Sudden stall on XJ6 then no spark

My Series 3 XJ6 was happily idling in the driveway this morning for a few minutes then suddenly stalled. I could not get it started. I noticed it had a very weak spark, almost non existent. As the distributor cap and rotor were worn I replaced those. No change. I also replaced the coil with a new one (with one for an external ballast resistor) I had at home. When I removed the old coil I notiiced one of the wires to the positive terminal was broken. There is over 12V at each of the new coil’s terminals, matching the battery voltage. There is fuel pressure at the rail, so that’s not an issue. I’m not sure how to test the pickup in the distributor, or the amplifier unit bolted to the manifold, although I believe the latter would not stop the engine running if it failed (?). I’ve checked the resistance on all leads, particularly the coil lead. All good. As mentioned, the engine was running smoothly and has been driven recently. It always starts easily, so this was a sudden failure. Any advice would be helpful. I’ve only had the S3 for several months, but it’s behaved extremely well during that time.

There is info in this thread that might be useful

Cheers
DD

Thanks Doug. I did see that thread earlier, but after you referred to it, I went through it diligently step by step. Everything ticks off as ok, except one obvious problem. The coil tests fine. It also has a pulsating light when cranking. And I can see that there’s spark on the coil ignition wire. However there is now no spark on any of the ignition wires. The cap and rotor are new. I’ve checked the resistance from the centre contact of the distributor to the end of the coil wire and that’s fine. All I can think of is that the distributor pickup coil is dodgy. I’d hate to buy one if it’s not though!

**
Question; does the injectors click regularily while cranking?

Injection is triggered by the ign amplifier, but is arguably less sensitive to ign amp faults than the ignition. That the injectors click isn’t proof positive that the ign amp is working correctly.

The standard ign amp test is to connect a test lamp between coil ‘-’ and ground. With ign ‘on’ the lamp is fully lit - in ‘crank’ the lamp should dim and flicker. Again not positively proving that the amp is working correctly, but ‘no flicker’ proves that the amp, or pick-up is defective. With correct readings of the latter as described by Doug; the pick-up itself is OK, but may just (very unusually) have come out of adjustment - which can be checked and ajusted…

The most likely fault, given the parts replaced, is a failed ignition module inside the square, black ign amp (AB14 igniter in the original set-up). The module is readily available and easily replaced…

Frank
xj6 85 Sov Europe (UK/NZ)

The parts are new - that’ll be the problem. You have spark so no problem before the cap.

Now there’s no spark at all on the coil wire. The new coil (from a Jag shop) tests at 1.2ohm on primary and 12kohm on secondary. Replaced the pickup module inside the distributor with a new one. How do I check if it’s adjusted properly? Is the gap particularly critical? Also replaced the coil with a a new unit. Tests ok. Perplexed and running out of light (and ideas!). Can’t actually hear injectors clicking when cranking. Is it particularly audible?

Lloyd

**
The gap is indeed critical, Lloyd - it should be between 0,008 and 0,014" between a ‘tooth’ and the pick-up. As the pickup is magnetic a brass or plastic feeler should be used…

The injectors should be clearly audible, but you may use a large screwdriver on the ear and an injector as a stethoscope.

That said; both the pick-up and the ign amp module may cause ‘dead’ ignition and injection - but the latter is far more common. Did you test the amp action with a test lamp as described?

Frank
xj6 85 Sov Europe (UK/NZ)

If there’s no spark looking at the injectors is absolutely pointless.

That 12k ohm secondary resistance is on the high side. I like to see something more like 8k ohm.

I’m wouldn’t condemn the coil at this point but if all other avenues become dead ends it might be worth discussing.

What coil did they give you?

More ideas perhaps after a second cup of coffee

Cheers
DD

I’ll check the coil resistance again tomorrow, in case I didn’t make good contact. The guy said it was a genuine part - to use without a ballast resistor. My original setup had a ballast resistor. I’ve been trying to find a good ignition circuit wiring diagram (the one in my manual is pretty ordinary). It appears that there are three wires on the negative terminal of the coil (white/black, white/blue and white (from the ignition amp). The positive side has two wires - a white one from the ignition amp and another white one from the ignition (I assume). Does that sound right?

Should be two white/black and one white/blue.

One of the white/black is from the ignition amp. The other goes to the ECU.

(the white/blue is probably white/slate/blue; it’s the tach feed)

Right !

Cheers
DD

Tested everything again checked pickup gap. It was a little larger than spec so brought it down to 10thou. There’s ~12.4V with ignition on and about 9V at ‘+’ and 8.7V on ‘-’ terminal when cranking. Remember, no ballast fitted. I’ve checked that there’s nice pulsation on a test light between ‘+’ and ‘-’ terminals whilst cranking. Wiring: I have white/blk, white/blue and white (from Amp) to ‘-’ terminal. And I have two whites (one from Amp) to ‘+’ terminal of coil. I can see the tacho sitting at a few hundred rpms whilst cranking. Primary and secondary resistances of coil are 1.1ohm and 16.4kohm respectively. If I plug the coil lead into a spark plug with triple the normal gap, it appears to spark nicely, yet when I plug it back into the distributor cap, there is no spark on any of the ignition wires. That’s what I don’t understand. Given that I’ve removed and replaced the central toothed wheel and pickup, is it possible that there’s a misalignment between the cap and the pickup, so when it fires it’s triggered to fire, the rotor is not making contact with an ignition wire contact inside the cap. Sounds ridiculous but just a thought. I might check the alignment with an ohmmeter.

**
If there is spark (strong, blue) on a directly connected spark plug; the coil/amplifier is delivering, Lloyd - and the dist lid/rotor are prime suspects…

However, if you replaced both the reluctor (toothed wheel) and the pick-up there is a possibility of reluctor misalignment as you say - theoretically firing the coil as the rotor is between two plug connectors on the dist lid. This is highly unusual (‘sounds ridiculous’ as you say) - but not quite impossible…

Ign timing is set by turning the dist to align a tooth with the pick-up as the relevant piston is at it’s ign advance position - and the rotor is pointing to that plug lead at the dist lid…

In this rather unusual situation; set the engine so the pointer points to 5 deg BTDC on the crankshaft damper timing scale. Check that a tooth on the reluctor is aligned with the pick-up. If not; unclamp the dist and turn it to the nearest position for alignment (or reposition) the reluctor). Next; check that the rotor is roughly pointing to one of the plug lead connector. If not; we are in deep waters, however unlikely, when you (needlessly!) replaced the reluctor…:slight_smile:

You should now have sparks at the plugs - but you need to retime the engine - using the correct procedure…

Also; remove dist lid and check the connection between the dist lid and rotor - usually a spring loaded carbon rod (or whatever) connects the dist lid with the rotor. If missing; ign voltage will not be transferred to the plug leads. You can ohm the connection between the lid and the rotor, but the there is no physical connection between the rotor and the plug lead connections. If connection seems OK; the first step is to replace the rotor. This is why I asked about the injectors clicking in ‘crank’; injection is also triggered by ign amp, which seems to be working - confirmed by clicking injectors

To elaborate; the pick-up coil delivers a signal to the ign amp each time a tooth on the reluctor passes the pick-up. Which ‘breaks’ the coil ‘-’ ground connection triggering the coil to deliver the spark. Any tooth will trigger the ign amp; it is the position of the plug leads on the dist lid that decides the ign sequence -and the position of the rotor that decides which cylinder is firing. Since you haven’t(?) repositioned the plug leads on the dist lid - your ign sequence is likely OK…

The coil data is sort of irrelevant; the CE system will work OK with most coils. The external resistor is sometimes fitted, mainly to reduce coil current - basically to protect the ign amp, against excessive coil currents, but is usually irrelevant for ignition.

Frank
xj6 Sov Europe (UK/NZ)

Double check the spade connectors that are crimped for the coil connection ect…i had a similar problem took ages to find as it always tested ok with a meter until by chance i pulled on a wire and it came out of the crimp. …it was obviously causing an intermittent bad connection…now i crimp and solder…Steve

1 Like

You could have saved yourself the trouble if you hat followed my post. Everything okay with your sparkles until they reach the cap, so nothing wrong upstream……

Is the graphite center in place in the cap?

Hi David and Frank,

David - I did follow your list of tests and everything checked out ok. Even though I have spark on the coil wire and it is healthy enough to jump a large gap, I also noticed that it’s not regular. That could be the inductive pickup of my timing light perhaps.

Frank - I’ll follow through with your advice as well. However, I wouldn’t have thought that the reluctor would incorrectly locate. Worth a look!

Cheers, Lloyd

Neither can I, Lloyd - it’s just to explore your theory…:slight_smile:

A reluctor tooth trigger the ignition as per ign advance setting - ‘when’ piston is in the correct postion. The distributor directs ‘where’ the spark goes - to the plug lead the rotor is pointing to. And with the center lead sparking the spark should indeed show up on the plugs, whether or not timing is correct - unless the connection between lid, or or the rotor itself, has failed. Or if your theory is valid…

That the sparking is irregular may of course be a timing light malfunction - or caused by distributor axle wobble varying pick-up gap? Or ‘something else’ with a bad connection - the amp itself is an unlikely fault source of this kind…

Frank
xj6 85 Sov Europe (UK/NZ)

Hi Frank, as you say, timing will not affect the spark as the cap moves with the distributor. As an aside, I changed the amp since I’d ordered one last week. No change there. Coil lead is still producing an excellent spark but absolutely nothing on any of the spark plug leads. I have swapped over the coil lead in case it wasn’t making a good contact at the distributor cap end. I had checked resistance on each lead from spark plug end to the internal contact on the cap. I removed the distributor and reluctor to make sure it was seated properly. It can only locate in one way given there are 4 teeth to locate on, with one larger than the rest. I doubt the circlip would fit back on the top if the reluctor wasn’t seated properly. That leaves me to think that the distributor cap (a new one) is faulty. Hard to believe though.
That would suggest either the internal contacts weren’t connected through the cap properly or the placement of the The rotor, also new, is seated properly and as long as the conductive brass strip along the top is ok, it should work fine. I got my daughter to crank the motor over while I gently adjusted the timing over a large range both adv and retard. For a second or so I got the timing light to flash on #1 lead. So something’s out of whack. Btw, the replacement cap looks identical to the old one, except for colour. I’m now wondering whether the locator seat has somehow moved on the distributor shaft?? Ever felt like you were chasing your tail? Lloyd

sorry typo "… or the placement of the the rotor, also new, isn’t seated properly "

I’ll mention this because it seems like you’ve tried everything sensible to figure out why your spark is stuck in the cap. There have been MANY no-spark failures in British cars over the years due to foreign-made, shiny-black plastic rotors. They are made with a some kind of recycled garbage plastic that’s theorized to have too much carbon in the mix - that coupled with the big, unneccesarily-long rivet make it a recipe for mysterious spark related issues. They will appear completely normal and can even work for many miles but then leave you mysteriously stranded with no visible sign.

What happens is that the long rivet (too close to the shaft) eventually provides a path for the spark to track through the plastic to the shaft and ground out the HT circuit. I’ve seen it multiple times in customer’s cars and it’s happened to me exactly once about 15 years ago. No warning, nothing obvious but I always carry a spare rotor so was back on the road in minutes. When I got back to the shop I cut the rotor in half to see if I could see anything inside. Couldn’t see much of anything.

Not saying this is definitely your issue but certainly worth checking if your new rotor is Shiny Black Plastic. Throw in your old rotor and see what happens. As I’ve said, this is a known issue - do a search here or on any other British car forum and you’ll find people talking about it.

At the beginning of your thread you mention it was just happily idling and then stopped - this is exactly how it manifests itself.

2 Likes