Pre-engaged starter fittment

[handi_andi]

Well I finally got her started after changing out the leads, the coil and the plugs for new items. Am still not happy at the power of the spark as still looks rather weak but will deal with that another day.

Once started though the electrics went completely made, with relays sitting there buzzing away and oen front side light on and both back indicators. All of them on dimmly and the interior ights were also dimmer with the engine running. Only way to cure the electrics was to pull the hot start feed from the solenoid and the ignition feed to the solenoid. Makes some sort of sense though, as the hot start feed is always at around 5V when the engine is running since it comes off the positive side of the coil, so would be feeding 5V down the starter feed. With an inertia starter this wouldn't make much difference, however, with the pre-engaged one with the feed and internal solenoid jumped together, as that was how it was supplied, then the interal solenoid is getting fed with 5V. I think this is partically engergising it and may even be engaging the starter a little turning it into a generator and hence putting AC into the DC circuits. Would that make sense?

This leaves me with two choices, either make use of the internal solenoid and run the cold start feed off the ignition lead, or just make do without a ld start feed to the coil. Anyone got any thoughts, I would like to keep the original look to the engine bay.

Cheers

Andrew

[alan71]

If you have a ballast resistor type coil I would leave the cable from the + side of the coil connected to the small terminal on the original solenoid, which will be open circuit when the engine is running and the 5V will have nowhere to go.

Alan.

[handi_andi]

The small terminal on the solenoid is surely connected to the feed to the starter motor, as they are both made +12V when the solenoid is actuated and there is only one set of contacts within the solenoid. Hence the 5V from the cold start lead will enter the solenoid and then pass down to the pre-engaged starter as the two are bonded together at the solenoid surely or am i missing something like the two small terminals are directly bonded to each other?
Andrew

[alan71]

The terminal with the white/blue wire will be 12V when the solenoid is operated. The rest or the time it is not connected internally but will have the voltage from the + terminal of the coil, which will fluctuate as the points open and close.

Alan

[handi_andi]

Alan
Point taken, I recently took my solenoid apart to clean it up and photographed it at the same time. You are indeed correct the 12V feed to the coil is not bonded to the starter motor line as it is off the "switching" contact as shown in the picture below. I think I had better put the meter to the solenoid and check I have not created an internal short when I reassembled it. IF I havent, then there is somethign very strange going on given that the cure was to pull the leads to the solenoid. Thanks for your help.
Andrew

[john.p.clegg]

Andi
Not a cure but a fix...a diode in line of the 5v....?

John

[Frank Howard]

Perhaps I can lend some clarity. First, thank you Alan for posting the illustration.

When you turn the key to start the car, you are running 12V from the key switch through the white wire through a loop in the tach to the ballast resistor. The resistor can be in the form of a disc attached directly to the coil as in the illustration, or it can be in the form of the more common white rectangular porcelin that holds a resistive coiled up wire in it. The resistor reduces the 12V down to 9V (I've heard all kinds of voltages quoted including 5V) and the 9V is sent to the + side of the coil.

When you turn the key to start the car, you are also sending 12V from the key switch through the white/red wire to the solenoid. When the 12V reaches the solenoid, it activates it causing two things to happen. First, 12V and a lot of amps are run through the heavy wire to the starter in order to engage it because the solenoid is connecting the starter to the battery. Second, 12V is run through the white/blue wire to the + side of the coil.

So when you have the key in the start position, you are running 12V to the coil through the white/blue wire and you are also running 9V to the coil through the white wire and resistor. So what happens? If you ran 12V to the coil through five seperate wires, you would not get 60V. If that were true, you could step up the voltage simply by adding more wires. Whether you run one 12V wire to the coil or five 12V wires to the coil, you will get 12V at the coil. By the same token, if you run a 12V wire and a 9V wire to the coil, you will not get 21V at the coil. You will still get 12V. And if you run 12V through a coil that is rated at 9V, you will increase your chances of producing a spark.

Once the car starts and you release the key, you will be disconnecting the white/red wire that goes from the key switch to the soleniod. When this happens, the solenoid will no longer operate, the starter will be disconnected from the battery and the white/blue wire to the coil will no longer carry the 12V from the solenoid. However, the white wire from the key through the tach loop to the ballast resistor will remain connected carrying 12V to the resistor and the resistor will step the voltage down to 9V going into the coil which is what a cold start coil is designed to run on.

I believe that some of the confusion comes in because when you let go of the key, the white/blue wire remains connected to the + side of the coil and because the coil is now running on the 9V supplied by the resistor, the white/blue wire will show 9V if connected to ground. But because the white/blue wire is no longer connected to 12V power supply at the solenoid and is not connected to ground, it will just be sitting there and not doing anything.

Hope this helps.

[handi_andi]

Thanks Frank for your explanation and having been round the system today with a meter I can confirm that it is working correctly, although the coil is seeing 10.8V through the ballast resistor rather than 9V.

What I also discovered was that with the solenoid disconnected there is a 800ohm continuity between the battery positive and the starter motor feed. I checked the solenoid and it is functioning correctly, so the only thing I can think is that the resistance through the solenoid on the starter itself back through the negative and then maybe through the points and coil or more likely through the boot lamp as i think the boot was open adds up to 800ohms. Am therefore thinking that I ought to unjump the solenoid on the starter and run it off the ignition key circuit to make sure the starter soenoid is fully disengaging.

I did note today that my coil is getting quite warm, is this normal?

The old girl has also developed a new habit, which I am not sure is electrical or fuel system related, although suspect the later.

Once she is warmed up and settled down, just like me she doesn't like waking up she is quite happy to purr along, accelerate or cruise. However, suddenly after 5 to 8 miles she starts sort of pinking and popping and back firing and all power is lost from the engine. The only way I have found to cure it, is to pull over and wait with the engine on tick over, which by this stage is rough and wait for the engine to settle back to a normal rhythm and idle at around 1250rpm. The waiting can take anywhere from 5 to 15minutes, and in the meantime the idle bounces up and down between 500rpm and a 1000rpm and the engine sounds rough and the addition of throttle or choke normally causes it to even rough and or cut out. Anybody got any bright ideas?

Ah that reminds me, the last time it happened today, she wouldn't restart after cutting out and then the electrics went made again when she did restart, with relays buzzing as though they were buzzers. I sorted out the plug today on the alternator as one of the connectors was loose. So I have also been wondering whether there was something go astray in the alternator to cause some of these problems. I am not sure it explains the rough running though as when it was on idle and rough the voltmeter was still showing good voltage, well till the fan cut in, which made the engine run even rougher, which i assume could just be the extra load coming on the alternator causing the rough running engine to try and work harder.

Cheers people.

Andrew

[billwill]

A great explanation, Frank, but I would add just one item.


You don't actually get 12v to the coil in the start position, because the starter motor is taking so much current from the battery that the internal resistance of the battery brings its output voltage down to say 9v. So the short circuit of the ballast resistor by the starting solenoid actually just ensures that the NORMAL sort of voltage is available at the coil. i.e the drag down of the battery voltage is compensated for.


On cars without ballast resistors like mine, the coil does not get its proper voltage during starting, which causes weak sparks, just at the time when you really want strong one.

[richardcox_lotus]

Andi,

I've experienced your rough running symptoms before, & it was caused by my coil failing. It would get v hot as well. Let the car cool down (10 - 15 mins) & it would run fine, for say 10 mins, & then recur. A limp home episode !

Swapping the coil over effected a cure.

[handi_andi]

Hiya
Thanks for the reply. Have brught a whole new ignition system and a new alternator to try and cure the problem once and for all.

Just need to get into the boot first! LOL

Andy

[Frank Howard]

Bill,

Thanks for that. I didn't know that. What you wrote makes sense. I guess you learn something every day.