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Won Won is offline
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can you describe knocking/pinging sound?

Hello everyone,

I've had my first 911 for about 4 months now, and still getting used to the car.

Now, there is this sound that I've gotten used to during that time. I can hear it when the car is in 3rd, 4th and 5th gears, perhaps a bit more pronounced in 5th, and I would describe it as a grinding noise. I can tell it is transmitted through the cabin, i.e. you could hear it loud and clear if you were to put your ear on a part of the shell.

I was no longer concerned about the sound after the first month or so, and have been planning a transmission fluid change. Then I came across some posts here in Pelican about carbon buildups in old engines and their tendency to knock. Then I realized I've never actually heard a "knock" on any engine and maybe the grinding sound that I've gotten used to is really knocking sound.

It is quite loud when I'm on, say, 30% or more throttle in 1K to 3K rpm range, fading as the rpm increases and is not noticeable above 3K. Whether the sound is actually disappearing or it's getting buried in the road/engine noise, I can't really tell. There is no grey smoke out the exhaust that is visible through the mirrors. I understand it is difficult to describe a sound verbally, but can somebody help me?

The PO said he always pumped highest grade gas, I've been alternating between 89 and 91 octane. Can using higher octane gas than necessary increase carbon buildup in the combustion chambers?

That's more questions than I came to ask, but all help is appreciated! Thank you!
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Last edited by Won; 11-12-2005 at 07:39 PM..
Old 11-03-2005, 09:41 PM
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iF YOUR '83 SC is a ROW model (Rest of the World) then the compression is rated at 9.8:1 and 204 HP. The US models are 9.3:1 and 180 HP.
Don't mess around with the lower octane fuels, put the Super (91 octane or better) in your car. Don't risk problems to save pennies.
Porsches like higher RPMs than most cars. When you are driving take the motor up to 4500 to 5500 RPM before shifting.
Shifting at lower RPMs tends to "load" the motor which can make "pinging"(detonation) worse.
If you must shift at lower RPMs, like in town, go easy on the throttle.
If you can find a gas station with higher than 91 octane buy your fuel there.
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Old 11-03-2005, 10:49 PM
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Doug,

thanks for your reply. I believe the engine is same as US cars. Funny, I would think that Canada should be part of the "rest" of the world excluding the US, but I guess not.

I am fully aware that our cars like high rpms. I mean, I like high rpms too, but being a student keeps my foot off the gas as I can literally see the needle in the gas gauge go down, in real time. When I got the car I said to myself, "I won't be able to afford driving it everyday, but that's ok, 'cause I'll be happy just owning a 911." But what do you know, you can't really own one and not drive it, that's the best part of my day! One of these days I'm gonna put the car on jackstands and, I don't know, clean the wheel wells or something until I save enough money to stop worrying about my fuel economy.

Anyway, good news is that today I put in some 94 at the same price as 89 just last week. What's happening with the gas price? I never thought it would go down again.

I remember reading from somewhere that 915s sound like a broken coffee grinder. That's exactly what mine sounds like. Does a knocking engine sound like a broken coffee grinder?

I know, I type a lot, but what's worse, creating separate threads for all the topic I ramble about, or making peope read long and boring ones like this?
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Old 11-04-2005, 12:00 AM
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Re: can you describe knocking/pinging sound?

Certainly sounds like you have a ping. It should sound like if you are shaking a few dry beans in a coffee can. It can be rather muffled. That it occurs under throttle at low rmp is consistent with pinging. I can see that you could describe it as a 'grinding'. It certainly is not a knock or real tap.

Carbon build up can be an issue, but I would bet on improper timing (too much advance) first. Definitely buy high octane gasoline for now. The octane rating of the gasoline should not affect carbon build up. If the PO ran high octane, that's really good, because he probably had no pinging. Higher octane fuel can take higher compression and more advance. You need to check into this very soon, because you can royally mess up your engine. Generally rings and piston lands tend to break if you have pinging.

George
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Old 11-04-2005, 12:03 AM
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Won:

I just read your latest post. Coffee grinder? I think you are describing a ping. A coffee grinder is actually a rather good description!

George
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Old 11-04-2005, 12:05 AM
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great.....
I feel like an idiot, but at least I'm glad I asked.


so, is timing something I can play with in the garage?


just googled advancing timing, and says that will give better fuel economy... maybe that's why when, during the first month, I put in 94 I got better MPG than now. I just thought it was the result of driving very very slowly then. I did shift around 3k though. It all makes sense now (famous last words before an engine rebuild?)

Thanks George!

[edit] after a quick search I am convinced that I can do this with a timing light. Cool.
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Last edited by Won; 11-04-2005 at 12:49 AM..
Old 11-04-2005, 12:20 AM
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Won:

No need to feel like an idiot at all! Idiots would keep driving without asking or blindly rely on a mechanic.

I doubt you hurt anything the way you seem to stay off the throttle. You didn't drive it for long this way and you did not floor it or take it to high rpms. It's not like these engines are super sensitive, but you definitely need to fix the ping!

You can play with the timing in your garage. You will need a timing light. You will check the initial timing at idle. This value may be off (too advanced) which would be the easiest thing to straigthen out.

The advance info you found through google was vacuum advance. The vacuum on the intake of the engine advances the timing when at cruise. This is of no concern at this point. You disconnect the vacuum line from the distributor (and plug it) when checking initial timing at idle.

There is also additional timing advance - a mechanical advance, which is done with centrifugal weights in the distributor. Generally you want more advance at higher rpm to make power! If you rev up the engine, the distributor shaft rotate and the weights move - the advance will increase. You can see this on your timing mark if you use your timing light and rev the engine. Generally the mechanical advance can get stuck. Performance suffers, but there is less advance = less chance of a ping! Mechanical advance therefore should not be your problem.

Your using 94 octane vs. the lower grade stuff shoud not influence fuel economy at all. The higher octane fuel is less prone to pinging, that's it. There are modern cars with knock sensors and electronic engine management systems that will take the advance back as soon as they sense a knock. In such systems, higher octane fuel will make more power, because the electronic engine management can add more timing advance until it senses a knock and then back it off at an optimum level. It will give all the advance (for performance) while keeping the engine from knocking. Needless to say, your SC is far from this.

Another reason for an engine to ping can be overheating. Make sure your engine runs at the proper operating temperature! You should definitely use the search function at this point in time and see what typical causes / fixes for pings are! Also get the bentleys manual, wayne's 101 project's book and do some reading!

Cheers,

George
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Old 11-04-2005, 12:56 AM
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Here's an update:

Checked the timing with both vacuum hoses off, it was very close to 5 degrees mark already. In the process I played around with idle speed screw a bit, and when it's more unscrewed there is a hissing or whistling sound coming from around the metering plate. Does the air for idle only bypass the throttle body and still come through the air filter and the plate?

Went down to Weissach and picked up a new distributor cap, rotor and spark plugs, but they gave me a wrong set, WR7DC for carreras, so those haven't been changed. Meanwhile, I checked sparks and they are fine. However, despite new cap and rotor and correct timing the sound persists. This is with a full tank with half 89 and half 94.
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Last edited by Won; 11-05-2005 at 08:52 PM..
Old 11-05-2005, 07:27 PM
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[Saturday night bump by spliting a post]

I searched the forum and found a couple interesting posts:

Is this engine sound normal?
The sound described in this thread is remarkably like what I'm hearing. I have a little "chatter" in neutral that goes away when the clutch is disengaged. Also, I can hear the same coffee grinder sound when I suddenly let off gas, exactly twice within a half a second interval, synchronized with the jerking motion of the car.

93 Octane pinging under load
So broken head studs also make pinging sound... They were all good when I purchased the car, but I'll check them on the next oil/valve change. That would be sometime in march next year.

New questions: if an engine pings at low rpm/ high load situation, does it necessarily ping at high rpms too? I suppose a correctly tuned engine should not ping even at low rpm/ high gear/ full throttle, correct?

When warm and idling the rpm oscillates between 800 and 900 with the O2 sensor plugged in. With O2 out, it's steady at 900. According to the "slightly pushing/pulling metering plate arm while idling" test, rpm increases a bit with plate pushed up, so I think it's running a bit lean too. Perhaps that's also related to "pinging"?

Now that I have a list of things that doesn't quite work right, I think my car is in need of an overhaul.
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Old 11-05-2005, 08:53 PM
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Won,

I've had my 83SC for about 5 years now, with a similar noise (I think, based on your description). I'm pretty good with a wrench, and would have no trouble determining if it's the transmission or engine preignition.

I you don't mind driving out to Maple Ridge, I would be happy to offer my diagnosis. PM me.



Al
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Old 11-05-2005, 09:23 PM
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Yes, a 915 at low RPM's sounds like dullen coffee grinder when trying to accelerate from a low RPM (2200 or less). I've heard this sound in many 911's and its pretty much repeatable from car to car.

I doubt its pinging, especially if you hear it on decel.

Pinging sounds like dropping marbles into an empty coffee can.
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Old 11-05-2005, 11:43 PM
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Yup, decel will not be ping, no way!

g
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Old 11-06-2005, 10:01 AM
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OK....

Met Al S over the weekend, apparently his car makes the same noise which is coming from the TRANSMISSION. Happy meal time!

But we also found bad injector seals, which could have caused/been causing a real knock that is either inaudible or muted by the transmission noise.

There are many things here and there that need to be fixed, but for now that's one less thing to worry about (one less thing to fix?)

Thanks everyone for your input, and especially Al for your time and the sticker! Now I really feel like a part of SCWDP
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Old 11-14-2005, 08:14 PM
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Won, It was great meeting you!

I also feel better knowing there is yet another Porsche with the same subdued "coffee grinder while lugging the engine" mystery noise.

My research so far indicates either of two things; normal and nothing to worry about, or pinion bearings. I hope it's not the latter, so I've convinced myself it's the former.

Welcome to the SCWDP and wear the badge with pride!
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Old 11-14-2005, 10:09 PM
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Come to think of it, how about the metallic banging sound when the rpm is too low so the engine is almost stalling, but still running, that is like valve noise, only much louder, would that be the pinging noise?
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Old 11-15-2005, 01:17 PM
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Quote:
Originally posted by i_got_an_SC
Doug,

I believe the engine is same as US cars. Funny, I would think that Canada should be part of the "rest" of the world excluding the US, but I guess not.

I
You know how to check the engine number, right?
We had a thread here a couple of weeks ago - search for "Show me your...engine numbers"

Frank
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Old 11-15-2005, 04:02 PM
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Engine number is 64D4015 so type 930/16 which is US spec
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Old 11-15-2005, 09:19 PM
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I was driving up a steep hill the other day and though I could stay in 3rd gear. Well, I was wrong. NOW I know what pinging really sounds like, not just grinding sound but with a distinctive "ring" to it. I guess "marbles into coffee can" describe exactly that, with the "attack" and the "ring", resonance, whatever.

Thank you everyone again for your help. I wish someday I can help somebody on the board too
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Old 11-24-2005, 11:43 PM
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Old 11-24-2005, 11:43 PM
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