hmaugans

Hi. I haven't posted here before, but I've been lurking for a while.

Recently my S2k has started having a pretty bad rattle at lower RPMs. It's the strangest thing... I start the car and it sounds horrible. I start driving, and the second I cross over 2,500 RPM like clockwork, the noise instantly stops. Every time (driving or idle), it always silences exactly when the RPM exceeds 2,500.

*Videos w/ sound at bottom of post*

My roommate is far more of a gearhead than I am, so he's helping me try to diagnose it. We began by pulling the CEL's that started popping up. It was showing 5-6 codes, one for every cylinder misfiring, and two more miscellaneous misfire-related codes. We then performed a full compression test on all 4 cylinders, and they showed perfect compression. We thought it might be a valve adjustment issue, so we dove into the engine and checked the spacing. The gaps between all the valves were perfect.

After toying around with it, we ended up unplugging the two cables on the front left of the engine for VTEC, and the problem went away! I thought, "Okay, it's a vtec issue, I'll just keep it under 6k RPM and fix the vtec later." Well, within a day or two, the sound hadn't returned so we decided to plug vtec back in and see what happened. When we plugged it back in, the noise was still gone. Weird. It now appeared whether or not vtec was plugged in, the problem wasn't affected. Thinking back, I don't know the vtec system very well, but I didn't think it kicked in at all until 6k RPM... so I'm not sure how this would have affected anything. I kept driving it, and about a day later the problem returned. I checked my oil and found it was low again. I topped it off, and the rattle remained. Is it normal for an S2000 to burn through that much oil in just a few days?

Okay, continuing to diagnose after that... reading around S2ki, it seems the next logical step was the Timing Chain Tensioner (TCT). We replaced the TCT with a brand new one, and the problem went away again! Great, that fixed it, right? Nope. A day or two later, the problem came back, and we noticed noticed my oil was pretty low (but not causing any lights or anything). We topped off the oil, but the problem persisted, so we decided the TCT may have died again. This time I took the worm gear out of the new TCT and took it up to a local power coating shop to get it sandblasted. We tossed the sandblasted worm gear back into the TCT and reinstalled that in the car again. No luck- the issue is still there.

I took it by the dealership early on (big mistake), and they told me that rattle means my engine was shot, and they had some great prices for me to replace my engine with a brand new one (ha!).

So here we are today. I'm worried driving the car as-is may cause damage (the noise is loud and sounds pretty bad at low RPMs).

Anyone have any recommendations, or have had any experience with issues like this before? I appreciate any and all replies... I really want to get my car fixed again. Thanks!

----
Here are two videos I've uploaded two videos to YouTube showing the issue:

This one is from the engine bay, so you can hear the clear-cut starting and stopping of the sound as the RPM goes up and down:
http://www.youtube.com/watch?v=zr3lsu0W0nE

And this one is from the gauge cluster, so you can see the actual RPMs themselves going up and down, however from this angle it's much more difficult to hear the engine, so you have to listen closely to make it out:
http://www.youtube.com/watch?v=foVmeVcRrSA

dagle

iTrader: (1)

and you're sure thats not rodknock?
sorry for being vague- are you sure that your motor's still bueno? when you said your oil was reading low, it sounded like (to me at least) that it was already low on oil prior to that. and if oil starvation happened, main rod bearing failure happened.. which leads to rod knock which sounds exactly like what you're describing. sounds identical to my friend's 00prelude-SH that has a toasted #1 cyl but compression showed up for his

hmaugans

I just updated the original post to include a clarification on the vtec issue.

dagle, if it were rod knock, it wouldn't magically quit at exactly 2,500 RPM, right?

Any other ideas? So far I'm leaning toward replacing the timing chain tensioner AGAIN... but I would like to get a few ideas for other possibilities first.

AP1_man

that is not your TCT. instead of revving it to figure out the problem drop the oil pan look for metal from your spun bearing, you have rod knock.



and the knock doesn't go away when you rev...you can hear it increase its rate of knocking as the RPMs increase, sounding like a buzzing or almost no sound.

dagle

iTrader: (1)

^-- bingo. i didn't wanna be mean.. and it does magically disappear because the lateral motion is cancelled out (my primitive logic) at higher revs..

AP1_man

only other thing i could think of maybe a broken valve or valve hitting piston.


my moneys on a bad valve and stem seal, spun bearing won't loose oil that fast, so time to pull the bish apart either way.

dagle

iTrader: (1)

i don't know mang, it sounds like the OP isn't losing oil but rather that he found that he was low on oil after the fact.

AP1_man

OP: have you done a leak down test?

hmaugans

No I haven't. What would that tell us?

And I'm really not convinced it's rod knock or an internal issue. Keep in mind when the issue first began, we replaced the TCT and the noise went away 100% for a few days. If it was an internal engine issues, why would replacing the TCT fix it?

And furthermore, the sound *does* disappear instantly at 2,500 RPM. I understand fully the sound mind balance out or speed up so it's hardly audible, but that's not the case in this instance. You can hear the sound clear as day (it's very loud in real life, the video doesn't convey this very well)... and as soon as the RPM's breach 2,500, it's like a switch flips and the engine sounds 100% stock and normal. No loud knocking. Keep in mind this also happens if we're sitting at idle in the garage and rev the engine with our ears right beside the motor. The knocking sound disappears instantly.

I've heard these cars have a high-strung engine and do burn a lot of oil, but how much is expected? I can't imagine it's normal to have to top off your oil every week if you daily drive the car... surely no one would put up with that.

Thanks for the feedback so far guys. Any other thoughts? I really do appreciate it.

dagle

iTrader: (1)

a leak down will tell you the status of your engine, and did you check your oilpan for metal shavings? I've never personally done a leak down test, but I recall that a 6% leakdown is normal. anything above that would be questionable, and in this matter I would bet it is indeed something internal.

AP1_man

s2k burns on average of .25qt of oil a month...if your burning as much fuel as you say you are then bad valve and stem seal are still my guesses. feels like we're running in circles...your oil is going some where, check you radiator for oil also

also you mentioned you thought maybe a VTEC issue, since oil pressure would be low it may not kick in or not be strong at all.

mattTc17

I have an almost identical problem, same noise, same rpms, on a 95 geo prizm with ~170k on it. My oil is fine though and it's a timing belt so there's not TCT and obviously no VTEC. So to me, all those things seem ruled out for both of us. Mine started after changing plugs wires cap and rotor (are the S2000's direct ignition?). I thought maybe accessories so took the alternator and power steering belts off but got the same noise, water pump is on the same belt too so it's not that. I'm going to take the AC belt off tomorrow and rule that out too. Did you try taking off any accessory belts? Since you posted were you able to take care of the problem?

brandonS2k

I don't know I say rodknock. It wasn't that long ago that someone posted almost identical videos to yours...outside the engine bay and watchin the rpms... and the sound/result was the same. Almost positive its a rodknock. I'd have it looked at if I were you.

mattTc17

I might expect that on a car with 170k, but how many does that S2000 have?

mattTc17

I'm surprised now that the TCT didn't fix it. Mine ended up being the timing belt tensioner. I turned the motor over by hand to see if I could hear better what was making the noise. I could then see it kinda jumping around in there like maybe it's bearing is shot or something. I'm going to replace it and the timing belt here in the next week or so so I'll let you know if the sound is gone after all that. With low oil in the s2k though the rod-knock mongers might be right.