Update: Mechanic's opinion about drone noise from turbo area

[Vroom]

9/8/01 Update: mechanic’s opinion about drone noise coming from turbo area

Hi guys, My mechanic has spent a fair amount of time trying to isolate this noise. We can get the noise on the highway, but not in the shop. He pulled the boot and checked the turbo, says it is fine. His feeling now is instead of spending hours and big money looking for it, he’d rather I drive it a while and hope the noise gets worse so he can find it in the garage, says it’s probably one of the exhaust pipes coming from the turbo...says these pipes are double walled and the inside wall often deteriorates, but says there are several pipes to consider and he doesn’t want to go searching without being sure of where to go.
He disconnected the turbo and tested, and discovered that the car ran without the noise, so it IS related to the turbo, but not the turbo itself. Anyway, we’re getting closer.
Have any of you experienced this kind of drone noise coming from the engine when you are accelerating in 4th and 5th, or even de celerating. The times when the air movement is the strongest in those pipes I imagine?

Any advice? He says I won’t hurt the car by driving it. But he doesn’t want to waste my $.
That I’ll just have to live with the annoyance until it develops more clearly.

I left some of my previous notes about this below.

Ave new owner of 86 951

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Porsche questions 9/6/01

For the list:

1. My mechanic just drove with me for about 15 minutes to get the noise to occur. It did, the droan in front of us, in 4th or 5th gear, but now also in neutral with a little revving. He checked the drivetrain and said there’s nothing wrong there. He thinks it is most probably something to do with the Turbo, something binding up maybe or something with the turbo exhaust. So he wanted to know if I was ready for him to dig deeper. He said it would be about 6 to 7 hours work and that once he got in there, he is sure that he can find the cause of this noise. It is a very obvious annoying droan sound. My brother in law , who sold me the car, also said that he was starting to hear some noise, and thought it was probably the turbo going bad.
I gave the mechanic the go ahead and am anxious to have it fixed.

Can I get your thoughts? Does this sound like it’s the turbo?

If the turbo does need to be replaced, where should we go for parts? This mechanic is a very nice guy, friendlier than any other guys I’ve worked with in the past. He is willing to work with me on parts, if I can find parts more affordably than he can.

Ave
86 951 white on black, .....getting TLC from its’ new owner!

[944Driver]

I had a similar problem with a previous car, Eagle Talon turbo awd. My drone came in 2nd and sometimes 3rd gear. As soon as I let my foot off the gas, it would drone and kind of howl. The higher the rpm, the louder the noise. It had all the mechanics scratching thier heads. I sold the car before finding anyone who knew how to fix it. Years later, I brought up the subject to a mechanic who claims to have seen this in turbo-charged cars many times. I can't remember the details of the conversation, but he said it was definately a turbo problem. Might be a place to start looking??

[geoffbaltz]

What do you mean by drone noise? Is this a rattle?

[Vroom]

The drone sounds like a drone of some sort, when the engine is warm, and I'm shifting 4th to 5th, and back, mostly in the gear, not neutral. We discovered it also happened when letting off the gas pedal quick and de celerating.
His opinion is that it's coming from one of the exhaust pipes from the turbo. That the interior of one of the pipes might be going bad. He has checked everything else, bearings, and so forth. Turbo is OK.
What else can crack and make noise as the engine gets to normal operating temp?

[bill*924s]

My 86 944 NA had a noise problem once while still under warranty. Don't remember exactly what the noise was but one of the things they did was re-align my exhaust pipe. I remember the guy at the dealership saying that if the got out of alignment, they'd make some wierd noises. Good luck with yours.

[geoffbaltz]

My 86 951 had a terrible rattle that we couldn't find either.

1st) Thought the O2 sensor was rattling in the exhaust - that was fine. Still rattled.

2nd) Thought the double-walled downpipe had separated - replaced it with 3" SS downpipe and cat bypass from fabspeed. Still rattled.

3rd) Checked the turbo, the heatshields, and anything else that might be loose. Still rattled.

4th) Replace the small (8" long) pipe that comes right off the turbo and the downpipe bolts to. THAT WAS IT!! That pipe is double-walled also and had split on the inside where the inner pipe is welded at the flange on the turbo side.

Smooth as silk now and no noises.

I have the original part still - I will snap some shots tonight and post them here of the split on the inner portion of the pipe.

BAD NEWS: THIS PART IS NOWHERE TO BE FOUND IN THE USA. I HAD TO ORDER FROM PORSCHE AND IT CAME FROM GERMANY AND TOOK ABOUT 10 DAYS. $400 FOR THE PART.

I would NOT replace it with a used one either. You are just asking for problems. This pipe is subjected to some serious temps and the expansion and contraction takes it's toll. Not easy to get to either.

Hope this helps.

-G


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Geoff Baltz
'86 944 Turbo
http://www.ninefiveone.com

[Vroom]

Geoff, Thanks for the info. I wouldn't describe this as a rattle, but a drone in gear accelerating or de celerating. And just a little when I quickly go to neutral and rev the engine.
But my mechanic seems to feel it IS related to those pipes coming out of the turbo. He just wants to be able to hear it happen in the shop so he can quickly isolate the problem area.
Ave 86 951

[geoffbaltz]

Here are the pix of the f'd up pipe:








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Geoff Baltz
'86 944 Turbo
http://www.ninefiveone.com

[geoffbaltz]

If it is this pipe you do not have to replace it immediately. It will not hurt anything except for your ego.

You could wait for it to get worse (and it will) to make sure of the source of the noise.

Only downside to that is if it's something else you might be causing some damage.

Good luck my friend.


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Geoff Baltz
'86 944 Turbo
http://www.ninefiveone.com

[Vroom]

Geoff, Thanks for the photos and feedback. The mechanic sincerely thinks that nothing is being damaged by the noise, I guess based on his examination of everything else. He even told me to make sure to run it hard, get the boost over 1 bar, thinking that this will get the noise to increase or stay longer.
For future reference, where are you located?
Ave 86 951

[geoffbaltz]

St. Louis