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PostPosted: Fri May 31, 2024 11:53 am 
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OK, so now I am confused.
About to fit a Powerspark electronic conversion to the distributor. They say that this is designed to run with a standard 12v 3ohm coil. Powespark also say that this will run with the standard coil and ballast resistor as long as they are both the standard fitment and working correctly.
As the later Dolomites have a resistor wire in the ign system, they are supposed to have a 15C6 coil (DLB102) , which is listed as a 6v 1.5ohm coil, which takes full 12v on starting, reduced to 6v via the resistor wire in normal running. So far so good.
Before fitting the electronic unit I checked the primary winding resistance of what I thought was the original coil (car only done 16k from new), but it gave me a reading of 2.9ohms, which as I understand it, would be correct for a standard 12v non ballasted coil. Ah ha I thought, is this the reason for my occasional misfire, a 12v coil being made to run on a ballasted 6v supply?
Imagine my surprise therefore when I checked the voltage coming out of the yellow and white resistor wire to find 12.25v (battery was reading 12.45v).
It would seem therefore that the yellow and white resistor wire is not doing it`s job, or is an ordinary wire and not a resistor wire at all, and therefore the coil is correct, and the extra white wire that comes off the starter solenoid to the coil to provide the 12v at start up is superfluous.
Has anyone else come across this, or am I just the lucky one?

Ralph


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PostPosted: Fri May 31, 2024 11:59 am 
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Was the coil connected when you measured the voltage at the wire? It needs to be in order to get a true reading.

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PostPosted: Fri May 31, 2024 1:21 pm 
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Agree with Clive's post but just to add that the contact breaker must be closed when measuring the voltage on the coil.


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PostPosted: Fri May 31, 2024 5:58 pm 
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Was the coil connected when you measured the voltage at the wire? It needs to be in order to get a true reading.
Ah, no, I just took the reading from the end of the wire. Also I took the coil off and it was the original stamped 15C6 on the base. I unbolted the terminals and gave them a clean up and then got the correct reading of 1.5 ohms through the primary winding so it was all correct as per the book. I put it all back on and fitted the electronic ignition module and it is starting well and sounds good when stood, but still misfiring when under load. Plugs and plug leads are all new, new rotor arm fitted with module, timing checked with a strobe. Tried a brand new 12v standard coil wired up by-passing the resistor wire and still misses under load. Checked the earth braid in the distributor for continuity and that`s good. Had carb off this afternoon and can find nothing amiss there. Last thing to change is the distributor cap which I will do tomorrow. Still on the same fuel I used 4 weeks ago when I did 170 miles in the day without any problem so I can`t see it being that.

Ralph


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PostPosted: Fri May 31, 2024 6:05 pm 
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The resistance wire is just an ordinary length of wire about 63 inches long to give a resistance of 1.5 Ohms. I'm pretty sure it's pink & white but may have changed over time.

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PostPosted: Fri May 31, 2024 6:58 pm 
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Quote:
Quote:
Was the coil connected when you measured the voltage at the wire? It needs to be in order to get a true reading.
Ah, no, I just took the reading from the end of the wire. Also I took the coil off and it was the original stamped 15C6 on the base. I unbolted the terminals and gave them a clean up and then got the correct reading of 1.5 ohms through the primary winding so it was all correct as per the book. I put it all back on and fitted the electronic ignition module and it is starting well and sounds good when stood, but still misfiring when under load. Plugs and plug leads are all new, new rotor arm fitted with module, timing checked with a strobe. Tried a brand new 12v standard coil wired up by-passing the resistor wire and still misses under load. Checked the earth braid in the distributor for continuity and that`s good. Had carb off this afternoon and can find nothing amiss there. Last thing to change is the distributor cap which I will do tomorrow. Still on the same fuel I used 4 weeks ago when I did 170 miles in the day without any problem so I can`t see it being that.

Ralph
When did the missfire start? It is quite possible new plugs, leads etc are faulty. Likewise rotor arms are notorious. In fact all ignition parts! I always keep an eye out for genuine old stock Lucas stuff (as in the old red/orange packaging, not the dodgy green stuff or I heard Lucas were starting to use red boxes again, but not seen any)
There are lots of fake NGK plugs out there too. I bough some via fleabay, and a simple check showed they were fake, seller refunded instantly when I pointed that out. Binned those.

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PostPosted: Sat Jun 01, 2024 8:49 am 
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[/quote]
When did the missfire start? It is quite possible new plugs, leads etc are faulty. Likewise rotor arms are notorious. In fact all ignition parts! I always keep an eye out for genuine old stock Lucas stuff (as in the old red/orange packaging, not the dodgy green stuff or I heard Lucas were starting to use red boxes again, but not seen any)
There are lots of fake NGK plugs out there too. I bough some via fleabay, and a simple check showed they were fake, seller refunded instantly when I pointed that out. Binned those.
[/quote]

To be honest Clive I have been chasing this missfire ever since I bought the car last year. It would run mostly OK but every so often it would skip a beat, most noticeable when cruising at 50 or so. At first I thought it was plugs or leads, so they were renewed. The plugs were white and seemed to be a very lean mixture, so I removed the waxstat with the old 2 penny trick and richened the carb up a bit but it made no difference. I realised that it was happening more at higher speeds and that`s when I started wondering about fuel starvation, I found the filler cap was hard up against the rubber body grommet (mentioned in a previous Dolly Mixtures) blocking the tank vent, and fixing that seemed to have cured the problem for a while, however on the first long run a few weeks ago when I did 170 miles in the day I noticed the occasional cough had returned. Last Monday I set off for a car show at Ripley and only made it about 4 miles, I managed to get home with the car coughing and spluttering. My suspicions turned to condenser or coil and yesterday I fitted the electronic ign and new rotor arm, it made no difference, so fitted the new spare coil I had for the TR and ran a new wire from the ign controlled side of the fuse box to the coil so by passing the resistor wire, and that made no difference either. Last thing I did yesterday was strip the carb down to check for debris or a blockage or an air leak at the manifold flange, and found nothing.
The carb float chamber was full of fuel and there was no evidence of water in the bottom of the float chamber and no debris blocking the jet tube or the jet. When I put the carb back on it took about 30 seconds of turning the engine over before the pump had filled the float bowl and the car started, it would idle happily and rev up quickly and smoothly in the garage, but as soon as I took it down the lane and put it under load it was mis firing again.
Today I am going to change the distributor cap which looks OK, but as I have a new one I may as well try it, and try another new set of spark plugs , the ones fitted are NGKs, but bought from my favourite spares shop which has a high turnover of parts and not off ebay.
I`m hoping I can get it sorted out for next Sunday as I think there is a Dolomite meeting at NW500, Pickering that I would like to attend.

The Saga continues,
Ralph.


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PostPosted: Sat Jun 01, 2024 8:59 am 
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Quote:
The resistance wire is just an ordinary length of wire about 63 inches long to give a resistance of 1.5 Ohms. I'm pretty sure it's pink & white but may have changed over time.
Yes my old mini was a pink and white resistor wire, but checked in the Haynes manual and the wiring diagram for the later Dolomite does show it as yellow and white.

Ralph


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PostPosted: Sat Jun 01, 2024 5:47 pm 
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Quote:
Quote:
The resistance wire is just an ordinary length of wire about 63 inches long to give a resistance of 1.5 Ohms. I'm pretty sure it's pink & white but may have changed over time.
Yes my old mini was a pink and white resistor wire, but checked in the Haynes manual and the wiring diagram for the later Dolomite does show it as yellow and white.

Ralph
The ballast lead has a coat of many colours!

It starts off white at the ignition switch, then depending on model/year, branches off from the plug and socket under the steering column or links via the fusebox supply. Whichever the source, it then makes it's way (still white) through the main loom to a point near the N/S bulkhead grommet where it joins into and becomes the ballast lead proper, which is pink with a fine white trace (but may have faded badly with age) Still within the loom, it travels right back across the bulkhead, out through the offside grommet and approaches the coil. At this (concealed) point it joins into and becomes the Yellow/White ballast bypass lead from the starter and finally connects to coil +ve.

Clear as mud? Yeah, I know! But that's how they are made! It's done this way to get the necessary 42" run of lead to give the required resistance. Personally I never knew what was wrong with the old block ballast resistors that early 1850s used!

Steve

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PostPosted: Sun Jun 02, 2024 10:28 pm 
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Is it too late to suggest you get a real electronic ignition, and not one that has "spark" in it's name and comes from China for a few dollars?
The appalling reliability of these useless things is just about the most common cause of breakdowns I see on classic cars, so much so that i now carry a small box of assorted points and condensers so i can "deconvert" customers cars by the road side to get them home....
I don't understand why anyone has a classic car worth thousands and then spoils it with a £30 ignition "improver".


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PostPosted: Sat Jun 08, 2024 7:40 pm 
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Finally, a RESULT. Turns out the miss fire which has plagued me since I got the car last year was nothing to do with the electrics, it was the fuel pump. The miss fire was due to a weak mixture at higher engine speeds and under load. The fuel pump had been checked and appeared to be working, but after all else failed to get a result I bought a new curved arm pump and the spacer and 2 longer studs. I fitted it all this afternoon and set the carb by lifting the dashpot piston from idle and listening for the slight speed up of the motor. I took it for a 20 mile run on a mix of fast roads and country roads and it never missed once, and is more responsive than it has ever been. I`m so chuffed I gave it a polish and hope to get to the NW500 tomorrow to give it a longer test.
Ralph


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PostPosted: Sat Jun 08, 2024 7:50 pm 
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Quote:
Is it too late to suggest you get a real electronic ignition, and not one that has "spark" in it's name and comes from China for a few dollars?
The appalling reliability of these useless things is just about the most common cause of breakdowns I see on classic cars, so much so that i now carry a small box of assorted points and condensers so i can "deconvert" customers cars by the road side to get them home....
I don't understand why anyone has a classic car worth thousands and then spoils it with a £30 ignition "improver".
It was desperation to rule out the points and condenser, but anyway this is the 4th car I have converted with a Powerspark module or distributor and have had positive results so far. Maybe I haven`t driven them long enough for them to fail, though I`m up to 5k now on the TR3. I do carry points and condenser but so far have not needed them.

Ralph


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