CIS Troubleshooting for Dummies

[Charles Freeborn]

Pros - cons on removing or bypassing the Decel Valve? Mine is showing all the signs of improper operation (high idle, slow return to idle). My guess is the over rich condition when lifting would cause backfire - is that all? Is it a serviceble part?
Thx.
-C

[gazzerr]

Everything I've read on this decel valve condition is that you have to squish the valve by 1mm with a pair of channel lock pliers or similar. There was a Porsche bulletin on it too.

[Charles Freeborn]

Originally Posted by gazzerr

Everything I've read on this decel valve condition is that you have to squish the valve by 1mm with a pair of channel lock pliers or similar. There was a Porsche bulletin on it too.

I'd like to learn more about this. Is there an online version of the service bulletin?
Thx

[tirwin]

My decel valve has always been bypassed.

[Charles Freeborn]

Originally Posted by tirwin

My decel valve has always been bypassed.

I'll give it a go. Thanks.

[Tom Sch]

Originally Posted by Charles Freeborn

I'd like to learn more about this. Is there an online version of the service bulletin?
Thx

Also interested

[gazzerr]

Yep here it is - it's a one page tech bulletin. I have not tried this.

[Tom Sch]

Originally Posted by gazzerr

Yep here it is - it's a one page tech bulletin. I have not tried this.

thank you!

[Charles Freeborn]

Looks like a later generation (3.0) CIS than my '74 has. Interesting read nonetheless.
-C

[gazzerr]

Hi Charles - I *think* there is a screw on the top that you can use to adjust the older style valve.

[dino_jr]

Originally Posted by tirwin

What you will need:
1) a set of CIS fuel pressure gauges

Hello, I'm stuck at your 1st point!

Can anyone point to a store that sells these gauges? I am in the U.K and it's not obvious what to buy, thanks.

[Bob Kontak]

Originally Posted by dino_jr

Hello, I'm stuck at your 1st point!

Can anyone point to a store that sells these gauges? I am in the U.K and it's not obvious what to buy, thanks.

But this book and read it with extreme enthusiasm. Especially the k-jet chapters.

https://www.amazon.com/Bosch-Fuel-Injection-Engine-Management/dp/0837603005/ref=sr_1_fkmr0_1?ie=UTF8&qid=1495568727&sr=8-1-fkmr0&keywords=charles+probst+Bosch+continuous+injection +systems

I am assuming you don't know how to use the gauges, correct? Read the book. You will ask better questions.

Here is an Amazon UK link to a pressure tester that will work fine with CIS.

https://www.amazon.co.uk/Jago-BZDP01-Steel-Pressure-Tester/dp/B00A78CCHY/ref=sr_1_1?ie=UTF8&qid=1495569045&sr=8-1&keywords=CIS+fuel+pressure+tester

[dino_jr]

Thanks Bob, that looks like the right set. Ordering now!

[hook682]

subscribed

[boyt911sc]

Originally Posted by Charles Freeborn

Looks like a later generation (3.0) CIS than my '74 has. Interesting read nonetheless.
-C

Charles,

You have the earlier type decel valve which is adjustable. Use a hand held vacuum pump to adjust and calibrate the valve's opening pressure (15"~ 22" Hg). I like the old one better than the newer version.

Tony

[Coastr]

I had high idle problems, slow rpm drop off and many other poor driveability issues. It made the car unpleasant to be in, when the revs climbed to 2000 while sitting in traffic, or gear shifts were botched because the revs didn't fall.

I disconnected the decel valve and put a golf tee in the vacuum line, as recommended here. Instantly fixed all these woes. PO had spent bulk cash with clueless mechanics trying to sort out the issue.
The only thing I'm planning to do further is to make up a proper dead plug for visual purposes rather than having a golf tee hanging off the side of the engine. I'll never reconnect the valve, and won't bother trying the crush method above.

It is a pollution control measure and does nothing to improve the driveability of the car, even when working properly it deadens throttle response. The only downside is the occasional pop and crackle in the exhaust on long throttle-closed downward descents. The same as you would get in a carb equipped car, because the high vacuum, fuel rich mixture is igniting in the exhaust.

[rwest]

Great reference thread Tim, thanks for doing the hard work.

Just thought I would share a couple pictures of the switch I made and the hookup at the fuse panel since I don't think I've ever seen the actual hookup and you know, the whole thousand word deal!

I made my switch with a very long length of fairly heavy gauge speaker wire (had it handy) so that I could operate it from the engine compartment- seems to me if something went wrong I could immediately shut the pump off as well as not knowing if something was going wrong as I made my way to the back of the car.

[Bob Kontak]

Outstanding, rwest.

[bugstrider]

Subscribed!!!

[pmax]

Collecting the charts here


1981 SC CIS - low idle - wrong WUR?