1977 SAAB 99 Won't start when warm.

[newmanr0623]

I'm looking at purchasing a 1977 SAAB 99. The owner says that it runs great and will start EVERY time when it's cold. BUT after it warms up, it won't start back up again until you let it cool down. When you try and start it, the engine will turn over just fine, it just won't fire.

I've googled for two hours and many people are saying it's the crank position sensor, because it turns over but just won't fire. However, I can't find a CPS for the 99. Is that because they 99 doesn't have a CPS? It seems like most of the forums describe exactly the problem that the car is having but are referring to the newer 9-3's.

Does anyone have any suggestions for me? Anyone know what the problem could be?

THANKS!
Ryan

[Matty1977]

I had this problem on my Saab (which is the exact same as this one). Is it fuel injected? If it is, the injectors are probably clogged. I was able to get the car started with a little starter fluid.

[Matty1977]

Woops. I just saw how old this post is. I hope that you've solved the problem by now.

[rpiereck]

Is the car carbureted? Vapor lock?

[Stottler]

As already mentioned, I hope you've solved this already, but if not, here's the story (I'm new to Saab Worls):

1) All US 99s from 75-80 have Bosch K-Jetronic Mechanical continuous Fuel Injection, sometimes known as "CIS" for Continuous Injection System.

2) Hot restart problems were/are common (universal?) on '75-'77 cars, some improvements were made for '78-80 which make it less likely although still not unheard of.

3) The problem results from a loss of "rest pressure" in the injection system after the engine is shut off. The system is supposed to hold pressure for at least 30 minutes after the engine is shut off. If it does not, then the fuel in the 4 injector lines boils and turns to vapor. When you crank the warm engine, the vapor does not allow liquid fuel to get to the injectors, hence the "no start". When the engine cools down, the vapor condenses back to liquid so the problem is not there; also the cold start injector will fire when the engine is cold.

4) There are several possible causes of loss of rest pressure - you will need the pressure test gauges and service manual to isolate the problem (you could also "shotgun" a bunch of expensive Bosch parts, or do a quick workaround if the car runs well other than this problem). Here are the causes:

-a) Check valve in the fuel pump leaks. In a '75-'77 car the only realistic fix is to replace the fuel pump with a new one ($200+). The check valves in later pumps '78-'80 were replaceable, but I don't think the replacement part is available any more. Almost every used pump is likely to have the same problem at this point, so I would not bother with that.
-b) The injector poppet nozzles are crudded up (technical term) and leak. Might not be a bad idea to just replace the 4 injectors with new, they are readily available from places like Rock Auto online, prices range from less than $50 to more than $150 for the set of 4 depending on the sale-of-the-week.
-c) The Control Pressure Regulator (CPR - also called "warm up regulator" or WUR sometimes) can leak internally. On '75-'77 cars the only fix for this is to replace the CPR. They can be rebuilt also, there is a DeLorean place online that will do them. Probably in the $200-$250 range. The '78-'80 cars have a means of blocking the return from the CPR so this is not usually a problem there.
-d) The Accumulator can fail and not provide the appropriate reservoir of pressurized fuel on shutdown. I don't think this is usually the problem, the common accumulator failure tends to be an overboard leak which is pretty easy to find. The accumulator also costs !$200.
Notice a theme here with the cost of Bosch parts? :-)

So, you can carefully sort the problem and find out which Bosch part is the problem and replace only that part (but realistically I expect to find at least a bad check valve and bad injectors in any car this old), you can "shotgun" all the parts for $800-$900, or you can rig up a push button in the cabin which will allow you to manually spray the cold start injector to get the thing started - this basically accomplishes the same thing as you can do with starting fluid. I am an engineer and don't usually go in for this type of band-aid solution, but in this case I would think it's OK. In fact, there was a service kit for this problem that basically included a timer relay which would fire the cold start injector if you cranked more than 5 seconds and did not start....

I hope that helps!

PS - you do not have a Crank Position Sensor, just an old-fashioned distributor with points and condensor. In the 99 with CIS fuel injection there's no relationship; the fuel injectors flow continuously, so there's no pulsing and no need to worry about where the crank is.

Gary

[jalpa3500]

This issue is exclusive to a bad accumulator

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