O2 dump causing knock?

[LarryJoe]

Hey my current setup is an evo 3 16g at 17psi currently. Now I've always had an issue with insane amount of knock. Like through a 3rd gear pull there could be 10 or more counts every logged second. I've tried richening the car, leaning it out, turning down the boost, nothing works. Right now I'm at 17psi with an AFR of 10.6:1 under WOT. I logged a 3rd gear pull and I had a few counts. I then logged a 4th gear pull like 20 minutes later and had massive counts of knock. Like 19 counts logged every second. So in total probably over 100 counts in one 4th gear pull. My lifters only really make noise when its cold. My only boost leak is one of the plastic caps on one of my injectors (the part that goes in the rubber insulator) is cracked. The only thing I can think of is my open dump, which is an ebay one with a short dump tube that dumps in the engine bay, is throwing the knock sensor due to the loud noise in the engine bay. Is it possible the dump tube could be causing my massive counts of knock? And I've been boosting like this for months and if it was real knock, I probably would have blown my headgasket by now. But I have no signs of head gasket damage.

 

[AngelOfPassion]

I really don't think the dump makes a sound similar enough for the sensor to think it is phantom knock... I've heard a lot of times the exhaust/heat shield is rattling but you don't really notice inside the car... maybe check all the bolts for that stuff...

 

[snowborder714]

Have you checked to see if your knock sensor is torqued down properly or if it may be leaking black goo out the back (sign of a bad sensor)?

 

[LarryJoe]

My sensor isn't leaking any black goo. And I don't have the heat shield anymore so I know it doesn't rattle. But an open dump being dumped in my bay makes a very very loud screaming noise. You don't think it could throw the knock sensor?

 

[AngelOfPassion]

I've just never seen anyone with that problem before and there are quite a few people running open pipe...

And I would think the sensor would be smarter than just picking up something that is loud. I think it would go for a specific sound like tapping or real knock. If it just picked up loud exhaust type sounds we'd all be getting phantom knock

 

[LarryJoe]

Well there was a thread on here where a guy was having knock issues like mine. He finally fixed it by extending his dump tube outside of his engine bay.

 

[snowborder714]

Then go get some flexible hose from the auto parts store, temporarily extend it out, secure with zip ties, and check your knock. Sounds like a pretty simple test to see if that's really your issue.

 

[AngelOfPassion]

I'm not saying it's impossible. I've just never seen it. Try it with a longer tube.

 

[LarryJoe]

Wouldn't it just melt the hose in no time? Plus I'd be worried about it dangling around and blowing hot exhaust all over who knows what.

 

[snowborder714]

They do make metal stuff. You can drill a hole in the very end, run a zip tie through it, and secure it and point it wherever you choose. Or just run the zip tie around the hose and whatever you're securing it to.

Yes, if your dump tube is >1' I probably wouldn't use plastic. If it's long enough, you can always try it if you can't find metal tubing. Worst that happens is you monitor it after a few pulls and see if it's starting to get soft or melt before it oozes over stuff you don't want it to.

 

[LarryJoe]

I could also throw on my stock o2 housing and see if it helps. I really think it's what is causing my knock.

 

[snowborder714]

Pick one route and test it. I'd be surprised if it is the cause though, especially with how many people run o2 dumps.

 

[DSMnoobsause]

I run a screamer pipe with no knock issues. It takes a mettal tap to trigger the knock sensor. It's not a microphone that picks up sounds. Reason most have to disable knock controll when running forged pistons. They rattle around alittle more then cast pistons.

 

[LarryJoe]

Well I'm at a loss then for my obscene amounts of knock.

 

[DSMnoobsause]

Well I'm at a loss then for my obscene amounts of knock.

I would check your crank pulley first to make sure the rubber it's seperating. And would continue to check your base timing by grounding out the pin and making sure you are at 5 deg. Also check your cam timing. I've seen one can jumps a tooth and bad knock after. He didn't notice due to having lopey cams.

 

[LarryJoe]

Yeah I'll try looking into that tomorrow.

 

[xxNocturnalxx]

But an open dump being dumped in my bay makes a very very loud screaming noise. You don't think it could throw the knock sensor?

.No.

 

[LarryJoe]

I logged some pulls today. I don't see any knock at part throttle while boosting. But as soon as my wastegate fully opens up and it starts screaming, it'll log over a 100 counts in one pulls. This is all logged using Evoscan btw.

 

[snowborder714]

I say make sure the sensor is torqued down and find a temporary extension tube and run it back past the front crossmember to get it out of the engine bay and retest.

You're providing us good data, but seem to be waiting for a definite answer of what you should do. Other cars on here run dump tubes with no excessive knock, but your car may be different. You've got to try some stuff out and report back with the results. You can also post up a log or two if you have one for us to check out.

 

[LarryJoe]

I checked my sensor. It's seems pretty tight honestly. Maybe even too tight, not sure. I have a brand new knock sensor from autozone I got awhile back that I could try throwing on but I don't have a stubby wrench big enough to even get back there to pull mine out. And as far as temporarily extending it, should I get some rubber 1" hose or see if the autoparts stores carry 1" metal flex piping? I just deleted all my logs but after I go out here in a bit I'll log a WOT pull and a part throttle pull and post it up.

 

[snowborder714]

I wouldn't get rubber. I'd see what sturdy plastic or metal piping you could find to extend it. You might be able to find something at a hardware store as well.

 

[dacowgod]

I have seen on SEVERAL occasions where open dump causes phantom knock that seems like very real knock by knock sensor feedback anyways... . get the outlet farther away from the engine and knock goes away...

My brothers car was the knock happiest car I'd ever seen..it knocked like crazy on his 2.0 and similarly on his 2.4 ...we tried everything including meth injection... and it it all boiled down to the o2 dump...one day we were just cleaning things up and built a new dump tube and he swore the car felt stronger... Went and played with the tune a bit and found we were able to remove the methanol injection from his car completely and today he runs 38 PSI on 93 pump gas on an HY35 w/o any knock at all..w/ peak timing around 14* .. ..

The "sound" of the dump may not be causing the issue, but it could also be resonating through the engine and causing the knock sensor to pick up a false reading...

I've mentioned this to several people I help tune through the years when their engines knocked way more than I would have expected..and at least 3 or 4 of them were resolved by extending the dump tube farther away from the engine..

 

[snowborder714]

Good info, Ricky. What length dump tube have you found to be too short and potentially cause knock? Or how far away from the engine (example locations maybe) would you say is safe to run to eliminate knock? I know some dump tubes offered by vendors are along 1-1.5' long, which is awfully short (other than the fact that it would dump right on the wires under the radiator on a 2g).

 

[dacowgod]

Good info, Ricky. What length dump tube have you found to be too short and potentially cause knock? Or how far away from the engine (example locations maybe) would you say is safe to run to eliminate knock? I know some dump tubes offered by vendors are along 1-1.5' long, which is awfully short (other than the fact that it would dump right on the wires under the radiator on a 2g).

That's hard to say man..it all depends on what kind of wastegate your running ...if its external off the manifold it obviously needs to be longer than if its off the o2 housing right..

What we did was just make sure the dump tube wasn't touching anything..and extended it down further towards the ground some...

I remember one guy in Alabama that I was chatting with a few monthes back actually extended his way back behind the engine bay so he eliminated any fumes that were getting sucked into the cabin as well..

I cant say what the magic distance is....My brothers car used to dump about level with the lower cross bar on the 1g... and its now about 2-3 inches below that and a little further towards the rear of the car..and his knock woes went completely away...

 

[LarryJoe]

Mines extremely short and up in the bay. And yes I feel like it would resonate a ton. If you go on ebay and search an o2 housing for our cars you will see the ones with the short open dumps. And that's what I'm running. You think I should extend it down to the middle support beam or maybe even further?