Constructing a WUR (Warm Up Regulator) Test Stand

[dkirk]

A fellow friend and 911 owner approached us about having engine running issues with his 1980 SC. These 3.0-Liter engines were equipped with the Bosch K-Jetronic (CIS) system and a known problem-prone component in this system is the WUR (Warm Up Regulator). A local Porsche shop stated that they won’t work on these WUR’s and that sourcing a replacement was the only option: however, if we came up with a method of testing, reconditioning and repairing these components, he would send us some business. Myself and my friend and colleague, Brian Kearns, accepted the challenge.

Knowing the operational principals of the K-Jetronic system, I designed a test stand as shown:



A Bosch fuel pump supplies system pressure which is controlled by the adjustable regulator to the set value of 5.0 bar. The system pressure gauge allows for an accurate regulator setting. The needle valve is set to duplicate the flow rate that is controlled by a fixed orifice in the fuel distributor. A control pressure gauge reads the important control system pressure, paramount to the proper functioning and calibration of the WUR. A simple electrical circuit is employed, allowing on-off switching of the fuel pump and WUR heater coil. An integral tank holds a supply of Stoddard solvent for supplying the “fuel”. The stand is mostly constructed of aluminum plate so it is quite light and portable.

Armed with this schematic, Brian constructed something that looks like a component out of the Space Shuttle – absolutely aerospace quality!








Our friend’s WUR was rebuilt with new internal components purchased from:

https://www.ebay.com/str/missingpartsde

We then calibrated the WUR on his engine, adjusting the system pressures and both cold and hot control pressures using a purchased gauge/valve tool made for this purpose. The WUR was then transferred to the test stand for verification and all pressures and control pressure cold/warm response values repeated exactly. Thus, the stand is now calibrated for future WUR diagnostics and adjustments directly, eliminating this operation on the engine.

With the WUR now refitted back to the engine, the car was test run and results were stellar – flawless running qualities throughout the operational range combined with rapid throttle response. This was a fun project and hopefully will provide some assistance to other 911 owners in our Wisconsin location.

[fanaudical]

Well built!

Is that a back-pressure regulator? Do you mind sharing manufacturer and part number?

[shoooo32]

You have Kerry's old car! I wondered what happened to it. It was pretty but needed sorting. We have stories...