CIS Troubleshooting for Dummies

[AndrewCologne]

For testing the fuel pressures just only disconnect the electrical plug from the WUR.
And ... later when pressure have been read ... as the plug is disconnected, ... do test the voltage at the terminals of the plug which will be plugged to the WUR, .... here 13 volts are mandatory when engine is running. Lower voltages will make the bimetal strip move slower and so the warm up phase will result longer.

The AAR is only needed for providing a bypassed metered air to the manifold air flow so the idle is higher while warming up a cold engine.

[mike sampsel]

Originally Posted by AndrewCologne

For testing the fuel pressures just only disconnect the electrical plug from the WUR.
And ... later when pressure have been read ... as the plug is disconnected, ... do test the voltage at the terminals of the plug which will be plugged to the WUR, .... here 13 volts are mandatory when engine is running. Lower voltages will make the bimetal strip move slower and so the warm up phase will result longer.

The AAR is only needed for providing a bypassed metered air to the manifold air flow so the idle is higher while warming up a cold engine.

Thanks,

it makes sense to me, as it was odd statement in a text on the subject, an unmissed error, I expect.

Cheers

[Jay Laifman]

What happened to Jim's website on CIS? I used to use that all the time.

[andino]

Originally Posted by Jay Laifman

What happened to Jim's website on CIS? I used to use that all the time.

It got moved and is maintained by Rarlyl8. Content is still the same though but URL a bit harder to find

https://cis911primer.com/home.html

[Jay Laifman]

Thanks!

[Jay Laifman]

Adding something I learned in separate threads on solving my problems, but is good for troubleshooting. I fully agree with the multiple comments above that this thread should not be for solving peoples' individual problems, but to provide answers and solutions. With that in mind, here is a problem and solution I found that differed from the specification testing.

I had a hot start problem - would start ok when cold. Would start great for 4 minutes after shut off, but starting 5 minutes and more after shut off, it would spin with the starter but not start. After lots of experimenting out of desperation, I did find that if I first tried to start without the cold start valve going, it would spin for a while, and when I got any type of flutter attempt at ignition (usually after a second try), if I then lifted the throttle engaging the CSV, it would start.

My injectors did leak a little bit of fuel after shut off. But, I tested for leak down, and my car absolutely tested to specification, holding the spec pressure after 20 min. So I figured the little bit of fuel was acceptable. I also read that leaking injectors are not leaks because of the injectors, but because of the fuel distributor.

Both turned out wrong. The injectors absolutely leak on their own, regardless of the fuel distributor. And, even though the leak down is to spec, the leak was still enough to make a hard start problem.

I just put in all new injectors, no more leak and my hard start problem went away completely. It now starts immediately like it used to. (And my other thought that "new gas" might be to blame was also unfounded)

So I thought it important to post here that testing to spec doesn't eliminate all problems for 50 year old parts.

[Phony930]

I've just found this thread and am pouring over the info now -- is the CIS Primer for 911s also applicable to the CIS system on turbo models? It only references 73-83 models from what I can see. I have a Carrera that was swapped with a 3.3T and CIS system and I am trying to soak in all of the info I can about this new-to-me fuel system.
I believe my Fuel Distributor is a 145 and WUR is a 153, just trying to get past the "I don't know what I don't know" phase and get into the much easier "I know what I don't know" phase.

[Schulisco]

Originally Posted by Phony930

I've just found this thread and am pouring over the info now -- is the CIS Primer for 911s also applicable to the CIS system on turbo models? It only references 73-83 models from what I can see. I have a Carrera that was swapped with a 3.3T and CIS system

CIS was still used up to the 964 3,3 turbo...I personally have no experience with a 930. But
I would say yes that you still can use the CIS primer for troubleshooting on a 930 for the basic things. The principle is pretty the same, but some of the details will differ for sure. Most problems on CIS are related to engine start cold and warm and running culture, performance and fuel economy and the components here are mostly the same ones as on naturaly aspirated cars.

Probably it makes sense to start a new thread describing the issue(s) and your car to support you.

Thomas

[HarryD]

Originally Posted by Phony930

I've just found this thread and am pouring over the info now -- is the CIS Primer for 911s also applicable to the CIS system on turbo models? It only references 73-83 models from what I can see. I have a Carrera that was swapped with a 3.3T and CIS system and I am trying to soak in all of the info I can about this new-to-me fuel system.
I believe my Fuel Distributor is a 145 and WUR is a 153, just trying to get past the "I don't know what I don't know" phase and get into the much easier "I know what I don't know" phase.

Conventional wisdom with any CIS system is that everything outside the CIS components need to be spot on. We are talking Valve adjust, timing, dwell, plugs, wires, etc. Vacuum leaks are a common problem. Once these are resolved, you may find your CIS is ok and merely needing a sight mixture adjustment.

What exactly is the issue you are trying to address?

[Phony930]

Thanks guys, haven't put the car through its paces yet -- bought it with some unknowns and some modifications and just trying to shake it down and go over everything to feel confident its good to go. I plan to install a Wideband soon so I can start there.
In speaking with RarlyL8 previously, he advised that my fuel setup with the 145 distributor and 153 WUR was not going to support the modifications and boost level of the car, so just looking to understand and navigate that as the previous owner seemingly ran it this way for years. Previous owner said "the fuel system was set up properly to support the modifications" but he did not know what was done.
Modifications include: K27-7006, Webb/SC cams, Billyboat full exhaust system, manual boost controller set to 1 bar. Engine was refreshed in 2001 and 15k miles ago, likely to stock spec, but some upgrades were at least quoted by the shop so I don't know for sure.
I just like to understand my vehicles fully so I'm on a bit of an exploratory mission to know where I am and then figure out where I should go.

[Schulisco]

Originally Posted by Phony930

I just like to understand my vehicles fully so I'm on a bit of an exploratory mission to know where I am and then figure out where I should go.

Troubleshooting a CIS you've never seen before is a not an easy job. But all in all - if you got the whole picture - basically it's a simple system. The confusing thing is the bunch of vacuum and other lines. But when you understood all components and their purposes it's simple.

Here in this thread you'll find many good sources, although some are no more available over time. Some have been mirrored on other URLs either.
I always recommend a set of resources t get familiar with CIS as follows:
https://forums.pelicanparts.com/porsche-911-technical-forum/1171604-cold-control-pressure-k-jet.html#post12375978

Thomas

[PeteKz]

"Phoney". You are going about learning your car in a good way. Except this: Drive it. Put a fresh tank of gas through it regularly and drive it hard. CIS does not like to sit with old gas in it.

[pmax]

WUR033, adjustment?

Adjusting the WUR