Can we talk about the factory stock fuel systems and how to improve the performance?

[Maxx1]

First of all, I hear alot about the CIS system, but even after a search, I'm in the dark about the details other than the European CIS was better than the USA version. CIS means Continuous injection system? How can you identify which fuel system your Porsche has? Did the Euro CIS cars have any difference in the head intake ports as well?

What upgrades can be performed from the stock Porsche CIS systems? What kind of HP gains can be made and at what cost? .... or is the CIS a pretty robust system and should be left alone?

[RarlyL8]

You're likely to get a lot of opinions on this subject.

If your 930 is an '82 and still has the stock CIS it is a Euro. All 930s had Euro CIS until 1986-1989.
The stock Euro CIS will support ~350RWHP or so with proper tuning and ~400RWHP or so with modifications for increased flow. The current popular CIS mods are the Leask adjustable WUR and the iA increased flow fuel head.
The Euro 930 long block is essentially identical to the US 930 long block. The bolt-ons (CIS and exhaust) are different.

[Maxx1]

So, 400whp with proper tuning for increased flow.

Naturally increased flow needs to be a proper balance of both air volume and fuel. Say you modded intake and added a header, what and where can you tweek on the CIS to supply the extra fuel? Next, how do you get a proper balance .... trial and error, taking plug readings, dyno runs ? The scary thing is, as far as I know there are no knock sensors on the old beast, so that would be a concern if the mixture wasn't rich enough.

[RarlyL8]

No, 400RWHP with modifications .

You have to tune the WUR and fuel head with an LM1 or on a dyno.
The purpose is to smooth out and optimise the A/F ratios throughout the rpm range. There are a few different ways this is approached. As you add power you will get to the point where the A/F ratio can no longer be adjusted to stay under 12.2:1 on boost. At that point you have to adjust the flow at the fuel head. When that is maxed you get the hi-flo iA head. When that is maxed you go EFI.

I always recomment getting an A/F graph of what you have before you buy any parts. You may not need any parts, just some tuning of what you have.

[Jim2]

What upgrades can be performed from the stock Porsche CIS systems? What kind of HP gains can be made and at what cost? .... or is the CIS a pretty robust system and should be left alone?

Perhaps there is some confusion here. The CIS mods only support power enhancing upgrades such as custom turbochargers, headers, intercooler, boost level etc. Upon or after installing these upgrades the CIS may need to be enhanced to prvide fuel flow if you develop an output beyond ~350HP. There is no improved performance (HP) derived from the CIS mods alone.

[Archie930]

I'm in the process of doing the usual mods, headers, intercooler, K27-7200 and muffler and having a lovely time with the header nuts. I'd be hoping to be up around the 380 crank HP mark.
When you say adjusting the 'flow' at the fuel head, is that different to the mixture adjustment, are you increasing fuel pressure? If so, how do you do it?
Is it absolutely essential that the A/R ratio be no leaner than 12.2:1 under boost?
There is a good dyno in town that can read the A/R ratio's etc.

Thanks guys
Archie

[NathanUK]

Do a search for
"Brian Leask"
"Adjustable WUR"
"WUR mod"

[DonE]

I just saw pics of your "new" 930. It looks pretty nice. Why are you diving into the CIS already? Is there something wrong? The stock system works extremely well, so go enjoy.

[Maxx1]

Originally posted by DonE
I just saw pics of your "new" 930. It looks pretty nice. Why are you diving into the CIS already? Is there something wrong? The stock system works extremely well, so go enjoy.

I want to learn about this car and how to work on it. Actually I am forced now to since it began stalling at just about every other stop light. I've wrenched on plenty of US and Japanese cars, so it's time to get familar with the Porsche. The fuel system and ignition are the most complex items to figure out on this car.

Actually, the car ran fine until I removed and replaced the intercooler ( trying to make more working room to install an ignition kill switch ). I probably screwed something up.

[RarlyL8]

Check the "O" rings on the intercooler base and the throttle body neck. Those can get pinched and cause a host of problems. I use a little oil on mine when replacing the intercooler.

CIS really isn't that bad once you get your head around how it works as a componential system. Most of it can be removed. The only components you actually must have for the car to run (in a mild climate) are the WUR and the fuel head. Everything else is for convenience or smog.

[Maxx1]

Originally posted by RarlyL8
Check the "O" rings on the intercooler base and the throttle body neck. Those can get pinched and cause a host of problems. I use a little oil on mine when replacing the intercooler.

CIS really isn't that bad once you get your head around how it works as a componential system. Most of it can be removed. The only components you actually must have for the car to run (in a mild climate) are the WUR and the fuel head. Everything else is for convenience or smog.

Thanks. For a while I thought you nailed it ... and that still may be the prob. I put some oil on the o-rings and reseated the intercooler assembly. It ran perfect for about 20 minutes through a series of stop signs, it was idling smooth as glass. I was heading home and it died again at the last stop sign, then died again pulling in my driveway. It just hit 180 on the oil temp gauge.

It's weird, the idle will drop from 1,000 rpm to about 500 rpm and then surge back up, then down again... but the whole time it's firing on all 6. In other words it's idling smooth, but erratic. When it dies it sounds like a flameout .... popping out the tailpipe or blowoff and such. Maybe the orings are shot... they don't fit real tight.

I went to the library today but they don't have crap on Porsches. Maybe I'll hit the book store and see what they have. I want to get a schematic of the intake system and see what's going on in an idle situation.

[mede8er]

Do a search on adjusting the air/fuel mixture with your 3 mm allen wrench tool...

Should get you smoothed out....

[RarlyL8]

That's what it sounds like, your idle mixture may be too rich.

Do you have access to a Gunson Gas Tester or an LM1?
If so check your CO% at hot idle and set it at 3%.

[Maxx1]

Originally posted by RarlyL8
That's what it sounds like, your idle mixture may be too rich.

Do you have access to a Gunson Gas Tester or an LM1?
If so check your CO% at hot idle and set it at 3%.

Yeah, that's what I was thinking since it runs fine while cold. I'll have to look into buying or renting a tester.... if they are affordable. Before I do anything, I am going to let it idle warm and then pull a few plugs and take a look. The strange thing is, it was running fine for the first week I had it, cold or hot, but then again I've been driving it easy and maybe the plugs are either too cold or mixture too rich, or both? Thanks for the input, I appreciate it and will post later once I troubleshoot some more.

[BMAN]

Originally posted by RarlyL8
That's what it sounds like, your idle mixture may be too rich.

Do you have access to a Gunson Gas Tester or an LM1?
If so check your CO% at hot idle and set it at 3%.

Does anything need to be unplugged? So just warm up the engine and turn the screw to get it as close to 3% at idle as possible?

Is this my CO screw to the right of the filter?

[mede8er]

Originally posted by BMAN
Does anything need to be unplugged? So just warm up the engine and turn the screw to get it as close to 3% at idle as possible?

Is this my CO screw to the right of the filter?

That's it.....

[WERK I]

Before going into changing the mixture control settings, have the CIS tested for the fuel system pressure. CIS uses varying fuel pressure to adjust for proper mixture under varying engine loads. If you're fuel pressures are off, you're going to be chasing your tail by turning the mixture adjustment screw.
The system fuel pressure test will tell you;
1. The delivery pressure from fuel pumps is correct.
2. The CIS fuel injection system pressure is correct.
3. This in turn will tell you if the fuel system pressure regulator (know as a Warm Up Regulator aka WUR) is working within system parameters.

After those checks, you can go after other areas that may be causing the problem. The Auxiliary Air Regulator (AAR) controls the amount of air going to the engine during cold startups. These devices sometimes stick open or closed, causing all sorts of problems.

In short, I found that electro-mechanical devices (fuel pumps, AAR's, WUR's) are usually the culprits in problems like you described over mechanical devices (idle mixture screws, idle adjustment screws). That is, unless someone tampered with the idle mixture screw to mask some other problem mentioned above.

[Maxx1]

Thanks .... Wow, the plot thickens. Sounds like a complex system. Most cars have a minimum acceptable fuel pressure spec and that's it.

I suppose there is a fuel pressure gage I can buy to put in-line to check all this? ...and then I'd need the specs to check at various engine temps and idle speeds? Looks like I'll be buying a service manual. I plan on keeping the car for the long haul, so I may as well get familiar working on it and don't mind investing the money in equipment if that's what it takes.

Am I in the ballpark with all this?

[WERK I]

Actually, the CIS is not that complicated and for the most part, it is extremely reliable. I think you can get the CIS fuel pressure tester fairly cheap....J.C. Whitney of all places. Other guys have used the tester and have gotten good results. It has two pressure gauges and the necessary hoses and fittings to hookup to various test points in the system.
Go to this web site and download the free copy of the Bosch K-Jetronic Tech Guide. Has something useful information in there to get you started.
http://www.phat-gti.com/downloads/boschtech-12d.pdf

[Maxx1]

Originally posted by WERK-I
Actually, the CIS is not that complicated and for the most part, it is extremely reliable. I think you can get the CIS fuel pressure tester fairly cheap....J.C. Whitney of all places. Other guys have used the tester and have gotten good results. It has two pressure gauges and the necessary hoses and fittings to hookup to various test points in the system.
Go to this web site and download the free copy of the Bosch K-Jetronic Tech Guide. Has something useful information in there to get you started.
http://www.phat-gti.com/downloads/boschtech-12d.pdf

Thanks a lot! I read some of that and assume since mine is an 82 euro, it has the new in 82 K-Jetronic setup? I don't think my car has any ox sensors.