cis test questions

[jkb157]

I have a 79 911sc with a cold start problem.I have bought a pressure gauge and I have a bentley manual.The manual recommends running the fuel pump without running the engine by using a fused jumper wire.They give a description of the jumper wire which uses a toggle switch.What amp does the switch need to be?By using the jumper wire method(engine not running) can the warm control pressure be tested by reconnecting the electric plug to the regulator?Thanks John






79 911sc
01 boxser

[MotoSook]

Why not just just hook up the CIS tester and run the engine. I've even left the tester connected and test driven the car (be careful make sure everthing is secured).

The recommended test procedure should be adequate to determine if your WUR is functioning properly and if your check valve and accumulator are healthy.

You can test the system pressure without jumpers. If you don't want to bother with jumpers that is. Just connect everything and with the isolation valve open, run the car to clear any air out of the tester loop (you'll have to bleed the system after you make all the connections to bleed the system, lift the plat with the ignition on, or it'll take more than a few cranks to start). Shut off the car. The indicated pressure should then be your residual pressure. Close the isolation valve, then lift the air plate with the ignition on. Run the pump for a couple of seconds (not much longer as you'll flood) and the gauge should jump up to system pressure.

I have not tried that method, but it seems like it should work.

[scphelps1]

I second what Souk says about testing the pressures with the engine running. I tried doing it without it running and flooded the engine. With it running you can easily flip between control and system pressures. It won't run well with the valve in one of the positions - I forget which, but it will be pretty obvious. You can leave it there long enough to get a reading though.

[MotoSook]

Closing the isolation valve will prevent fuel from bleeding away from the fuel distributor giving you system pressure. The WUR controlls the rate of of flow back to the tank to maintain the correct "control" - operating pressure. Closing the valve (installed upstream of the WUR) prevents flow out of the system. The WUR is simply a back-pressure regulator with a temperature dependent "set" pressure (your control pressure). It ain't voodoo, y'all.

A CIS engine CAN run with 70 psi of control pressure! Just runs like crap..at idle..and at other RPM, but it'll lean at higher RPM, just like when you get crappy gas and your filter and WUR are junk before you figure it out after a long DE weekend, just before a proposed long drive/trip in the 911...!