Knocking at WOT - lowering boost - The Saab Link Forums

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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 10-26-2012, 10:23 PM   #1
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Knocking at WOT - lowering boost

Hello,

I have a problem with my 9-3 99 maptun st 4.
TD04HL-15T, crossflow IC, 3" dp etc etc.

It's been working fine for half a year now, but recently when I picked it up from repainting the hood and the first WOT I did, I noticed my knock-LED started flashing alot and boost was lowered to 0,9 bar by Trionic. Should be 1,35 bar.

Last weekend I tried replacing the fuel pump, because the old one had some weird sounds. Didn't help tho.

The weird thing is, some WOT:s it works just fine, almost no knocks at all. But next WOT it could be horrible.

Please help me, I don't wanna destroy my T5 engine =)

Any guesses?


Last edited by olof.a; 10-26-2012 at 10:26 PM.
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Old 10-27-2012, 05:22 AM   #2
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What are the chances they did you a favor and put 87 in the tank? (did you mark the miles before/after?)
Take the MAF/filter apart and clean it. with painting, there's LOTS of dust.
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Old 10-27-2012, 06:08 AM   #3
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T5!
what you just recommended doesnt apply to T5
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Old 10-27-2012, 06:41 AM   #4
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Im 100% sure there's the correct fuel in the tank (RON98 here in Sweden). I've also refilled the tank about 3-4 times without any changes, since I drive alot, and live pretty far from my work.

The first thing I did was cleaning the airfilter, that was also my first guess. Not much of a dust in it, and didn't help.

I have a feeling this is gonna be a hard nut to crack!
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Old 10-27-2012, 08:27 AM   #5
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Did you change the fuel filter when you did the pump? I tend to think they are not all that prone to clogging, but it would be a cheap easy thing to try.
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Old 10-27-2012, 10:01 AM   #6
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I did not, I changed it 18000 miles ago tho, to a new Bosch one.
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Old 10-27-2012, 12:16 PM   #7
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fuel filters can really make a difference,, if you can get a scan tool on it, you should see if the knock is happening on all cylenders, or just one,, if its a single cyl issue i would check out your fuel injectors, and maybe plugs, if its a multi cyl issue that its probably something more severe.
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Old 10-28-2012, 10:49 AM   #8
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fuel filters can really make a difference,, if you can get a scan tool on it, you should see if the knock is happening on all cylenders, or just one,, if its a single cyl issue i would check out your fuel injectors, and maybe plugs, if its a multi cyl issue that its probably something more severe.
Has the weather changed as of late? Colder? Hotter? How many miles on the plugs? Do you have live-logging capability or just a knock LED? If you have the former then you can see what cell at what load and MAP T5 is getting hiccups. From there we can also make inferences. Did you check your intake piping? If the turbo is starting to go it can spit oil into the intake manifold which causes knocking because of low octane of oil.
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Old 10-31-2012, 05:09 PM   #9
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My car (99 9-3 stg 4) misses (knock)? At 23 psi. I changed the di and it worked great for about 5 months and it slowly came back. I just changed my plugs the other day and I gapped the plugs to .34-.35 instead of the . 39-.40 they were. Works like a champ runnin 23-26psi no problem now.....ehh ya I don't know where I was goin with that. Good luck though.
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Old 10-31-2012, 06:01 PM   #10
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Start with new NGK plugs, go from there.
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