Idle tip-in/throttle blip knock

[Nfsundrgrnd]

Originally Posted by Clipdat

I hear you, it feels like you're doing something bad. I replicated it again today after driving home and was able to do so with both clutch depressed and up, didn't seem to matter.

It doesn't do it every time, but it's fairly easy to replicate. Interesting how if the revs are above the ~600rpm resting idle it doesn't do it whatsoever. So if you just feather the throttle slightly and then stab it, it revs normally and sounds fine/healthy. It only hiccups/clunks/knocks or whatever when you "surprise" it with a throttle stab when it's at rest.

I checked the DI computer bolts and all three were snug. I'll have to do some datalogging with the OFT as well and see if this is a knock event. At least if it is we'll know if it's something gasoline/fueling related.

Yup we both have the exact same problem, hopefully I'll report back with some logs too either today or tmrw.

[fredzy]

Oh wow, I just happened to see this thread at a glance. My 23 does this. I figured it's just standard awful Subaru engine BS.

I noticed it right away the first day I had it, did it pretty reliably. I figured 100% the dealer filled it up with 87 and they probably did. I took it easy on the long ride home of course and filled up with 93 on the way so wasn't worried. But I have noticed it here and there since - like you said, quick stab/surprise the engine and you hear it. Not an abusive stab by any means. It's with clutch pedal depressed as it's always when I'm getting going in a hurry. Sometimes hard to say what the sound really is, but seems like it's more prone to make the noise when hot which tells me it's knock. Would love to see what logs say the car is actually doing.

[NoHaveMSG]

Originally Posted by Nfsundrgrnd

Yup we both have the exact same problem, hopefully I'll report back with some logs too either today or tmrw.

The issue with logs is they show a symptom and not the issue. It will be helpful but may not have the answer.

Originally Posted by fredzy

Oh wow, I just happened to see this thread at a glance. My 23 does this. I figured it's just standard awful Subaru engine BS.

I noticed it right away the first day I had it, did it pretty reliably. I figured 100% the dealer filled it up with 87 and they probably did. I took it easy on the long ride home of course and filled up with 93 on the way so wasn't worried. But I have noticed it here and there since - like you said, quick stab/surprise the engine and you hear it. Not an abusive stab by any means. It's with clutch pedal depressed as it's always when I'm getting going in a hurry. Sometimes hard to say what the sound really is, but seems like it's more prone to make the noise when hot which tells me it's knock. Would love to see what logs say the car is actually doing.

I can say from experience with my first gen that poor fuel does not cause this symptom. We can't pump our own gas in Oregon, and I have had attendants put 87 in multiple times. The ECU does a good job at knock correction, the IAM will usually drop out to .4-.6 depending on temperature and how hard I am driving the car and it feels super sluggish and extra slow. No odd noises though.

@Clipdat I saw you post a picture of your OFT screen. Out of curiosity what tune revision are you running? V4? I see your IAM is less then 1, what did it start out at? V4 tunes default to .7, so if it is climbing it is not detecting enough knock to pull down the IAM.

[humfrz]

Originally Posted by Tcoat

Dude If your Model A is acting up Hum is your man. If you need help calibrating the 6 pack on your 440 Magnum I can help. Otherwise you have the best crowd here already.

Well now, @Nfsundrgrnd and @Clipdat , I figure it's a fuel thing. I reckon the leather washer on the pick-up pump plunger, in the carburetor is shot. Just get a carburetor kit from JC Whitney and replace the washer. -

Wait one - where am I?

Who are YOU?

If you can't find the carburetor, slowly close the hood and take your machine into your local Bubba's garage and ask him to fix it.

Seriously, I have no idea of what is wrong with your cars, all I know is that mine don't do that -

[DarkPira7e]

I might be off base here.. but are you sure you're not just hearing the sudden induction hiccup from the throttle snapping open?

[fredzy]

Originally Posted by DarkPira7e

I might be off base here.. but are you sure you're not just hearing the sudden induction hiccup from the throttle snapping open?

Funny you mention, I was just out running errands today when I realized/remembered that induction slug is the sound that can make it hard to distinguish. (It was my second time driving the car since October.) Came back to mention it.

I get it from a stop/idle mostly but also from the around town blips for rev matching. It’s easiest to hear from a stop. I only heard it twice today, once getting going and then a really gut wrenching one sitting at a light when I blipped it just to see if it would do it definite knock, that one.

[NoHaveMSG]

Originally Posted by DarkPira7e

I might be off base here.. but are you sure you're not just hearing the sudden induction hiccup from the throttle snapping open?

That is what I am also curious about. Do we have an actual running issue or is it just another funky FA noise. I am not sensitive to such things.

[Ultramaroon]

Originally Posted by NoHaveMSG

That is what I am also curious about. Do we have an actual running issue or is it just another funky FA noise. I am not sensitive to such things.

Also just occurred to me that I removed the stupid kazoo on my second day of ownership. Could that be in play here?

I've never heard a knock stabbing the throttle from idle but I've always had a horrendous tip-in knock when resuming from a long period of fuel cut / zero throttle, for example, coasting on a long downhill at highway speed. I've learned to ease onto the gas to prevent it.

[Clipdat]

Originally Posted by NoHaveMSG

@Clipdat I saw you post a picture of your OFT screen. Out of curiosity what tune revision are you running? V4? I see your IAM is less then 1, what did it start out at? V4 tunes default to .7, so if it is climbing it is not detecting enough knock to pull down the IAM.

The car is currently on the stock tune.

[Nfsundrgrnd]

Originally Posted by DarkPira7e

I might be off base here.. but are you sure you're not just hearing the sudden induction hiccup from the throttle snapping open?

It's definitely knock unfortunately. My last motor threw a rod bearing and it's the same knock sound but very brief. Also it's much louder than the induction noise.

It's very much looking like the car isn't getting fuel fast enough to keep up with the throttle snapping open so it leans out for a split second and knocks. Maybe my injectors are a little clogged or something but the issue seems very much like a lean condition on the throttle blip. Once the injectors are kicked in with a bit of revs you can jab the throttle as hard as you want and it won't knock, even at 1k rpm. With how common this issue seems I'm surprised there's not much answers out there.

Won't have a data log or video today, but I'm curious to see what the AFR's are gonna look like when I do get the logs done.

[Clipdat]

Originally Posted by DarkPira7e

I might be off base here.. but are you sure you're not just hearing the sudden induction hiccup from the throttle snapping open?

You mean that suction/induction noise that you can hear from the air intake/throttle? It's not that.

Originally Posted by Ultramaroon

Also just occurred to me that I removed the stupid kazoo on my second day of ownership. Could that be in play here?

Are you talking about the noise generator piping bs? I'm running the Perrin silicon inlet, so no more noise generator.

[Clipdat]

Originally Posted by Nfsundrgrnd

It's definitely knock unfortunately. My last motor threw a rod bearing and it's the same knock sound but very brief. Also it's much louder than the induction noise.

It's very much looking like the car isn't getting fuel fast enough to keep up with the throttle snapping open so it leans out for a split second and knocks. Maybe my injectors are a little clogged or something but the issue seems very much like a lean condition on the throttle blip. Once the injectors are kicked in with a bit of revs you can jab the throttle as hard as you want and it won't knock, even at 1k rpm. With how common this issue seems I'm surprised there's not much answers out there.

Won't have a data log or video today, but I'm curious to see what the AFR's are gonna look like when I do get the logs done.

Great description. I also picked up a bottle of Chevron Techron concentrate fuel system cleaner the other day when I bought the MAF cleaner spray. Planning on using it at next fuel up.

But yeah the car/engine seems to be running fine aside from this. Pulls hard and seems to be making the normal amount of power. Plenty of regular tractor-like noises and clicking/ticking coming from the engine as well, which by FA20 standards is a-ok normal. I can really hear all these lovely engine noises now after putting on this quiet axleback. Previously the crazy boom and resonance of the old muffler just completely drowned out the engine noises almost entirely.

[Nfsundrgrnd]

Originally Posted by Ultramaroon

Also just occurred to me that I removed the stupid kazoo on my second day of ownership. Could that be in play here?

I actually have no idea if it's still on my car haha, but I'm 95% sure it's knock since it's the same sound as when I threw a rod bearing but very brief.

My best guess is fuel delivery issues but I'd need to check my AFR's to be sure. Runs like a champ other than the Idle Knock noise. Not sure where I would start when it comes to diagnosing the source.

[Clipdat]

Originally Posted by humfrz

Well now, @Nfsundrgrnd and @Clipdat , I figure it's a fuel thing. I reckon the leather washer on the pick-up pump plunger, in the carburetor is shot. Just get a carburetor kit from JC Whitney and replace the washer. -

Wait one - where am I?

Who are YOU?

If you can't find the carburetor, slowly close the hood and take your machine into your local Bubba's garage and ask him to fix it.

Seriously, I have no idea of what is wrong with your cars, all I know is that mine don't do that -

I love your senior moments lol