The mysterious CIS system..careful guidance required!

mingmong · mingmong's Garage

Well..things are now getting strange as I enter the mysterious world of the CIS system. Here's the script so far...The cars a '77 C3 with bog standard CIS on it. It's be re-built and runs a treat ONCE HOT. Starts from cold with no problem...then 'hunts' for awhile as the WUR and AAR warm up...and then it's fine. This 'hunting' means the mix is too rich (apparently). Now I've inspected the WUR and it functions correctly, as does the AAR. I was thinking 'where can it be getting this extra enrichment from while it's warming up?' Ahh...the little cold start injector perhaps. Got this out (lucky I've got 'ET' fingers cos it's a right fiddle!) and tested this. Found that it's wired up wrong (connects to pin15 off the starter not pin 50) so it only ever gets 1V not 12V. Anyway, it's not firing so it's not feeding in the extra fuel. So where is it coming from...I'm stumped for now. Any ideas?? Did find one injector that was dripping ever so slightly which I'm replacing very soon. Could that be it? Cheers for your time...
Mark

Paulporsche · 02-16-2006, 12:25 PM

Since the CSV is not working, it's possible someone has richened your mixture to make up for it upon cold starting. If you hook up the valve correctly you may find if you lean the mix slightly, then it will start and warm up correctly.

It is also possible your WUR is out of spec, although this usually produces a too lean mixture. Of course, someone could have then enrichened the mix to make up for that. A check w/ a fuel gauge will tell you if your cold control pressure is within spec.

It's also possible your mixture may simply be too rich.

In any event, replacing the dripping injector is a good idea.

Jim Williams · 02-16-2006, 07:42 PM

Mark,

I read your explanation of how your CSV was hooked up, and it left me with a couple of questions. You say the CSV was hooked to pin 15 on the starter. I'm not aware of a pin 15 on the starter. Usually #15 is reserved for battery voltage that is delivered when the ignition key is in the "Run" position. I know that some of the starters have an extra spade lug (numbered 16) that the CSVs are connected to that delivers 12 volts when the starter is engaged. I don't have the factory wiring diagrams for the '77 3.0 Carrera, but I'm betting it's close to the same as for a '78 SC, which has the pin 16. The US '77 2.7 liter engines did not have the pin 16.

Did you actually measure the voltage at this pin when the starter is engaged? If it's a pin 16 and you are only getting 1 volt, then I'm guessing you have a problem with the internal relay on the starter that is supposed to provide 12 volts.

mingmong · mingmong's Garage

Jim, Cheers for your reply. Sorry but I can't remember the correct pin numbers on the starter. Details are at home and I'm at work at the moment (teehee). Basically...one small pin from the inition key energises the starter coil (yellow cable) (not the big fat red one that feeds the starter) and the other small pin is a switch that switches when the starter coil is engaged. This second pin is the one the CSV should be connected to. On my car the CSV has been connected to the first energising pin, which means that most of the current feeds the starter coil. I tested the voltage getting to the CSV and it was roughly 1V. Not enough to trigger it. (My starters brand new.) I'm correcting all this next time I drop the engine.
M

javadog · 02-17-2006, 04:34 AM

Mark;

You stated that your WUR functions correctly. By this, do you mean that you have measured the relevant fuel pressures and compared them with the numbers and graph for your engine in the Porsche technical spec book? Or do you mean you have visually inspected the WUR and it seems to "function correctly." Likewise, have you checked for false air leaks and set your CO correctly, using a properly calibrated gas analyzer?

JR

mingmong · mingmong's Garage

JR,
I'm in the process of working out how to check it correctly. All I've done so far is take it out and make sure it actives when current it applied. Bear with me...I'm on a steep learning curve here! Thought I'd start somewhere and see where I end up. Taking the car to a garage to get it the mix set correctly very soon as I don't have a gas analyser.

javadog · 02-17-2006, 01:48 PM

Mark,

While you're at the shop, have them do a pressure test of the whole system. The engine will need to be cold, so you should probably plan on dropping the car off the night before. If it's been a lot of miles since your last oil change, you ought to consider having them change the oil before setting the CO.

Focus on air leaks, correct fuel pressure and the CO setting. After 30 years, it'll be a miracle if there isn't a fault in one of those areas. Make sure the shop that does the work really knows what they are doing and has all the correct equipment. Otherwise, you're likely to be wasting your money.

There are several good books on Bosch fuel injection systems. If you don't already have one, they are worth buying to educate yourself on the ins and outs of CIS. It's a simple system, for the most part. What gives most people trouble is they try and short-cut the diagnostic process. If you start with the basics, it's pretty straightforward. With CIS, everything revolves around fuel pressure.

Good luck,
JR