Flormat

Is there some sort of pressure sensor in the CIS injection system? Maybe something that would be affected by changes in pressure associated with altitude? I live in Reno and every time I drive over the pass and down to Sacramento the car quits right around the foothills. It acts like it is starving for fuel. This has happened the past 3 times I've attempted the trip. Once I get back to Reno the car runs perfectly. It's an 1981 Euro S model. Thanks for any help.

Simon Jester

The CIS system is self correcting for altitude.

The air flow meeter is a plate that is displaced by the air flowing around it to get to the throttle body. The lower you are, the more dense the air is, the more plate displacement you get, the more fuel you flow. So, it is really an air mass flow device.

I'm not sure if you're problem is related to the CIS system. Could it be that you have something like a bad fuel tank vent? Are you able to make long trips at altitude to verify it isn't unrelated to altitude?

Try driving your car for a bit, then go open the fuel tank. Does it hiss when you open the gas cap?

Dennis Wilson

Altitude will affect your vacuum and vacuum is normally used to alter the control pressure on the euro warmup regulator. Have you checked to see if your vacuum line(s) to the warmup regulator are connected to the correct ports and not leaking?

Dennis

hupp

Flormat,

I'm relatively certain that altitude corrections are made by the WUR. The Bosch manual illustrates all of the different WUR's and one such WUR design is decribed as being able to make altitude corrections.

Ian928

I have had similar problems with my '80 EuroS. I have had a few starvation problems to the point of stopping when going at higher altitudes. Sometimes it runs just fine, other times it stops. It seems to me the problem is worse if it is hot weather! I've even had the same symptoms near sea level and that was on a very hot day.

Flormat

Well, I know that when I fill up the fuel tank up all the way it leaks a little from the top. This is a bad vent hose, correct? So would this cause the problem? Also, if I hear a hiss from the gas tank does that mean I have a vent problem? THanks for all the replies.

Simon Jester

If your tank is leaking a bit, that means it's unlikely it's causing fuel starvation by means of not having a vent.

It is my understanding that the warm-up regulator does not compensate for altitude and is not sensitive to changes to altitude. The WUR derives it's source of vacuum from the intake manifold, which will be porportional to the engine load. It's source of ambient is from a vent in the WUR body. Both pressures will vary porportional to atmospheric pressure, thus the pressure differential will not vary with altitude. This feature allows the WUR to widen the bandwidth of the fuel distributor, giving better mixture control. Air density sensation is still obtained from the fuel distributor plate. HUPP may have a later Bosch manual than I do. Altitude compensation is made by adjustment, as a mixture control adjustment in the CIS models used on the early 928s.

After that, the WUR is simply a thermal switch that uses engine vacuum to reduce the control fuel pressure to the fuel distributor making the mixture richer at startup.

Dennis Wilson is correct in that if you have a vacuum leak, you will run lean. But you will run lean all of the time.

Some models are equipped to enrich the mixture at wide open throttle.

Here is a link to an excellent article on the care and feeding of your WUR....

http://www.landsharkoz.com/images/pdf/wurfix.pdf

If your Shark is runnign fine sometimes and not at other times, it would seem to me that it's not an adjustment problem. I'd look for something broken in the engine control hardware somewhere. Aside from the CIS the other thing on the car that might have some thermal sensitivity would be the ignition coil. They are known to fail when hot while working at cold temperatures. Ditto for the spark plug leads.

G Man

Hey Matt. I thought you had gone MIA. Glad to see you made it back out this way. Sorry I can't help you with your question. I just wanted to say hi. Drop me a pm if you want to meet sometime.