Simon's new Xantia V6 and Leaf blog

[Mandrake]

Well not all is well on the V6 front lately...

In the last week or so I've noticed the performance has been somewhat flat again - nothing like the trouble I was having with the other car, but definitely not what it should be - lacking the eagerness and responsiveness it should (and usually does) have, so I decided to dig into the problem a little bit.

I'm fairly sure that the problem is spark plug leads, but I decided to lift the top styling cover to see what things were like under there and found a few things I don't like the look of...

The first obvious problem is two massive cracks in the top of the coil pack - they probably don't show well in the picture, but they are the worst cracks of any of the coil packs I've had, and being in the top epoxy could potentially be causing high voltage leakage:



The next thing I noticed (no picture, sorry) is the right hand spark plug lead was crushed under one of the cover cooling fins - something I had trouble with on the other car too. Despite the protective conduit (which was also completely crushed) the wire is badly kinked and damaged - it wouldn't surprise me if the wire inside was broken.

When refitting the top cover on these you need to poke your pinky finger through the right most cooling hole in the cover and push the right hand wire to the right slightly as you clamp down the bolt next to the oil filler - if you don't, the wire usually gets crushed directly under the cooling fin. A piece of poor design if you ask me.

Finally I discovered bad corrosion on the right hand ECU earth lug:



This is interesting because the other car has the same problem - badly corroded right hand earth lug but the left hand one was fine. This is the earth lug that the right hand spark plug wire gets crushed down on top of due to the cover design, I wonder if the close proximity of the spark voltage causes an accumulation of dust/dirt around the terminal that triggers corrosion... or perhaps the carbon marks are from the plug lead flashing over to the terminal ?

Hard to know, but it needs a new earth terminal and new spark plug leads. Another interesting thing I noticed is that the design of the rubber boots that attach to the top of the coil pack is very different from the new replacement ones I fitted to the other car, or indeed compared to the ones that it came fitted with.

They have both a white insulator around the centre terminal that is not present on the others, and a larger much squarer boot. Has anyone seen this version before with the white insulators ?



What I'm thinking is that these are the factory original leads still fitted to the car and that the other car had ALREADY had the spark plug leads changed before I got it...

Anyway I decided to swap my original coil pack from the first car in to see if it made any difference - sadly the new(ish) coil pack I had went with the silver problem child - if I'd known it would end up in Iran I would have swapped the original coil pack back into that car and kept the new one!

I didn't check the spark plugs but they looked new and there are receipts for new plugs about 2000 miles ago so I don't think there will be anything wrong with them...I also swapped the boot on the coil at the filler cap end for another one as the boot was a bit swollen from oil contact.

I went for a drive afterwards and initially the performance seemed a lot more responsive but after a while driving it was only so so again. That's not too surprising because I've always suspected my original coil pack from the other car started to play up when it got hot.

So I'm thinking about trying to epoxy the two cracks on the top of this coil pack and put it back in until I get a chance to change the spark plug leads.

Jim - do you happen to know whether 5 minute araldite epoxy has a high breakdown voltage rating suitable for the task ? I think it does, but I can't honestly remember...

If I can find a spare eye terminal sitting around I'll replace that iffy looking ground terminal as well.

[Mandrake]

I've glued the cracks in the coil pack with supposedly fast setting epoxy but despite setting within minutes several hours later it still hasn't completely hardend, possibly due to the low temperatures out in the shed...

I've decided to leave the substitute coil pack fitted for a week anyway to see how it runs - today it seems to be running just fine using it!

That may mean both coil packs are ok (despite the cracks) and that it's something else that's intermittent like the leads...

[CitroJim]

Simon, I'm sorry to hear all is not good. You have the expertise to sort it though

Jim - do you happen to know whether 5 minute araldite epoxy has a high breakdown voltage rating suitable for the task ? I think it does, but I can't honestly remember...

Araldite is not bad stuff dielectric-wise. At DC it is a very good insulator but it does tend to fail at high RF frequencies. We found this out 35 years ago when using Araldite to repair flash-over damage in 10Kw HF transmitters. On a coil pack it'll be fine..

I've not seen an OE coil that's not cracked. Mine is.

It's not a good indicator of their goodness or otherwise but I'd certainly fill the cracks if only to keep contaminants out which may one day cause a bit of mischief..

I've seen may while insulators Simon. As you say I believe too they're the originals...

[Mandrake]

Thanks Jim.

Yes RF frequencies certain do behave strangely - they have a tendency to "burn" insulation (and fingers ) rather than arc or spark, and it's a much tougher strain on dielectric material than low frequencies...

So I got a bit impatient and swapped the epoxy repaired original coil pack back into the car today.

I had been out last night to pick someone up and although it was running well enough to begin with, after it had done about 30 minutes driving and the engine bay was head soaked the performance went flat again and it started to sound noisier/raspier under acceleration which to me suggests a misfire.

I had seen the same symptoms on the silver problem child but was never sure if it was the coil pack or not.

I swapped the original coil pack with epoxy repair back in and went for a longish drive and touch wood it's not showing any signs of the performance going flat when the engine bay heats up.

Out of curiosity I was looking on Mr Auto and noticed they have two different coil packs available - a Beru one for £139 and a Valeo one for £149:

http://www.mister-auto.co.uk/en/ignitio ... _g689.html" onclick="window.open(this.href);return false;

Given the OEM Sagem units are around £220 - £240 that's not a bad price - does anyone have any opinions on the likely quality of the Beru and Valeo replacements ?

I managed to get a NOS Sagem coil pack for only £75 a couple of years ago from a clearance house but the source of cheap Sagem units seems to have dried up now leaving the Beru as the next cheapest one still available.

I'm not that thrilled about the quality of the Sagem units - is it possible that the Valeo one could actually be better despite the cheaper price ? By all accounts the Valeo version of the ES9J4S coils are more reliable than the original Sagem type which were notorious for failing...

I'm not planning to replace the coil pack any time soon, (spark plug leads will be replaced first) but if after doing the rest of the ignition system I still have this intermittent issue and can't get to the bottom of it I might circle back around and consider the Valeo coil pack.

[CitroJim]

Beru should be OK Simon but I never realised they made coils and thought they just concentrated on the end result - the spark plug!

Barely a fag paper between them I'd have thought...

Normally Simon, the coil packs fail totally when hot bit I have known one fail and go a bit funny when hot in the manner you have seen...

[Mandrake]

My theory on failing when hot and then recovering again when cold is a dry joint on the primary feed to one of the coils inside the epoxy somewhere - the same failure mode of the coil and/or diode in the Hydractive electrovalves by the way.

So when it heats up the primary resistance goes high on only one coil - causing a weak spark to one pair of cylinders - enough to still fire the plugs at idle or a light throttle but when you put your foot down and increase cylinder pressures you get a two cylinder misfire and a large loss of power.

When you consider the primaries are only 0.5 ohms with a peak current of around 10-12 amps it wouldn't take much of a dry joint to significantly reduce the peak current and thus the peak spark voltage.

It should show up on the primary current ramp measured on a current clamp probe, but I don't have one.

[CitroJim]

Sounds like a good bit of theoretical diagnosis Simon. It's just proving it now...

Could you make up a current probe? A very low value resistor and measure the voltage drop across it to determine current perhaps?

[Mandrake]

Yeah it's just a theory. The other possibility is a shorted turn in the coil windings when it expands with heat. That too could be proven with a current clamp on the primary as the large drop in inductance from the shorted turn causes the ramp to have a much steeper than normal slope. In fact that's exactly how the pros diagnose shorted turns on an ignition coil.

I can't see it being an external insulation breakdown if it's always ok again when it cools down, I would think symptoms of insulation breakdown would be fairly independent of temperature. Once the insulation cracks or flashes through it should be permanently damaged...

Cutting into the feed wire and adding a resistor is probably not a good idea as its too invasive, I was talking about using one of the automotive Hall effect current clamps that can measure from DC to a few hundred KHz, you can get a good one that will measure from a few hundred milliamps up to about 40 amps for around £90 - they'll connect to a scope or multimeter as the need arises and clamp directly on most automotive diameter wires.

A very handy tool to have, something I've wanted for a long time and something I plan to add to my tool box eventually.

[bxzx16v]

What are the cost of the plug leads for the V6 Simon, mines still on original leads and coilpack 15yrs on.

Mark

[Mandrake]

What are the cost of the plug leads for the V6 Simon, mines still on original leads and coilpack 15yrs on.

Mark

Mr auto has the OEM plug leads for about £45 - I've bought them before from there for my previous V6. If you keep an eye open they have site wide discounts from time to time too.

http://www.mister-auto.co.uk/en/ignitio ... _g685.html" onclick="window.open(this.href);return false;

[CitroJim]

Simon, you could make up a set of test resistors on a plug and socket arrangement that goes in series and thus saves cutting the originals which I agree is not a good thing to do down there...

[bxzx16v]

Thanks Simon I'll check that out.

Mark

[lexi]

My mk1 had the cracks on coil packs too. Didn't affect running although I sealed them with the clear epoxy anyway.

[Mandrake]

Simon, you could make up a set of test resistors on a plug and socket arrangement that goes in series and thus saves cutting the originals which I agree is not a good thing to do down there...

I did think about that when I was troubleshooting the problem child but I was unable to track down any suitable plugs and sockets at the time...

By invasive I also mean that by adding resistance (including an extra couple of plugs/sockets) you're changing the operating conditions of the ignition system - even 0.1 ohms would have a significant effect on the spark voltage.

The nice thing about the hall effect clamps is you can piggyback on any wire you can separate out from the bundle enough to get its jaws around, without adding any resistance or changing the circuit under test in any way.

The fact that they can even measure DC current would make it a very useful test probe for auto electrical work - imagine being able to accurately measure the current through any wire in a wiring loom without cutting it!

[Mandrake]

My mk1 had the cracks on coil packs too. Didn't affect running although I sealed them with the clear epoxy anyway.

It all depends on where the crack is I suppose. The two cracks on this one were quite wide - I'd say half a millimetre wide, and I could definitely see a shiny silver wire running at right angles to the crack down at the bottom of one of the cracks - although I'm pretty sure it's one of the primary bus bars running from the connector on the end to a coil primary not on the secondary side, so it probably wasn't doing any harm.

The car is running like a dream again tonight with the original glued coil pack back in place, lots of power, very responsive even low down and smooth/quiet when accelerating. No complaints at all tonight.

The air is very dry tonight though - any time a car runs better in very dry air I suspect secondary ignition leakage - I'm reasonably happy now that the coil pack is ok but still pretty sure the spark plug leads are iffy and explain why it's running so well in the dry air. (Since secondary ignition leakage from faulty leads increases in damp air)

When I refitted the original coil pack yesterday I also applied a very thin lick of silicone grease around the outsides of the posts on the top of the coil pack to seal between them and the rubber boots, so that may have helped a little bit too.

I'm hoping that once I replace the spark plug leads the niggly variations in performance will vanish.