8 replies to this topic

[red81]

Can anyone help please

I have an optilux motor tester 8PD 004 836-001 yes it's old but it works.

I am trying to test the condition of the points, so black clip to distributor housing, red clip to neg on the coil, ignition on, points closed.  On my Mini the test shows the pointer in the green ie good, on my midget 1500 bad, despite new points.

 

Mini has 12v std coil

Midget has resistor wire and ballast coil

Both points had continuity when out of the car.

Ignition off good continuity between neg coil to distributor body

 

So if the optilux is testing the resistance, (with the current on ?) I assume I may have faulty, points condenser or wire, but I don't understand why the the  Midgets test is showing bad when she runs fine?

 

Any help greatly appreciated

[Spider]

I've gotta say, I'm not crazy about any type of tester that does the thinking for the user and shows like in this case 'good' or 'bad'.

 

I'd say these testers are not actually measuring the resistance of the contacts, but the voltage drop across them.

 

And here's where it's likely the Midget one falls over, it don't know that you have a ballasted system and so it thinks you are getting excessive voltage drop across the points when in fact, it's the normal voltage drop that occurs through the ballast. Not actually knowing with certainty the principal on which these testers work, this is my best guess.

[Ethel]

I thought that, but the ballast + coil should be near enough the same as an unballasted coil & either setup is the same between the tester's probes. Though having the ignition permanently energised is likely to bump up the resistance with more heat than 50% dwell on a running engine & I doubt it's the same for different coils & especially the resistance wire.

[red81]

Spider

I think your right.  My problem was caused by a supplier selling me a std 12 volt coil instead of a ballasted (silly me I didn't check I just fitted it a few years ago)  any way over time it broke down and I had fun and games trying to id the problem.  With this std 12 volt coil my tester always showed "good points".

 

I changed coil, leads points, condenser & plugs, as I suspected the damage had been done, but the new ballasted coil is probably doing what you said - " it don't know that you have a ballasted system and so it thinks you are getting excessive voltage drop across the points when in fact, it's the normal voltage drop that occurs through the ballast.

 

The reason I thought it might be resistance, is that I noticed the condenser had a long steel wire and not a copper type fitted.

 

Ethel, I have 6 volt from the ignition to positive on the coil, via a resistive wire, on my Midget which I believe is correct, whilst on my mini its 12 volt from ignition to the + coil. I always thought my Midget started up with 12 volt but then run with just 6 volt, are you saying that's not the case?

 

Thanks for your help in understanding my girls

 

Steve I

[Ethel]

I think it should be closer to 9 volts.

 

 

You're right(ish)

 

When the starter motor is running  the battery voltage drops. The ignition ballast resistance creates a similar voltage drop when the starter isn't running, so the ignition can be optimised for same supply voltage whether running or starting. The actual bit of the system that makes it work is the bypass supply to the coil that the solenoid connects at the same time it connects the starter. That's not resistive, so would supply 12v if there was no voltage drop from the starter.

[red81]

Thanks Ethel

When the starter motor is running  the battery voltage drops

I notice this on my dash volt meter it drops to nil as the power goes from the battery through the solenoid to the starter motor the earth.

 

The Midget has the extra spade connection, so when the 1st small wire energises the magnet (relay) and the connection is made to send 12V to the starter, it also sends 12 V to the coil just whilst the key is turned.  My 1981 Mini hasn't got this, as it uses a 12V coil.

 

So my resistive wire from the fuse to the positive side of the coil, might be worn it's been there since 1976, and only giving 6V, how often should these wires be replaced or is there a way to check the resistance to see if its still to spec whatever that is?  

 

I'm beginning to think the fault might be the optilux motor tester 8PD 004 836-001

 

Happy days

Steve I

[weef]

This post intriuges me, why do you want to know this ?.

[red81]

Because the tester says my points are good on one car and bad on another.  I've learnt over the years that you need to learn how your car works, to be able to keep it going.

[68+86auto]

The ballast resistor doesn't effect this test unless you have the wrong coil or resistor installed causing too much current. The resistor is usually on the positive side of the coil, you are only testing the voltage drop across the points. You could also test at the distributor lead and case instead of the coil negative in case of poor wiring (which would need to be fixed).

 

Look closely at the points. Are they aligned properly? Are the points clean? By brand new do you mean you just installed them? Also try disconnecting any tachometer if fitted

If there's a voltage scale on the tester then it will likely still apply when testing points.


I don't believe the tester will be at fault.

Edited by 68+86auto, 08 April 2024 - 06:16 AM.