Both are great threads,
Just be careful with possible information mixup as one is for 6 pin and the other is for 3 pin CDI

I opened her up and don't see anything looking burned out to the naked eye. And there appears to be at least 16 solder connections to undo if I want to take it one more stage and remove the board. Yikes!

Any thoughts on things I could quickly check for failure, such as might cause the incorrect timing? Also, I'm IM'ing Ingo now...

CDI arrived safely and when I plugged it in she started right up. After warming up, she is idling quite high - about 2.2K or so.

Normally, she would be around 2K for the first 30 seconds until she gets warm, and then drop down to about 900 RPM. Right now she started at 3K and settled to a little over 2K. I have the mechanical advance set to just the same physical position as with the old CDI box.

With my timing light while watching cylinder 1 and at the 2.2K idle speed, it is around 20 degrees or so on the left side of the TDC mark. Normally spec is at 5 degrees right of TDC (although I ran closer to 7 due to higher engine compression since the rebuild 60K miles ago).

I adjusted the advance slowly to bring it closer to aligned, but she started to sputter and RPM got all choppy so I stopped and put it back. Maybe my idle needs to be adjusted? Any ideas would be appreciated.

Osomoore, you need to adjust the timing when the idle is set correctly. As you are running at 2,200RPM the advance will be kicking in hence the 20degrees. What you need to do is get the idle down to 900RPM or so and then check timing.

I am not the right person to advise how to adjust the idle speed on your car but I have read plenty of threads on it so the information is there. My post was more to point out that the timing should only be adjusted at the right idle speed (and at other RPMs to check against the advance profile of your distributor).

Best of luck,

Neil

Screw in the idle adjuster on the TB to bring the idle down.
You will want to set the CO as well. (as long as you know your fuel pressures are all in spec and operating properly.)

I turned the TB screw one way and the idle went up. I turned it the other way (in) and the idle came back down to 2.2K. 2.2K is the idle at the lower end. I didn't turn it above 3K. This is with the engine warm. I think it started all the way in and at its lowest directly adjustable idle.

FYI when I was testing two weeks ago (with my friend's CDI) the idle was high. But we only had the car on for less than a minute (the alternator started whining so we turned it off), so I didn't think much of it.

Also it may be worth noting that I have to crank the engine for close to 10 seconds to get it to start from cold. This was not surprising yesterday when it hadn't run for 2 weeks. It was surprising this morning. After being warm, it starts much more quickly. In the past, it always started fairly quickly.

Could a vacuum leak drive the idle up?

Sounds like a big vacuum leak to me if the idle air screw is adjusted all the way in as you describe.

Hmmm, I don't yet know that much about CIS, and I had assumed a vacuum leak would result in rough idle or no start (can't suck the valve open in back of air box).

Get out the soapy spray and put the air blower into the exhaust? Or try the carb cleaner trick?

Do you have access to a shop near by that can 'Smoke Test' the intake and also check mixture with a Wideband Controller? At this time it would be money well spent to diagnose the issue very quickly.

I wonder if when searching for leaks the other way (pressurize and shoot soapy water) I loosened a fitting or gasket by pressuring it from the inside.

Thinking about replacing all the vacuum hoses. It looks like they aren't very expensive. Found some info here: http://forums.pelicanparts.com/porsche-911-technical-forum/584340-air-hose-911-sc.html#post6042845

Also looking around for smoke test... worried it may be expensive.

Got home and poked it some more.

In the comparatively warmer weather (55 degrees vs 70 degrees) it started up right away at about the right idle, but died within about 10 seconds. Restarted her and she went right up to 2.2K idle immediately. Idle moved around a bit on its own and then died after about a minute. Then wouldn't start.

From my limited experience, this is sounding quite vacuum leak related. After weighing the time and expense, it seems like it might be worthwhile to just replace all the vacuum hoses. Does anyone sell a kit for this? Standard hoses seem pretty cheap online.

Take a look at the vacuum drawing on Jim''s. CIS Primer page.
911 CIS Primer - Index
Also all of the rubber boots on the air box to the intake runners, intake gaskets, all the cold start air hoses on the back of the CIS etc. maybe just try plugging the Auxiliary air valve vacuum connection. (Lots of discussion about that golden round piece in the forum)

Hehe... I just linked this same site to myself a few hours ago. Although I have to be careful because they changed things a little between 79 and 80. Fortunately, he differentiates.

Collecting more links for myself: http://forums.pelicanparts.com/porsche-911-technical-forum/370222-high-idle-cis-issue.html#post3512498
Good pics: http://forums.pelicanparts.com/porsche-911-technical-forum/710107-cis-removal-engine-out-82-sc.html
CIS removal w/out engine drop: http://forums.pelicanparts.com/porsche-911-technical-forum/700716-removing-cis-engine-car-writeup.html
Might be able to get new injector o-rings locally, I'm not sure much is special about ours as compared to what the local auto parts store would have.

Still no luck on a kit for vacuum hoses. I may break down and take all mine out, measure, and order afterwards.

I suspect that turning the idle screw down to min idle may be what is now keeping it from starting. Hurray for hunting for issues!

I'm really tired tonight, so I did a quick check. With the idle backed off a bit from minimum, it starts up and runs fast and then drops off and dies after it warms up.

So vacuum hunting will the my future. Going to get some carb cleaner and some lengths of vacuum hose I think. Also lots of reading from links around here on the forums.

Ran it again (it had cooled off) and as it was dieing after warmup, I heard the echoing air "woo" noise referenced in my old thread. Sounds like blowing over the top of a glass beer bottle.

Had a few minutes tonight. Measured lots of vacuum tubes in the engine bay. I can't get to the entire CIS because it is in the car, but tomorrow I hope to read (again) the CIS primer and begin understanding more of what is going on. I'm going to find this darn thing!!!

Plus it is so nice outside it is killing me to drive the SUV every day...

Been following this thread since day 1,,,,,,,,,,,,
 

OsoMoore,

I've been reading the posts since the very beginning of your thread. The guys were trying to help you but use some wisdom that some of the suggestions may or may not be related to your problem. An example is injector o-ring air leak. If it is leaking air under low pressure, it would suck air under vacuum. A whinning (sound) CDI indicates it is getting power but could still be defective. While a dead (quite) CDI is a sure sign of a failed unit. Lastly, you have not tested or confirmed that your CIS airbox is not leaking nor your ignition system is working. You were hoping it is not leaking but you do not know it for a fact. You are relying on luck which is often times not in your favor.

We all learn from our experiences (good or bad). This is the main reason why many had trouble doing an effective CIS troubleshooting. They do quess-work troubleshooting procedures. The key to a successful diagnostic is to test and confirm.

I have two (2) SC engines that I recently completed the rebuild and would soon undergo start-ups and tuning. If I failed to successfully get the motor to start the first 2 attempts of turning the ignition switch, I would be disappointed.

What I am trying to share with the community is that it is not rocket science to get a CIS engine to start and run every time and all the time. There are a few things that could prevent it from running and they have been documented many times over in this forum.

Tony

Hey Boyt911sc! I'm trying to work through things logically. There are a lot of components with lots of interplay. I'll try to cover what I'm working with, starting with your observations.

Current Issue: Starts but engine dies after about 30 seconds of warm-up. Then won't restart until it cools again.

1) Injector O-Rings. If these were the leaking too much air, would we even have the engine start and run? I'm not sure, but from my reading I didn't find anything to indicate that.

2) CDI Box. With my original CDI box, turning the key resulted in no start. If I disconnected my CDI box cable and connected another CDI box, it would start. From this I concluded that at least the CDI box was failing. The CDI box I received was tested and known working when I received it. And it runs the car (albeit with the aforementioned failure after initial warmup) Form this I concluded that the new CDI box is not at fault.

3) Airbox Leak. I could tow the car to a shop and have them smoke test it. I am also considering removing the CIS entirely (without an engine drop) to examine all the components. Would a leaky air box result in the initial start but then failure after beginning warm up? I don't know.

4) Ignition System. CDI, distributor, coil, and wires are new and sufficient to start the engine running. Perhaps something in this system fails after it begins to get warm? Is something in the key ignition switch possibly failing 30 seconds after start? Maybe fuel pump?


Saturday I have more time to test things. Some things I am considering trying:

A) Try plugging the auxiliary air valve as suggested by timmy2. Which opening?

B) Do the warmup and wait for it to fail. Then check for spark at a spark plug. Check for gas at the fuel injector. If I have both gas and spark, I can presume that I am lacking proper air.

C) Spend a lot of time feeling the back of the CIS and ensuring all wires and pipes are still in place. Work on creating a full diagram of exactly what my 79 SC has and doesn't have. These cars had variations from year to year. Hopefully find something loose.

D) Borrow the fuel pressure tester from my FLAPS. Start checking pressures.

E) Remove the entire CIS. Replace all air hoses. Examine air box and all seals.

A friend came by (guy with 80 SC) and we messed with it for a while. We got it warm by adjusting the mixture and holding the throttle open. After slowly adjusting the idle and mixture, we got it to idle at about 900-1000. But she hunts around, and if you give it gas it balks and doesn't respond right away. You have to hold the throttle for a second before it starts to go. Also, it has a tendency to stall when the hunting drops to below 600.

It seems like the throttle screw and other CIS components have gunk on them, possibly residue from backfires or unburnt gas. Leaves a sticky gunk. I am planning to do some basic opening (rubber off, screw out) and clean them very well. We suspect that may be leading to the erratic behavior.