73.5 CIS WUR not getting 12v

[Jay Laifman]

I am trying to figure out why my WUR is not getting power. I found the CIS wiring diagram. It shows that the power to the WUR comes from a relay. I see there are two relays in the left rear. A big square one and a round one. But I can't see the wires under the relays to see if they are the colors that the diagram is showing. And I also can't get to the wires to use a meter to see if they have power when they should.

I happened to have one of the round ones and swapped it in. No change. I can buy a square one. But I hate to do that if there is a test I can do first.

I've never had the WUR lose power in the 35 years I've had this car. Not sure what to check.

Any suggestions?

[Jay Laifman]

It looks like the square one is for the rear window defroster.

So only the round one? When I pulled it, I did find that it had power to #30. But nothing else.

[Jay Laifman]

Is it possible to add people here? Trying with the CIS kings: @boyd911sc @harryd @e_sully @rarelyl8

[boyt911sc]

Jay,

This should be a piece of cake for you! First, test the relay and confirm it is good and working. The coil could be bad for all you know and makes the relay unable to do the switching process. Do you have a spare relay? This is a very common relay used as automotive devices.

Tony

[PeteKz]

Yes, the "rectangular" one is for the defroster. The round one is for the CIS components. Unless you have messed with the wiring, it's good chance that the relay is just old and flaky. Double check your fuses too.

Pull the relay, and make sure you have 12V at pin 30 in the socket (IIRC, it's always hot). Test for resistance to ground at socket pin 87. It should be the resistance of your WUR. Test for direct connection to ground at pin 85. If those test correctly, then troubleshoot or replace the relay.

[Jay Laifman]

Thanks! I did test the prongs of the round relay. I'm not getting power to 86 with the ignition on. As I read that wiring diagram, that should be getting 12V which would allow 30 to cross over to 87. Where would I trace 86? The diagram says it is a black wire going to 61 of the voltage regulator. I will go look.

[PeteKz]

The "prongs" of the relay? Or the socket?

Pin 86 goes to the VR and alternator. I "think" that will be powered only when the engine is running and the alternator generating. Start the engine and check for voltage there.

[Jay Laifman]

Ohhh. Did I forget I need to jump 12v to test WUR?

Bummer.

[Jay Laifman]

Ok. That was embarrassing. I guess my only saving point is that it is not something I do very often!

Maybe you can help now with the problem I'm trying to solve: hard warm start. WUR working perfectly. Draining to spec as well. New accumulator. New check valve on top of fuel pump. New rubber sleeves for air box. Injectors working great and not leaking - one dripped a little more than the others, but I got that Mercedes CIS injector cleaner and it took care of it.

I also pulled the cold start valve and confirmed it is working nicely.

The car is running beautifully. Start right up when cold. But after sitting for an hour or more, it does not want to start unless I crank for a long time.

Any other suggestions to check?

[HarryD]

Sounds like a possible heat soak issue.

Idle ok?

Will it start easier if you pull up the hand throttle?

[PeteKz]

Since you have checked or replaced the usual stuff, there's one more check you can do without gauges: Warm up the car, then shut it down. Wait a half hour. Then crakc open the fuel line connector on the fuel filter or FA (whichever is easier for you to get at). You should get a spurt of fuel under pressure, a teaspoon of fuel or so. If you get no spurt, then it is not holding residual pressure.

Otherwise, it's time to put the CIS gauge/vavle on it and check SP, CCP, WCP, and residual pressure.

[Jay Laifman]

Harry: Yes, idle is beautiful. Smooth as a sewing machine. I will say that I always noticed how nicely my car idled. But then for a period it would have an uneven little burble here and there. That's gone.

It is not better with throttle pulled. And I noticed in the manual the factory actually says to use the pedal wide open when warm. Tried that too. No change. (Note that I inquired in another post if that was now considered correct, since over the years I've seen it warned as a big no-no to start with anything but the hand throttle).

Pete: That's what I just did - and the whole reason I started this thread. Checked all pressures, including residual pressure. Right to spec. After 20 min more than 1 bar.

[HarryD]

This chart may be helpful:

[Jay Laifman]

Yes, I know. I have the Porsche CIS Troubleshooting Guide too. The only thing on the list I haven't rechecked is that the sensor plate stop is too low. I did check it not that long ago. It was spot on. I can't imagine it has changed since then. I just went and looked again. Looked right to me. But I think I convinced myself it might have been the tiniest bit low, like maybe 1/3 of a whisker. So I lifted it up just that much.

I also have a smoke check tool. Checked that not that long ago too. No leaks. But the rubber boots still showed external cracks. So I just replaced them anyway.

[HarryD]

Random question. Do you use exclusively ethanol free fuel?

[pmax]

You can measure the residual pressure. Have the fire extinguisher and rags handy.

This is spec for my 80. Your 73.5 will vary.



https://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies-4.html#post9671930

[Jay Laifman]

HarryD. Hmmm. I do believe in California we do have ethanol in our gas. I don't know that I even have a choice. I will look. Looked. No choice. Yes ethanol. Think that could be it? It otherwise runs beautifully.

pmax. Yes, I have already checked that multiple times. To spec.

[HarryD]

Check https://www.pure-gas.org/ to see if there is any near you.

E10 is bad news for our CIS Cars. It tends to absorb moisture in the air to cause rust to the mild steel components and degrades the standard gaskets and other elastomers in the system. You can use Sta-bil 360 Marine to get some corrosion inhibitor in your fuel to protect the steel. There is nothing to protect the elastomers.

My 1970 bus has a clear fuel filter. Before I switched to non E10, it always had black particles in it even though I used Sta-bil. Once i switched, the particles went away. Pretty sure it was bits of elastomer getting into the fuel.

As a random thought, try changing your fuel filter to see if it helps.

[pmax]

Originally Posted by Jay Laifman

pmax. Yes, I have already checked that multiple times. To spec.

Ah, the other thing I can think of is that the CSV is supposed to kick in when the engine cools enough so the thermotime switch is "on".

Perhaps it isn't when it should have.

[HarryD]

Originally Posted by pmax

Ah, the other thing I can think of is that the CSV is supposed to kick in when the engine cools enough so the thermotime switch is "on".

Perhaps it isn't when it should have.

There is no Thermotime switch on a 1973.5. The hand throttle serves this function by cracking the throttle plate open and closing a microswitch that energizes the CSV when the engine is cranked.