Strange sound during VTEC engagement -> RESOLUTION in post #40 - Page 5

Cloud9 · 04-04-2007, 08:30 PM

this is good to know

devore · 04-04-2007, 10:32 PM

Just to add my own experience with the same problem:

My 06 MT is up to about 16K mi. I first started hearing this noise in the fall of last year after I had owned the car for a few months. At first it didn't happen all the time, but over the winter, it seems to happen almost continuously. There are still some times it does not happen, though.

I've had the dealer look at it on 4 separate ocassions, each time took it out with a technician and had them hear (and agree they heard) the noise. The first two times, they inspected everything and told me it all looked fine, and I didn't want them to drop the exhaust when the car was still pristine so I didn't ask them to try "fixing" it.

The third and fourth time I actually brought in PsyDoc's printout. They looked at the part, looked at my car, dropped the exhaust and agreed that what's going on is that under higher pressures, the pipe pushes down into the doughnut/gasket and rattles around because of how the parts come together there. (I realize this is a somewhat vague description, it was months ago and I have forgot some of the exact detail.) They agreed it didn't seem like it should make this noise but also said it didn't look like it was resulting in any problems. I got the impression it's sort of the purpose of that part to absorb this pushing.

On the fourth time they were all ready to fix the issue with that other part and were seeking approval from Acura to cover it under warranty. Acura came back and said they would not authorize it. Dealer was very apologetic, agreed they heard the noise, but couldn't fix it under warranty. They said again they don't think it's affecting the performance of the car (and I don't think so either) so I let it go and just stopped trying to fix it.

I'm not sure why some people seem not to hear it. I think it has a lot to do with the weather - temperature and humidity. That sounds a little crazy but I swear it's worse when things are wet, and when they're cold. On drier and warmer days, I don't hear it as much and sometimes not at all. I'm very curious to see if it goes away during the hot part of the summer.

Because the whole VTEC thing is one reason I bought the car and one of the things I really like about it, it's definitely a real gripe about a car I otherwise love almost completely. It's just that it sounds so *mean* above 6K rpm when it's not rattling, but so impotent when it does rattle.

You really can't hear it with the windows down, BTW.

PsyDoc · 04-04-2007, 11:51 PM

There are somethings that are just 'idiosyncracies' of our car. Too bad it happens in the 06's though as I thought the sound was sequela only to 04-05's. Yeah, other than that and the creaking clutch pedal, I love the car

BigBen · 04-05-2007, 05:20 PM

I just had my clutch pedal replaced so that clicking would go away in the pedal. It was driving me crazy!

gmchu · 04-06-2007, 09:38 AM

It happens on and off with my 07. I don't think it is really a big deal though. I will see if it continues to happen after I get my first oil change.

cryo · 04-06-2007, 02:49 PM

if that's the cause, how come you don't hear it anymore when you turn down the heating to "Lo" setting? I've tested it and it works: no sound when heating is on "Lo"...

My second Accord (2006) has this problem; my 2005 didn't have it.

devore · 04-06-2007, 04:17 PM

You're saying that if I set the temperature in my car to "Lo", I won't hear the rattling noise during VTEC engagement? I'll try that, but it doesn't make much sense. Does the A/C need to be off or on? Do you need to select any particular vent configuration?

cryo · 04-06-2007, 05:02 PM

Try it. I heard somewhere a theory (I think also on this forum), that it's because of some air in the coolant fluid. When the coolant passes through the radiator core at high rpm, the air bubbles "cavitate", producing that noise. When you turn the heating to "Lo", there is some valve that shuts, preventing the coolant from going through the radiator core, therefore the noise disappears.

Don't know if the explanation is true or not, but the "fix" works as a charm in my case.

P.S. Tried with A/C off, no special vent configuration... I'll try it also with A/C on...

devore · 04-06-2007, 05:33 PM

Interesting. I will defininitely give that a try tonight on the way home from work. Thanks for the suggestion!

PsyDoc · 04-07-2007, 12:21 AM

By the way, the creaking clutch pedal turned out to be a bad master clutch cylinder. 2nd time I am having this replaced....... Honda quality....go figure.

devore · 04-08-2007, 12:03 AM

cryo - that totally worked!

It's about 32* up here. With the temp set to "lo" I rev it up and it sounds perfect, no weird noises, just loud and mean, like it should. With the temp set to 72*, I rev it up and hear the weird noise I've heard all winter. I even heard the noise come on as I turned up the temperate from "lo" at high revs. You can also set it to "lo", then hit the "off" button and it's still noise-free. Maybe it only happens when the temperature you set in the car is higher than the ambient outside temperature (meaning the car needs to heat the air.)

I was pretty amazed and happy. I don't know if this would work for everyone but for me it definitely does.

If it is indeed caviatation, it looks like it might be harmful. It's enough to make me avoid revving my TSX high if I'm running the heater. Whether or not it actually is, the noise sounds harmful...

cryo · 04-08-2007, 03:31 AM

PsyDoc, maybe you can show this to the dealer?

I wonder if there's a (simple) way to remove these bubbles, if this is indeed the cause. I heard some "techniques" (alternating different revving regimes on the highway), but they seem voodoo to me.

P.S. Just a small note, here the cavitation does not take place in the engine, it seems to happen in the heater core....

PsyDoc · 04-08-2007, 09:12 PM

Cryo, I'll be damned! You method totally worked.....I heard nothing when turned down to Lo. However, I turned it up and nothing as well. I had the air turned off. Either way, I will continue to try this. If it is repeatable I will go with this information to the dealer. Jesse, the service manager will definately look into it. They will be replacing the CMS this week. If it is cavitation in the heater core, there must be a way of bleeding this off. Lets ask Noel.....Thanks for the info.

devore · 04-09-2007, 05:41 PM

If it is cavitation caused by the water pump operating at high speed (under high RPMs) then simply bleeding off the bubbles won't do anything, because there aren't any bubbles to bleed off.

Cavitation is the formation and subsqeuent collapse of voids/bubbles in the liquid. The water flowing around the propeller spnning at high speeds creates low pressure. When the pressure is low enough, the water vaporizes and creates a void. It then subsequently collapses, producing a mini shock wave, and the noise you hear. There are no permanent bubbles created.

I think to prevent this problem you'd need to either redesign the water pump impeller so it doesn't produce cavitation, OR redesign the water pump so it doesn't spin fast enough to produce cavitation.

I'm due for a service visit so I'm going to ask the Acura folks about this again with the new info and see what they say.

PsyDoc · 04-09-2007, 09:25 PM

Good point on the cavitation. The bubbles aren't created until the pump is spinning and disappear once off VTEC.

Anyway, I tried this again four more times and without fail it worked. Air at 75, up to VTEC, buzzing sound heard, then air set to LO, up to VTEC, and no sound. I tried several variants on this and it is a reliable finding. Good going Devore. Now to see why some have this and some don't and to determine if this condition could be fixed or even damaging in any way to the water pump itself.