924Board.org

[00Smurf]

Just picked up my 1980 931 this week. Not new to porsche's but new to the 931. Previous cars included a 1987 928s4, 83 944na and a 86 951 turbo.

I'm running into a couple of problems with the new purchase. When it was parked by the PO 4 years ago, it ran fine no problems. It was also stored with a full tank of gas. From reading ive seen that these cars don't like to be not driven for a while. The day before i came to pick it up, the PO drained the old fuel and did an oil change for me. When i got there the car started up and ran fine, there were a couple of misses and some hesitating but i attributed it to the old fuel. We completed the title change over and I proceeded to drive her to the gas station and fill her up with a full tank.

With the new tank of fuel, the misses and the hesitation went away. About 15 miles into my journey home, the car starts bogging down very bad under throttle, but when i lift it idles fine. I babied it for a while but eventually the rpm's gradually dropped to where it could only idle, then it wasn't able to idle either. There was also a loud whine from the back that got louder as the rpm's dropped(fuel pump i think).

Pulled over, checked things out figuring it was a boost leak. Looking it over I didn't see any problems, this was after about 30mins. I got back in and the car started back up after about 20sec's of turning the key over (hot start problem?). Rev'd the car a bit and things seemed good to go. The whine was gone as well) Got back on the freeway and got about 10-15miles before it did the same thing. Once again the whine came back as the rpm's lowered. (by lowered i mean that i could only throttle the car to a certain rpm before it bogged down, as it got worse it would only rev to 5k then 4k then 3k etc), once again lifting to idle was fine, until the very end.

What my buddy and i think is the cause is that the old fuel left in the tank rusted it a bit plus any old detritus was dislodged when i put the new tank of gas in. As I ran the car, more and more gunk clogged up either the inline sock or the fuel filter which caused the fuel pressure to drop gradually and eventually choke the engine out. The loud whine i believe was the fuel pump being starved for fuel. Does that sound correct to you?

I believe i've burnt one of the fuel pumps up either the in tank or external one (how would i check). When going about fixing this, what all should i replace (pump's, filter etc?). My thought was to replace the entire fuel tank but i can't seem to find one at all. I found an 86 951 being parted out, will the tank from 951 fit into the 924? I know they are basically the same frame.

Other small problems are electrical gremlins mostly. Wipers are intermittent, fuel gauge doesn't work, the oil pressure gauge jumps back and forth when you mess with the air controls. Lights don't go up or down all the time. Horn doesn't work nor do the electric mirrors or the rear defroster. The speedometer jumps back and forth quite a bit below 55mph. Are most of these just bad grounds? Nothing more than cleaning up the contact points to fix?

Also fuses 7 and 9 keep blowing. What accessories or components are wired to these 2 fuses?

Thanks for any help you can give. Great board btw.

[00Smurf]

Some pics

[tuurbo]

Hey Smurf Guy, nice car!

Ok I'm not a technical dude but I can parrot what other people have told me and maybe give you the benefit of some expensive experiences. My car was stored for 2 years outdoors and was a mess. I don't think these cars like being stored - I think it screws them up big time.

1. Paul will probably say you should check your system and control pressures and I'd say that is the first thing you should have examined.

The whole fuel system seems (from my meager investigations) to be based on a 'balance' or 'stasis' between system and control pressures. There are, as I understand it, a few points along the system where you can measure the system and control pressures. Once you have these pressures measured and logged, you can bring these numbers back to the experts here at the site and probably get your guesses narrowed down to ONE or perhaps two only possible problems. That will save loads of cash. And it's exactly what a competent Porsche dealer would do.

The other options, of course, are (1) adjust your fuel mixture until your head explodes and (2) replace parts based on likelihood or best guesses where there are more than one likely culprit. I've found this to be expensive in terms of time and money.

2. I was told I wouldn't regret replacing as many vacuum lines as I could possibly reach. So I took a Saturday and replaced about a dozen or so vacuum hoses. I bought about 10' of hose and I think mine is 3.4 or 3.5 mm ID hose. Smaller stuff (1/8" ID) won't slide into place so go slightly larger. I've been very happy since doing it.

Rasta might say get the right steel squeezy fittings from Porsche and he's right. I picked up some that are pretty close but I didn't have time to install the steel pieces yet, so I used zippy ties just temporarily. They work fine for now and allow me to run the car. I'll get to the steel pieces once the other 20 tasks on my list are done.

3. I replaced my WUR and (going to replace) the throttle positioning switches. Since replacing the WUR the performance of the car has been much better. You might want to keep some money aside for a rebuilt WUR ($250) and a couple of switches ($50 a piece) before jumping in and buying a new pump. But your control/system pressure tests will lead you in the true direction. I compared my new TPS against an old one and the difference is night and day - one clicks, the other doesn't. No wonder the car had problems, right?

4. There are documents, on the web, that contain the 1980 Factory Service Manuals, and other junk. Here's a list of what I've got.

Porsche_924_Workshopmanual_VOL-1-Engine.pdf
Porsche_924_Workshopmanual_VOL-2-Transmission.pdf
Porsche_924_Workshopmanual_VOL-3-Chassis-Heating-AC.pdf
Porsche_924_Workshopmanual_VOL-4-Body,%20Electrics.pdf
product_variation-installation_pdf-8-1.pdf
Porsche PET 924 -79.pdf
Porsche 924 Turbo Model 80 Service Information.pdf
Porsche 924 Turbo Assembly and Adjusting Instructions 1980 MY.pdf
Porsche 924 technical Specif.doc

The electronic ones are illegal because of copyright but they ARE available on the web and I got mine from a Spanish speaking site and a European site - a clever web search should help you find them. I can't give you the link because the Administrators here will remove my nuts if I do.

5. I replaced all the visible grounds in my car. I also cleaned the fuses at the fuse box and I always clean any electrical connection I can find.

Anyway, that's my two cents worth. It should get you started thinking in the right direction.

Look for a thread here on how to resurrect a dead turbo.
_________________
1980 924 turbo, MSD, Meth. Inj, otherwise stock.

[924guy]

good post above, i would add a few things though.

1. find and clean all grounds. you can search here for the locations. bad grounds will results in all sorts of strange behavior that is easy to mis diagnose in these cars.
2. disconnect, clean, reconnect the plugs for the ignition control computer under the dash. generally more of an issue with the ditc cars, but it cant hurt.
3. change the fuel filter, drain and clean the fuel tank (again?) .. sounds like the drive home and new gas loosened up allot of sediment.. then check the spray patterns at the injectors (search and you will find the proceddures..)

take care of the basics first, if the problem persists then you can move on to the more complicated solutions and more accurately diagnose the trouble areas. I think most of us on here have at one point spend allot of time and money on a complicated solution, only to have it turn out to be something very basic.
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[00Smurf]

Excellent post's thank you. I'm starting my diagnosis monday. MY big concern is a new tank though. Will the 91 tank fit on a 931? I haven't found anything thru search?

[Smoothie]

From vague recollections of topics here long ago, I think there'd be problems swapping to a 951 tank. Would need verification, but I think the 951 tank would be plastic? -And I think the 951 would have a removable cross-piece that comes off before or during tank removal. -While the comparable cross-piece on the 924-931 is welded on. -And I'm pretty sure there's something about it on 924.org in the tech section or faq.
_________________
"..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

[Mike924]

I raised the question of fitting a plastic 951 tank to a 924 a few years back and was told very emphatically (by gohim) to 'forget it'!
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[Smoothie]

http://www.924board.org/viewtopic.php?t=9669&start=17
http://www.924board.org/viewtopic.php?t=16059
_________________
"..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

[00Smurf]

[pettybird]

You bought that about 3 minutes from my house--I was going to go look at it but I'm not sure what to do with mine, or what I would do with another!

What did you end up giving for it? It was on craigslist for quite a while...

Doug
(in Brooklyn)

[ideola]

I have an extra gas tank removed from a 1981 931 if you're interested, including the mounting straps.

Here is the aforementioned resurrection link...definitely worth a read.

Good luck, and welcome to the board.
_________________
erstwhile owner of just about every 924 variant ever made

[00Smurf]

[00Smurf]

[00Smurf]

also where do i get the replacment vacum hoses. i got 3 ft of each size from advanced auto parts. but i have a feeling i will need some bigger sizes. these were like 3/32 5/32 7/32 9/32

[ideola]