My Three-Year CIS Journey – From “What’s a WUR?” to “Fully Dialed In!”
 

(Apologies in advance for the length — but hopefully this helps someone else on the same road!)

When we bought our 1981 911 SC in the summer of 2022, I knew I was signing up for an education. The car had been driven less than 10k miles since the early ’90s. It was my first Porsche, and part of the allure was learning to sort it out - doing some of the work myself along the way.

Back then, I had no idea how an SC was supposed to run. Looking back, it was… pretty rough.

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The First Clues
The first issue to emerge: it wouldn’t start when warm. A quick search on Pelican pointed to the fuel accumulator, which was an easy swap — and boom, the issue disappeared.

Feeling confident, I kept reading. A forum member then pointed out something I hadn’t noticed: my car had the wrong WUR — a 033 instead of the correct 090. That’s when the real learning started.

I bought a rebuilt 090, installed it, and… the car ran worse. No power, no life. So, back went the 033.

Then the fuel pump started leaking, so I replaced that too. Each time something in the fuel system got refreshed, I’d try the 090 again — and each time, same story: worse.

Then came a high idle when warm (around 2500 rpm).

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First Engine-Out & High Idle Solved
When the trans needed a rebuild, we did the first engine-out service. The shop replaced all the vacuum hoses and miscellaneous bits on the back of the motor. That finally killed the high idle — so likely a vacuum issue.

But now, the car started popping at idle. Turned out the intake gasket on cylinder #6 was leaking. Around this time, I tried the 090 again — and it ran horribly, with backfiring galore.

That’s when I learned about the fuel relay under the passenger seat. Replaced it — and boom! — suddenly with the 090, the car ran better than ever.

Turns out the 033 was bypassing the ECU and O2 sensor. Every time I installed the 090, those systems came back into play — and the bad relay had been my real culprit all along.

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Second Engine-Out & Rebuilds
Next came the second engine-out service, this time to fix the intake gaskets and sleeves. The mechanic suggested sending out the fuel distributor and WUR for inspection/rebuild.

Both came back fresh — and the car was noticeably stronger.
• Popping at idle: gone.
• Pull at speed: fantastic.
• Cold start: still not great and actually worse than before.

Now it needed throttle feathering for the first two blocks until it would idle on its own.

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Enter the CIS Deep Dive
At this point, I went all-in on CIS testing and learning. Here were my first fuel pressure readings:
68°F (20°C)
System Pressure: 4.35 bar
Cold Control Pressure: 0.4 bar
Warm Control Pressure:
1 min – 1.0 bar
2 min – 1.7 bar
3 min – 2.0 bar
4 min – 2.7 bar
5 min – 2.9 bar
Residual Pressure:
0 min – 2.3 bar
10 min – 1.5 bar
30 min – 1.35 bar

Low cold control pressure (CCP) stood out, suggesting a rich cold mixture.

A flow test showed slightly low fuel flow, so I replaced the tank screen — found sediment in the tank and dirty fuel in the filter. Retested: system pressure improved, but CCP still low.

48°F (9°C)
System Pressure: 4.95 bar
Cold Control Pressure: 0.8 bar
Warm Control Pressure:
1 min – 1.5 bar
2 min – 2.0 bar
3 min – 2.35 bar
4 min – 2.65 bar
5 min – 2.9 bar
6 min – 3.2 bar
7 min – 3.3 bar
Residual Pressure:
0 min – 2.75 bar
10 min – 2.05 bar
30 min – 1.8 bar

A Helpful PCA Visit & WUR Revelation
I posted my results to our local PCA group, and a kind soul dropped by to retest with his own gauge. Readings matched — so my test method was sound. He suspected what I did: the WUR pin depth was too low, making CCP too rich at cold start.

He’d just opened a new shop nearby, so I brought it over rather than risk botching the WUR.

He found the pin flush with the top of the WUR (usually they’re recessed slightly). He adjusted the diaphragm, then reset the pin higher to raise CCP. Success — but then warm pressures went too high.

Turns out, despite the recent rebuild, the spring or bimetal strip was likely off. I had a second 090 I’d picked up on eBay to tinker with, so he swapped its spring in. That let him get both CCP and WCP dialed in perfectly. He mentioned the spring that was in the WIR was very tight - with very little - spring!
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The Result
Drove Maverck for the first time after the adjustments and… wow.
• Cold starts perfect.
• Idles rock-solid at 950 rpm.
• No popping.
• Pulls hard and clean through the revs.

After three years, I can finally say: I think she’s dialed in.

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Lessons Learned
• Test before guessing. Fuel pressure readings are your best friend.
• Fix known issues first. Each resolved problem made the next one clearer.
• Learn CIS — don’t fear it. Once you understand what each component does, it’s actually a straightforward system that can run incredibly well when sorted.
• And never underestimate a bad relay.

Thanks to everyone who’s posted CIS wisdom here over the years — you all helped me learn enough to finally get this car running like it should.

Maverick: Thanks for posting your experiences and results. I will help people with CIS in the future.