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  #1  
Old 7th August 2012
Superaero Superaero is offline
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Default Spark plug gap

I think I've changed my mind about proper spark plug gap for these engines.

I used to use 0.89 mm gap, thinking this worked better than the standard 1.0 mm supplied by NGK ( maybe 1.1 mm?).

I now think my preference for the smaller gap resulted from the engine adapting to that gap. I put in a new set of NGK platinums PHRF611 and forgot to re-gap them down to my preferred 0.89mm gap.

Initially, I noted rougher idle and less power, at least it seemed so.

However, now a few weeks later my engine is running really well again. I suspect I needed to wait for the ECU to adapt to the fresh plugs at the wider gap.
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  #2  
Old 7th August 2012
Twinsen Twinsen is offline
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Interesting. Maybe the smaller gap increased the knock sensing current causing timing loss. On the other hand, a larger gap may stress the drive circuitry more. Did you have a knock LED installed?
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  #3  
Old 7th August 2012
Superaero Superaero is offline
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Nope, just my butt on the seat. Also, the boost gauge is pretty informative as long as you realize it shows relative boost, not actual (which is why SAAB wisely put no numbers on the scale). I have an aftermarket boost gauge on my Audi S4 with actual numbers on the gauge face, which shows minus 3psi with the engine switched off! I live at 3,000 ft elevation so an uncalibrated boost gauge should show negative pressure at atmospheric.

I was intrigued by the idea that the ECU takes some time to change the adaptation after new plugs are installed. Previously I was convinced that the smaller gap was superior. Now I am not so sure.
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Old 15th August 2012
spadar spadar is offline
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Default spark

hi.wasn't there something like-- "plugs open, points close" -- that is going back to prior to computer/electronic ignition.
i used to always set the plugs to the narrowest setting and the points to the widest pre-saab.
now at 30-40k when i replace the plugs in the '88 and the '94 i go with the ngk settings.
has anyone a circuit to connect an obd1 socket(10 pin) to and obd2(16 pin) connector.i am now the proud owner of a tech2. love that car.cheers
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Old 15th August 2012
Superaero Superaero is offline
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For maximum spark energy you needed a fully charged coil ( points as closed as possible) and the widest spark plug gap that would consistently fire under all operating conditions. That way the coil would discharge at the latest possible moment producing the highest voltage spark.

With direct ignition things are not so simple. The electronic capacitive discharge can produce a hot enough spark under all conditions. The issue is whether the spark will have sufficient time to fire at the correct timing.

Dual plugs have been used in some emission controlled engines to ensure the sparks have enough time to completely combust the mixture. DI systems use very high voltages to achieve reliable sparks in sufficient time over wide plug gaps.

Too wide a gap can cause misfire under high rpm or high cylinder pressures. This is why I thought mine needed 0.89 instead of 1.1. My jury is still out on this issue. The engine makes great power but stumbles a bit, odd since a too wide gap should have the opposite effects I should've thought.
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Old 15th August 2012
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  1. Check the electrode gap
The spark plug electrode gap is extremely important for proper engine performance.
The spark plug gap should be 1.0+0.1 - 0.0 mm

Too wide a gap will cause misfiring under full load conditions.

Too small a gap will result in lumpy idling and hesitant running under light load conditions.


The above is from Saab's service manual.
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Old 15th August 2012
spadar spadar is offline
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Default spark

hi. this is one of those grey areas where no one is wrong as there is theory and practice and we could go on ad infinitum. my hypothesis of "plugs open, points close" is from the times when all petrol vehicles used points in the distributor. the advent of cdi and other electronic ignition systems changed all that dramatically. on the points system ,as we know, when the fibre/plastic on the points wore down then with the wider setting an optimum situation was reached but that was dependent on the points themsleves not burning and the plugs at optimum and the timimg spot on.how many times have i timed using the timing light and not been right as the harmonic balancer had flutter.how many times have i statically timed an engine and that has been perfect? today once the timing is right the only variable we have control on is the plug gap. btw i too have tried the smaller gap in my "88T and not been satisfied. with the '94 aero, i check the gap is 1.1 from the box and let the computer work it all out. another variable now that we don't have a lot of control over is the O2 sensor-wow another can of worms.no wonder we are getting greyer and greyer, let the old blokes worry about it and lets enjoy life. love that car. cheers
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Old 15th August 2012
Superaero Superaero is offline
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I posted this thread because I had previously been convinced that the best gap was 0.89 mm, and the correct specification of NGK platinum plugs for my car actually came pre-gapped from NGK at that gap, as well as a version pre-gapped at 1.1 mm.

Now I have slipped in a fresh set of PHRF6 11 NGK platinums without closing the gap down to 0.89 mm( forgetting to do so) so they are at NGK 's pre-gapped setting of 1.1 mm, and after a few days (which I think resulted in ECU adaptation) the engine is now performing very well.

So, I am now pretty sure I have been incorrect that the 0.89 mm gap works better. It does work but I am starting to think the factory spec of 1.0 to 1.1 mm is best.

I will confirm after a few weeks of driving with this set of plugs. Add to our database if you will.
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Old 20th August 2012
spadar spadar is offline
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Default spark plug

hi superaero.you can get a tech2 from uobd.com or greebig.com for around $US479.99 to $US499.99 (+ shipping) including the saab 10pin connector/adapter. bought mine from greebig.com with the saab info card. someone has the tech2 for $US421.99 but it doesn't appear to have the 10pin connector/adapter.they are chinese but then how many things are made in chikna these days-even if stamped "made in usa".i'm trying to get the 16pin obd2 connector connected to the 10pin so i can use any obd scanner including my tech2 and maxiscan ms509 and the IScancar OBDII EOBD Cars Trouble Codes Scanner $US55.99 free shipping which is coming.the maxiscan and iscancar do not have the saab 10pin connector/adapter--only the obd2 connector. love that car.cheers
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