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Discussion Starter · #1 ·
I thought I'd pass on a bit of info from the 9.3 site, given by /John.

Apparently the DI unit POLARIZES the plugs so if you take them out to check the gaps, you've got to put them back in the same holes.

Well worth knowing, thanks John!
 

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But wont polarisation vanish when the power is removed?

I can understand that the DI cart / ECU will profile each coil to the plug in it so it makes sense to ensure that the plug goes back in the same hole as it came out of.

Steve
 

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StephenA, why not swap your plugs about and report back?

I am afraid I am layman in this respect - but when a Saab technician gives me a piece of advice to save me taking my car back next week for a new DI cassette, then I tend to listen to him and his experience.
 

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/john - it just seems odd that no-one seems to have mentioned this before.

If "polarised" plugs put in different cylinders than they were in before can ruin a DI cart then I wonder what tjhe implications are of putting a New DI cart onto an old set of plugs.. or an old cart onto New plugs.... still as mine is up for a 100K service and is still on its orginal DI cart I guess I may well find out soon enough


Steve
 

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Originally posted by StephenA:
[qb]/john - it just seems odd that no-one seems to have mentioned this before.[/qb][/b]
I think that there is an awful lot that we still do not know - so I do not think that it is necessarily unusual. Let's face it - people still ask if they can use non-NGK plugs and we give them the same answers everytime

Originally posted by StephenA:
[qb]If "polarised" plugs put in different cylinders than they were in before can ruin a DI cart then I wonder what tjhe implications are of putting a New DI cart onto an old set of plugs.. or an old cart onto New plugs.... still as mine is up for a 100K service and is still on its orginal DI cart I guess I may well find out soon enough    :eek:  
[/qb][/b]
Steve, I fear your are making a bit of an assumption here. I was not told that changing plugs around would "ruin" a DI cassette. I was told that the DI is senstive to changes such as a change of plug spec or changing the plugs around in the cylinders. This might not necessarily cause a failure, though the advice to be followed is replace plugs of the same type and do not swap existing plugs between cylinders.

Like I said, I am a layman on this - so I am just passing on info that I was told by a Saab tech.
 

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Discussion Starter · #6 ·
If the Saab techie is correct, following his advice could help the DI last longer.

If he's wrong,following his advice will cost nothing and do no harm.

Unless any auto electrician out there can advise differently, I'll do as he says - I can't afford a new DI
 

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Hmm... polarising spark plugs? I'm not sure I understand the phsyical mechanism that would cause this- the only polarisation I can think of that can occur is due to one terminal of the spark plug being permanently at a higher potential than the other- and as the outers are all at the same potential and it's a DC ciruit I would expect the centre electrodes to therefore have the same polarisation as one another.

However... Trionic is adaptive and I can see that you might have slightly diiferent characteristics between different spark plugs after a period of wear and if you swapped them round it would have to re-adapt.
 

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Originally posted by Bubbles (fka Mark E):
[qb]the only polarisation I can think of that can occur is due to one terminal of the spark plug being permanently at a higher potential than the other[/qb][/b]
The only thing I can think of is ignition systems such as in the 2CV and some other "wasted spark" systems, where two plugs are fired from opposite ends of a double-ended coil. The 2CV service schedule recommended swapping the spark plugs between the two cylinders halfway between plug replacements. Due to the opposite polarities of the sparks, one plug would wear on the centre electrode while the other would wear on the earth electrode. Swapping them evened out the wear.

I agree that he is most likely talking about the adaptation to the individual spark plugs. Given that the system must adapt to new plugs, I don't see any long-term problem with switching the plugs around - the engine would just run less-efficiently for a while until Trionic adapted to the plugs again.
 
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