[Jb2007]

Every time I gain speed, there is a louder than usual noise coming from the either the middle of the car or the engine. The loud sputtering sound always starts exactly at 4000rpm and up. The best way to really describe the sound is that is sounds like a fast/loud misfires while driving or metal grinding. I’ve tried looking for leaks by covering my exhaust with a rag and nothing. No exhaust smell either through the vents. My mechanic plugged it into his computer and no codes. Please help!

 

[magnnum_paul]

The first thing that came to my mind was something related to the VTEC but the K20 engine has VTEC engaging at 5800 RPM. This sound only happens when the engine is engaged to the wheels via the transmission or when coasting in neutral as well?

 

[bakumar]

Every time I gain speed, there is a louder than usual noise coming from the either the middle of the car or the engine. The loud sputtering sound always starts exactly at 4000rpm and up. The best way to really describe the sound is that is sounds like a fast/loud misfires while driving or metal grinding. I’ve tried looking for leaks by covering my exhaust with a rag and nothing. No exhaust smell either through the vents. My mechanic plugged it into his computer and no codes. Please help!

First you need to identify whether the noise comes

1. Only when you are driving and in all the gears - It maybe related to the transmission and you need to check the wheel bearings, drive shaft, gearbox, steering box and the differential.

2. Even when the car is parked and revved above 4000 RPM - it maybe related just to the engine and you may need to check everything related to the engine from the ignition timing, plugs, rings, etc.

Also suggest that you check and confirm if the noise comes with the AC both on and off.

Based on your inputs we can try to narrow down the possibilities and identify the cause.

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[Jb2007]

The first thing that came to my mind was something related to the VTEC but the K20 engine has VTEC engaging at 5800 RPM. This sound only happens when the engine is engaged to the wheels via the transmission or when coasting in neutral as well?

yes, just when I’m accelerating only. I don’t even know the RPM range for VTEC on an R18.

 

[Jb2007]

First you need to identify whether the noise comes

1. Only when you are driving and in all the gears - It maybe related to the transmission and you need to check the wheel bearings, drive shaft, gearbox, steering box and the differential.

2. Even when the car is parked and revved above 4000 RPM - it maybe related just to the engine and you may need to check everything related to the engine from the ignition timing, plugs, rings, etc.

Also suggest that you check and confirm if the noise comes with the AC both on and off.

Based on your inputs we can try to narrow down the possibilities and identify the cause.

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This has happens with the AC on or off. I’ve done extensive research and all I can come up with is a possible cases of either:
Heat Shield Rattle
Cracked or Loose Header (Exhaust Leak)

I don’t smell any signs of exhaust through my vents but I feel like this is the closest culprit.

 

[magnnum_paul]

R18 VTEC has economy and normal cam, teh economy one being on between 1k-3.5k RPM and loads below 70% aprox.. Bakumar's advice is good: you want to pinpoint the system that is malfunctioning, since it only happens when accelerating and in gear it could still be the engine or the transmission since some problems occur only when the tranny has load on it. I'm affraid I can't give any more advice Keep narrowing down when and how the noise appears and that might give more clues about what it might be.

 

[bakumar]

yes, just when I’m accelerating only. I don’t even know the RPM range for VTEC on an R18.

The VTECH on R18A works for fuel economy and not for power unlike other Honda engine variants.

It works between 1200 - 3200 RPM.

Also there is no header in the R18A engine. You just get one exhaust outlet from the engine head and it leads straight to the CAT.

The R18A engine was basically developed for high fuel efficiency and low emissions rather than for power like the other Civic engines.

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[bakumar]

This has happens with the AC on or off. I’ve done extensive research and all I can come up with is a possible cases of either:
Heat Shield Rattle
Cracked or Loose Header (Exhaust Leak)

I don’t smell any signs of exhaust through my vents but I feel like this is the closest culprit.

Heat shield rattle is quite easy to find and fix and it maynot be the problem your case.

Exhaust leak due to cracked header would usually set off the O2 sensor code.

The other possibility you can check is the exhaust system. Please check if any of the weld points on the pipe gave in and the pipe is rattling against the underbody. Especially the muffler which hangs by a rubber boot.

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[Jb2007]

Heat shield rattle is quite easy to find and fix and it maynot be the problem your case.

Exhaust leak due to cracked header would usually set off the O2 sensor code.

The other possibility you can check is the exhaust system. Please check if any of the weld points on the pipe gave in and the pipe is rattling against the underbody. Especially the muffler which hangs by a rubber boot.

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We’re talking about checking the intake manifold right? Just to clarify. And thanks for the info so far!

 

[Jb2007]

R18 VTEC has economy and normal cam, teh economy one being on between 1k-3.5k RPM and loads below 70% aprox.. Bakumar's advice is good: you want to pinpoint the system that is malfunctioning, since it only happens when accelerating and in gear it could still be the engine or the transmission since some problems occur only when the tranny has load on it. I'm affraid I can't give any more advice Keep narrowing down when and how the noise appears and that might give more clues about what it might be.

Appreciate it man!

 

[bakumar]

We’re talking about checking the intake manifold right? Just to clarify. And thanks for the info so far!

Not the intake but checking the exhaust manifold. Usually we've the exhaust outlets coming out separately from each cylinder but in the R18A engine, there is only 1 exhaust outlet from the head.

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[Jb2007]

Not the intake but checking the exhaust manifold. Usually we've the exhaust outlets coming out separately from each cylinder but in the R18A engine, there is only 1 exhaust outlet from the head.

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Definitely gonna take a look when I jack my car up for a coolant change. I’ll keep you updated for the end result!

 

[stvn.00]

when you hear the sound, does it sound like pop rocks? (metal clinking when accelerating) May be pinging. Could be your knock sensor, spark plugs or your gas.

 

[Jb2007]

when you hear the sound, does it sound like pop rocks? (metal clinking when accelerating) May be pinging. Could be your knock sensor, spark plugs or your gas.

(Update) My mechanic (former Honda Tech) said he didn't really hear much. He took a half an hour drive as well. And with time, it actually went away with time. But I will be changing the spark plugs very soon. Thanks man!