SC poor performance

[Groesbeck Hurricane]

Bob,

I wonder what would happen if he taped up the carbon canister feed? It is a small hole but could it not create a slight vacuum loss? Just wondering out loud here...

Johntom,

The frequency valve is still providing some control but it is likely just providing a standard loop as Bob states above.

Nothing at all wrong with being in the UK, wish I were there now!!!

There are UK members, they are likely not up at this hour though. I would update my location to UK and hopefully some of them will jump in to help as well.

Cheers,

[Bob Kontak]

Tape it - right now it is just sucking air (and dirt) in after the filter and before the air sensor. No false air issues.

Edit - professionals say you want the canister functional. Gasoline vapor can be vented into the atmosphere vs being filtered thru the canister - then back into the intake.

[psalt]

johntom,

If you have a ROW SC, you can ignore the advice about the lambda system.

Paul

[Paulporsche]

Have you had your CO checked? How about your control pressures (WUR)? A too rich mixture can cause exhaust popping on throttle back off. Sometimes people richen the mix to try to make up for other problems, like vacuum leaks or incorrect control pressures.

I think I read someone suggesting timing and distributor function, but I'm not sure if I noticed that you checked it.

Did you test or replace all ignition parts as part of your tuneup?

[Bob Kontak]

psalt is absolutely correct.

To be honest, I thought US and RoW cars both had the O2 system. I looked at the Porsche parts diagrams I have in pdf format and they show a picture of the O2 sensor for RoW cars but no corresponding parts listing. The only O2 part listed is the rubber grommet used to plug the drivers side inner fender hole the wire passes through on Lamda cars.

[trond]

my 80SC was gutless too, felt like maybe a 90 hp car. What I found was one bad spark plug connector and a maladjusted throttle cable giving it maybe 3/4 throttle only with the pedal to the floor. WIth that sorted it was still low on power especially in the midrange with no throttle response at all. It was lean surging and the exhaust tip was almost white and the CIS was obviously not working as it should. It was all cured by installing a tbitz EFI kit. After the install the car has sharp throttle response and dramatically more power especially in the midrange. It is in my opinion a much better option than throwing money at the out of date CIS. I recommend it for any CIS equipped 911 whether it is running good or not because of the added throttle response

[johntom]

Hi
I took the car to a local specialist to try and sort out the performance issues, he immediately said the car was running too rich. In fact the CO was around 6.9 so he reset it to 3 and adjusted the tickover to 900rpm. Before the adjustment the car backfired occassionally when taking your foot off the gas to change down the gearbox, now the backfires seem quieter but happen everytime when you take you foot completely off the gas - ie at the moment when the throttle closes ?
Would incorrect timing cause this?
Also whilst changing the hose from the oil filler to the intake i noticed that the air sensor plate doesnt sit perfectly square, there seems to be a gap at one side but not alround, is this correct ?

[David Borden]

clogged injectors?

[DanielDudley]

Originally Posted by gathomas

My bet is a clogged-up filter screen on the WUR intake line. Simple enough to take off the line and blow it out w/ some compressed air.

Did you try this ?

[boyt911sc]

Originally Posted by johntom

Hi
I took the car to a local specialist to try and sort out the performance issues, he immediately said the car was running too rich. In fact the CO was around 6.9 so he reset it to 3 and adjusted the tickover to 900rpm. Before the adjustment the car backfired occassionally when taking your foot off the gas to change down the gearbox, now the backfires seem quieter but happen everytime when you take you foot completely off the gas - ie at the moment when the throttle closes ?
Would incorrect timing cause this?
Also whilst changing the hose from the oil filler to the intake i noticed that the air sensor plate doesnt sit perfectly square, there seems to be a gap at one side but not alround, is this correct ?

johntom,

CIS engines are easy to maintain and will start on demand regardless of weather. But the key is keeping all CIS specs within reasonable variance. Don't expect the car to run great if you have it set incorrectly. The air sensor plate should be set precisely centered @ idle. Air gap all around it. The control and system pressures both at cold and warm should be closed to spec. And lastly, not being able to find an air leak does not mean you don't have a vacuum leak. There are so many spots and locations that could have an air leak specially at the rear side of the engine which is not accessible for inspection with the engine installed in the car. Many CIS owners have given up their CIS due to frustration and failure to keep the CIS running good!!!!

But what I found out from a few of these previous owners of CIS, is the lack of understanding and knowledge about CIS!!!!! They blame CIS engines to be difficult to maintain and unreliable. TRUE!!!! Simply because they lacked the knowledge about the system. Talking about outdated technology, carburated engines is pre-historic compared to fuel injection systems!!!!

One of the most blatant mistake commited today even by experience DIY guys or mechanics is tinkering the mixture screw without verifying or knowing the presence of vacuum leak/s in the system. Like in any other fuel injection system, fuel pressures and vacuum should not be compromised!!!!

TR Conway's engine. A Pelican member from NJ.


J Wirth's engine. A Pelican member from PA.


A. Tiongco's engine. A Pelican member from CT.


T. Donato's engine. A Pelican member from PA.


CIS troubleshooting is a lot of fun and I do it for free!!!! Avoid the quess work and you'll enjoy it like I do. BTW, this is just a hobby for me. I spend most of my free time in the golf course or travelling.


Tony