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Join Date: Oct 2006
Location: Southern MA
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Tony,

I agree, lower R (resistance) will yield higher I (current) and in theory more heat at the wire to heat the arm quicker.

My understanding of the WUR internals: once the arm heats to a certain point it pulls away from the internal regulator contact point. Once that happens the heat arm no longer has any effect. Correct?

Nice explanation here:
http://jimsbasementworkshop.com/CIS/page_images/73%20911T%20CIS%20Print.pdf
see page #9
Tons of great info on CIS at this site!
911 CIS Primer - Introduction
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Sal
1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible
Old 03-29-2017, 07:33 PM
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And this other great pdf:
http://jimsbasementworkshop.com/CIS/page_images/k-Jetronic-book-1.pdf
See page 16
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Sal
1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible
Old 03-29-2017, 07:36 PM
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Correct........

Quote:
Originally Posted by scarceller View Post
Tony,

I agree, lower R (resistance) will yield higher I (current) and in theory more heat at the wire to heat the arm quicker.

My understanding of the WUR internals: once the arm heats to a certain point it pulls away from the internal regulator contact point. Once that happens the heat arm no longer has any effect. Correct?

Nice explanation here:
http://jimsbasementworkshop.com/CIS/page_images/73%20911T%20CIS%20Print.pdf
see page #9
Tons of great info on CIS at this site!
911 CIS Primer - Introduction


Sal,

Never thought you would be interested in CIS. This subject is too easy and simple for you. BTW, if I would encounter an electronic subject that I could not comprehend, I know I could always rely on you. The website is a great source for reference.

Tony
Old 03-29-2017, 08:01 PM
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Tony beat me to it - lower resistance = more amps = more watts = more heat = more (or quicker) bending of the bi-metallic strip.

Just remember - infinite resistance = an open. No (0) resistance = a dead short = big current - think of accidentally grounding the positive of the battery - enough heat to melt a lead battery post, or weld a screw driver to the chassis. I can't recall if this circuit is fused, and if so, where. Seems unlikely that a dead short would happen here.

I'm unsure how ambient would affect resistance. A coil's resistance can get lower if adjacent wires in the winding fuse or lose their insulation, though I am unsure how often that actually happens.
Old 03-29-2017, 11:18 PM
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Tony,

I help dial in CIS systems often here locally. The principles for dialing in AFR are the same no matter what the engine is. CIS is a fantastic fueling strategy that works well when all components are in spec and properly functioning. The only thing I'd change on a CIS car is the ignition setup, I'm surprised no one has yet designed a complete electronic ignition for CIS with true full tunable ignition mapping. That would really help the CIS cars but the fuel system really does not need changing.

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Originally Posted by boyt911sc View Post
Sal,

Never thought you would be interested in CIS. This subject is too easy and simple for you. BTW, if I would encounter an electronic subject that I could not comprehend, I know I could always rely on you. The website is a great source for reference.

Tony
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Sal
1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible
Old 03-30-2017, 03:12 AM
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Quote:
Originally Posted by Walt Fricke View Post
Tony beat me to it - lower resistance = more amps = more watts = more heat = more (or quicker) bending of the bi-metallic strip.

Just remember - infinite resistance = an open. No (0) resistance = a dead short = big current - think of accidentally grounding the positive of the battery - enough heat to melt a lead battery post, or weld a screw driver to the chassis. I can't recall if this circuit is fused, and if so, where. Seems unlikely that a dead short would happen here.

I'm unsure how ambient would affect resistance. A coil's resistance can get lower if adjacent wires in the winding fuse or lose their insulation, though I am unsure how often that actually happens.
Heat = Power (watts) = resistance X current X current = R X I^2 = V^2 / R = V X I
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Old 03-30-2017, 04:35 AM
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I measured my 090 WUR (82 SC) this evening cold (86F ambient). Upon disconnecting the electrical connection, I found the male and female contacts to be very corroded. The vent on WUR was also corroded. Male connections had Infinite resistance. I did what I could to clean them up with my Dremel and then checked the resistance. It was about 10 ohms.

The problem I’m having is that the car runs very rough for the first 2 mins or so and then the idle smooths out and it runs fine. I have to give it some throttle to keep the revs up at first but after that first 2 minutes everything is great.

I will be doing a pressure test probably this weekend, but my question is this: if the resistance on the WUR is very low (again, 10 ohms) won’t I need to replace it anyway? Should I go ahead and just order a new WUR?
Old 06-13-2018, 06:30 PM
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It will need to be rebuilt to work properly. Tony (boyt911sc) is the guy to talk to. They are hard to find NOS and really expensive $500+. The only option really is a rebuilt WUR. Tony's very reasonable and you'll save a bunch of cash for a nicely rebuilt unit in exchange for yours. Or he can rebuild yours. I bought mine from him and it works great. Almost 2 years later and it's still working great.

Your WUR is causing the mixture to lean off too quickly so it's not allowing the engine to warm up in lockstep with it.

Last edited by gazzerr; 06-13-2018 at 07:07 PM..
Old 06-13-2018, 07:03 PM
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Quote:
Originally Posted by Gretz View Post
I measured my 090 WUR (82 SC) this evening cold (86F ambient). Upon disconnecting the electrical connection, I found the male and female contacts to be very corroded. The vent on WUR was also corroded. Male connections had Infinite resistance. I did what I could to clean them up with my Dremel and then checked the resistance. It was about 10 ohms.

The problem I’m having is that the car runs very rough for the first 2 mins or so and then the idle smooths out and it runs fine. I have to give it some throttle to keep the revs up at first but after that first 2 minutes everything is great.

I will be doing a pressure test probably this weekend, but my question is this: if the resistance on the WUR is very low (again, 10 ohms) won’t I need to replace it anyway? Should I go ahead and just order a new WUR?
Measure your fuel pressures first.

Who told you 10 Ohms at that ambient is bad ?

If the WUR needs a rebuild, there are a few rebuilders who post here regularly. One (?) is an authorized Bosch shop from what I can tell from the postings here.
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Old 06-14-2018, 08:24 AM
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