'82 SC WUR question

[wgirardot]

I tested the resistance of my WUR and got 9.1 ohms. I know this is way out of spec; what are my options to remedy this? Could this have anything to do with my poor gas mileage, and sub-standard performance (power) when the car heats up on hot days vs. it driving like a champ in the morning when first run? Looking to improve my 911 experience

Any suggestion/comments would be appreciated

thanks,

Bill

[ossiblue]

Any issues involving the wur and whether or not it is working properly, needs to begin with fuel pressure tests. What are your cold control, and warm control pressures? If the heating element is not working, the wur will still adjust from heat from the engine so you should get a warm control reading after the engine has warmed up.

Test you fuel pressures and report back the results. A too low warm control pressure can cause an overly rich setting which can cause poor performance and poor gas mileage.

[wgirardot]

Originally Posted by ossiblue

Any issues involving the wur and whether or not it is working properly, needs to begin with fuel pressure tests. What are your cold control, and warm control pressures? If the heating element is not working, the wur will still adjust from heat from the engine so you should get a warm control reading after the engine has warmed up.

Test you fuel pressures and report back the results. A too low warm control pressure can cause an overly rich setting which can cause poor performance and poor gas mileage.

Will do, thanks. I was hoping the ohm reading (low as it is) would give me an instant fix by replacing/rebuilding it. Car pulls so strong when "cold", and is anemic when fully warmed on a hot day.............all bark, no bite. I'll research more, and perform tests when schedule allows. Other comments, suggestions appreciated


Bill

[Jim Williams]

IIRC, the '82 WUR, number ending in 090, has a dual resistor as the heating element. There is a set of contacts inside that opens (or closes, I forget which and am not by my notes that spells this out) that places the two elements of the resistor in series in one position and the elements in parallel in the other as the WUR warms up.

I forgot for a bit that this is covered in my CIS Primer. Look here under WUR. I'll have to double-check the actual connections inside the WUR but the concept is still the same. I'll post from my notes in a couple of days. Some one else may have the actual wiring already available.

[RarlyL8]

Simplistically, a lazy bimetallic strip will not allow the pressure to climb as high as it should causing a rich condition.

[T77911S]

check pressures.

[wgirardot]

Originally Posted by RarlyL8

Simplistically, a lazy bimetallic strip will not allow the pressure to climb as high as it should causing a rich condition.

What should be done to remedy this? Does an adjustable WUR help adjust out of this situation? Rebuild/replacement? I will eventually get around to getting a set fgauges and test my pressures...................but will entertain repair/replace/experiment to see if I can fix this

Bill

[Jim Williams]

Originally Posted by wgirardot

What should be done to remedy this? Does an adjustable WUR help adjust out of this situation? Rebuild/replacement? I will eventually get around to getting a set fgauges and test my pressures...................but will entertain repair/replace/experiment to see if I can fix this

Bill

Checking the pressures should be the first thing you do, not something you will eventually get around to. Without having checked the pressures, you are trying to address a problem without knowing what the problem is.

[Jim Williams]

The heating element is a tapped resistor with 17 ohms on one end and 27 ohms on the other, with the tap in between the two values. The tap goes to the +12 volt input. The 27 ohm end is permanently connected to ground. The 17 ohm end is connected to a bimetallic switch internal to the WUR. At ambient temperatures below about 50˚F, the switch is open so that the applied + 12 volts "sees" 27 ohms. at ambient temperatures above 50˚F, the + 12 volt input "sees" about 10 ohms. My wording in post #4 above is not quite correct about the two resistance elements being is series before the switch closes. The 27 ohms resistor is alone in the circuit before the switch closes.

At temperatures below 50˚F, an applied + 12volts will produce around 5 watts of heat (12*12/27) to heat the resistor and the bimetallic strip. At temperatures above 50˚F, the bimetallic strip closes, grounding the 17 ohm end of the dual resistor, and the two elements of the resistor are now connected in parallel, creating a 10 ohm resistance to the 12 volts and producing about 14.4 (12*12/10) watts of heat, bringing the bimetallic strip controlling the fuel mixture to it's final position more quickly, and leaning the mixture at the fuel distributor faster.

In practice the actual heat produced by the heating element will be higher, as the alternator will bring the actual battery voltage up to around 14 volts while the engine is running.



So the measured resistance of 9.1 ohms is not far off, if the ambient temperature of the WUR was above 50˚F or so. Cool the WUR off for a while in the frig and see what the resistance measures. And measure the Cold and Warm control pressures.

[Andy911sc]

If you need a rebuild I highly recommend Brian with RarlyL8. He just recently rebuilt my WUR and FD. I also had my injectors cleaned and flow test and the car runs like I just pulled it off the dealer lot. He does great work and the rebuilds come back all cleaned up looking bran new and professionally packaged up with care. His prices are very fair for the quality of work he does.