911sc running rough

chockymonster · 08-09-2012, 02:59 PM

Hi all,

I've just purchased an UK 82 911sc that has been parked in a garage since '99 with no prior thought to laying it up.

I've replaced the battery, fuel tank, fuel pump, fuel filter, oil and filter and got the thing running.

The first fire was fantastic, the car ran as sweet as anything, steady idle, revved freely (tacho doesn't work though)
The next fire up couldn't be any more different, the car now runs as rough as anything, lumpy idle and then stalling.

I was wondering if anyone had suggestions of where to start to try and diagnose. I'm going though checking the wiring that has been displaced to do what we needed to do but the oddities of the porsche is new to me!

Joe Bob · Joe Bob's Garage

CIS is always about fuel pressure. Get some gauges and work from there......may also have clogged the fuel filter from residual crud in the lines.

OsoMoore · OsoMoore's Garage

Check your oil cap. If you took off the cap to check the oil and didn't put it back on properly, you will get that problem.

Bob Kontak · Bob Kontak's Garage

Welcome

I would focus on the fuel system.

The fact that it fired and ran ok is great news. However, 13 years of resting will cause deposits to form and you more than likely broke some of those loose and clogged some passages.

There are some tests you can perform to make sure your car is delivering fuel to the injectors.

Also, CIS routes fuel back to the gas tank if it does not use it. If that passage is clogged your control pressure (like a metering pressure) jumps up about 40 PSI to system pressure and confuses (leans) the hell out of the fuel delivery to the injectors.

Others with more knowledge than me will respond. They will advise you to get a set of fuel pressure gauges. Please do this as you will be a blind man without them.

Read some of this CIS primer to help you on your way.

CIS Primer for the Porsche 911

limble · 08-09-2012, 06:25 PM

My 79 occasionally runs rough (sticky injectors) so I take a 1 foot long rod and a hammer and lightly tap on each injector. This usually loosens them up. Another tool for the CIS tool kit.

jeffs9146 · 08-09-2012, 07:19 PM

Check the WUR, clean the injectors and flush all the lines leading into and out of the injection system! Old fuel in the injector lines can mess with just about every part of the injection system!

I just went through this with an 82 3.0L SC that I had sitting in my garage for 14 years! It ended up being a gummed up WUR and a leaky intake box! Now it runs like a champ!

chockymonster · 08-10-2012, 01:31 AM

Thanks for your suggestions all.
Oil cap is definitely on properly, fuel lines are a good point as the original fuel tank was actually blocked solid.
The thing that is confusing me is that when we get it running, even lumpily as it does, there is no power to the WUR etc.

timmy2 · timmy2's Garage

Check your large multi pin connector from the engine to the fuse block, should have constant power to WUR and the AAR.

chockymonster · 08-10-2012, 02:57 AM

AAR?
Is that the 14 pin plug? Car is in the garage and I'm in the office so I'm going from memory!

chockymonster · 08-10-2012, 03:33 AM

I'm guessing that the AAR is marked as supplementary air valve on the current flow diagram?

I'm trying to follow through the current diagram from this site, I understand how to follow the diagram but can't make sense of the T designations, on the earlier diagram for the 78sc the first page has a reference section which would lead me to believe that the WUR is fed from a 14 pin connector, but what does the little 10 mean? is that simple enough to mean pin 10 (here's hoping!)

Bob Kontak · Bob Kontak's Garage

There are three air valves.

AAR
AAV
Decel Valve

Only the AAR (Auxilary Air Regulator) has juice going to it so your assumption about the supplementary air valve has to be correct.

See the CIS primer link in my post and look at the parts ID link for pictures of the parts. The decel valve is different on ours vs the earlier SC's. The decel valve on the newer SC's is one of the two flying saucers on the right hand side (driver's side for RHD) that has a small hose port. The AAV has a larger hose.

The T is for Terminal I believe which is the connector. The 10 would mean which pin in the 14 pin connector. The numbers are cast into the connector. I have the connector locations for at least my 81SC and bet there is one for the 82 in my factory manuals I can send you (Although little if any difference)

PM me your e-mail - click on my user name and you have options to send a PM thru Pelican or send me an e-mail. If you choose the e-mail option it will deliver your e-mail address to my e-mail inbox with message.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by chockymonster

but the oddities of the porsche is new to me!

Oddities? What oddities?

chockymonster · 08-10-2012, 06:45 AM

Quote:

Originally Posted by Bob Kontak

Oddities? What oddities?

Who knows

I like it when problems are easy to fix, bad connection at the 25A fuse in the front compartment caused the power issue. There was enough power to prime the pump but nothing else. The rough running was corrosion on the engine harness.
Now to find out what else needs attention after 13 years in a garage. (Tyres and brakes first!)