No spark!

[rbgosling]

My Excel has decided to stop sparking

A couple of times over the last month it wouldn’t start, then I’d wiggle a wire and it magically leaped into life.

Then a week before Christmas it just wouldn’t spark at all. I spent 45 minutes faffing, then it sprang to life just as my wife arrived to rescue me, so I drove home without further incident.

Since then, no sign of life whatsoever.

Today I finally managed to spend some time (in the cold drizzle) trying to diagnose, but no luck.

I’ve generally been checking for spark by disconnecting the king lead from the distributor cap and holding so the terminal is millimetres from the starter motor boss, and turning the engine over to look for a spark. Never had any hint of spark.

Things I’ve tried:

• Checked for loose connections (including earth) on coil, AB14, over-run solenoid controller, rev limiter, and distributor.
• Replaced coil
• Disconnected rev limiter
• Checked for voltage at both coil terminals, including when engine is turning over
• Visually checked distributor cap and rotor arm - although the king lead should still spark regardless of the condition of these
• Removed and visually checked distributor. Can’t see anything wrong. There was a stray strand of wire magnetically stuck near the sensor which I removed
• Checked resistance of the sensor in the distributor. It was 1,500 ohms - no idea if this is right, but at least it confirms that there aren’t broken connections in there
• Put it all back together, still dead.

I’m now out of ideas. No idea if there’s any way to check if the AB14 is doing what it should.

Any suggestions? Please??

[richardw]

I think Stu might have a Lucas YWB135 tester that can be loaned out?

Also do a search on the forum for AB14 - lots of informative posts come up.

Cheers, Richard

[AndyC]

You've checked lots already but I'd suggest checking in a system approach. My approach for this (and I've had it on a few Excels) is to pick a point part way of the system and check if the system is working at that point, if not then go part way of that, if it is then part way of the remainder.
So, if you are sure there is no spark at the king lead/ coil then we need to look at a point from power to the system and output of the coil. you could next check whether the coil produces a spark if manually induced such as manually removing and making the contact for the input of the coil. If that's OK, then it's before the coil, so AB14 / pickup / speed limiter. and keep going by checking for whether the system is working at a certain point, rather than just keep going for random (but possible) items.

[Hawaiis0]

I think Stu might have a Lucas YWB135 tester that can be loaned out?

Also do a search on the forum for AB14 - lots of informative posts come up.

Cheers, Richard

Correct - never had an AB14 fail yet. Always something else.

Let me know if you want to borrow it

[Alan_M]

Hi Richard, as said above a methodical approach slowly narrowing down the search is often best in these cases.

Not sure if you’ve already got a copy of the Lucas test card for this system - if not here’s a link.

http://mossmotorsltd.wpengine.com/wp-co ... Card-6.pdf

[bash]

I had a fail to proceed incident with the ignition a couple of years ago and the fault was a wire in the harness to the coil, sometimes it was fine.........
Try an independent feed to the coil if all else fails.
Bash

[rbgosling]

Hi Richard, as said above a methodical approach slowly narrowing down the search is often best in these cases.

Not sure if you’ve already got a copy of the Lucas test card for this system - if not here’s a link.

http://mossmotorsltd.wpengine.com/wp-co ... Card-6.pdf

That Lucas test card is great! Wish I'd seen it before - requires printing out and laminating.

I got as far as Test 3, which I hadn't come across - check voltage between battery +ve and coil -ve while cranking. The voltage should increase. In my case, it didn't budge whatsoever. From their diagnosis this should then indicate a problem with the amplifier (AB14) or pick-up. The pick-up should have a resistance of 2.5 kΩ; I measured 1.5 kΩ, so I'm not sure if this is far enough out to be a problem (making it a pick-up fault) or it's OK (making it an amplifier fault).

One other test was that the coil should read 1V lower than the battery - I got pretty much identical readings. But since the only indicated faults were if the coil voltage was lower than that, I don't see that as indicating any problem.

Based on this, it does seem to suggest a problem with the amplifier or pick-up. Unless anyone has got a spare I can borrow and test with, I can't see how I can diagnose any further short of going over to Lotusbits and letting them swap in parts to see if they work. And that's a bit of a hike to tow the car - unless they'd let me borrow bits and bring them back. Guess I'd better call them and see what they suggest.

[rbgosling]

Actually the other simple thing it could be is a duff HT king lead - not checked that yet. Don't think I have a spare I can swap in though.

[MetBlue]

Richard. I've got a spare AB14 which I'm pretty sure is good.
Also sure I've got a King lead off the Excel that may help diagnosis - But then again, the one on my Excel ain't exactly busy right now so could use that for diagnostic purposes.

Are you working this week or at home?

Tony

[rbgosling]

I'm at home tomorrow, working Friday, then over to my parents in Suffolk for the weekend.

If I could pop over tomorrow and borrow those parts, that would be truly helpful.

[barker_001]

Something else to try Richard - take the measurement of the distributor pickup resistance again. This time, while the meter is reading the resistance, take off the cap and twist the rotor arm against the centrifugal advance. You should see no (or only a couple of ohms) change in the value. If it fluctuates wildly or goes open circuit, you have a break in the wire, probably within the distributor. They have a "design feature" whereby there is a small loop of the pickup wire which gets flexed every time the distributor advances the timing - an obvious point for breakage. That said, 1500 ohms seems a bit low anyway, the ones I've measured have been 2500 - 3000 ohms or so.

[Alan_M]

One other test was that the coil should read 1V lower than the battery - I got pretty much identical readings. But since the only indicated faults were if the coil voltage was lower than that, I don't see that as indicating any problem.

I think you may have misread that test. There should be a maximum of 1v difference. Anything higher would suggest a power drop between battery and coil, so not good. Less than 1v difference is ok.

Having no difference, as you have, is the best result you can have.

[rbgosling]

And... we have ignition!!

Many many thanks to Tony / MetBlue who came over this morning to lend me a hand. In the end we didn't fit the spare AB14 he bought over, but having a second pair of eyes and a second brain on the problem, we diagnosed the issue.

And the culprit was.....

The immobiliser. The one fitted to my car disables both the starter motor and ignition. The feed between the coil -ve and the AB14 is diverted via the immobiliser, which disconnects it when the chip is not in place in its holder. Simply re-connecting the AB14 directly to the coil, rather than the divert via the immobiliser, and it fired straight up.

The immobiliser still affects the starter, which seems rather safer anyway - without the chip you cannot start the car, but once it's started it will continue to run even with the chip removed, so it cannot suddenly cut out while driving if the thing plays up or the chip falls out.