98 Civic HX making weird noise when accelerating

Lydia Morris

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My 98 Civic HX (automatic) is making a weird revving sound when accelerating. The RPM'S are also going up and down by 100 while this is happening. I have some videos and am going to try and post a video of this later...

Does anyone know what I'm taking about and what the issue may be?

Thanks!

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HeX

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"Weird noise" is way too vague to make any reasonable opinion. Can you try to explain the type of noise? Is it a ticking, grinding, whining, consistent, intermittent? Is your check-engine light on? Does it do this only in neutral, when stopped, while in motion?
 


Lydia Morris

New Member
"Weird noise" is way too vague to make any reasonable opinion. Can you try to explain the type of noise? Is it a ticking, grinding, whining, consistent, intermittent? Is your check-engine light on? Does it do this only in neutral, when stopped, while in motion?
Sorry, I'm new to this whole forum thing. No clicking/grinding/whining. It only does the sound when accelerating. And mainly only when going up hill or even slightly uphill. It doesn't do the sound when driving on a flat road or downhill. I'm going to try and upload a video.


(Also, ignore the SRS light. I know about it and know that I need to get the clock spring replaced.)

And no, the check engine light is not on. Car feels fine when driving it, even when it's doing this thing. No smoke or smell from the hood.

My mechanic buddy says he really thinks it's the IACV...but I wanted some more opinions..

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mc360

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From the video it sounds kind of like rocks or something going through the motor, does it sound like this to you in person? I had a similar sound when my catalytic converter was plugged. How many miles are on the car and does it seem to be under powered more than normal?
 

Lydia Morris

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From the video it sounds kind of like rocks or something going through the motor, does it sound like this to you in person? I had a similar sound when my catalytic converter was plugged. How many miles are on the car and does it seem to be under powered more than normal?
Sometimes I feel like it takes a little bit longer to actually accelerate, while the RPM is going up. And sorry, I'm not very mechanically or car savvy but do you mean legitimate rocks? Like rocks hitting the under carriage of my car?

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mc360

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No I mean the sound, kind of like putting a pile of rocks on the ground and sucking them up with the hose on a vacuum. You could possibly have a plugged cat converter, easy way to find out would be to remove the exhaust manifold and drive it without to see if it feels a little more powerful. Beware that a honda with no exhaust sounds like a tractor but it's just a quick test. Not sure if the cat can be seperated from the manifold but if it can then you can look through it and tell if it's plugged
 

Lydia Morris

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It's not making that sound. It sounds more like the engine is revving every second.... I can hear it in the video..

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mc360

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I can hear the revving and something else, I'm not to clear since I have ear plugs in at work but it sounded familiar to when my cat plugged up and my car lost probably 20hp while it was plugged
 

Lydia Morris

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Omg....sorry, now I realize what you are hearing. It's raining here! Ha! Sorry!

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HeX

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The rock sound appears to just be coincidental road noise, I agree that it may be the catalytic converter. If it looks to be the original then it makes more sense. If its clogging up then your engine cant push air out properly which throws off power production. Drive it a few minutes until the engine reaches operation temperature on the gauge, then park with the engine on, open the hood, and see if the catalytic is glowing red. If its badly clogged it may glow from the trapped heat. I know standard catalytics do so, but HX catalytics are wider in shape which may or may not have the same effect.

If you're not mechanically inclined enough to want to remove the catalytic to test it, then go to a muffler shop and ask them to do so or at least look inside the catalytic. If its clogged, either have them put in a new one or ask then to hone it out (remove the internals) and reinstall it. That'll resolve the issue but may cause temp reading issues at the 2nd O2 sensor which could lead to running richer or prompting a check-engine code. HXs are much more finicky about exhaust readings, what with the 5-wire O2 sensor.
 

5SpeedEJ6

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Vacuum leak would be my first guess. Question for the guys who say it's the cat converter, wouldn't the engine light be on in this case? Not trying to start a huge discussion, just trying to understand if it would be possible to have a clogged cat converter and no check engine light.
 

HeX

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Yes, its possibly to have a clogged cat with no code. Its happened to me with another car. In that case I figured it out one day when I walked away and had an easy enough view to see glowing red under my car. I had it changed and the car ran soo much better.

I dont believe it could be a vacuum leak because as far as I know vacuum leak induced fluctuations are more prevelant at neutral than in gear. The fact that she experiences only in uphill drives tells me the engine is struggling to push upward so the clog is impeding that much more.
 

Lydia Morris

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Yes, its possibly to have a clogged cat with no code. Its happened to me with another car. In that case I figured it out one day when I walked away and had an easy enough view to see glowing red under my car. I had it changed and the car ran soo much better.

I dont believe it could be a vacuum leak because as far as I know vacuum leak induced fluctuations are more prevelant at neutral than in gear. The fact that she experiences only in uphill drives tells me the engine is struggling to push upward so the clog is impeding that much more.
Thanks guys. Is this an expensive fix? Just curious...

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mc360

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If it really is the cat then yes it is expensive, legally you cannot buy a used cat so no shop sells them, the hx catalytic converter is on the manifold requiring a whole new manifold and if I recall is 500$ just for the genuine honda part. This is my video from when I was trying to figure out my plugged cat, I did have a cel on for a little but it went away for a while, not positive but I do believe in my video the cel is off (hard to tell because steering wheel is in the way)
 

Diana Nam

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Vacuum leak would be my first guess. Question for the guys who say it's the cat converter, wouldn't the engine light be on in this case? Not trying to start a huge discussion, just trying to understand if it would be possible to have a clogged cat converter and no check engine light.
most of the time you won't get a CEL light for it.
 

HeX

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The factory HX cat bolts onto the manifold, so there are aftermarket catalytic options. The one-piece MagnaFlow set-up is a one-piece that can cost around $500, but Im pretty sure an aftermarket replacement is less than $200 at the most. Buying a cat from Honda is just a waste of money. Thats also why I suggested having a shot hone her potentially clogged cat, which should cost less than $100 at worse.
 

mc360

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It's been a while since I owned my hx but I had a cel code for bad cat on it and I can't fully recall but I thought honda listed it as one part. I do recall seeing the aftermarket ones being two piece but then again something as important as a cat I wouldn't want a cheap aftermarket model (besides most are not cali legal so I couldn't use them anyway), since op is in Washington an aftermarket unit might be ok but I don't know the emissions laws up there.

Another thing to mention is most aftermarket cats have less rare metals in them which means they don't work as effeciently as oem
 

Diana Nam

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It's been a while since I owned my hx but I had a cel code for bad cat on it and I can't fully recall but I thought honda listed it as one part. I do recall seeing the aftermarket ones being two piece but then again something as important as a cat I wouldn't want a cheap aftermarket model (besides most are not cali legal so I couldn't use them anyway), since op is in Washington an aftermarket unit might be ok but I don't know the emissions laws up there.

Another thing to mention is most aftermarket cats have less rare metals in them which means they don't work as effeciently as oem
it was a big thing people used to go around and steal those cause they contained a lot of rare metals including gold so they was just extracting those metals to pawn and make easy quick money
 


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