WUR help

[CEO]

I need to do an experiment and make my WUR think the car is cold all the time. Any clue on how to do this?
81 911 SC

[Dave Kost]

I quick off the cuff thought-

Why not plumb a valve between the top of the fuel distributor and return line and eliminate the WUR? You can add a pressure guage and dial in any control pressure you want.

[CEO]

Dave, has this been done before? Sounds to simple of a fix lol.

[rwest]

I would think that unplugging the heater and mounting the WUR up high so it doesn't get the engine heat either.

[boyt911sc]

Originally Posted by CEO

I need to do an experiment and make my WUR think the car is cold all the time. Any clue on how to do this?
81 911 SC

Kenneth,

RWest gave you some good advice which I wanted to offer to earlier but refrained from doing so. What is your goal or objective? Are you using this for a test stand or for a driving test? A CIS pressure kit with shut off valve would be difficult to use to control the fuel pressure. Are you troubleshooting a particular CIS problem you care to share with us? Keep us posted.

Tony

[Dave Kost]

Originally Posted by CEO

Dave, has this been done before? Sounds to simple of a fix lol.

No, but I thought about it when I could not get a WUR from a 73.5 control pressure right.

I think it could be done.

What are you trying to accomplish? Do tell!

[T77911S]

remove the electrical connection but if you drive it for a long time the WUR is a heat soak. it will get warm/hot from the engine heat and pressure will go up.

why do you want to do this?

[CEO]

The reason I want to do this is that my car runs like GT3 when it is cold. Amazing throttle response no hesitation no popping fun as hell all with a stable idle. But when it warms up it is much slower to rev and feels extremely laggy on acceleration. When I unplug the WUR...It runs similar but I with a bouncing tach and then stalls but as long as I don't have to stop at a red light when I'm driving it is so much fun. Trying to figure out what this is all about.

[boyt911sc]

Originally Posted by CEO

The reason I want to do this is that my car runs like GT3 when it is cold. Amazing throttle response no hesitation no popping fun as hell all with a stable idle. But when it warms up it is much slower to rev and feels extremely laggy on acceleration. When I unplug the WUR...It runs similar but I with a bouncing tach and then stalls but as long as I don't have to stop at a red light when I'm driving it is so much fun. Trying to figure out what this is all about.

CEO,

Is the engine an '81 SC USA spec. or a ROW? Is the WUR a -090 or a -089 or something else? Have you checked the control fuel pressures using a CIS gauge kit? I suspect the presence of unmetered air going into the system. Test and verify. Keep us posted.

Tony

[RarlyL8]

When I unplug the WUR...It runs similar but I with a bouncing tach and then stalls but as long as I don't have to stop at a red light when I'm driving it is so much fun.

You already did your keep the car thinking it is cold test.
Running blind until you get a set of gages on there and see what the pressures are when it runs well and when it runs badly. The bouncy tach is likely idle oscillation that occurs when the mixture is too rich and would be consistent with unplugging the WUR.
Is the Lambda system still intact? Is the O2 sensor still in place? Failure mode for the Lambda system is a lean condition, which you are describing. Vacuum leaks also create a lean condition. Has your car backfired or had a hiccup lately? Cracks in the air box are a common vacuum leak source. A few things can cause these symptoms. Verify your fuel pressures then check for vac leaks including the airbox. If you have an AFR meter that will help also.

[pmax]

Originally Posted by CEO

I need to do an experiment and make my WUR think the car is cold all the time. Any clue on how to do this?
81 911 SC

A video of someone making adjustments to the K Jetronic WUR, on a VW though the operating principles look identical to our cars...

[T77911S]

you HAVE to put gauges on and see what the pressure is doing.

in the mean time, check the inlet screen on the WUR for dirt. could just be clogged raising the CP

[theiceman]

I have a somewhat related question so I will post here ( probably for Tony to answer ) but if you guys feel it warrants its own thread and I am hijacking please let me know.

Since my engine rebuild and base CO setting everything went great , in the spring this year when I first started it, it would fire up fine then idle would immediately start bouncing and oscillating to the point of almost stalling , then " catch" for the first minute or so, then the idle settle out. Im thinking now based on comments on this thread it was rich when it first starts until the wur warms up and then it leans out . I didn't do anything with it other than check my base CO when it was warm and it was fine ( of course it was as this is checked with the engine warmed up ) . As the ambient temp increased through the summer the problem disappeared and stopped doing it completely and started and ran as expected . A couple weeks ago we had a cool morning and the problem was back , so sounds like I am right on the threshold of something that is being impacted by ambient .

Also . I have a spare WUR I bought several years ago , I have no idea if it works, but the resistance measurements are in range. Would the correct course of action be to just wait until the fall when the problem will reappears and try swapping in my replacement WUR ?

I do have gauges so I guess logical next step would be to check system and cold control pressure.

oh in relation to the original thread I thought the idea of the wur was to bolt it to the runner so it intentionally would sense the temp of the engine. ( I thought the bottom of the wur was designed that way intentionally ). I always considered the heater a bit of an " update" thinking that in an ideal world the wur would lean itself out based on the heat coming from the runner. I guess not but it seemed like a cool idea.

[theiceman]

Originally Posted by pmax

A video of someone making adjustments to the K Jetronic WUR, on a VW though the operating principles look identical to our cars...

That's in interesting video. Should not just putting 12v on the heating element do the same thing as starting the car ? do they do that coz its just easier ? or is thee some other intricacies that require you to have the car running ?

[pmax]

Originally Posted by theiceman

That's in interesting video. Should not just putting 12v on the heating element do the same thing as starting the car ? do they do that coz its just easier ? or is thee some other intricacies that require you to have the car running ?

All I know about the WUR during startup is that the 12V heats the bimetallic strip which slowly bends allowing the pressure to go from cold control pressure to warm control pressure, resulting in the control pressures going from low to high. The strip is kept warm by the engine heat.

When fully warmed up, the metallic strip is completely off the spring at the bottom of the WUR. That spring controls the eventual warm control pressure which is what the video is adjusting.

[boyt911sc]

Originally Posted by pmax

All I know about the WUR during startup is that the 12V heats the bimetallic strip which slowly bends allowing the pressure to go from cold control pressure to warm control pressure, resulting in the fuel pressures going from high to low. The strip is kept warm by the engine heat.

When fully warmed up, the metallic strip is completely off the spring at the bottom of the WUR. That spring controls the eventual warm control pressure which is what the video is adjusting.

Sean,

From cold control pressure (low) it goes up to warm control pressure (high). Not the other way around as you understood it. BTW, the heating element inside the WUR is the primary heat source when the engine is cold.

Tony

[pmax]

Originally Posted by boyt911sc

Sean,

From cold control pressure (low) it goes up to warm control pressure (high). Not the other way around as you understood it. BTW, the heating element inside the WUR is the primary heat source when the engine is cold.

Tony

Yes, low control pressure when cold to high when warm.