Series 3 ignition

Is there a way of testing the ignition amplifier and what resistance should the ballast resister have .i have chopped and changed coils and at my wits end to sort out my ignition . I have a yellow spark at the coil and at the plugs

Here’s a CEI test which might help although it’s intended to address a no spark condition rather than weak spark.

The test assumes a fully charged battery

1. Measure voltage at coil “+” terminal with key “on”. It should be within
one volt of battery voltage. If not suspect a problem with the wiring to the
ignition switch, or the switch itself.
2. Measure voltage at the coil “-” terminal. Result should be the same as at
the “+” terminal. If Ok, go to step 3. If not…
Disconnect the wire from the amplifier from the “-” post of the coil and
measure voltage again. Less than 2 volts means the coil is faulty. More than
2 volts means the amplifier is faulty.
3. Disconnect distributor pickup coil from the amplifier (this is the
harness from the distributor that plugs into the amp). Measure resistance
across the terminals. It should be 2.2k to 4.8k ohms. If Ok, go to step 4.
If not, replace the pickup.
4. Reconnect the pickup to the amplifier. Measure voltage at coil “-” post
while cranking engine. The voltage should drop. If OK, go to step 5. If
not, the amplifier is faulty.
5. Check distributor cap and wires, distributor rotor arm, spark plugs, coil

For a weak spark I’d suspect the coil or ballast.

What coil are you running?

I don’t know the resistance value of the ballast but just bypass it and see if anything changes. More than a few of the ballasts have been tossed over the hedge, I reckon.


Does the engine start/fire at all, Tony…?

While a weak spark is a suspect in a non-start; it may not be the reason for it. That the work you have done made no changes makes me suspicious…:slight_smile:

One ign test; dram each cylinder with a teaspoon of petrol and crank. If the engine fires up and runs briefly - the ignition is ‘adequate’ and not the cause of a non-runner…

But do bypass that ballast resistor as Doug says - it is not required, and with some coils it is very counterproductive…

xj6 85 Sov Europe (UK/NZ)

I’ve been increasingly entertained by my smart VIZIO TV ! You tube. Johnathan Winans. Tow service operator by day. Old car addict by spare time. Gets old engines to run that have been still for decades. All point and condensor ignition. Clean the points. Some methods a bit brutal. Grind stone…

Jumps volts to coil. Usually jumps volts to the starter. Old truck running to provide “jumper” volts.

Adds gas to carb by the 'bottle". Much cranking. poor starter. Alll except one ran, at last. At least on the videos I’ve seen…

The Packard V8 in the Studebaker required major surgery to get enough compression to run…

I’ve used the “jump 12v to the coil +” process a lot. works well.

My “lump”’ responded well to a new coil to distributor wire. original corroded and loose??/ why??? … …


Thanks Doug I will try your tests out and let you know how things go

Thanks frank I will try this too

Hello frank yes tried the wee dram and it fired up , it ran for about 20 secs with foot to the floor , as soon as I lifted of the thotle it stopped , couldn’t restart it the plugs were sooty I also removed the ballast resister , so are we talking fuel ?

If the engine fires up after dramming, Tony; the ignition is ‘satisfactory’…

In principle; after a dramming start the engine will run briefly, couple of seconds, on the dram only.

Flooring the pedal will likely add fuel enough to keep it going until pedal is released. However with the pedal floored and the fuelling to spec; the engine would race up to max rpms - hot or cold…

…so I think you have a fuelling problem. However, the ign amplifier is also involved in fuelling - giving injector trigger signals to the ECU. However, this function is rather more ‘robust’ - and an iffy ign amp will likely trigger the injectors even if the ignition itself fails…

Use a test lamp, preferably an injector test lamp, NOID, to check injector signals. Disconnect an injector plug and connect it across the injector plug. With ign ‘on’ the lamp will be ‘off’ - while cranking; the lamp will flicker, indicating that the ECU is triggering…

A supplementary test; the voltage on both plug wires should be ‘12V’ with ign ‘on’. Which basically verifies that the connections between ign key through the main relay and injector resistor pack to injectors - and the connection between the ECU and injectors - are all OK…

If all checks out to specs; fuel pressure is an initial suspect…

xj6 85 Sov Europe (UK/NZ)

Hello Doug , I ran the tests you advised and all seems to be ok , this really foxes me I would be happy if I had a nice blue spark , I did try what frank said and give each cylinder a dram of fuel and it did fire up albeit very rough and only a few seconds
Thank you for your advice Doug it is really helpful

Hello frank I haven’t been able to access a noid yet but can confirm I get 12 volts at the injector connection

On both wires, to ground, Tony…

One wire feeds 12v

One wire feed injector power from the main relay, Tony - the other grounds the injector through the ECU when triggered. As the grounding typically lasts milliseconds; it can be observed only with an oscilloscope - or by the flickering of the test lamp while cranking.

The flickering is not really an absolute proof that injection time is adequate for required fuelling - but confirms that the ign amp is working well enough to trigger injection. That the engine fires up when fuel is added indicates that the ign amp operates the coil sufficient to give adequate spark…

xj6 85 Sov Europe (UK/NZ)

If I were you I would connect a fuel pressure gauge between the fuel rail and the cold start injector and measure fuel pressure. Although the yellow spark means ignition is still suspect, the fact that the engine ran briefly with the dram fuel makes me wonder if you have a fuel delivery issue.

What is the history of this car? Was it running fine for years and this problem suddenly occurred? Or did you get a non-running car that you are trying to get running for the first time?


Hi frank , I haven’t heard the petrol pump lately so thought I would fiddle around , I hope this makes sense to you , so I took the air filter of to see if the air flap opens or not and it was shut , so I turned ignition on and pushed open the flap and the petrol pump started up . So I know the pump works , my question is if that air flap doesn’t open when cranking the engine the pump won’t start and I am not getting fuel , is there a way of checking the air flow meter

Hi Paul the car was an excellent runner it never missed a beat , until I pulled into our shop car park for groceries , when I went to start her up there was nothing , she would crank over well until I drained the battery


It could be an internal failure of your ignition switch. This happened to me about 17 years ago in my 1984 XJ6 Vanden Plas. The symptoms for me were intermittent “cranks but doesn’t start” and “doesn’t crank”.

Search the archives for ignition switch failures and you will find many posts about this kind of failure. It seems that the internal parts of the ignition switch get worn or overheated and then they don’t work properly any more. This could be your problem.


No worries. The pump circuit has two branches. One for starting and one for running. The “starting” branch operates, via the starter relay and diode pack, when the key is turn to ‘start’.

As soon as the engine begins to fire the AFM flap is pulled open by vacuum, thus triggering the “running” branch of the circuit


Hi Tony, are you sure you have fuel? Have you tried starting on your other tank? I have had fuel problems in the past turned out to be a blockage in the tank that stopped as soon as the pump turned off and the suction stopped. Turned out to be a loose screen from the intank filter was being sucked up to the outlet and blocked the fuel. I removed the screen filters from both tanks and fitted external inline filters before the change over valve. All good now.
The fact that your motor will start when dramming the cylinders suggests to me you may have a low or no fuel problem.
By the way my, spark is not as healthy in colour as I would like but it seems to work ok anyway.

As Doug says, Tony; ‘no worries’…:slight_smile:

However, you should also verify that the fuel pump also runs in ‘crank’. Set gear lever to ‘D’ or ‘R’ and turn key to ‘crank’ - you should hear the fuel pump running…

Con also points out that switching to the other tank if lack of fuel is suspected as a standard procedure. A further, primitive but easy, fuel pressure test is to open the filler lids and listen to fuel returning to tank. Prop open the AFM flap as you did previously; with ign ‘on’ and fuel pump running you should hear fuel returning - indicating adequate delivery to force the fuel pressure regulator open…

No return fuel; inadequate pressure - faulty pump or line blockages. However; fuel returning may be caused by a faulty pressure regulator - or delivery is as it should be…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Well Frank I’ve got fuel returning to the tank after propping open the air flow flap , not sure what to do now or what order it should be done
Thanks for your help