Electronic Igniton on 240k

[The C110]

Cheers, yeah not a bad combo eh? Well she goes indeedy :classic:

[Alfadog]

Hello!

Well, at the Prince Nationals in Bathurst Bruce (240K&Beyond) and Steve (?) were talking to me about my engine and said that basically the first thing I should do is convert to an electronic distributor! I somehow missed or skipped this topic back in 2004...

Anyway, in a cruel twist of fate as I drove over the Blue Mountains to Sydney my car developed an odd problem, and started coughing, spluttering and generally sounding "out of tune". The tacho was bouncing around every now and then - and that was the clue. The old distributor had announced its plan for retirement!! I guess it overheard us badmouthing it previously...

I did make it back up to Queensland (it wasn't much of an issue at anything over 2000rpm) as I thought I should save my money for the upgrade rather than fixing the old thing. Luckily, there's a wrecker nearby which had a 280ZX still with distributor. I took that off and away I went.

I should have read this topic first.

I made a few of the same mistakes as Tom did - mainly I didn't take the "pedestal" off the 280ZX. I didn't realise it was a removeable piece (it was quite hard to remove the distributor alone as I had to stand on a bonnet and lean over and into the bonnet of the (fender at shoulder height!), while it swayed around on top of a 1980s Corolla.........

Anyway, I soon worked out it wasn't going to work with the old pedestal and timing plate, but if I rotated the dizzy around so that no.1 was pointing forwards the car would start up! So that was good... the dizzy just wasn't attached.

Anyway, after going back to the wreckers, I got the pedestal aswell. Also got some new spark plug leads as the ones that were on I had not even changed since I got the car, so who knows how old they were.

Tom informed me that you can get it to work using the old pedestal and timing plate but I felt I may as well get the pedestal as well since it was only 5 minutes away. It started right up. EUREKA!

So the 15 minute swap only took 3 days, that's not that bad. I know how to do it now, and if you have all the right bits in the first place it would be easy as !!

So thank you to everyone who has contributed to this thread, and also especially to Bruce for helping me out via PM and phone.

Not sure if it's just my imagination, but the car feels much better now! Sounds a lot smoother and "cleaner" I feel...

Here are some pictures. I disconnected the small cylinder below the coil to attach the other wires to it..... what is the small cylinder there for?? After reading the posts here, I'm not sure if I will be OK using the old coil or not? Is this ok?

[kyteler]

Ideally Lachlan you need to run the electronic dizzy's coil because of the voltage differences between the two (points and electronic), yes it will and should sound nicer and rev a lot more freely than before, I know mine certainly did when I changed it over (all them years ago )

The "small cylinder" is basically to stop electronic noise interference with your radio, capacitor or condensor or resistor, buggered if I can think properly at the moment but it will do no physical harm whether it's attached or not.

[Alfadog]

Ooh ok, I'll see if I get any noise with the radio (had it turned off when testing it of course ).

An electronic dizzy's coil......... best to just get whatever Bosch makes for the 280ZX I guess?

[kyteler]

There's quite a few of them littered about the wiring so you might not notice any difference at all.

Re: The coil, the difference between them is the points ones can't handle a full 12V or the points themselves would burn out. So they spark at something like 6 or 8V, the electronic is a full 12V, so your current points coil won't be giving MAXIMUM SPARK! etc. Which basically means it won't be burning the fuel as efficiently as perhaps it could.

...I think

[aarc240]

If I can add a bit of info.

First we should look at the old points system (Kettering igbition)

In more modern example, the coil usually runs at about 8V, and in the case of the 240K the 'ballast resistor' is actually a resistance wire built into the wiring harness. No wonder it couldn't be found!

On start this resistance is bypassed to provide the coil with full battery voltage which in most cases will be no more than 8 or 9V while the starter is cranking the engine.

So, the result is that the coil can provide full output in both conditions.

On the 280zx there is no ballast resistor and it appears that the coil is being fired from a full 12V.

In that case you have three problems with the installations outlined in these posts.

1. the ignition module is being supplied with reduced voltage via the built in ballast resistor

2. eventually the output transustor is going to cry 'enough!' since it is supplying a reduced voltage to the coil with a specific resistance which will result in increased current (remember E=IR or I=E/R)

3. if you fix the coil resistance issue with a 12V unit, you will increase the resistance thus saving the module but the output (ie spark) will be weaker because less current is flowing in the coil primary.

The fix is bypass the resistance wire, install a 12V coil and connect that 'condenser' (actually a capacitor) from coil positive to ground.

That's the 'little cylinder', and it is VERY important in that it also protects the module from electrical spikes.

The other 'condensers scattered around the system will help noise induced through the radio power supply but they are much to far away for the safety of the module.

hth

Art

[Alfadog]

Interesting! Thanks for the input Art ...

The fix is bypass the resistance wire, install a 12V coil and connect that 'condenser' (actually a capacitor) from coil positive to ground.

Sorry, but to clarify (in Layman's Terms :knockedou ) do you mean get a new (280ZX) coil, and run a new lead directly from the battery to the coil is the best way to get full (12V) power? And reconnect the capacitor obviously.

[440k]

and run a new lead directly from the battery to the coil

Err not quite. If you do that, you won't be able to switch the engine off (a trick we used to play on the less technically minded business and accounting graduates when I first moved to Mt Isa )

One good way to do it is to hook up a relay which is switched from the ignition switch (insure it has power in both the "On" and "start" position - this has caused many a wasted hour of frustrating troubleshooting - allegedly:cross-eye ) and feed power directly to the coil that way.

[aarc240]

I should have been a little clearer there!

The relay method will certainly get you the 12V you need BUT the tacho represents a problem.

The best fix is also a fairly major bit of surgery on your wiring harness AND requires a modified tacho.

Getting down to basics, the harness used in the long wheelbase and short wheelbase cars is basically identical except that there is a link in the SWB harness that bypasses the tacho wiring. The tacho wiring is actually still there, just that there is no tacho anyway.

This link is made inside the harness down on the right frame rail, just behind the engine mount. So the factory kindly provided a lot of what we need for a change!

In our case, since we want the tacho, we have to approach this differently.

The ultimate solution is to

1. open up the front harness from about the area of the starter motor wiring exit all the way to the coil wiring exit.

2. locate the (fused) ignition feed that goes back to the tacho.

3. splice into that with a black/white wire of at least 18G long enough to reach right around the front of the car to feed the ignition. This is your new 12V fused ignition feed for the coil and module.

4. neatly re-wrap the front harness

5. pull out the instrument panel and identify the tacho type. An early 240K should have a small two wire connector with the wire actually being continuous which makes a single turn through a block on the back of the tacho.

6. on the small two wire connector going to the tacho, cut the wire which has 12V ignition on it. This has isolated the tacho from the fused ignition feed.

7. have the tacho converted to an electronic sensing inner board with the single turn block eliminated. The actual meter movement and the dial face do not need to be replaced.

8. connect the sense wire now coming out the back of the tacho to the wire that goes all the way to the coil area (the old feed for the coil, no longer connected to the coil +ve)

I know it sounds complicated but by working through it step by step, it's not that hard.

When finished, the wire that originally went to the coil positive (and which contains that elusive ballast resistance) is used as a tacho signal wire only.

The new wire from (3) above is now your ignition wire.

Why go to all that trouble? Once done you have a system that looks stock standard and can be interfaced to ANY ignition setup down the front without further modification.

Does it work? That's how both our '73 240K and '72 240Z are done, which run two completely different electronic ignition systems. Of course, the Z doesn't have the ballast resistance inside the harness and is more messy to source the fused ignition feed but is otherwise similar.

I just hope I haven't made that sound too hairy!!

hth,

Art

[240K&Beyond]

Arh forgive me here, but my understanding of Ohms law and transistor theory tells me differently when operating at lower voltages.

Firstly, The resistance of the coil is fixed, likewise the resistance of the wire feeding it (or for that matter a ballast resistor), regardless of any voltage applied.

Secondly, Transistors will operate correctly for years at lower ratings then their maximum voltage or current ratings. They specify a maximum "safe" limit for a device to operate reliably. If you exceed it, then it could and most probably would fail.

Finally, If you reduce the voltage applied to a circuit and keep the resistance constant then the current must reduce as well. (You don't magically get more energy appearing in a closed system). V=IR which transposes so that Current (I) equals Voltage (V) divided by the Resistance ®

Example: If V=4 and R=2 then I will equal 4/2 or 2 Amps.

Now if V only equals 2 and R remains at 2 the I will equal 2/2 or 1 Amp.

Thus, The current will reduce if the voltage applied reduces.

And, The transistors in the electronic Dizzy will operate at lower voltages and current. (transistors generally need 0.6 to 1.2 volts minimum to operate correctly - which in this case is a lot less than the 8 to 12 volts it has to operate now)

All this being the case, we have still drifted of the point. Which is, will Alpha's car fail the way it is now. - Answer NO !

We are forgetting the main source of concern, wether the coil will burn out if the wrong voltage is applied. Well, only 8 volt coils burn out if 12 volts are applied for too longer periods. 12 volt coils will not burn out if only being driven by a lower 8 volts. The only problem in the later case is that the high voltage side of the 12 volt coil will not be as high if driven by only 8 volts. These voltages are normally around 15,000 Volts. And in this case would only reach aroun 10,000 volts. The effect, the car lacks a little performance and fuel ecconomy.

In layman's terms, unless I'm missing some vital facts, your car is fine now Lachlin. Although, I would reconnect the noise supression condensor back up to the coil.

[aarc240]

oops, didn't explain that too well, did I?

Correct situation is that with the 8V coil, it has a lower resistance than the transistor module is supposed to be working with so excess current will be drawn. That's when the output transistor will quit (eventually).

Put the correct 12V coil in place and the higher internal resistance solves that problem.

The other issue to consider is the voltage the module is operating on when the engine is cranking.

You have a resistance in series with the supply such that you have 8V or so on run.

When the battery is pulled down by the starter, you will still have that 4 to 5V drop across the resistance so the actual voltage getting to the module will be more like 5 to 6V. This is because the average battery will be putting out in the order of 10V while supplying the 200 to 250 amps needed to crank over the engine.

Don't know what the designed minimum limit is for the module to function but the two that I tested both quit at slightly under 5V.

That, in my estimation, is much too close for comfort (and is one of the reasons I don't use the 280zx system).

You can probably guess that the situation becomes worse if you have increased compression, more than usual initial ignition advance and/or a lean mixture.

btw, if you are down to 10kV at the plugs then you better have a rich mixture or it ain't gonna fire too happily.

Art

[240K&Beyond]

Thanks Art, I didn't know that the coils had different resistances.

To recap, what your suggesting is to :

1) Replace the original 8 volt coil with a new 12 volt one.

2) Provide an "ignition switched" 12 volts to the "b" or +ve side of the coil.

Alpha, I'm guessing it's a good plan. Personally, I don't think you need to panic as I have been running "just the dizzy mod" for a year without failure. But you and I will have to do it for best reliability.