Dan wrote to the list:
While on this subject of cold start - My 78 runs very rich and rough on cold start. After warm up it is as smooth as glass. New plugs, cleaned
injectors, new fuel filter and some hoses and set timing. It also jerks a little when cold and decelerating.
Often the symptoms are confusing. Most cars need a little extra fuel on cold start to get running, and that is supplied by the cold-start valve or the choke. If the cold-start enrichment circuit fails, the lean mixture will cause a misfire, and the smell of unburned fuel may be apparent. Many owners will mistake a startup lean misfire for an overly rich mixture because there's the fuel smell and possibly the soot in the tailpipe.
Over-rich condition on startup on your car is tough. About the only thing that can cause it is a leaking fuel distributor, or maybe a leaking
cold-start valve. Control pressure is modulated by the warm-up regulator, based on temperature in the car's cooling system. Failure mode of the warm-up regulator tends to be toward the rich side, but that manifests itself only --after-- the engine has been running for a couple minutes.
If I was exposed to the common symptoms you describe, I'd look carefully at the normal lean-run causes like cracked hoses and the like. After that, verify the control pressures while you go through a cold-start cycle. This will verify the function of the warm-up regulator. You can verify the cold-start valve itself by pulling it and putting the end in a jar, and watching the spray time during a cold-start attempt. The service manual details the time-vs-temp values, and also temp-vs-control pressure values for the warm-up regulator. The gauges for measuring are available from JC Whitney if you don't have local access to a set.
At 08:33 PM 6/15/00 -0700, you wrote:
>The first set of conditions sound exactly like what I am experiencing. The car was stored for 15 years in my garage and I just have it running the past six months or so. When we first started it the car ran very lean. I took the warm up regular off and cleaned out a bunch of junk with Berryman's put it back on and the car ran fine - except when cold.
So how do I go about this adjustment - If I adjusted the hex screw through the air filter when cold I will also be messing up how it runs when it is hot. Is there a way to adjust the warn up regulator or do I need to get a new one?
The adjustment for the airflow flap is separate from the warm-up regulator;
as you point out, adjusting the hex screw will affect mixture at all engine speeds. The warm-up regulator has a bimetal thermostat strip in it that's heated by the engine (it's typically mounted near or at the water outlet) and also has an electric heating element in there to speed the warm-up sensing on colder mornings when the chambers warm up rather than the water jacket. The regulator works by bleeding control pressure when the engine is cold. That same crud that you cleaned out of other places is likely plugging the bypass n (it was open while stored cold), so the control pressure remains at hot-run levels even when it should be lower.
Diagnosis involves a set of gauges for fuel pressure and control pressure. The service manuals have a set of graphs that chart the ambient vs control pressure curves, and allow you to pinpoint the problem pretty quickly. Unfortunately, the diagnosis requires the gauges. Because of the expense, you might seriously consider having a knowledgeable mechanic do this little task for you. Remember that the engine needs to be stone cold to get the cold-start control pressure.
Keep in mind that the warm-up regulator is not considered a serviceable part. While it might be possible to flush through it cleaner to help it a bit, disassembly is very much a hit or MISS! operation. The thermo strip is delicate, and getting it correct is not real likely on reassembly. I guess I'd probably not be too shy about doing it myself, knowing I can dash down to my local 928 parts warehouse at 928 International whenever I booger something. Should you decide to take yours apart, make sure you have a ready source for a replacement on the 90+% chance that it won't work correctly on reassembly. I've had some luck with getting the things to work OK, but in every case I ended up getting a new one to make things just right again.
>The car only has 40K on it and I can find no fuel leaks. All of the hoses have been replaced, gas, water and vacuum along with the pressure regulator (forget its real name) under the real fender by the fuel filter - it was leaking). I was thinking of taking out the cold start valve and cleaning it with Berryman's as I did originally with all of the other injectors. As per your scenario if the cold start injector has some dried gas deposits in it and was not putting out enough gas then the same symptoms would occur.
You can definitely clean the cold-start valve. You'll want to energize the valve while you do the Berryman's flush, and for that you'll need a 9 volt supply. If you use 12 volts directly, the little coil inside will be history in a short moment... trust me. A little 9 volt battery and an old fuel injection nozzle wire connector seem to do the job OK. Take the retainer wire out of the connector, of course, so you don't have to fight that on and off. Once that's working, remember that you are looking for a good spray pattern from the nozzle too. It's a fan spray when everything is working correctly.
>Do you know of where I can gat a book on the CIS system?
There are a couple real good ones. The best by far is the genuine Bosch book, available from better bookstores, but easiest to find online at one of the Big Three suppliers. I know for sure that Devek (www.devek.net) has it shown on their website, and I'm sure it's available from 928 International and 928 Specialists too. Once you have the book and the gauges, the last step is the charts from the service manual.
Hope this helps, and good luck with your project.