When starting out with a cold engine I hear a faint, rapidpopping sound while accelerating coming from the engine. Any ideas? The problem goes away once fully warmed up. It started a few years ago only on very cold winter mornings. Now it happens even during cool summer mornings. If I let up on the gas and really baby it, it goes away.

96 civic ex, 165k
replaced plugs, wires, cap, rotor
tried higher octane gas and it made little difference.

 

does it sound engine related? (the popping speeds up with the speed of the engine, and then slows back down with an upshift) if not, I would check your CV joints...

 

Check for exhaust leaks, I had the same problem and ended up being a cracked exhaust manifold.

 

Basil:
I'm pretty sure it's engine related. The cv joints do make a rythmicfaint beatwhen under power in a turn, but that's something I'll replace when it gets worse (they were probably ruined when the boots tore and were contaminated, It tookuntil the next oil change for me to notice the boots were open. I replaced just the boots but the damage was already done. They've lasted another 2 yrs so far.) The popping from the engine ismorerandom than the noise from the cv joints which occurs at even intervals.

gwl:
You say you had the same problem, did the popping go away once the engine was warm? I wouldn't have guessed a cracked exhaust manifold would only make noise when cold. I'll look at it this weekend.

 

As the engine warms up,small cracks will get smaller because of heat expansion. About the time I got around checking for cracks, I could smell some exhaust fumes around the engine compartment. I think I replaced about a year later when I first started hearing the popping sounds. I had to replace it because I was due for a smog check.

 

what are you complaining for?? break out the butter!

no, i think we have heard this problem before, smell around, get your ear around the exhaust pipes and smell and listen.

 

It's been a couple years since I first posted but the engine noise was slowly getting worse over time. I finally changed the exhaust manifold and there was a visible crack in the old one but the noise is unchanged with the new manifold. I also adjusted the valve clearance back to spec but that had no effect either.

Any ideas out there or has anyone else had a similar problem. The engine (d16Y8, 177K) makes a faint, irregular popping noise when cold (less than about 4 miles of driving, but on really cold days <20, it can happen even after idling at a light). It is louder under load, especially on the first hill of the drive, usually when trying to accelerate and climb a hill at the same time. If I back off to about 15"Hg vacuum it will go away but I also won't get above 30mph. I was skeptical that it was exhuast related because it is irregular, it doesn't happen every exhaust stroke. It's very rapid and varies with engine speed.

My first hunch a couple years ago was that it was a misfire because it is irregular. I've changed ignition components (cap, rotor, plugs, wires). No change was observed.

I tried higher octane gas thinking maybe it was knock, which doesn't make much sense to happen on a cold engine and go away once warm but it was easy to try so I gave it a shot. Again no change was observed.

Now the exhuast manifold and valve clearance are ruled out as well.

Any ideas? If it were a misfire wouldn't the check engine light come on? Doesn't the CKF (or whatever that sensor is that you have to remove to put the timing belt on) sense misfires and wouldn't I fail emissions? Or does the computer ignore misfires on a cold engine? I don't have the money to keep swapping parts here.

 

Out of curiosity, did you ever do a compression test? Dunno if it would be diagnostically significant yet.

Also, does it sound ANYTHING like this?
http://smg.photobucket.com/albums/v1...t=MOV01368.flv
You have to listen carefully to hear it. That's a cold start during cold weather on a D16y7 with 107K.

 

rod bearings, possibly.

does it sound like popping, or like a knocking noise (not engine knocking, but as in dense metal knocking dense metal)?

 

I think you should reconsider components of the exhaust system.

1) Exhaust pipe A is located immediately downsteam of the exhaust manifold and is followed by the catalytic converter (cat). I have read that exhaust pipe A has a pipe-within-a-pipe design to insulate the exhaust gas and maintain its high temperature so that the cat can work efficiently. The internal structure of exhaust pipe A can apparently break down and cause a rattling noise.

2) Likewise, the cat has an internal ceramic structure that can crack and loosen, thereby creating a rattling noise.

For both components mentioned above, the rattling noise can change with engine temperature due to expansion and contraction. Food for thought.