Rattling under the hood, help me diagnose!

[Ecky]

Honda Del Sol - B18B1 motor (same as 90's Acura Integra LS/GS)

I have two rattles I need help diagnosing. The problem is, they only occur during conditions that I can't replicate with the hood open, so I can't easily tell where they're coming from.

Rattle #1: From my driver's seat it sounds like it's coming from the transmission-side (passenger side) or maybe from the middle of the engine bay, perhaps the throttle body or even clutch/flywheel. I can't rule out that it isn't one of the valves on the far side of the engine either, as it's really hard to tell where it's coming from. It occurs when at high vacuum, 3500+ RPM when letting off the throttle, only when the throttle plate isn't completely closed (typically 100MPG on MPGuino and decelerating, but not quite closed enough to cut off the injectors). The sound resembles a loud metallic chattering and made me jump the first time I heard it, a few days ago.

Is it possible for a throttle plate to become loose and rattle when it's almost closed? What else might I look at?


Rattle #2: Occurs only between 2500 and 3000RPM, sounds like it's coming from directly in front of the driver's seat, so water pump/timing belt/possibly valve-train/accessory belt area. I only hear this one when there's some load on the engine, revving it in neutral creates no rattle. It's a quiet rattle/chatter that sounds the same at low load as at WoT.

I'm afraid it might be the timing belt tensioner rattling but I'm puzzled as to why it would rattle only under load and between specific RPMs. I'd replace it tomorrow except I'm in the middle of a move and money is particularly tight for the next few weeks. What else in the area might behave this way?


^ Sorry about poor engine bay image. I don't have any taken in the past 2 years. Rattle #1 sounds to be coming roughly from the red circle, while #2 is roughly near the blue circle.


Despite these rattles, the engine appears to be running great, just did 37MPG 120 miles cruising at 65, not drafting.

[kaiba]

Possible noise may or may not be exhaust pipe, exhaust heat shield, transmission dust shield, motor mounts etc......

Record a video of it.

[bestclimb]

is the sound "tinny" or "heavy"? If it is a tinny sound it seems like you have described every loose heat shield, muffler shroud, skid plate, etc I have ever had.

[Ecky]

Rattle #2 can be heard at the end of the video but it's so quiet you may not be able to make anything of it. #1 is clearly audible though:

http://www.youtube.com/watch?v=6FH25xEChVc

FYI - that's 5th gear.

[bestclimb]

still sounds like a heat shield/shroud.

[Ecky]

Originally Posted by bestclimb

still sounds like a heat shield/shroud.

I don't have any of 'em. The previous owner of the car basically stripped it under the hood - no spark plug cover, no exhaust heat shield, no shroud, no cat, no muffler cover, no plastic wheel well panels (it was lowered). For the life of me I can't figure out what might be rattling except for maybe the hood itself.

Not an alarming sound though?

[baldlobo]

engine mounts?

do you still have accesories? are they on an serpentine or v-belt?

do you have all your exhaust hangers and springs?

[cbaber]

#1 noise sort of sounds like a bearing in the transmission. Possibly the input shaft bearing. I can hear mine under light loads, deceleration, and when the car is in neutral with the clutch out idling.

[Ecky]

Originally Posted by baldlobo

engine mounts?

do you still have accesories? are they on an serpentine or v-belt?

do you have all your exhaust hangers and springs?

All mounts are brand new as of a month ago.

Pulley has 3 belts, one for alternator, one for A/C, one for P/S - all attached and working.

Exhaust is on hangars and they look ok. The sound doesn't seem to be coming from any exhaust rattle, but I'll check it out next time I have the car up on ramps for anything touching. About 6 months ago I put a flex pipe in just after the header, the previous owner had just run a straight pipe from header to muffler.

Originally Posted by cbaber

#1 noise sort of sounds like a bearing in the transmission. Possibly the input shaft bearing. I can hear mine under light loads, deceleration, and when the car is in neutral with the clutch out idling.

Come to think of it, I do hear a kinda similar-ish rattling on occasion when at a stoplight, and pushing on the stick lightly makes it go away. How difficult/expensive is an input shaft bearing, and is it safe to let it go for a while?

[some_other_dave]

The "classic" ISB symptoms on an earlier (88-91) Civic/CRX are as follows:

- Rattle noise in neutral with the clutch pedal not pressed
- Press the pedal, the noise slows down and stops
- The noise may also be heard in gear

Replacing the ISB isn't awful, but it means removing the transmission from the car and pulling the transmission case apart. And then pulling the input shaft seal and then bearing out, which requires a puller. (I know some who say they've done it with a screwdriver; I couldn't figure out how to do that without destroying the bore they ride in.)


Noise #1 sounds a little like detonation ("pinging"). Which in my non-Honda, sounded kind of like a "spitting rattle" noise, not a metallic "ping". If your engine is on the edge of detonation, moderate loads and medium RPMs and warm temperatures would be the most common times for it to happen.

-soD