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Recovery & Restoration of '80 931 in storage for 17 yrs.

 
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sat Nov 13, 2021 2:21 am    Post subject: Recovery & Restoration of '80 931 in storage for 17 yrs. Reply with quote

Thought I'd start a new thread here as I know I'll be having tons of questions on getting this car running and on the road.

I am a seasoned mechanic but never professionally, but been wrenching vehicles of all kinds for almost 60 years and have a full shop....almost finished restoring a sweet '76 914 after 4 years and over 400 hours of B,S & T's....all worth is.

Car was stored properly in dry building, under car cover, full tank of gas, for 17 years and is in incredible condition. Engine starts instantly on ether & runs smoothly & sounds great - but at my insistence owner only did it for 30 seconds....as I was 400 miles away. Owner moved from Ohio to CA, but later returned. Bought car in '86, thinks he was 3rd owner. Car put in service on 5/25/1980.

Car does not have M471 pkg, but many of its parts like 23mm front and 14mm rear sway bars, leather-wrapped steering wheel, Pasha interior (interior in very good condition). Wheels are 15" w/rear drum brakes, but I may be able to live with that as I'll not be tracking the car, but driving it for my own enjoyment. But I will push it as I do my other Porsche's on the twisty roads where I live between Richmond and Charlottesville VA.

Both fuel pumps are bad, want to eliminate in-tank pump - have read that there is no problem with doing that.

Is that true?

TIA,

GN
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sat Nov 13, 2021 9:03 am    Post subject: Reply with quote

Friend found this, so I'm good to go.....

http://www.924board.org/viewtopic.php?t=38783

Putting in newer fuel pump from '88 924 S that doesn't have in-tank pump, the fitting in tank that just has the screen, Part # 924-201-081-04-M100

GN
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chuck21401  



Joined: 20 Feb 2005
Posts: 460
Location: Annapolis, MD

PostPosted: Sat Nov 13, 2021 11:11 pm    Post subject: Reply with quote

Looks like you've been doing your homework. I didn't see it mentioned on the other thread...you know that you should replace the timing belt before getting it running right? The 931 is an interference engine, if the old belt breaks that will shut down the fun in a hurry.

Looking forward to more updates.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler.
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sun Nov 14, 2021 5:20 am    Post subject: Reply with quote

Chuck -

Yes, you might read in other posts that timing belt is at top of list. When sitting for so long they are more likely to break than if they were running all that time....

Keep the suggestions coming - you'll be sure to hit one I've missed....

GN


chuck21401 wrote:
Looks like you've been doing your homework. I didn't see it mentioned on the other thread...you know that you should replace the timing belt before getting it running right? The 931 is an interference engine, if the old belt breaks that will shut down the fun in a hurry.

Looking forward to more updates.
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sun Nov 14, 2021 11:59 am    Post subject: Reply with quote

Well, well, well. Turns out the tank was empty. Bad fuel gauge sending unit.

Drained what little gas was left and trash well looks incredibly clean. Yes, some small piles of rust, but really not much. Tank looks really good looking into sending unit hole - very pleased. Will clean out trash.

Have strainer fitting and new fuel pump to install in next few days.

Incredible "divine appointment" this morning at local Cars & Coffee.....met a guy who specializes in finding, restoring & selling old Euro cars, especially Porsche's. He is both a dealer and a mechanic, searches the country for cars to restore & sells them world-wide. What a resource.

He gave me some incredible tips - and warnings. Said the fuel distributor on the 80 & 81 931's was a real issue and that I needed to carefully open it (not disconnecting any banjo fittings to the injectors) to see if a rod moved freely.

I know this unit is very sensitive and cannot be rebuilt, and has to be replaced.

He said if the needle is stuck, which often occurs after long term storage, it can inject raw fuel in the cylinders and damage the engine.

Can anyone help me with this? Can't find anything about this in the Haynes manual.

TIA,

GN
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Cedric  



Joined: 27 Aug 2004
Posts: 2354
Location: Sweden

PostPosted: Sun Nov 14, 2021 6:24 pm    Post subject: Reply with quote

It's not really a common issue with the fuel heads, especially on cars that are run from time to time, not sure why he was saying thay. , the Fuel head can be rebuilt, but its easy to make it worse than it was before. I wouldn't even touch it at this moment. When you are done just run it, if it works and give the proper AFR don't touch it. Check out autoanatomy on YouTube, he did a video when he rebuilt his fuel head.
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sun Nov 14, 2021 11:42 pm    Post subject: Reply with quote

Pricesless advice Cedric - THANK YOU!

He did say something in them would get stuck when the cars sat for a long time. I'm much more comfortable not touching it.

I will flush fresh fuel to it with return line removed at connection between hose and hard line, then maybe pull each injector line at the injector & test for flow individually.

GN

Cedric wrote:
It's not really a common issue with the fuel heads, especially on cars that are run from time to time, not sure why he was saying thay. , the Fuel head can be rebuilt, but its easy to make it worse than it was before. I wouldn't even touch it at this moment. When you are done just run it, if it works and give the proper AFR don't touch it. Check out autoanatomy on YouTube, he did a video when he rebuilt his fuel head.
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sat Dec 04, 2021 12:42 pm    Post subject: Reply with quote

Guys -

While I am not unfamiliar with Bosch FI systems, this CIS on my 931 is totally new to me.

Wondering what this sensor in the boosted intake plenum is where my screwdriver is pointing? Cannot find in Haynes manual. What does it do? and what should be its resistance cold? I'm getting less than 1 ohm.

JUST FOUND IT ON P. 116 of Haynes manual - the Boost Pressure control switch! Duh!

So what would have been the effect to remove this switch from its circuit?


Or, HOW does it control the boost pressure? Read how to test it - it's just a N.O. pressure switch that makes at 15.6 psi and breaks again at 21 psi. I thought the waste gate controlled boost pressure.......


Thanks!

See note after my pic.....



The PO told me a switch on the console was a secret kill switch - and it appears to have been wired to this sensor to either have it in a circuit or removed from it. Two non-original wires ran from this sensor to the console switch.

Anyone who can point me to an electrical schematic of the sensors in the CIS system, I would greatly appreciate it. I do have original factory manuals but have trouble finding stuff.

TIA,

GN



Cedric wrote:
It's not really a common issue with the fuel heads, especially on cars that are run from time to time, not sure why he was saying thay. , the Fuel head can be rebuilt, but its easy to make it worse than it was before. I wouldn't even touch it at this moment. When you are done just run it, if it works and give the proper AFR don't touch it. Check out autoanatomy on YouTube, he did a video when he rebuilt his fuel head.
[img][/img]

Last edited by Gatornapper on Sat Dec 04, 2021 10:45 pm; edited 2 times in total
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Sat Dec 04, 2021 12:46 pm    Post subject: Reply with quote

Another question: New water pump, idler pulley, timing belt, alternator belt all IN.

Heck of a time getting A/C belt off even tho tensioning screw was loosened with slack.

Now I cannot get the A/C compressor belt back on the compressor pulley. No matter what crowbars & large levers I've used, I cannot get the compressor close enough to the crankshaft pulley to get the belt back on. It simply will not get any closer.

Tips or techniques? I must be missing something.

GN
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chuck21401  



Joined: 20 Feb 2005
Posts: 460
Location: Annapolis, MD

PostPosted: Mon Dec 06, 2021 11:56 pm    Post subject: Reply with quote

Gatornapper wrote:


JUST FOUND IT ON P. 116 of Haynes manual - the Boost Pressure control switch! Duh!

So what would have been the effect to remove this switch from its circuit?



A better name for it might be the overboost switch. When that switch senses an overboost situation, it cuts the power to the fuel pump. The overboost switch is the ground for the fuel pump relay. If the switch is bad, the car does not run. Many will ground the wire running to the overboost switch to eliminate it as a possible cause for the fuel pump not running.

The 1980 924 turbo wiring diagrams are included in the document "Porsche 924 Turbo Assembly and Adjusting Instructions" starting on page 52.

The overboost switch is called the "manifold pressure limiting switch" on the diagram. A brown/white wire runs from the back of the fuel pump relay to the switch. A bad connection and/or bad switch can be the source of trouble.


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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler.
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Tue Dec 07, 2021 11:48 am    Post subject: Reply with quote

THANKS Chuck!

So simple. A fuel-pump emergency cut-off. Pretty fool-proof, but then preventing a blow-up on a turbo-charged engine is hyper-critical.

One more question: Haynes manual says the switch is a N.O. switch, and does not "make" until it sees 15 psi. It stays "made" (closed) from 15 to 21 psi, when it opens again - cutting off the fuel pump.

But how does the intake reach 15 psi without the engine running? If switch is open at less than 15 psi, there is no fuel pressure with which to start the engine.

This obviously is not the case as all good 931's start easily. That would tell me there has to be some bypass switch to provide power to the fuel pump until the 15 psi is in the intake.

Or is the Haynes manual just plain wrong?

Thanks,

GN
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Gatornapper  



Joined: 23 Oct 2021
Posts: 254
Location: VA

PostPosted: Tue Dec 07, 2021 1:00 pm    Post subject: Reply with quote

I think the Haynes manual is wrong. Switch is N.C. - normally closed - and only opens at 21 psi.

Otherwise car would not start.

Need to go back and re-read the testing section for the switch.....maybe I read it wrong........

GN
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