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What Causes an Overboost Condition?


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Plugs are tight.

Only way its an exhaust valve is if its stuck closed. If its open or not seated properly, I don't think it would cause the overboost problem.

You mentioned fuel additives are bad for superchargers, they eat seals, well superchargers never see fuel only air. That point is invalid.

I've had 0300 codes off and on since I got the car new, meaning the cats have seen alot of raw fuel, and heat, and could very well be damaged.

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I just toked but I don't think you got a single bit of advice yet and I'm cracking up at your responses. You know your shit.

I don't know the year of your car but how modified is it? Are the specs in your profile accurate?

I bet a fiver it's your cat.

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Plugs are tight.

Only way its an exhaust valve is if its stuck closed. If its open or not seated properly, I don't think it would cause the overboost problem.

You mentioned fuel additives are bad for superchargers, they eat seals, well superchargers never see fuel only air. That point is invalid.

I've had 0300 codes off and on since I got the car new, meaning the cats have seen alot of raw fuel, and heat, and could very well be damaged.

Umm, most of the time on street cars, and 100% of the time on race cars, it is a benefit to introduce a small amount of fuel before the supercharger, but only on a screw or roots. It helps cool the the rotors/screws, and usually makes significantly more power. I assumed it was done in this instance...

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The more I though on it, you might have broken a follower. Dropping a cylinder will make the exhaust note deeper, change rhythm, and flash the CEL.

And btw, it takes 5min to check if it's a cat. If it has seen that much raw fuel to cause that to happen, you need to rethink tuning it yourself if that is the case. No offense intended, but it is MUCH more involved than people think. If you don't do it on a chassis dyno everytime, fuggitaboutit. You'll hurt something.

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"MY" supercharger "NEVER" sees fuel.

I appreciate you trying to help out, but I you're a little off base in regards to my car. The S/C is a Kenne Bell twin screw, basically a bolt on setup. Its not near a race car. And it has been on the dyno many times, we can never see anything on the dyno sheets or while data logging to explain the misfire codes. Car has run fine up until this problem.

Only one thing causes a belt driven supercharger to overboost, and that is a backup of pressure. Cat makes sense. If you can name anything else, specifically, that causes overboost, please post it.

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Check your followers, make sure one hasn't broken or jumped. Make sure a cam lobe isn't worn flat (unlikely). Roatate the engine by hand and look at every valve stem and spring. Make sure you boost sensor is tight, as some are referenced to outside pressure, and if it is loose, air can be drawn past it and the reference end will see lower pressure (fast air = lower pressure), and then when the boost pulse reaches it, it could seal for a millisecond, causing a high reading due to it not being able to keep up with the oscillation of boost. (VERY unlikely, only have seen that once).

Checking the cats should take 5min, just unbolt the exhaust, reset the ecu, and drive a little bit. If it throws a code, it should only be O2 sensors. That will be the best place to start the process of elimination.

I'm not super familiar with that particular blower, does it have an internal throttle style bypass? Where is the boost sensor located?

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