Is coil failure the answer?

[speedyK]

The last time I drove my Beta Spyder was about 4 months of months ago, when it ran without problems.

When I wanted to start it recently (with battery jump leads connected to another car which was supplying a healthy charge), it turned over happily but would not fire at all.

I replaced the plugs. Still nothing 

I thought maybe the small amount of very old petrol in the tank was the problem, so added 10 litres of fresh 98 RON, disconnected the fuel feed and pumped it through until about 300 ml was collected into a bottle. This did at least show that the fuel pump is working.

Connected it up and tried again. Nothing 

Checked the spark at the end of the plug lead. Nothing! 

Checked the spark coming off the coil to distributor lead. Nothing. 

Does this mean that my coil has failed? Any other possible explanations? 

[Neil-yaj396]

Points failure (if an early car), or the electronic ignition pack has failed? If you can borrow a coil a quick swap will rule that in/out.

[lukasdeopalenica]

Check if there is voltage at primary coil terminals when ignition switch is in ON position

[speedyK]

It's a 1981 (electronic ignition) car. There is a spark at the coil terminals and having looked more carefully, there IS a spark at the end of the coil to dizzie lead, but that doesn't necessarily mean that it is working properly, does it.

Not really feasible for me to borrow a coil. Can anyone tell me what the exact spec of the Bosch coil on a 1981 Spider 2000 is?

[Thotos]

Bosch electronic ignition on Betas (on my Trevi at least but I suspect all betas are the same?) is a bit strange in that it uses a 9V coil with ballast resistor but there's no ballast bypass when cranking the engine. Try bypassing the ballast resistor. It's easy, simply take the 12V feed from one end of the ballast and connect the 12V straight to the coil. They are all spade terminals so no tools needed. You need the wire off the ballast that doesn't already go to the coil 12V terminal. In the case of my Trevi that's the wire on the ballast nearest the inner wing. I've been running the Trevi like that for a while now and haven't burned the coil but then again my 12V feed only has 10V on it with the engine running.

[speedyK]

Try bypassing the ballast resistor. It's easy, simply take the 12V feed from one end of the ballast and connect the 12V straight to the coil.

Just checking before I do anything: you're saying take red lead no.1 coming out of the loom and connect it directly where red lead no. 2 attaches to the coil terminal, yes?

[Thotos]

Yes, that's what I'm saying. Just to be sure, check that lead number 2 on the coil at the moment goes to the other side (non-1) of the ballast resistor. If you have a voltmeter it's worth checking how many volts you have at wire 1.

[speedyK]

Yes, that lead no. 2 loops round from the ballast resistor at the top of the pic.

I'm just a bit concerned about what peteracs said in another thread:

"I suspect that the ballast resistor may have been left in

a) To keep with the same part, though why there is no bypass is maybe just a price cutting exercise when batteries improved and with electronic ignition.

b) If the coil shorts then you have some safeguard against the wires burning out and potentially causing a fire under the bonnet. Also it limits the current drawn when you connect/disconnect the coil which is done via the elec ignition, presumably a transistor in it."

I wouldn't like to see it go up in flames!  

[Thotos]

I certainly wouldn't want to try to convince you to do something you don't want to do. But bypassing ballast resistors during engine cranking is very common practice and it's what all ballast ignition systems that I have seen do except on the Beta    The same Bosch electronic ignition system is fitted to the Gamma and that bypasses the ballast resistor during engine cranking. I am not suggesting that you run your car with the ballast bypassed permanently (although that's what I've done with the Trevi and it hasn't gone up in flames yet - I'll fit a bypass relay one day...). I'm only suggesting bypassing the ballast resistor to see if you get a spark and the engine starts. You need a certain amount of voltage to get a spark to jump a gap (about 20,000 volts) so if your 9V coil only gets about 7 volts while the starter motor is drawing lot's of amps from the jump leads, you may have 'only' 15,000 Volts out of the coil and it may just not be enough to produce a nice strong spark.

[Neil-yaj396]

.....there IS a spark at the end of the coil to dizzie lead, but that doesn't necessarily mean that it is working properly, does it.

The presence of a spark here seems to indicate that the coil is working. As Theo suggests it's probably the strength of the spark that is the problem.

[speedyK]

I certainly wouldn't want to try to convince you to do something you don't want to do. (...) I'm only suggesting bypassing the ballast resistor to see if you get a spark and the engine starts.

it's not that I don't want to do it, it's more that I want to understand what this will tell me.
If it starts by bypassing the ballast resistor, does that mean that the ballast resistor is defective and needs replacing and the coil is actually OK?

I'm not the greatest expert on electrics, so want to tread carefully 

[MattNoVAT]

it's not that I don't want to do it, it's more that I want to understand what this will tell me.
If it starts by bypassing the ballast resistor, does that mean that the ballast resistor is defective and needs replacing and the coil is actually OK?

I'm not the greatest expert on electrics, so want to tread carefully 

A highly commendable approach!


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[Thotos]

If it starts by bypassing the ballast resistor, does that mean that the ballast resistor is defective and needs replacing and the coil is actually OK?

Most likely it'll mean that there's nothing wrong. If the car starts by bypassing the ballast resistor, then put everything back to normal, fully charge the battery and the car will start again.

You said you were trying to start the car with jump leads from another car. The starter motors on these twincams can be up to 1.6KW which would require over 130Amps. Depending on the quality and length of your jump leads and the quality of the connection to your car's battery, you may lose a couple of volts so you may only have 10 volts going into the ballast resistor and about 7 volts or less going to your coil.

[peteracs]

Yes, that lead no. 2 loops round from the ballast resistor at the top of the pic.

I'm just a bit concerned about what peteracs said in another thread:

"I suspect that the ballast resistor may have been left in

a) To keep with the same part, though why there is no bypass is maybe just a price cutting exercise when batteries improved and with electronic ignition.

b) If the coil shorts then you have some safeguard against the wires burning out and potentially causing a fire under the bonnet. Also it limits the current drawn when you connect/disconnect the coil which is done via the elec ignition, presumably a transistor in it."

I wouldn't like to see it go up in flames!  

Hi

Completely forgotten about that post......

As a test, I would not worry, shorting out/bypassing the resistor will be fine, just be aware that the coil is not designed to run at 12V or more and will likely fail if you run for more than just a test, the most likely failure would be overheating I guess?

Hope you manage to sort it. I would suggest substituting a known good coil as a failing coil may appear to work without the resistor, but not with and you may just think the resistor is to blame. ideally have one of each to play with of course.

Peter

[speedyK]

If it starts by bypassing the ballast resistor, does that mean that the ballast resistor is defective and needs replacing and the coil is actually OK?

Most likely it'll mean that there's nothing wrong. If the car starts by bypassing the ballast resistor, then put everything back to normal, fully charge the battery and the car will start again.

You said you were trying to start the car with jump leads from another car. The starter motors on these twincams can be up to 1.6KW which would require over 130Amps. Depending on the quality and length of your jump leads and the quality of the connection to your car's battery, you may lose a couple of volts so you may only have 10 volts going into the ballast resistor and about 7 volts or less going to your coil.

Ah, my mistake, I forgot to add in my first post that I then also replaced the battery with a brand new one which was fully charged - and I added a booster battery pack. All to no avail.

[speedyK]

I would suggest substituting a known good coil as a failing coil may appear to work without the resistor, but not with and you may just think the resistor is to blame. ideally have one of each to play with of course.

Peter

If you had to make a choice, would your money be on the coil as the source of problems, or the ballast resistor? I'm guessing the coil...

[lbcoupe76]

When you are trying to turn it over does the coil get hot?, does the ballast resistor get hot?. And i do mean hot.

[Thotos]

If you had to make a choice, would your money be on the coil as the source of problems, or the ballast resistor? I'm guessing the coil...

I would guess neither. If you have no spark then I'd suspect the ignition pickup in the distributor, the wire to the electronic control unit or the electronic control unit itself. If you have a weak spark then I'd suspect the car's wiring and connections causing a low voltage at the ballast resistor and hence low voltage at the coil. If you don't want to bypass the ballast resistor to try and see if the car starts, get a voltmeter and measure the voltage at the ballast resistor and the voltage at the coil + terminal while cranking the engine. You should have 12 volts at the ballast resistor and at least 9 volts at the coil.

[speedyK]

This is getting complicated 

[speedyK]

I got a multimeter and checked what was happening at the coil:

The voltage measured at the outer poles (the primary winding) = 6.2 volts

The resistance measured from the centre pole (to distributor) to an outer pole = 7.2kohms.

It doesn't mean much to me, but the voltage seems low.

The ends of the ballast resistor get very hot.

Thoughts anyone?