Bentley Error?: CIS 15* temp switch

ohecht · 12-08-2002, 02:02 PM

Another weird CIS problem:

I replaced my 15* temp switch with a "superswitch" from Stoddard that is supposed to enrichen the mixture below 78 degrees F instead of 58 degrees. My car has always idled roughly within these transition temperature ranges, so I thought I'd give the cheap switch a try.

Here's the weird part. I tested the old switch ina bath of water many times, and it is functioning in an opposite way from the way the Bentley manual describes its operation. Either the manual is wrong, or my switch was not only defective, but found a way to work backwards!

Page 240-28 of the Bentley manual clearly states that the switch is normally open and closes at 15 degrees Celsius:

"When the engine reaches operating temperature, the switch closes and provides a ground input to the control unit and the system goes into closed loop (feedback) operation".

The test on the engine is to use an ohmeter between the chassis and the switch terminal at operating temperature and above. No specs are given, so I looked for continuioty when hot and none when cold.

Using a hot water bath with the one lead on the terminal and one on the switch housing, I got continuity below 15 (sometimes 20) degrees, and the switch was always open above 20 degrees.

What gives? Does anyone know if this is an issue with the Bentley manual? Even if my switch was defective , I would be surprised if its operation would be reversed. I would expect it to either be stuck open or closed if it was not working.

I just checked the new switch description, and it is a little vague, but it definitely makes it sound like the switch closes when the temperature is colder, which matches my tests. Maybe the manual is wrong. If so, please be aware of this issue.

Thanks,

Olivier

Early_S_Man · 12-08-2002, 03:09 PM

Olivier,

What switch are you talking about ... Thermo-Time Swich for the cold-start solenoid???

ohecht · 12-08-2002, 04:50 PM

Warren,

It is the 15* Celcius switch on the closed-loop CIS models. It is located on the far right side of the passenger side timing chain cover.

The decription indicates it signals the closed loop system to go into closed loop (feedback) mode after running open loop during warmup.

Olivier

Wayne 962 · Wayne 962's Garage

The Bentley manuals are an excellent resource of Porsche 911 information. Unfortunately, they are also rife with many errors. I had a chance to look at their engine section very, very carefully when I was writing the engine book.

The photograph on page 102-21 of the Carrera book is my favorite! There are a few things wrong with this photo:

- Rod holding tools installed incorrectly! The two smaller tools are installed incorrectly - the correct orientation is shown in the original factory manuals.

- Generic engine stand used to rebuild engine. This is dangerous, and also can damage your case.

- Screwdriver sticking out of the engine case somewhere. Off on the left-hand side in a "where's waldo?" flashback...

I recommend using the Bentley manual as a good reference, but to verify all information with the factory manuals. (which also have their own set of inaccuracies).

-Wayne

ohecht · 12-09-2002, 06:06 AM

That is somewhat disconcerting...especially if the factory manuals have their own issues.

I know I have seen some 3.2 engine shots in my SC manual.

Does anyone have a good list of addendums?

I remember Warren found many things when the Bentley's first came out after going through them with a fine-toothed comb, his encyclopedic knowledge about these cars, and a critical eye.

Olivier