CIS Problem Solving

[Glenn75S]

I have had some issues with the mid range running of the old 75S. From what I have read the with Th e Early CIS system it is essential that the vacuum and fuel systems are in fine fettle.

Looking back in the history file I found the same problem occured some 10 years ago, and the problem was solved by fitting new leads and injectors at Bob Watson.

I decided to take out the CIS system and check it out for problems. the system looked in good condition but the following was found

Throttle gasket compressed
Fuel Distributer Gasket damaged
Air Boot had micro cracking
vacuum pipe split
Air box unused pipes unblocked

Parts replaced

Injecters and O rings
Air pipe gaskets and rubber boots
Air Boot
Auxillary Air device
Fuel accumulater
Leads (with Magnecor)
Fuel Distributer gasket.
Engine bay silencing foam

Having the system on the bench was great to identify possible problems, hopefully the running problems will be solved.....

It has certainly been a good chance to get to know how the CIS system works and has been a good chance to give the engine bay a clean, I won't win any prizes but it certainly looks alot better.

[impmad2000]

The CIS system is very vulnerable to leaks, especially between TB and metering head. It should go a lot better with that un-metered air out of the inlet !
Have you seen http://www.bitzracing.com/products/Comp ... index.html
This looks like the best way to fix the CIS system to me
Tim

[Gary71]

Don't tell him that now Tim, he's spent that much on all the O.E Porsche bits and for about another £60 you could ditch the distributor as well:)

When is it due to run again Glenn so you can see if it worked? Mine can be disabled if you like as we can possibly have both cars running with an MOT at the same time

[Glenn75S]

Plan to get it finished this weekend hopefully???

[Glenn75S]

This looks like the best way to fix the CIS system to me

Hey Tim thats cheating!!!!

I love the old CIS system, the fact that Porsche never got the cold start sorted so you have to use the hand throttle, and you are also told not to drive under load at low RPMs as it kills the injectors , Its like saying sorry never quite got that fixed, so its your problem now, Vielen Gluck

Also love the temperature adjustment device which just reduces the system pressure at cold temps, and the earlier throttle position valve which did the same, but was removed from the 75 model???

What is this strange majik??

[Gilbert '71 T]

I love the old CIS system, the fact that Porsche never got the cold start sorted so you have to use the hand throttle, and you are also told not to drive under load at low RPMs as it kills the injectors , Its like saying sorry never quite got that fixed, so its your problem now, Vielen Gluck

I'm with you on that Glenn, having lived with CIS for just over a year I'm actually quite happy with it, really quite simple once you get to know it, and easy to set up ball park with a cheapo gas analyzer, I took mine to my friendly MOT man to check my settings afterwards and it was spot on (that was at the beginning of summer) of course then I had to change it again for the colder months

I'm sure you know that fuel pressure is also essential, I had a pressure tester made, once you've got it all buttoned up you're very welcome to borrow it if you need to, replacing the accumulator should help but it's the pressure regulator or WUR that's the main controling component.

Good luck putting it all back in, I imagine you'll find many missing horses

[Glenn75S]

I got everything back together this afternoon. Certainly took some time getting everything bolted up and ensuring that there was no contact with the fuel lines aand other items in the engine bay such as the heating fan. Took it for a short test run, it is definately running smoother and it certainly seems to be running better in the mid range. Need to get the idle speed and mixture set up right, as the throttle control is needed at idle. Not enough time today. The car is sounding great, sitting on the drive it was sounding super:lol:

[Gary71]

Nice one