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Discussion Starter #1
Hey all,

I’ve got a JDM D15B VTEC in my 93’ Civic DX hatchback. I’ve been having a problem where once the engine is warm and I coast up to a stop in neutral or with the clutch in the engine will make sort of a small “knocking” sound. It’s not like a rattle or anything, more like a hollow popping noise. Usually once I come to a complete stop it will take a second and the idle will drop from like 1,1000 rpm to about 700ish rpm where it should be and the sound completely goes away. I don’t hear any other sounds when driving (although the cheap rock auto exhaust is very scratchy sounding).

I don’t know if the engine is toast or it’s something setup related. Oil is clean and not burning any. I’m using a CX one wire O2 sensor that I’ve plugged into my 4-wire stock harness (rewired connector). Running a P08 ECU. No CELs or anything. I do wonder if the cat is bad since the old engine puked a ton of oil into it. Spark plugs are the extended type. I reset the ignition timing when I got the engine in the car.

When starting from cold the engine almost dies but then goes to normal idle for warm up, and doesn’t do it again. This is my first engine swap and any help would be much appreciated.

Thanks!
 

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Does it only ever knock in that very particular scenario? Can you reproduce it sitting still and just playing with the throttle in that rpm range?

And yes, good quality video/audio please.
 

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Discussion Starter #4
Okay, sorry for the super late response. I've had a bunch of other things (including other problems with the car) to deal with in the meantime. Generally it will only make the sound at around 1000-1100 rpm. Occasionally the car will idle a bit lower than normal so it will make the sound at a lower rpm.

The car will not make the sound when you start it from cold, however it does almost die when starting from cold. Once the engine has warmed up and you are say coasting up to a light in neutral or with the clutch in the car will idle at around 1100 rpm and always make the sound. Once the car is stopped completely it will continue making the sound for a few seconds and then settle into a normal idle at around 750 rpm sounding normal. You can reproduce the sound playing with the throttle by keeping it at that rpm and with the foot really light on the gas.

I took a video this evening, how do you upload it, just embed a youtube video or something?
 

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Wow, that is interesting. Kind of sounded like the turn signal relay lol "tick, tick, tick, tick". I'm honestly not sure with just that sound clip.

Does it sound different down low versus up top?
 

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Discussion Starter #11
The sound only gets made at that low RPM, if it is making the sound at a higher RPM (certainly possible) I can't hear it. There does seem to be a slight knocking sound (more like rattling) when starting the car cold in the morning. I feel really great about that...

Regarding the timing belt, it certainly could be too tight, but I didn't do anything special when replacing the timing belt. I replaced the timing belt when I got the engine but did not replace the tensioner. As far as I'm aware the D15B VTEC tensioner is no longer available so I left it alone. It had some rust on the surface, but it spun fine without any harshness or noticeable play.

Are there things I could try replacing or doing? I didn't do a valve adjustment when I got the engine, perhaps I could try that? Maybe try replacing the catalytic converter, who knows how many miles it has on it. I'd really love to not have to pull the engine for a rebuild.

Thanks all for the responses so far. I'll see if I can get a better video, when I took the video last night it wasn't making the noise as loud as usual.
 

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That "whirring" noise has to be one of the most common noises found on all hondas after the majority of tbelt replacements haha.

Those tensioner bearings just screaming due to slightly too much tension!
Such a pet peeve of mine :-|

As far as I'm aware the D15B VTEC tensioner is no longer available so I left it alone.
I reckon you'd be able to find a replacement, also if you're going through the effort of replacing a belt it's crazy not to do the waterpump and tensioner at the same time. What's the engine code, what car year/model did it come out of?

Sounds like the belt just needs its tension reset.

The knocking sound, has the motor always made that noise? Does it change if you engage the clutch? Does it get worse if you lightly ride the clutch with the handbrake on? Try adjust the valve lash, see if that helps.
 

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you mention extended spark plugs. you might be hitting the straps and crushing the gap to nothing

Remove and inspect them.

Then throw them away, and install plugs that are FOR the motor specifically.

online honda dealerships will show the information.

Generally a set of NGK ZRF5-11 plugs are what you want.

no 92+ honda had single wire o2 sensors. VX had factory widebands on federal 49 state vehicles, else all got 4 wire as standard.
 
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