CIS Rebuild First Steps
 

So, I keep having stupid issues with my CIS and given it's pretty much all original 40-year-old crap, I've decided to be methodical in tracking down and fixing all the issues.

I've read the CIS for Dummies thread, I've got the pressure tester and I have the smoke tester coming. My question is, what order am I testing things, and once done testing and replacing, how do I get everything to a baseline state?

For example, the idle screw. What's the initial position it should be in? The air metering plate, how do I adjust it to baseline? Where should the enrichment screw start out?

I want to dial everything back to factory baseline and then proceed from there.

I highly recommend seeking out Tony Donato, AKA boyt911sc, for any issues with your CIS system. Tony rebuilt my fuel distributor and warm-up regulator, and thoroughly tested several other components. Tony is a great guy!

Tony and I have had a long chat, but it was mostly about the WUR specs. I'm wondering if anything is written anywhere.

I'm sure others will chime in with a list of steps you will want to take, but I think the first order of business is to not touch the idle or mixture screws, and check for vacuum leaks with your smoke tester. The vacuum lines, intake runner "sleeves", and the airbox and pop off valve are common sources of vacuum leaks.

When you remove the oil filler cap with the engine running, the engine is supposed to change idle in response to the vacuum leak the open tank has introduced. If this happens, I have been told this indicates you are generally in good shape. Others with more experience will correct me if I am wrong!

Also, this video is a great intro to CIS

https://youtu.be/slCzVrrST2Q

I'd suggest getting the Bentley manual as it describes adjustment of the metering plate and mixture adjustment. It's also just good to have on hand.

There does appear to be a "baseline" mix adjustment described here: http://forums.pelicanparts.com/porsche-911-technical-forum/767733-base-setting-mixture-cis-1980sc.html#post7620250

Otherwise, "baseline" is whatever makes the engine idle at the right rpm with the right CO% after confirming there are no vacuum leaks, timing is right, and injectors, timing, spark plugs and wires are all good.

I know you have another thread on Zoidberg, and it's TLDR for me, so please summarize in this new thread the problems you are having. Just saying that you are "having stupid issues" is too vague to start advising on troubleshooting. If it's running now, don't make any adjustments to the CO (mixture) or idle screws just yet. Be methodical, and one change at a time.

I didn't go into detail here because I was just asking about getting a baseline setup for CIS once you've done all the testing.

But the issue I'm having is high idle (1200RPM) and a severe lean condition on acceleration or under load (hesitation, popping). WUR is within spec but on the high side hot, DV is tested working. AAV and AAR are untested. Opening the oil fill lowers RPM, and I can adjust the idle screw.

I'm following your Zoidberg thread, as you and I have cars of similar mileage and bought around the same time. You've been doing a great job so far making that car nice again! Also, we both got our engines rebuilt pretty much right away...

I've been taking care of issues with my CIS more or less one at a time. When I got it, the lambda system was completely disconnected in the engine bay, so it ran like crap initially. Anyway, I don't find the system really THAT complicated, and folks here have been really helpful when describing the various issues that I've had. The most recent being the "green wire", which I hope addressed an issue that doesn't sound too dissimilar to some of your bucking/hesitation issues.

Anyway, in addition to the smoke tester, I'd probably get an AFR gauge. That's the only way to really know what your mix is.

Good luck!

I have one in the dash - that's how I knew I was running lean. When I put my foot down it buries the needle past 15, which is as high as it reads.

I will also check the timing and confirm it's correct but it's hard when I can't get it to idle below 1200.

Like the Bosch MFI that preceded CSI, the expectation is to be sure everything else is "dead on" prior to messing directly with the CIS Components.

Be sure your plugs, points (if you have them), wires, CDI etc are new or in tip-top shape. Valves need to be adjusted correctly. Timing and dwell need to be spot on. Be sure the distributor advances correctly as rpms increase. You may need to make some SMALL adjustments to the air or mixture screw to get it to run sort of. Document every adjustment you make. Once these are ok, then worry about optimizing the CIS part.

I mean if you can't get the car to idle under 1200rpm then something is either wildly out of adjustment or just plain broken. Vacuum test first.

Also is the vacuum still hooked up to the deceleration valve? I'd disconnect and cap that line first. When that fails it can lead to a high idle and maybe screw up everything else you're trying to adjust for. It wouldn't cause a lean condition (downstream of metering plate) but at least you could get the right rpm at idle to check stuff.

I tested it out of the car and it held 20Hg of vacuum on the intake side and released it at 19Hg on the top, which is within spec. So the DV is working.

Still trying to figure out the starting point for things like the idle screw - do I screw it all the way in clockwise and then back out until the car runs? I'm trying to put together a list of baselines for each component to rule them out.

Don't worry about a starting point for the idle screw and mix. The idle screw baseline is whatever makes the engine run when everything is working right and the mix/timing are accurate.

There's a baseline setting for the mixture adjustment, linked above, but if the engine runs that's not the problem.

Make sure nothing is broken and then adjust to good idle, that's all. Test the AAR and AAV, both will give a high idle, but failure mode for either won't lean the engine out under load--a vacuum leak will.

There is no factory baseline setting or starting point per se for the idle and mixture screws, as David has said.

However, you need to make sure that the metering plate at rest is set correctly, ie its top surface is even with the part of the cone where it changes from sloped to vertical. The you can adjust from there with the mixture screw. That should get you started.

Joe Engineer on Youtube recently produced a test in which he felt that a good start point was to set the mixture screw to the point where the injectors just start to flow fuel. This would be another way to get started.

There is also a field test on this forum developed by poster Souk in which he raises and lowers the metering plate while running and sees whether the revs rise or fall. Check that out. It will probably also get you started.

You could even try, once idling, revving the engine and quickly snapping off the throttle and observing what happens. If the revs stay up you are probably too lean. If the engine wants to stall by quickly dropping or if the revs rise and fall rhythmically, then probably too rich.

Any of these methods will probably get you in the ballpark for further tuning.

Later you can check mixture with an A/F meter or, as I understand on Lambda controlled cars, with a dwell meter. FYI, re the dwell method, I am not positive since I have no O2 sensor on my car.

When doing CIS work, always make sure all the ignition components are working correctly first.

If you really want to do it right so that it runs perfectly and you don't have to touch it for the next 40 years, here's what you need to do. Completely disassemble the entire CIS and fuel injection system including the airbox, runners, fuel distributor, and fuel injectors. Then inspect and test each and every component and repair or replace anything that isn't in great shape or functioning perfectly. Between the Bentley manual and Pelican there is an inspection and test procedure for everything including FV, WUR, AAR, AAV, throttle switch, etc. Put it all back together paying particular attention to good fitting and clamping for all lines and hoses. For the fuel injectors, just buy new ones...they're not that expensive. Run a smoke test to ensure no leaks. The manual contains the set up procedures for the mixture screw and idle as a baseline starting point to get the car running. From there you can adjust the mixture screw and idle to their happy places. If you have lambda control you can easily set the mixture with a dwell meter and the test port near the CDI...takes about 2 minutes to do and it is then perfect.
Make no mistake, this is a lot of work and will take a bit of time. Anything less though and you could be chasing the next gremlin in a couple years ad nauseam. Feel free to PM me for any info on this if you'd like.

Looking at the last couple posts on your Zoidberg thread, it appears that the car started running badly on your trip to the swap meet.

Some of my thoughts so far:
- Air leaks cause problems at idle and low throttle settings when high manifold vacuum sucks air past the leaks and the leaks comprise a significant amount of air into the manifold. At high throttle settings, small air leaks don't affect running because there's much less vacuum drawing air past the leaky places, and much more intake air volume, so air leaks don't lean out the mixture appreciably. In other words, your very lean condition at full throttle almost certainly is not because of intake air leaks, although the high idle and poor running at low throttle may be due to leaks.
- If it started running poorly suddenly, I would think about whatever you did to it just before it started running poorly. There's a good chance that you knocked something loose or reinstalled incorrectly, or some hose worked it way loose while on your drive, etc.
- If you can't get the idle below 1200 RPM when fully warm, that strongly indicates you have some air leaks into the intake side, or something in the auxiliary air system is stuck. You can defeat the AAV and AAR by blocking off the air hoses to those devices. You can also bypass the decal valve and block off its air connections. Blocking these off will simplify your troubleshooting.
- IN your case, I think I would start with looking for air leaks. A smoke tester is great if you have one, but you can also squirt carb cleaner or starting fluid around the injectors, air box seams, and other fittings or use propane from an unlit propane torch, to see if the idle changes.
- Since you are dealing with CIS, you will need to measure the system and control pressures, and you will need a testing gauge to do that. If you don't have one, get one. Then test your system pressure and control pressure. Start with it cold and immediately measure the cold control pressure, then let it warm up and measure the fully warm control pressure. Then test for residual pressure after 20 minutes. Use either the shop manual, the Bentley SC book, or the blue "Bosch Fuel Injection & Engine Management" book. Or look for the procedures on other threads here.
- Have you checked the injector spray patterns and delivery yet? Do that too.
- Have you changed the fuel accumulator yet? I don't think it's responsible for your running problems, but these seem to have a 40-year life, especially with the ethanol-contaminated fuel we now are forced to use. Check it by: remove the drain line from the bottom of the FA, plug or pinch off the drain line, then run the pump briefly. If you get any fuel leaking out the bottom of the FA, replace it.

Easy starting test:

According to the Porsche CIS troubleshooter, you can check quickly for a serious air leak by screwing the idle screw to cut off the air (idle should decrease as you turn the screw clockwise). If this causes the engine to die, then your air leak is not serious, if it still runs you have a "serious" enough leak to correct.

My car stalls/dies when the idle screw closes off the air flow.

I just checked the timing - 29° @ 6000. Seems good. Idle drops when I open the oil cap.

I can get it to idle at 850 now, I think the cruise control cable was too tight and holding up the throttle. I do need to pull both the AAV and AAR to test them properly, but getting the AAV back on will be interesting, given it's basically hidden back there.

Any good suggestions for pulling that off and getting it back on?

My smoke tester will arrive tomorrow. I have Tony rebuilding a WUR for me since mine tested on the high side.

Thanks everyone for the various suggestions, I've written up a detailed guide for myself to go through each system one by one.