Troubleshooting my '74s CIS system

[BrianH74]

Hi Tony,
I already did the CCP and warm CP tests on the WUR. However, with base system pressure out-of-spec, I kind of figured the numbers were invalid. I'm going to do as you suggest and get SP within spec (aiming for 4.8 BAR), then re-run the CCP and warm control pressure over time tests.

One thing I CAN confirm is that the WUR heating element works, since I saw variation in control pressure over time when it was plugged in.

Brian

[PeteKz]

Brian, also measure and post the resistance value (ohms) of the WUR heating element. That may help narrow down what you have.

[BrianH74]

The resistance value of my WUR is 49 ohms.

Brian

[PeteKz]

The ones I've seen on Porsche CIS are in the 20-ohm range, or in the 30 ohm range. 50 ohms would result in a slower warmup. Interesting data point. Thanks.

[E Sully]

Tony has a lot of experience and would have a better knowledge of the correct resistance value range than me. I have 3 WURS. The 001 at 18 ohms, an 008 at 54 ohms, and the one that Brian's resembles, a 129 at 45 ohms.

[BrianH74]

Anyone have a clue about where my particular WUR came from and what the proper control pressure graph to use would be? Once I shim my FD and get system pressure corrected, I will re-test my WUR, but without a graph to go by, I won't have any idea if it's functioning within spec or not.

Brian

[boyt911sc]

Originally Posted by E Sully

Tony has a lot of experience and would have a better knowledge of the correct resistance value range than me. I have 3 WURS. The 001 at 18 ohms, an 008 at 54 ohms, and the one that Brian's resembles, a 129 at 45 ohms.

Ed,

The early CIS warm-up regulators like -001/-008/-129 would have mid 50’s Ohms resistance. So Brian’s mysterious WUR would work plus a good working TPR.

Tony

[BrianH74]

Hey that's good news Tony. I'm going to adjust system pressure into spec tomorrow and then run the cold and warm CP tests. I'll post the results.

Brian

[boyt911sc]

Originally Posted by BrianH74

Hey that's good news Tony. I'm going to adjust system pressure into spec tomorrow and then run the cold and warm CP tests. I'll post the results.

Brian

Brian,

If you need some help testing and evaluating your TPR, I could do that for you for FREE. It would take me only a few mins. to do the test in my CIS Bench Tester. Send it to me with a RSL (Return Shipping Label) preferably UPS or your favorite carrier. I will be leaving this weekend for Amsterdam and be back in 2 weeks.

BTW, you will need a good TPR with your non-vacuum assisted WUR for enrichment in your engine to run well. Keep us posted.

Tony

[BrianH74]

Thanks for the offer Tony. I may take you up on that.

I was going to follow the steps in the Porsche manual to test it. Basically measure control pressure at half-throttle and at full-throttle to see if they are in spec. Is there anything more to testing the TPR?

Thanks,
Brian

[boyt911sc]

Originally Posted by BrianH74

Thanks for the offer Tony. I may take you up on that.

I was going to follow the steps in the Porsche manual to test it. Basically measure control pressure at half-throttle and at full-throttle to see if they are in spec. Is there anything more to testing the TPR?

Thanks,
Brian

Brian,

Testing is easy. Knowing the values of the control pressure @ idle, mid-throttle, and WOT are critical. All three (3) control pressures should be with in specification. And you need the fuel line fitting to accommodate the WUR and TPR.

Tony

[BrianH74]

OK, so I spent the afternoon doing some testing and adjusting of the CIS system on my '74. First, I removed the pressure valve on the back of the FD to raise system pressure. It was initially 4.2 Bar. I disassembled it and found two factory shims in there. I cut up an aluminum pop can and made two more shims, which I sandwiched between the two factory shims. I thought that would land me right at 4.8 Bar which is middle of factory spec. I reassembled the pressure valve and tested system pressure, which is now 4.65 Bar. A bit lower than expected but in spec. Next, I checked cold control pressure on the WUR. Cold control pressure (no power to WUR) came in at 0.85 Bar @ 7.2 deg C. I don't have a graph for my WUR so no idea if that is OK or not. Next, I plugged in my WUR and measured control pressure over time. Here are the results:

Initial CP - 0.85 Bar
@1 min - 1.4 Bar
@2 min - 1.9 Bar
@3 min - 2.2 Bar
@4 min - 2.5 Bar
@5 min - 2.65 Bar
@6 min - 2.8 Bar
@7 min - 2.85 Bar
@8 min - 2.95 Bar
@9 min - 3.0 Bar

After 9 minutes, the WUR pretty well leveled out at 3 Bar. I also did a smoke test to check for vacuum leaks by sealing off the throttle to prevent air leaks, pulling off a vacuum hose and tapping the smoke tester in. The only real leak I could find was on the pop-off valve in the air box. If I pushed down on the flapper, the smoke stopped. I smeared vaseline on the o-ring to see if that would help. Maybe I need a new o-ring - I don't know. I know engine vacuum should pull down on the flap when running so maybe it's fine.

I'm going to put the bellows between the air flow meter and throttle back on tomorrow and run the engine with the adjusted system pressure to see how it runs. Control pressure seems a bit low (rich) to me. I'm considering throwing another shim in the pressure valve to raise system pressure to 4.9 - 5.0. That should lean out the control pressure a bit further at the same time. Thoughts?

Brian

[BrianH74]

Tony, just saw your response. I ordered that FD fitting to get the TPR plumbed back in on the same port as the WUR. I'm not 100% sure the place I ordered it from can source it though. If anyone has a good one off a junk FD I could sure use it. As soon as I can source one, I can check the TPR control pressures.

Brian

[PeteKz]

Brian, I would add another shim or two to the FD SP valve. That should put you pretty close to 5.0 bar.

[BrianH74]

I added a couple more shims to the FD SP valve. Pressure is now up to 4.8 Bar which is right in the middle of spec. I have to re-run my control pressure numbers later today. I took the car for a short drive yesterday and it ran pretty well. Beforehand, I could barely get it to idle under 1500 rpm. It now idles at about 1000 rpm, which I know is a bit high. The idle seems to drop down to an unsteady 600-700 rpm and wander for 15-20 seconds when I pull up to a light, then settles back in around 1k rpm. Not sure what that's about.

Brian

[FunWithPaul]

Hey Brian,
Did you get that 74 CIS issue solved?

I have a 74 too, and have my CIS out for a leaking fuel line (hose clamp?)
That is well documented on other posts.

I have a 017 FD and a 001 WUR, the car ran great.
I recently found out the 017 FD is not original (who knew? I got it that way in 1986)

This what I have for the WUR connection.
(sorry the pic is sideways, it looks OK on my computer)


''

The 73.5 and 74 CIS are unique, you know what they say "NEVER buy the first model year, they haven't worked out the bugs!"
That is true in this case, I just read that the 73.5 CIS was the first time it was ever used in a passenger vehicle. And I know they made NUMEROUS changes as they learned more (who is THEY? Porsche and Bosch...)

The experts here know a lot. Ask a question. Someone that has experience in that matter will answer. I have learned a lot here (much by just searching and reading)

It looks like Rube Goldberg owned that car before you. You will need to correct his "jury rigged" repairs. The car is worth it (finally).

Paul

[FunWithPaul]

Originally Posted by PeteKz

The ones I've seen on Porsche CIS are in the 20-ohm range, or in the 30 ohm range. 50 ohms would result in a slower warmup. Interesting data point. Thanks.

Hey Pete,
I just checked my 50 y/o 001 it is 20.7 ohms
(thanks for the info. I "thought it worked" because the car started and ran great. And another "data point" for you)

[FunWithPaul]

Originally Posted by BrianH74

Here is a clearer pic of my WUR. There is NO model number after the Bosch part number. Now what?

A couple more questions - if I want to replace my fuel line from the FD to the throttle valve regulator, how do you get these polyamide lines off and back on again at the throttle valve side? There is no fitting or clamp. Are these lines supposed to be heated to get them off or on? I'm not used to working with lines like these.

Does anyone know where I can get that banjo fitting on the top of the FD that supplies fuel to both the WUR and the throttle valve regulator? I'll need that to reconnect mine.

Thanks,
Brian

I have bought 911 fuel fittings (and many other things) from
Belmetric
https://belmetric.com/fittings/banjo-fittings/

and Special T Auto
https://www.specialtauto.com/

Paul