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Discussion Starter #1
Spark plugs! I'm not wanting to start an argument but wondering about changing plugs:

Just checked the plugs in my 99 9-3 B204i and expected NGKs but found Bosch Super 4s. Should I change them and what difference might I notice? The Bosch plugs are 4 electrode variety, clean but larger gap than I expected (I believe i should use NGK BCP5EV with a 0.6-0.7mm gap, these are more like 0.8-0.9mm)

Any thoughts welcome.

Just to add, she's always run well just feels underpowered a little.
 

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Spark plug choice for the NA models isn't as critical as the turbo cousins. The owners manual should have the exact ones to use and correct gap. I know in the US the correct ones are available at the dealer only, but there are a few alternatives that are very close.

If you are having a subtle performance issue, I wouldn't hesitate to change the plugs, its cheap and easy, maybe a good time to change the cap and rotor too.
 

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Yes, check the cap and rotor as well. I would say that if there are no obvious misfires at idle or other engine speeds, the ignition is not the problem. However getting the properly gapped plugs will at least reduce strain on the coil and wires, since less voltage will be needed to jump the gap.

The 234i uses NGK BCP6EV. Interesting that if the 204i used BCP5EV it's a hotter plug. Do you know what the compression ratio of the 204i is?
 

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Discussion Starter #5
Thanks for the thoughts guys. Much appreciated.
I did have a "failure to fire" problem a few months back which my garage finally found to be the CPS but not before replacing distributor cap, rotor arm and distributor itself! Im not convinced the distributor needed changing (worked fine one day then no spark next morning) so I'm looking after the car myself now.

So the cap and rotor arm has been changed 1kmiles ago, and I'll get some new plugs when I have a chance.
 

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The B204i is listed at 10.1:1, I've seen both 10.0:1 and 10.5:1 for the B234i though.
All the owner's manuals I've seen for the NG900 say 10.5:1.

So the cap and rotor arm has been changed 1kmiles ago, and I'll get some new plugs when I have a chance.
You may still want to pull the cap and see the state of the rotor and the interior of the cap. There shouldn't be any burn marks around the terminals on the inside of the cap. Also check for oil inside the distributor cap. Did you get to keep your old, working distributor?
 

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The Wikipedia H engine page has two listings for the B234i same HP/TQ but different compression ratios listed.
I wonder if one of those was the DIC-equipped non-turbo 2.3 that I have seen mentioned in some early '90s 9000 brochures (but never in person).
 

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Just my experience...I have used the Bosch plus fours in both my 95 Saab 900SE with V-6 and my 99 Saab 9-3 SE, but found NGK's seem to provide better performance overall. I have become a NGK believer and also use them in my wife's BMW 740i
 

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Discussion Starter #10
You may still want to pull the cap and see the state of the rotor and the interior of the cap. There shouldn't be any burn marks around the terminals on the inside of the cap. Also check for oil inside the distributor cap. Did you get to keep your old, working distributor?
No I didn't get the old parts. odd because they do usually save them for me to see what they've used.
I'll check the cap when next inside the car.

And I think I'll get some NGKs when next shopping for parts. Can't hurt!
 

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Discussion Starter #11
Taken a look at the distributor cap and it seems to be more worn at one side With sooty deposits. Cleaned it for now but will fit a new cap and arm.
 

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Taken a look at the distributor cap and it seems to be more worn at one side With sooty deposits. Cleaned it for now but will fit a new cap and arm.
Hmm, that's not so good. Isn't it only a few months old....or did they reuse the old cap/rotor? Take a look if the black areas are systematically offset in one direction or another. That might indicate incorrect ignition timing (firing too early or too late will happen when the rotor is well offset from the terminal post).

The Saab maintenance programme says nothing about replacing cap or rotor that I've seen. Miraculously for something can can see a hundred sparks a minute (at 3000 RPM), the cap and rotor ought to last 50,000 km or more without undue wear.
 

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Could well be, not sure of the reason for the added expense of coil on plug ignition with no performance benefit, but this is Saab after all, things don't have to make sense.
No benefit?

One of the many compromises with a mechanical/contact ignition (besides its inherent imprecision due its mechanical nature and that fact that the points wear and the cap can collect moisture and crud, all of which make it even less precise and reliable) is the fact that the conventional single coil's available saturation time decreases as engine speed increases. As a result, the induced voltage will be decreased and the coils HT output reduced accordingly.

The constant energy, or available voltage produced by the coil remains stable and constant with C.O.P. ignition. So, regardless of engine speed, the coil voltage will remain constant as opposed to that of mechanical/contact ignition systems where an increase in engine speed means the contacts are closed for a shorter time period. The saturation time of an individual coil in a C.O.P. system remains constant as fixed by the ECU regardless of the engine speed. Most importantly, from a "performance" standpoint, the saturation time is considerably lower than that of a mechanical/contact system because the coils supply voltage is approximately double that of a ballasted contact system, and the individual coils' primary resistances are approximately halved as compared to that of the large single coil found in the conventional distributor system. This results in a substantially higher current saturating the coil with an amperage that is simply not possible on a contact system (lest you burn the points up).

All of those factors drove the industry forward in search of a better mousetrap, from the early electronic HEI systems to the current (pun intended) most modern flag bearer, the C.O.P. systems that are becoming more ubiquitous as each day passes.
 

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Well I said performance, I guess I worded it wrongly. I should have said I would have thought a change like that would have resulted in different HP/TQ/performance figures, if albeit minimal and if it didn't while there is a benefit (like you mentioned) I'm not sure it would have out-weighed the cost of having a completely different setup on the same engine.
 
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