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Old 12-30-2012, 06:37 PM   #1
hybrid gti 2
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Default Rod knock

So my mom has an ej251 rebuilt by outfront motorsports. It has a unusual sound under a load. Only on acceleration. I'm thinking it's rod knock. So i need your guys help to determine this sound.

Thanx in advance
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Old 12-30-2012, 09:07 PM   #2
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Wouldn't a rod knock happen all the time? Not just under acceleration. As this problem seems to be mostly above 3500 rpm.
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Old 12-30-2012, 09:37 PM   #3
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What spec is the engine built to? If the compression was ratio was brought up you probably aren't using a high enough octane fuel and are experiencing preignition, otherwise known as knock (fuel knock).
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Old 12-30-2012, 10:03 PM   #4
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Quote:
Originally Posted by d3d9 View Post
What spec is the engine built to? If the compression was ratio was brought up you probably aren't using a high enough octane fuel and are experiencing preignition, otherwise known as knock (fuel knock).


OP you need to upload a video. Better yet, why don't you call Outfront and talk to them?
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Old 01-02-2013, 07:02 AM   #5
hybrid gti 2
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I have no experience with rod knock. So don't get all crazy on me now. This is why I'm asking you guys. This isn't rod knock if it's just on acceleration? It's more like a need for higher octane? Been a long time since I had delt with such problems. I will try different fuel, I guess. Only reason I mention outfront is due to rumors that it's not uncommon to have this happen with there motors. No idea on the compression it's mostly stock parts. Oem spec rebuilt ej251. Sti head gaskets. Arp head studs. Single large port heads. Then port and polished throttle body, through the heads. To a modified y pipe on the factory exhaust.
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Old 01-02-2013, 12:59 PM   #6
Dentedsubie
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Maybe lifter noise
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Old 01-02-2013, 10:39 PM   #7
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Who tuned it?
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Old 01-03-2013, 12:32 AM   #8
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Rod knock usually occurs between 2500-4000 rpm. You should be able to tell if it's a mechanical rod knock vs the fuel knock mentioned above which is also a possibility.

If you can't tell the difference fill the car with super and see what happens.

Depending on when the rebuild was done if it is a rod I would pursue the builder.
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Old 01-03-2013, 07:25 AM   #9
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Knock, as in preignition, has a "tinny" sound under load. Some say, "It sounds like a billion ping-pong balls bouncing inside a steel drum". You should get a CEL for this & power will dip as timing is pulled.

Knock, as in a bad bearing, can be louder at higher loads. It also is a duller sound in the engine. Engine temperature can also affect the sound, colder will have thicker oil and a little less noise.
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