What's making my motor knock? - Saab Performance Bulletin Board - Saabnet.com
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What's making my motor knock?
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Posted by gorper (more from gorper) on Thu, 20 Nov 2003 18:33:40 Share Post by Email
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Trying to chase down a knock problem; '89 900T (LH2.4), self-tweak APC('red box' spec), 3 bar FPR, DIY timing mod (20* static --> 12* full ret.).

Recent trip to dyno showed almost 17:1 A/F, with severe knocking.

Car boosts fine to 12psi; anything above it and I get *lots* of audible knock.

- Fuel pressure is good @ idle (~40) and @ full throttle (~60); rises quickly with boost
- Confirmed timing retards as it should to 12*; capsule holds vacuum/pressure
- Injectors professionally cleaned less than 10k miles ago
- Swapped out AMM with known-good unit
- Plugs show lean (bit white-ish) but are all similarly colored, so I don't think it's one injector
- NTC resistance @ ~315 Ohms, engine warm, having sat turned off for 20 min. I believe this is in spec.
- Ground wires all over the place were cleaned recently.
- O2 swings 0.1 to 0.8v nicely, quickly; 0.8v at the orange/red line (for me, that's 12 psi).
- Driveability is otherwise good.

Prior to this, I could run the redbox spec just fine, even running deep into red in cold wet weather.

Motor was out of the car in September (not by me).

I haven't checked injector pulsewidth yet - is it possible for an ECU to squirt out abbreviated pulses?. Other than ECU problems, what else should I be looking for?

posted by 216.160.93...

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