Hey I'm back again, because, why not right?
Basic details.
Z3 M52B28 rebuilt into a 3.0L using an M54 rotating assembly.
S50 cams. Stock ECU, OBD2.
Pretty stock otherwise.
Has about 11,000 miles since the rebuild.
I've never fully had peace of mind with this motor. There's always been cooling concerns, and ticks and noises. The power has been good, and the only engine code I have currently is for an emissions system part I haven't installed yet.
The main problem:
At idle, the engine moans like the soundtrack of Interstellar, when it does that low-frequency "woom" like you hear in every movie trailer now. It lasts for at least a second, and repeats maybe every 2 seconds. Raising the RPM only affects it a little. It sounds like it's coming from the center of the engine, on the intake side. It kind of goes away when the engine warms up, but I can still barely hear it after a while.
A video of the sound
A second, nearly identical video of the sound
The low-bass sound I'm trying to describe isn't captured well in the video. Instead, you hear a lot more of the ticking. That's another annoyance. But you should still hear that "trombone" sound.
My guess so far is a vacuum leak. Here's some clues.
I can hear a suction sound from inside the car. Like the induction sound, but a bit like a hiss. For some reason I can't hear it when I'm outside looking directly at the engine and revving it. It might be getting drowned out by the ticking.
When I've driven home at night, I have to climb a moderate grade up a freeway. It's a few minutes long, and my engine temp always rises.... an unusual amount. Depending on my speed/load, it will jump at least 10°F. So say it's 195° at the bottom of the hill, it easily hits 205-210° at the top. And then it kinda levels back down to 200 when the road levels. My freeway exit is shortly after the climb. There, at the red light, my engine does 2 things:
The engine shudders, sending vibrations throughout the whole car.
Sometimes, the idle drops to cause the Low Oil Pressure light to come on, and stay on for as long as I'm at the light. If I give it a little rev, the light goes away. Yes, I have enough oil.
When I'm driving again, it might happen one more time at the next light, but my the time I'm home, the engine has "cooled" to the point where the engine doesn't shudder at idle anymore. This specific issue has been going on for a very long time, probably since the rebuild.
I've also suspected there's an air leak because of the cooling issues I've always been having; maybe it's been running lean causing the extra heat. I will find out soon.
I haven't noticed a drop in power, nor have I noticed any other specific issues. That "trombone" sound is about a few days old at this point, so that's my biggest worry.
I've bought an at-home smoke machine tester, which will arrive soon. I can't wait to use it and find no problem and still be confused.
I don't understand how vacuum leak could cause that sound, and why it doesn't really change with RPM.
It's too slow and drawn out to be a mechanical issue, so what else could it be?
Thank you!
Basic details.
Z3 M52B28 rebuilt into a 3.0L using an M54 rotating assembly.
S50 cams. Stock ECU, OBD2.
Pretty stock otherwise.
Has about 11,000 miles since the rebuild.
I've never fully had peace of mind with this motor. There's always been cooling concerns, and ticks and noises. The power has been good, and the only engine code I have currently is for an emissions system part I haven't installed yet.
The main problem:
At idle, the engine moans like the soundtrack of Interstellar, when it does that low-frequency "woom" like you hear in every movie trailer now. It lasts for at least a second, and repeats maybe every 2 seconds. Raising the RPM only affects it a little. It sounds like it's coming from the center of the engine, on the intake side. It kind of goes away when the engine warms up, but I can still barely hear it after a while.
A video of the sound
A second, nearly identical video of the sound
The low-bass sound I'm trying to describe isn't captured well in the video. Instead, you hear a lot more of the ticking. That's another annoyance. But you should still hear that "trombone" sound.
My guess so far is a vacuum leak. Here's some clues.
I can hear a suction sound from inside the car. Like the induction sound, but a bit like a hiss. For some reason I can't hear it when I'm outside looking directly at the engine and revving it. It might be getting drowned out by the ticking.
When I've driven home at night, I have to climb a moderate grade up a freeway. It's a few minutes long, and my engine temp always rises.... an unusual amount. Depending on my speed/load, it will jump at least 10°F. So say it's 195° at the bottom of the hill, it easily hits 205-210° at the top. And then it kinda levels back down to 200 when the road levels. My freeway exit is shortly after the climb. There, at the red light, my engine does 2 things:
The engine shudders, sending vibrations throughout the whole car.
Sometimes, the idle drops to cause the Low Oil Pressure light to come on, and stay on for as long as I'm at the light. If I give it a little rev, the light goes away. Yes, I have enough oil.
When I'm driving again, it might happen one more time at the next light, but my the time I'm home, the engine has "cooled" to the point where the engine doesn't shudder at idle anymore. This specific issue has been going on for a very long time, probably since the rebuild.
I've also suspected there's an air leak because of the cooling issues I've always been having; maybe it's been running lean causing the extra heat. I will find out soon.
I haven't noticed a drop in power, nor have I noticed any other specific issues. That "trombone" sound is about a few days old at this point, so that's my biggest worry.
I've bought an at-home smoke machine tester, which will arrive soon. I can't wait to use it and find no problem and still be confused.
I don't understand how vacuum leak could cause that sound, and why it doesn't really change with RPM.
It's too slow and drawn out to be a mechanical issue, so what else could it be?
Thank you!
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