CIS problems
 

I know the anwer is probably already out on the site somewhere..but I can't find it. Please excuse the redundancy.

Is it true that the likely cause of hard starting of my 78SC when warm after sitting for half an hour or so is the accumulator? Is it possible there is another cause? What is the remedy?? New part??

I also have an irregular idle when cold. Bounces from 100-2000 rpms for a few minutes and then smooths out. Tolerable but annoying. Is this likely to be the cold start mechanism or some adjustment? Is the remedy new parts or ??

Finally, a mechanic I trust has told me I must use high octane fuel or fuel will boil in the heat of summer and cause vapor lock. True? I've been using standard 87 octane thus far (last June) with no pinging or other issues.

Thanks for any advice.
Drew. SmileWavy

To prevent vapor lock, the fuel system on a CIS car is design to hold pressure for at least 30 minutes. The accumulator is just one item that is involved in this. Other things that could cause a loss of pressure retention are, check valves, cold start injector, fuel distributor etc....


If the car fires up when cold, but then idles rough, the likely problem is that the mixture is too lean. The WUR is supposed to enrichen the mixture during cold starts. Also, any vacuum leaks will cause a too lean condition.

I've never heard that one before. Higher octane fuels will ignite at higher temps/pressures, but I don't know if they boil at a higher temp.

The hard starting when warm sounds like a bad check valve on the fuelpump. If it is bad the fuel pressure will drop and when the car is warm there will be no extra fuel delivered and you have to crank for 1/2 a minute or so to get it started.
The check valve can be bought as a sparepart and you can cange it from under the car. Just remember to block the fuel line going to the pump before you remove the fuel line on the valve...

Your mechanic doesn't know anything about fuel. Vapor lock tendency is related to vapor pressure (RVP) and has absolutely nothing to do with octane rating or additive packages.
The RVP is manipulated seasonally to adjust for ambient temperatures. The RVP is lower in the summer and higher in the winter. It is basically a measure of the tendency to evaporate.
The lower the percentage of hydrogen and LPGs in the gas has something to do with it, but not all of it.

Your hot start problem is a common one. It is either the fuel pump check valve (cheap), the accumulator, injectors, or cold start injector. It is also possible that there is a problem in the fuel distributor, but I doubt it. Check the other things first.