Raising cold control pressure, another CIS question..

[makaio]

I just performed a pressure test, to try to fix my continual cold starting problem, and the pressure was only 10 PSI on the cold control pressure (50 degrees F.). I know this is way out of spec, and need to raise it to 25psi. So since my WUR is not modified yet, do I have to dis-asemble it and push the pin back out? Or can I just twist the nut on the bottom a little?

[john walker's workshop]

i usually start at 1 bar. that's 15# roughly. at 10#, it should start easily, and rev up fine without spitting and popping, but possibly surge a lot for a minute or two. you will know when the pressure is too high when it does the spit, pop, stumble thing after it starts. don't forget, this unit is for a richer warmup, and proper control pressure when hot, not cold start. the cold start valve does that.

[makaio]

Thanks JW.

I guess that's not my problem then.

The car initially fires, then dies right out, within 1-2 seconds when cold. When the ambient temp is above say 60 F. or I store it in the garage over night, she fires right up, and idles fine. That's why I thought it was the WUR, and the pressure was way off. Once running for 5 minutes she screams and always fires right back up after shut down.

I guess I have more searching and reading to do.

[john walker's workshop]

maybe the gauge is incorrect. can you get a metric CIS gauge? sounds like you need to go richer (less control pressure) on the WUR, which means moving the pin down a hair or two.

[stormcrow]

I've been having the same problem with my 78 911 SC Targa. What I found out is my warm up regulator is the problem.

I put the pressure gauge on from the fuel distributor to the regulator and fired it up. It ran for about 20 seconds and died. What happened was, the pressure started to build up on the fuel distributor and eventually the pressure became so great that the air flow sensor plate would not move.

Disconnected the regulator, installed the pressure gauge in place of it and started it back up. The pressure going through the gauge was reading 10 PSI. I slowly closed the valve and when I got to a certain point, the engine idle went up to 2000 rpm and stayed there for a short time and eventually came down to 1000 rpm without adjusting the valve on the gauge.

So, I have to remove my pressure regulator to see what's going on. I have a feeling it's blocked because a in October, I had a fuel problem and the fuel filter was plugged with rust.

Steve

"A Porsche does more then just go fast in a straight line"

[makaio]

Steve, great idea on using the valve to manually change pressure.

JW, what's the best way to tap the pin down?

As for the gauge, I'm pretty sure its on the money. I just got it from JC Whitney not too long ago. Everything else was well within spec during the rest of the test.

[47silver]

check the ohms on the wur should be around 26 to 40 i understand. my contacts were corroded also and cleaned them

the wur relay gets gets power to operate from the alternator so the car has to be running, the relay closes a set of contacts and the relay supplies power to the heater. so check for power at the plug connector after you start the car.

i am of the opinion (though in a small majority) me, that the heater is an important part of the wur and must be working for the wur to operate properly. see other threads about this most believe that the heater is out of the system after the car warms up but i think it is always being used.

i think that if you unplug the wur the car will run very rich, as the heater will not bend the bimetal in the wur. i have never had one apart so i am guessing. my background is thermostats and control systems but i have been wrong many times, and may be wrong about this.

use your gages, unplug the wur and see what happens. i have not been able to test mine due to time and location problems but if if get to it soon ill let you know what i find.

by the way my points were not set correctly and caused the car to be hard to start especially in the cold.

gary

[dougcl]

47, you are absolutely correct that the heater is important, and is required even after the car is warmed up. Unless your car is running hot, the WUR does not stay warm enough to do it's job without the heater. The symptoms in this case would be: car cold starts fine, runs too rich after warm up (idle surges and car fails to idle at low < 1200 RPM), and runs great immediately following a warm start (after heat soaking).

The other theory regarding the bimetallic strip requiring a vent to ambient air in order to deflect is false.

Doug
75 911S

[47silver]

the more i looked at it i believe that i am wrong, the only connection to outside air is the one to atmospere which must be used to sense atmosperic pressure and then allows the wur to compensate, richer with a highe pressure and leaner with a lower

but i still wonder why the heater is in the circuit, it does not seem necessary although it may act like some sort of time delay for richness i guess.
i would like to get a used one to tear apart.


gary