Intermittent Spark

[Range Rover 2 Door]

Hi Ramon.

Here's a picture of my ignition amp (the brand new one):



The wiring looks different to yours. The wire from the resistor to the coil test pnt.

I have decided to try a points distributor in it...I know where I am with them! I will report back. My plan is to get her running sweet on points, then put in a Lumenition system. The greatest advantage of this for me, is the ease of changing back to points if required.

Cheers.

[ramon alban]

Well Chas, thats certainly got a condenser so I reckon the others had too,, so, a new condenser eliminates that from the poss faulty list providing you had it substituted for the other which may of course be faulty if its still on the car..

Not much left now except to verify the source of that rogue 12 volts you found, with ignition off.

I'm surprised you have no answer to that yet as it is clearly wrong which ChrisC also twigged..

I am also surprised you need to move back to your comfort zone,

Why not try the lamp indicators too. If you are still so convinced its an ignition issue your past experience should carry you a long way to diagnosis. this is not rocket science, as I am dicovering too.

I dont think the module wiring is different but i'd need to zoom both to be sure - more accurately so do you, unless the clours change, just that the image I took from a forum has a joined wire going to a test point which is not used anyway.

Thats another thing you could do, check the component to component wiring against my schematic and at the same time removing any thing that is not needed - perhaps like alarm or immobiliser. who knows.

with your conviction, should be shaking down this problem not sidestepping it.

Ramon

[ChrisJC]

Hi Chris.


What's the difference between using an LED on the coil negative and a voltmeter? How come one is recommended and the other meaningless?

Basically because a voltmeter won't respond quickly enough. The voltage on the coil -ve will be changing between 0V and 12V four times per engine revolution. A voltmeter will smooth the voltage out and give a rough average. A test lamp has a time delay to warm up / cool down (compare lamp indicators with LED indicators - the LED ones are instant). An LED will only emit light when a current is flowing, the turn on / off time is instantaneous. So with an LED you can see each pulse individually.
An oscilloscope is even better because you can see how the voltage changes, measure the length of the pulses, overlay them etc etc.

I don't have any LEDs to hand and figured it was worth seeing what was going on there. My readings were all 12V or more. Wouldn't that make an LED light full on, indicating a problem?

What about your 19V reading? You'll never see how that occurs with a light. You need an oscilloscope to see that one.

What about the reading from battery positive to coil negative (ignition off). According to the Land Rover manual, there should be zero voltage. I get battery voltage.

Gotta nip out - I'll think about that one and reply later...

Chris.

[Range Rover 2 Door]

Thanks again, Ramon. Really appreciate you taking the time to respond.

I've been working at this for nearly three weeks solid now, and I'm tearing my hair out! I only just got the car and haven't driven it in any meaningful way as yet. I'm dying to get her up and running (she's a nice car)! Hence my decision to try the points. That aside, it will also be a good exercise to confirm my diagnosis (or otherwise)...what if I fit the points distributor and still have the same problem...now that would be interesting!!

I am intrigued though, by the battery voltage I am getting when it should be zero. If that leads to a definite line of inquiry, I could check it out and report back.

Thanks for now.

[ChrisJC]

I am intrigued though, by the battery voltage I am getting when it should be zero. If that leads to a definite line of inquiry, I could check it out and report back.

Thanks for now.

OK, I confess to not quite understanding what the manual is getting at, having re-read your quotation from it.

However, this is how it should be:
- With ignition off, both sides of the coil should measure 0V when measured between ground and the coil terminal. If you measure between the batt +ve terminal and either coil terminal, I would expect to get 12V.
- With the ignition on, but the engine not running, you should have +12V on both sides of the coil, when measured between ground and the coil terminal. If you really have +12V on one side, and 0V on the other, then the coil will get hot fairly quickly, which is wrong.
- With the engine running, the coil +ve should be +12V, and the coil -ve should be pulsing between 0V & 12V too rapidly for the voltmeter readout to respond, so you'll get a meaningless result, e.g. 19V!

If you decide to go the LEDs route, you'll need a handy technical mate to sort it out for you.

Chris.

[Range Rover 2 Door]

Hi Chris. Thanks for the clarification, much appreciated (electronics are not my thing!).

Here's a picture of the Land Rover manual item concerning the coil negative voltage. This is where I am getting battery voltage where I apparently should be getting zero. There is only ONE wire on my coil negative terminal, going to the amp.

I didn't check the voltage when cranking (working on my own and couldn't see the meter!). However, when I switch the ignition on, I get 0.1V (battery positive to coil negative).

With the ignition on, I get a tad under battery voltage at the coil +ve to earth AND coil -ve to earth (which I believe as you said earlier, is expected).

Cheers.

[Range Rover 2 Door]

Forgot to mention. This business of getting battery voltage when I should be getting zero. Same thing happens with my original amp and the brand new one.

Even with my limited knowledge of electronics, I can see that the coil -ve must be earthing at this point, to give me the battery voltage. The only connection on the -ve terminal is to the amp, so it must be earthing through there somewhere. According to the book, it shouldn't be doing this.

[Range Rover 2 Door]

However, this is how it should be:
- With ignition off, both sides of the coil should measure 0V when measured between ground and the coil terminal. If you measure between the batt +ve terminal and either coil terminal, I would expect to get 12V.
- With the ignition on, but the engine not running, you should have +12V on both sides of the coil, when measured between ground and the coil terminal. If you really have +12V on one side, and 0V on the other, then the coil will get hot fairly quickly, which is wrong.
- With the engine running, the coil +ve should be +12V, and the coil -ve should be pulsing between 0V & 12V too rapidly for the voltmeter readout to respond, so you'll get a meaningless result, e.g. 19V!

Thanks Chris. From the various tests I have done over the past few weeks, I think I am getting the above (will need to double-check, just to nail it for the archive). The 0.1V I am getting at the coil -ve is from the battery +ve to coil negative (ignition on, engine static) as per the test in the book. I do get +12V on both sides (to earth) with the ignition on (engine static).

I mentioned before but I'll repeat it. I got the largely meaninless 19V (coil -ve to earth, engine running) on my new amp. I was getting 12V rising to 19V when I revved the engine.

I did the same test on my original amp, and the reading stayed around 12V at all times. I know it is largely meaningless but we are comparing like with like here and I thought it was interesting that the two amps behaved differently.

Cheers.

[CastleMGBV8]

Charle,

Just went back to re read your original thread, more carefully, I notice that you mention a Lucas DCB 198 don't know if thats a typo and you meant DLB198 and if thats the coil you are currently using.

If so that coil is 12v for 35DLM8 distributor as fitted to my car and runs unballsted.

I am not so familiar with the earlier remote mounted and far more complicated amp for the 35DM8 distributor but if it is a ballasted system that may be part of the problem.

I fitted a different spec but 12V coil and my engine wouldn't even start, no spark at all, after doing some research I found out that it is the low tension resistance side of the cioil that is critical, if it's wrong it wont trigger the amp correctly or not at all.

Just a thought.

Kevin.

[ramon alban]

what if I fit the points distributor and still have the same problem...now that would be interesting!!

Interesting how? If its not sparks then what?

I am intrigued though, by the battery voltage I am getting when it should be zero. ---- I could check it out and report back.

OK! Existing connections are bringing voltage to that measuring point, so take away connections one at a time to find the culprit, then trace back to the source and decide if it is supposed to be there.

BUT HANG ON!

All this may be a false trail. You already have sparks - or did have at the getgo of this thread.

Suppose what you are observing is not a fault but a characteristic of the system as it is currently connected?

Maybe with all the component changes a wire has gotton relocated or some parts are not compatible?

The way sparks manifest themselves to the eye! The way you apply the measuring equipment? Simply a quirk of the extraneous connections such as alarm/immobiliser/what-have-you might lead to them absorbing some of the input signals to the amplifier?

One or more making it entirely possible that we are diagnosing a fault that may not exist (but depends somewhat upon your self-confessed lack of electronics knowledge, use of meters and lamp/LED characteristics).

We might just be in red herring territory here, barking up the wrong tree whilst chasing wild geese, as it were?

In which case why not just go back to the simplest of all tests?

Set up those two lamps/LEDs as ChrisC suggests. run the engine until the described problems are present, observe the lamp behaviour and make a diagnosis. Even a filament lamp will glow at different intensity depending upon the nature of the pulsing voltage so you could even steer clear of LEDs for a start off.

What do you think?

[Range Rover 2 Door]

Just went back to re read your original thread, more carefully, I notice that you mention a Lucas DCB 198 don't know if thats a typo and you meant DLB198 and if thats the coil you are currently using.

Well spotted, Kevin! I hand-wrote the number from the coil...my L looked liked a C! It is indeed a DLB 198.

If so that coil is 12v for 35DLM8 distributor as fitted to my car and runs unballsted.

I am not so familiar with the earlier remote mounted and far more complicated amp for the 35DM8 distributor but if it is a ballasted system that may be part of the problem.

My system is unballasted.

I fitted a different spec but 12V coil and my engine wouldn't even start, no spark at all, after doing some research I found out that it is the low tension resistance side of the cioil that is critical, if it's wrong it wont trigger the amp correctly or not at all.

Good info, thanks.

[Range Rover 2 Door]

What do you think?

I think you're a hoot and I could read your stuff all day!!

You're going to be disappointed with me, Ramon...I fitted a points distributor, now she runs like a dream!!

So it wasn't fuel (hee hee!). Could have been any of the parts I removed: coil, amp, amp to distributor lead, distributor including pickup module, rotor arm and cap. Now that she's running sweet, I can check the rotor arms and caps I was using, see if they are all dud!

Fitted a points distributor, Lucas 35D8 (came with the correct female wobbly drive dog for the oil pump) ballast coil and ballast resistor. All new parts. Now there's a simple system!!

She actually runs pretty well but I got a Lumenition kit to fit to it.

Now that she's running, I feel I can relax a bit. I can maybe go back to the original electronic setup and figure out what was wrong with it. At least I know it's an ignition issue!

Thanks again.

[Range Rover 2 Door]

However, this is how it should be:

Hello again Chris. Just to nail these voltages...

With ignition off, both sides of the coil should measure 0V when measured between ground and the coil terminal.

Check

If you measure between the batt +ve terminal and either coil terminal, I would expect to get 12V.

Check

With the ignition on, but the engine not running, you should have +12V on both sides of the coil, when measured between ground and the coil terminal.

Check

With the engine running, the coil +ve should be +12V...

Check

...and the coil -ve should be pulsing between 0V & 12V

Yet to confirm.

[ramon alban]

Good news then Charles?

You have succeed where the Major Government failed. Back to Basics really does work.

Two step backwards and nil steps forwards is the way to the future because time really can go backwards in Scotland (or London). (Time is the mechanism that prevents everything happening at once).

Disappointed? Moi? Not at all! Your convictions have carried you through to a successful conclusions without needing any help at all, so the whole thread has been a virtual waste of time, except for thee and me.

Me? I'm a happy bunny cuz I'm researching electronic ignition systems for an upcoming essay and pissing about with other people's systems is the only way to drag out a potential diagnosis because in 15 years of dabbling I never had a major ignition prob on any one of my 4 SD1's that went beyond changing a rotor arm or the odd plug lead.

Mind you, whether I can find the balls to recommend reverting to a points system is another thing altogether.

And for thee, when you get the urge to revert to modern technology all you have to do is plough thro' the dross on this thread because hidden somewhere is the answer from one of the contributors.

On the other hand you might commence a new thread and draw in better expert diagnosis from future contributors who will try to deal with these electronic issues for you.

I wish them an you good luck.

Bravo Mr C. - you got yourself a Cupi Doll

[Dangerdoc]

Ramon is pretty near the point.

An open mind is essential. Maybe you did start playing about with sparky things 30 years ago, so did I but you had to light them with a match and stand well back or hold them at arms length, ah then came cars - damn things.

Even after 30 years of sparky things, it means you have done something for one year 30 times, nobody says it is spot on. None of us are !

Just to add to the bag of spanners being shaken about here I had a very similar set of problems (Ramon remember the garage not being able to tune the beast !).

It turned out that the coil was a dud and even the new one was a dud, causing the injectors to pulse twice per cycle !!!! and also - the throttle position sensor was mouldy inside and had an intermittent broken wire. The old wiring loom had a damaged wire causing an intermittent fault.

If you are getting wet plugs, you simply MUST consider over fueling and not just a dodgy spark.

Things do not always happen in singularity so think outside AND inside the box. That's exactly what Ramon does and I would trust him anytime with ignition stuff.

Think of all possibilities. My beastie runs really well now but after eight weeks in the garage and even the lads with over 250 years of combined exerience stopped billing me and took the think on as a project.

If it stumps guys with that experience, 30 years is nout. Still, more than me so I'm not on some high horse crusade but just want to suggest thinking more laterally.

Doc