark in the present set up. I use an old analogue Avo, using the highest voltage range (1kV or 2.5kV) hook up a wire from the negative prod to the junction of a sparking plug & its connector. Take the positive lead to chassis assuming it is an earth return system.

Briefly crank the engine. An upward rise of the needle indicates a negative spark. Downward a positive spark, so swap the LT terminals on the coil. There is something to be gained (600v) using a coil of the correct earth polarity rather than the quick trick of swapping the LT connections.

This is from an article I posted on here about screened ignition but the spark polarity issue is the same. I have edited to suit.

It is important to verify you are using the correct type coil. It is also important to confirm that it has been connected up

correctly. The wrong polarity of coil or the correct one incorrectly connected will have three consequences.

1. The polarity of the HT spark will be reversed. The ignition coil doesn’t mind the change of polarity but the

sparking plugs do not function so well. Engines are designed so that the polarity of the sparking plug terminal is

negative. If the polarity of the spark is wrong, it would need a greater voltage for proper functioning. This is

because a spark finds it easier to jump from a hot central electrode than from the cooler side contact that is in

thermal contact with the engine casting. If the polarity is wrong up to 40% more HT may be required to create a

spark at the plug.

2. Sparking plug life will be shortened as metal will be lost from the side contact making gap adjustment short

lived. The central electrode is much longer and is designed for this erosion.

3. Similarly there will be increased erosion of the rotor arm. This will be explained in the distributor section

later.

I know of one Rover that left Army service with the connections to the coil reversed. The engine ran poorly and

needed a lot of choke, the rotor arm and the adjacent lead terminals were markedly carbonised. Correcting the

polarity of the LT terminals on the coil gave easier starting, smoother running and more power.

Modern unscreened coils have terminals marked – and + so that in a negative earth vehicle the – terminal

supplies the contact breaker, which on older systems was marked CB. Older coils used in a positive earth

vehicle should have the + terminal supplying the contact breaker. In either case the other coil terminal is fed

with the energising supply originating from the ignition switch that used to be marked SW.

That is often the case same or similar symptoms different cause. Patience and persistence.Just like humans age related faults.

Allright chaps,

we're getting a bit nearer now,

borrowed a vac gauge & rigged it up today & after finding out that i'd been thrown a curved ball with the new coil i bought, things are improving.....

bought a new coil to rule out the old coil, asked for a 6volt but did'nt realise they'd sold me a 12volt. (had no reason to doubt them & it was'nt marked up 12v or 6v)

So its been running really well on the 12volt untill you aproach a hill, took the old coil to my auto electrician & firstly he said this is a 6volt & then said its working fine....

So thinking i'd got a faulty new coil i fitted the old coil back in & according to the vac guage, all is very nearly well...

The vac guage fluctuates between 18 & 19 inches of mercury at idle & according to the book this could be a plug gap or fuel mixture problem......

So maybe the 12v coil was using all the volts & under load not producing a big enough spark.???

Fitting the old coil has transformed hill climbing no end.!

The 12v coil would have about twice the resistance of the 6v coil. So when fed with a 6v supply it would nowhere near saturate the coil core with magnetism to give the full HT output.

You need to establish whether the coil is for a negative or positive earth & that it matches the polarity of your vehicle. To ensure not only that you are getting a negative spark but you are not having to fudge it with a wrong polarity coil wired in reverse to give a negative spark. If it is the latter case you will lose 600v of HT compared to the correct coil. Not a vast voltage but may make all the difference up hill.

As an aside to this thread.

The fault chart for the Vac gauging.

I know that that is for Petrol engines.

Is there anything similar for Diesel engines?

Or would it not work at all?

As an aside to this thread.

 

The fault chart for the Vac gauging.

I know that that is for Petrol engines.

Is there anything similar for Diesel engines?

Or would it not work at all?

Bryan,

Diesel engines do not produce a vacuum in the inlet manifold like petrol engines do. Hence why you have to have a vacuum pump fitted to a diesel to operate a servo.

Been back over the plug gaps this morning & re set the mixture & base idle, its now running really well & vac gauge is holding pretty steady at 19.

Thanks for all your help & suggestions guys,

All the best, 2door.....

No butterfly across manifold so no vacuum with a few exceptions

Been back over the plug gaps this morning & re set the mixture & base idle, its now running really well & vac gauge is holding pretty steady at 19.

 

Thanks for all your help & suggestions guys,

All the best, 2door.....

Pleased it's looking sorted,

the vacuum gauge as a diagnostic tool has faded from the modern tool box with the advent of fault codes and fuel injection systems, but for over 60 years is was the standard first choice for intermittent engine faults as it looks at the dynamic state of the system as a whole.

If used in conjunction with compression and leak down tests it's an invaluable guide to whats actually going on in the engine at any given time and removes guess work and haphazard replacement of components I certainly wouldn't be without mine

Pete

Bryan,

Diesel engines do not produce a vacuum in the inlet manifold like petrol engines do. Hence why you have to have a vacuum pump fitted to a diesel to operate a servo.

Thanks for that Richard.

Just thinking aloud to myself and wondering if it could be of use for the Diesel side of things.

As you may have gathered I am not a mechanic despite what RSME Chatham tried to drum into me on a POM course.