924Board.org

jg4454 · Joined: 07 Dec 2004 Posts: 34

Thanks to all of you who make this website happen, especially Mr. Scott.

I have a 1982 MY 924 Turbo, manufactured 8/81, and have noticed a very alarming problem. When I step on the throttle, it seems like my turbocharger doesn't want to quit, and I get a lot of power until my car actually dies for a split second. It feels like the engine stops, sometimes my tires even squeal. I know it has to be bad for my clutch. It happens in higher gears, usually 3rd and up. It even happened on the interstate in 5th. My car seems to "kick start" and continue running, but I must fix this problem soon.

I've read all the posts here about overboost, the wastegate diaphragm, but before I go to Air-Cooled Classics, a great Porsche shop here in East Tennessee, I wanted to post this on 924Board.org, and ask for your advice.

Is it my wastegate diaphragm? How many hours will it take?

I love my 931. There are only two here in Knoxville. I've had the car for one year now, and consider the Porsche experience to be fun and educational. 924.org is the reason I bought it. Any help from the regulars here is greatly appreciated.

Again, thank you to all the Porsche drivers who have helped me enjoy my car.

Sincerely,

Richard J. Gettelfinger
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"Speed is a matter of dollars. How fast do you want to go?" - Somebody said this in Road and Track once.

Smoothie · Posted: Fri Dec 24, 2004 1:06 am Post subject:

It's most likely the diaphragm, with just a very slight chance that it's a loose connection at the overboost switch. Also, check the wastegate control line that comes off the charge tube opposite to the overboost switch - make sure that's tight. Assuming you checked the connector and control line... The diaphragm part might cost anywhere from approx. $60->$100. Part of that variation's due to different prices from different retailers, and part's due to different diaphragms - you can get them made of either rubber or teflon. I've done it myself, but tend to goof off and take my time and can't even guess how long it's supposed to take professionally, but having experience doing it already, I'd guess it should be done in 2-3 hours.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

...and don't forget that to pull and replace the wasegate, 4 gaskets will have to be replaced, add another $80 bucks or so.

As Smoothie suggests, double check that switch and both ends of the control line. With luck maybe the line has vibrated loose or has a hole in it.
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'79 Eurospec 931

bass gt · Posted: Fri Dec 24, 2004 6:36 am Post subject:

Smoothie,

What is the exact purpose of the over boost switch? Is it something that can be ditched, or is it a vital part of the management system?
The reason i ask, is that i currently appear to have a 1 bar spring fitted to the wastegate, and was wondering if the switch cuts in at the original factory boost level(0.7 bar IIRC)Euro car) thus making the new spring pointless

As always,

Many Thanks,

Steve

Smoothie · Posted: Fri Dec 24, 2004 7:24 am Post subject:

I don't recall exactly, but the overboost cutout works at something around 1.5-2 bar boost. 23psi comes to mind for some reason and that's a little over 1.5 bar, so it shouldn't cause a problem with a 1 bar spring.
Definitely keep it in service. Its' purpose is to save your engine in case of something like a wastegate failure that allows boost to build unchecked and it does this by cutting power to the fuel pumps.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

numbbers · Posted: Fri Dec 24, 2004 11:15 am Post subject:

The overboost switch, which is located in the upper pressure duct, provides ground to the fuel pump. The idea is, that if your wastegate fails, the overboost switch will cut off ground to the fuel pump, and kill the engine, to prevent castrophic failure (read big bucks).

The overboost switch is supposed to come into play at 21 PSI, but I have tried three new ones, and they all limit boost to 16 to 17 PSI. You can bypass the switch by taking the wire off of the switch, and grounding it to the block. But, you are taking a chance. I eliminated my overboost switch several years ago, because I run 17 PSI on my '80, and the damn switch kept cutting me off in first gear. However, last year, my wastegate failed, and my boost guage was pegging (~ 23 PSI). The car went like hell, and never blew-up, but I was too chicken to keep running it that way. I rebuilt the wastegate, and went back to 17 PSI.
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1980 924 Turbo

bass gt · Posted: Fri Dec 24, 2004 6:57 pm Post subject:

Ah,

Well seeing as my car has been gutted, including the wiring, i think i may as well do away with it. I have just bought some SPA Digital gauges and they promise the boost gauge is extremely accurate. I was then planning on putting a manual boost controller in line with the wastegate pressure line. The reason for this is i am fitting a modified 951 intercooled, and with all the extra piping and bends, i want to be sure i can generate around the 1 bar mark at the plenum. Luckily, the boost gauge has an alarm function, so i guess I'll wire that into the fuel pump circuit.

Happy Holidays!!

Steve

jg4454 · Joined: 07 Dec 2004 Posts: 34

So what is our boost limit? I've heard the standard boost in the US is 4.5 psi, then 7 psi, then I heard the Euro figure is 7 psi, I 've read the CGT is 8 psi, and on this post people are talking 17 psi.

At what point is it safe? Reliable? Of course I want a faster car, but I don't want to blow a head gasket, or prematurely destroy a transmission. Both jobs are in the $1200+ range, and even the very wealthy think that is a good chunk of money.

Since it looks like I may have to do a complete wastegate job, can I consider the 1 t-bar spring a good option? Is it safe?

Thanks for all the good advice on my car, guys. This is the best 924/931 forum out here. Rennlist doesn't come close.
_________________
"Speed is a matter of dollars. How fast do you want to go?" - Somebody said this in Road and Track once.

Lizard · Posted: Sun Dec 26, 2004 4:36 pm Post subject:

jg4454 · Joined: 07 Dec 2004 Posts: 34

Thanks.

Is there a spring that will let me reach 10psi boost, without using an ic. The ic installation seems to be expensive.
_________________
"Speed is a matter of dollars. How fast do you want to go?" - Somebody said this in Road and Track once.

Paul · Posted: Mon Dec 27, 2004 9:40 am Post subject:

Yes but they are hard to find, it took me several months to find one. Unfortunately that is the only one my source had.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.