fuel injection

What's a good book for trouble shooting the fuel injection system (1980 911SC Euro) and how many of the various components are repairable (rebuildable)?

I bought the "Bosch Fuel Injection and Engine Managment" book by Probst (sp?). It's not specific to Porsche, but it does provide a good understanding of CIS (and DME) along with trouble shooting guides. The
CIS system on '80s are K-lambda systems and are slightly different than my K-basic. You can buy rebuilt warm up regulators and fuel distributors. I've taken my WUR apart and cleaned and adjusted it, and I've taken the fuel distributor off the car and cleaned it, but I don't think it's rebuildable by the home mechanic. I've gotten pretty good at working on the k-basic system. Are you having specific problems?


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Bill Krause
'79 911SC Euro


[This message has been edited by wckrause (edited 10-31-2000).]

The car is idling pretty rough on startup and for about the first 3-4 minutes and then seems to even out and settle down at about 1000-1100 rpms.

Dana

A real quick way to tell if your idle problem is because the mixture is running too lean is to reach into the airbox and gently lift up on the sensor plate. If the idle smooths out and raises up to around 1800 rpm, then your mixture is too lean. On a K-lambda system this could be either a warm up regulator or a problem with the lambda system. I know WUR's, but I don't know the lambda system very well. To trouble shoot the WUR, you will need a CIS tester (about $55 from JC Whitney).

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Bill Krause
'79 911SC Euro


[This message has been edited by wckrause (edited 10-31-2000).]

Bill-

The mechanic was leaning toward a faulty cold start valve or a leak somewhere in the system. I'll try your suggestion.

Thanks for the information.

An air (vacuum) leak in the system would result in a similar lean condition. If there is a leak, then simply adjusting the mixture will not result in proper running.

Cold start valves are not hard to test, but vacuum leaks can be difficult to identify or locate.

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'83 SC

Dana,

If your car fires up strong, but then settles into a low rough idle, then the cold start valve is probably working. It only injects fuel while you are cranking the engine, once the engine turns over on its own, then the cold start valve turns off.

The mixture during cold idle should be very rich, rich enough to handle a small vacuum leak. I had two mechanics tell me that my similar cold start problem was due to vacuum leaks, yet neither one could find any leaks. I think it's a convenient way for a mechanic to tell a customer that they don't know what's wrong.

In any case, it's usefull information to know that the engine will cold idle at a high RPM given a richer mixture. The next step is to determine why the mixture isn't rich enough (vacuum leaks, WUR, lambda, etc). If the engine doesn't fast idle, then you'll need to look at the aux air regulator that provides the throttle bypass air needed for fast idle.

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Bill Krause
'79 911SC Euro

Hey, Bill. His '80 911SC Euro does not have the lambda sensor. His configuration is the same as your '79 Euro.

Brian -- Thanks for that info! That makes a big difference. That's the big problem with ROW cars, you never quite know how they compare with the US versions.

Dana -- Another test to try. On the WUR, there are two vacuum connections. The bottom one goes to the thermovalve. If you disconnect that vacuum line, it will reduce control pressure about 10 psi. On cold start try starting the car with that vacuum line disconnected. You can clamp the disconnected hose closed with a visegrips or something like that. The thermovalve should be closed on cold start, and then open up to lean the mixture as the engine gets warm. My car had a bad thermovalve, and it had the same symptoms as yours.


[This message has been edited by wckrause (edited 10-31-2000).]