Some CIS WUR Advice to share

[Jay Laifman]

I have a 73.5 T with CIS. I had a long run with bad WURs. My original 001 went bad. Then I got two allegedly good 129 WURs. But they didn't make the car run better. With the help of one of the CIS vendors, I got an 009 WUR (from the 1975 911 and 911S), with advice on how to hook it up. The advice I received was that the 009 had a vacuum port that enriched the injection better than the mechanical throttle position valve. So I put a T in the bottom of the deceleration valve to get vacuum to the WUR (on searching, it seems that is not a vacuum hose. That could be the problem all along. This just goes to show how hard it is to get good advice online!). And I unhooked the throttle position valve.

The car was definitely better than it was with the bad 129s I got. But it was never exactly right. This last week, with some input from Brian Leask and Brian Bodart, I took off the vacuum to the 009. And WOW my car was as smooth as ever and wonderful again.

I'm going to get the throttle position valve running again (and I have a separate thread on that to get that right).

Maybe there is a way to get vacuum to the 009 and make it work better than with the throttle position valve. And I just got vacuum from the wrong spot. Or it simply is a bad idea for the 73.5. But, I thought I'd share in case anyone else goes down this road.

[Rick Cabell]

Good info Jay, as I am putting together a mess that I did not take apart. Also a 73.5

[J-R]

Vacuum port on 009 for 75 on and 73,5 throttle position valve are doing the same job on CIS.

In part-load, they decrease enrichment for fuel economy on cruising operation.

On a customer car, both were connected and the engine was not happy with that, way to lean.

I was considering finding and rebuilding a 129 unit but came across a NOS 004 on thesamba.com in Italy (I'm in France) and now it run like new !

On another car, a 74' with the same set-up, someone has interverted the inlet and outlet lines, there was no WUR correction and the car was working under 3000 rpm but struggle to go above.

On this CIS early distributors, the two connecting are push-on and same diameter and side-to-side...

Watch out !

Fuel pressure gauge is a must to find if wur, throttle valve and distributor are correctly operating.

[Jay Laifman]

I agree that the function is supposed to be the same. Though I'd describe it a little differently. They don't cause it to be leaner at part load - they cause it to be richer in other conditions. That is, the WUR either releases fuel back to the tank instead of to the injection which lowers overall fuel pressure and richens the system, or it doesn't release fuel to the tank and all fuel pressure stays in the system, leaving the rich/lean state alone. So, it really increases enrichment or does nothing, leaving the system alone.

It does it two ways. First during warm up. The little heat filament causes the valve to let fuel pass while it is cold. Once it is fully heated, it no longer lets fuel pass. Thus, richer while cold.

Second the WUR releases fuel pressure back to the tank during certain driving conditions. The 73.5-75 Throttle Position Valve is a physical cam that rotates with openings at both ends - that is at idle throttle position then again when rotated to WOT. It is static and fixed as to when it is rich/lean. The 009 WUR uses vacuum to release fuel regardless of throttle position.

The problem with the TPV is that it always does the same change at idle and WOT, regardless of engine state. So the idea was that the vacuum adjustment should be better. Yet, it wasn't on my car. So I can only assume that I just hooked it up to the wrong vacuum. I assume that it had too much vacuum even during cruising, so it was reducing pressure even then. The 73.5 technically doesn't have a vacuum port that Porsche designed for the WUR. Someone told me to port it off the vacuum hose on the bottom of the deceleration valve. The only other options I think are the vacuums off the top of the deceleration valve or the one to the distributor. I don't know if using either of those would mess up those functions. All I know now is that the bottom of the deceleration valve is not good.

[J-R]

You are right about the WUR, I compare the vacuum port and TPV for their leaning action.

If Bosch change from TPV to vacuum is as you describe probably because the vacuum is more precise in operation than a cam with online 3 steps to adjust back pressure.

Vacuum port position and size is critical for good operation, in my 73,5 case, they connect the wur vacuum line with a T piece on distributor retard can. It wasn't working.

I'm agree with you as the fact it is very satisfying to understand how it work and make your car go better