Weird CIS problem
 

I have an odd cold start problem on my 82 with CIS...I have become pretty good at troubleshooting and adjusting CIS over the years, and this one has me stumped. I have checked the forum and tried every test I know without any change.

The symptom is the car will start and die the first one or two times I start it very cold (i.e. 40s or below outside). The cold start circuit works and it will fire right up initially, but it will then die. If I give it even the slightest amount of throttle right after it starts, though, it will run fine and I can back off the throttle and let the AAR keep the idle high. Without doing anything, it will usually start on the 3rd try with a low idle and slowly work its way up to a normal idle for warming up. The only other symptom that seems to be related is a restart in cold weather after 30 or so minutes sitting will just "dribble" from starting to running without the characteristic "wump" of a 911 starting.

Could it be something like the air sensor plate sticking when cold? Here is a list of what has been tested and verified:

- Control pressure in specs and CPR adjusts it correctly during warmup.
- System pressure is in specs.
- Residual system pressure is in specs.
- Mixture is right at 14.7 using a Innovate wideband O2 sensor, which is what I run all the time in the car using the analog feedback signal as an input to the factory OXS system.
- Frequency valve works
- No vacuum leaks
- AAR works fine
- Air sensor plate moves freely in both directions (but I have not checked this when it was freezing cold after an overnight)
- Decel valve is hooked up to vacuum
- Vacuum advance/retard works (engine speeds up when disconnected)
- All 1982 OXS-related temp switches are switching per specs.
- Pop-off valve is tight.
- Thermo time circuit works all the way to cold start injector (have not pulled injector to verify spray, though, since I can't see how to do that without dropping the engine. I tried to run the CSV with the ignition disconnected to see if there is fuel spraying in the airbox. I smelled something, but it was not an overpowering gas smell...how strong should the smell of gas in the airbox be with such a test? )

It has never done this before and the only recent adjustment before it started was to back off the timing closer to specs 5BTDC when I was running 10+BTDC this summer but had some pinging.

Since it does fire up initially and will stay running it I open the throttle a little, the only thing I can think of is that its somehow related to the fuel distributor and air sensor plate somehow. Has anyone found a sensor plate to stick when cold? I have never run across that one before in these forums.

Could it be related to backing off the timing a few months ago?

Thanks in advance...this is not too hard to live with, but it is annoying and really has me stumped.

Olivier

Olivier,
I had a similiar problem with a '78 SC Row. Spent a lot of time trying to diagnose the problem. Basically, went back to square one and checked everything. The CIS system on car was hacked. The AAR had the problem, but the mechanic that worked on it last got it to run by adjusting the throttle body idle adjustment screw. When the AAR finally went kaput, and a new one was put on, the thing idled like crap.

Get the car the up to full operating temperature, plug the intake to the AAR, and adjust the throttle stop on the throttle body to the desired idle speed. Then unplug the cap on the AAR. You should see little or no change in the idle quality or speed. It really sounds like you are not getting enough air for the fuel mixture at cold start.

Also, are you sure the right AAR is on the engine? Maybe you can check the part number that is cast on the AAR and cross reference it in a PET.

Howdy neighbor!
I just went through this on a buddies 81SC and believe it or not it was some poor wiring (PO) with the ign sys. Just an idea

ohecht,

I think Werk-I is right on the money. I drove a CIS car where the AAR was not letting in enough air, and it would start right up and die, start and die, start and die, until it finally warmed up enough to run with the throttle cracked just slightly. Look to your AAR - I don't think it is opening up enough.

Rex

I will check the AAR again...it is one of the first things I checked, and it is a part I have adjusted many times in the past. In fact, I made it adjustable years ago using washers on the bolt at the base of the bimetallic strip. It is the right part and the CIS system is stock except for my own careful modifications (adjustable CPR, WBO2, etc.). I had the AAR off about 2 weeks ago to check it again for air leaks and made sure it was air tight by re-sealing it with anaerobic sealant. I have watched it go from almost full open on a cold day to beyond all the way closed on the heating element alone using a mirror with the fuel pump only running.

It is possible it needs to open more, though, since it is still going past closed and the idle does not seem to be as high as I would expect on the coldest days. Since cracking the throttle with my foot seems to help, that could be the problem and I will adjust it to open more and let you know what happens.

Thanks,

Olivier

Hoses to AAR......
 

Oliver,

Had similar problem like this before in my car. Check your air hoses to AAV and this is a source of air/vac leak often overlooked. The way you described your cold start problem, I would concentrate on your AAR and vac. leak. Good luck....

TD

Maybe a sluggish switch sensing the air sensor plate? On cold starts, it does not "flip", therefore the fuel pump relay cannot engage in the RUN mode?

I would say your main problem is that you actually live somewhere that gets down to 40 degrees or below. ;)

Seriously, AAR like they said, or it is just too darn lean.
14/7 at idle is great for smog reasons, but it will idle much better at 14 to 1.

Try richening the mix as Sammy suggests. You may have to raise your idle speed a little when you do this too.

I would check the timing as you suggest. Let us know if that makes a diff.

I think it's certainly possible a sensor plate, plunger or throttle flap could stick.

Also, I just had a similar problem. It appears that a broken head stud was leaning the cylinder during warmup in cold weather.

Thanks again, everyone...I will have to try most of those ideas next weekend now...I hope it's not a head stud as Paul experienced!

I richened the mix to 14.0 and adjusted the AAR several times for a higher idle. The AAR is well-sealed and the warm-up RPMs respond very predictably to my adjustments, but it is not helping the initial start-up issue.

Is there a way to test the CSV to see if it is spraying without pulling it from the airbox? I am hesitant to pull something with a fuel line connected that is in a completely blind location. I hate the way the Bentley manual casually lists the spray test as if the CSV is sitting right in front of you on top of the engine while it is in the car?

Could retarding the timing (back to stock) late in the summer cause something like this?

Olivier, there's no substitute for following the CIS troubleshooting procedures. Of course, they start with a pressure check of system and control pressures. Could be that your fuel pressure is bleeding down too far, although it takes very little fuel pressure to start a cold engine. Pressure problems are usually hot start problems. But also, air flow sensor plate adjustments are in the troubleshooting steps. A long slip of paper placed between the plate and the cone will center it, if it is not centered already. If the car initially fires but then dies, I suspect your CSV is working. At very cold temps it is supposed to spray for a few seconds. You might want to just pull the plug to it and see if the unit is getting voltage for a few seconds. This unit is dependent upon a temperature sensor located, I believe, on a chain housing cover plate.

Super,

I checked all fuel pressures and the voltage at the CSV right off the bat, and they are all in specs. Besides the CSV actually spraying, the air sensor plate, or the timing adjustment, nothing else seems to make sense. I will look at the air plate next. I have never tried or had to adjust it, but it almost seems like it is "sticking" on initial start up and not giving the motor the fuel it needs right after the initial spray from the CSV. It does always fire right up on the initial few turns of the engine, but immediately struggles around 200 rpms and dies.

The various CIS books have the troubleshooting steps. Most folks just guess, which is by far the least effective and most expensive troubleshooting method. Air flow sensor plate position check is early in the procedure. I think one edge of the plate sticks above the lower edge of the cone, and one below. And it must be centered fairly perfectly. Do not loosen the screw in the center unless you plan to reposition the plate. if it does need to be centered, a piece of paper placed around the edge of the plate makes a nice centering fixture.

spark plugs?

A few months ago, echrisconnor started a long thread about symptoms similar to yours: starts cold then dies. In his case, it was apparently a sticking plunger in the fuel distributor. Do a search on "sticking+plunger" in the 911 forum and his thread is near the top.

As I am sure you know, Olivier, you would be very careful with that plunger if you remove it. This is one of the parts on my car that I understand what it does but have a hard time believing that it does what it has to do. This plunger is round and roughly a half-inch in diameter. A couple of inches long perhaps. Its fit into the bore of the fuel distributor is so perfect that gasoline at 60 psi does not leak past it. There is no o-ring. The plunger slides up and down easily. And gasoline cannot leak past. Frikkin' amazing if you ask me. I'd happily use carb cleaner or brake cleaner on the FD and plunger, but I wouldn't wipe it with anything rougher than a baby diaper.