strange 72 s engine sound

youzoid · 07:46 AM

I just got my 72 s back from having a 'tune up' on a rolling road, and I've noticed a new noise.

Between about 2200 and 2800 rpm there's a distinct rushing sound, kind of like air but a bit more mechanical. There's no sign of it outside this particular rev range and it disappears quite abruptly when the revs move outside that range. It's noticable enough that even my mum commented on it from inside the car!

Also, it only happens once the engine has warmed up a bit.

The engine seems to otherwise run ok though I do have some popping. Also it's a bit slow getting back to idle when you take your foot off, with the revs reducing quite slowly through the 'noise zone'.

Any ideas? My mechanic says theres a point in the rev range where the MFi changes over the timing mode (or something like that). There was aparently a problem with this mechanism before, which I think he fixed in the recent tune up. He also says the engine has worn butterflies. Could the noise be related to either of these things?

Should I get it looked at again (by someone else)?

Thanks guys

Jerry

jeff m · 10-09-2002, 01:25 PM

This is too good a post to be on page 2 without a reply,
Let me put you back on page 1

I can't help with the noise, but the return to idle could be that the mech forgot to re-adjist the micro switch after he checked your rack. (you have to adjust it out of the way to check the butterflys and rods)

Jeff
911t

youzoid · 10-30-2002, 01:40 PM

*bump*

has anyone got any ideas about this sound? The motor seems to drive ok, but I want to know if I should get it checked out.

Jerry

GIBSON · GIBSON's Garage

Jerry
Hard to tell but here's some questions that might help.

1. With the engine idling and warm, can you produce the sound
moving the throttle arm and reving the engine from the engine compartment?
2. Did the fan belt get changed? Check for the correct number of shims and belt tightness.
3. Did the transmission linkage get adjusted or the shifter busings changed. Sometimes a slight adjustment problem with the shifter can cause noises in the cabin.
4. Is the intake air pre-heater installed and working? It has a thermostat to allow it to open and close depending on operating temps of the engine. It's possible noises could be coming from
that system but I've never heard of it.
5. Drive the car with the air cleaner assembly off. It will make more intake noise (nice sound..) but you might be able to tell something that you could not tell with it in place.

Something to get the ball rolling....

jeff m · 10-30-2002, 08:26 PM

Sorry to hear you still have this problem.
In addition to what Bruce has suggested.
As it's rpm related, set the hand throttle to the rev range till you get the noise, go to rear of car and listen could be just vibrating tin.
I'm not sure if a worn injecter pump belt would cause this, but it's worth checking if you have a mirror.

I suspect you are not too happy with your mech, or you would be back there!
I'm not sure what he meant "changing over the timing mode". I'm no expert, but I have adjusted my pump, and I've read quite a lot and I'm not aware of any change of timing re pump. The pump timimg is set at about 400 degrees after TDC # 1.

For your popping I suggest you hold revs at 2000 (hand throttle off) by the rack and press the micro switch. The fuel shutoff sol will operate and cause the engine revs to drop. This will prove your speed switch, micro sw and fuel shut off sol.

Post again with your findings.
Also which part of London are you, as if you are the Essex side I know someone who has a P parts business, maybe he could help you or reccomend someone who can.
But with this type of car it's better if you can do it yourself.

Jeff
911T

youzoid · 01-08-2003, 03:08 PM

well it turns out it was a failed tensioner on one side. I found a great mechanic who knew as soon as he heard the noise.

He also found plenty of other things to fix, including the heat exchangers which were completely rotted away. So as well as the engine running a whole lot better, now i actually get some heat in the cabin.

Sounds so sweet now, I'm not so worried about investing in it a little more...

Next on the list is a new front A-arm and new shocks all round.

Unfortunately he also said (and I agree) that a couple of synchros have gone, so pretty soon i'm going to have to get the gearbox opened up.

After that it'll be a visit to the body shop.

And finally (if I live that long) I'll start on the interior.

jeff m · 01-08-2003, 03:33 PM

Nice of you to post the solution after so long.
Jeff

Bobboloo · Bobboloo's Garage

Lady luck shined on you. You dodged a failed tensioner bullet.

Bobby