Modified my WUR

[GBStu]

The more I look at the sketch I'm having trouble seeing that cold pressure adjustment could affect warm pressure. After the bimetalic strip is warmed it is no longer biasing the regulator, hence has no affect on warm control pressure.

I'm thinking the only way to change the warm pressure is to change the spring force on the regulator?

[Paulporsche]

Fist, it seems that warm pressure, for some reason, doesn't appear too often as a problem for these cars. It's the cold pressure that almost always comes up in threads. Maybe this is because adjustments are always made on warm engines? I don't know.

As was previously said, knocking the plug appears to change both, as if there is a preset fixed relationship between them.

You can vary the relationship between the cold and warm by adjusting the screw found behind the brass cover on the bottom of the WUR. I've read that clockwise is lower (richer) and that it is a lot less sensitive than the fuel mixture screw on the mixture control unit.

Someone in a previous thread bent the control arm inside the WUR, rather than knocking the plug, and got the desired result. You may have to search to see if he mentioned both cold and warm issues.

[Gunter]

Originally Posted by GBStu

Thanks for the post........it has got me thinking:

I have just run my run my car (79 911SC) on a dyno, the A/F ratio was 12.1 at max power. I think this is too rich, does this modification adjust the cold control pressure or warm control pressure, ie can I lower my control pressure by "knocking in the pin" to lean out the mixture during normal operation?

Thanks, Stu

It is my understanding that knocking the plug down will lower the pressure but make the mixture richer.

Why is 12.1 A/F at max power not good?
I thought that a richer mixture is desired to prevent detonation at high RPM.

[stevemfr]

Hi Guys,
There seem to be some misconceptions about the WUR here:
- The metal plug holding the bi-metal strip adjusts only cold pressure. The cross-sectional diagram Gunter provided shows the WUR in a cold state. Warm, the bi-metal strip bends upwards and just hangs free; that is, it applies no more pressure to the spring under the diaphragm plate (round plate with the 2 fuel fittings). Warming comes through the heating coil or heat soak from the motor.
- Both the plug (how 'bout Cold Pressure Plug CPP?) and the diaphragm plate are press fitted into the housing. Warm pressure is adjusted by knocking the warm pressure diaphragm plate (WPDP?) up and down in the housing to increase or decrease spring pressure from below thus increasing or decreasing the control pressure. This can only be adjusted when the WUR is in a warm state - that is the heating coil has had 12V for several minutes.

SOP for adjusting a non-modified WUR is:
1. disassemble the WUR
2. punch both the WPDP and CPP upwards in the housing and reassemble
3. apply 12V to the heating coil circuit for several minutes so tha the bi-metal strip has moved upwards and is def. not affecting the warm control pressure
4. adjust the warm pressure by using a drift to slowly knock the WPDP downwards until the warm pressure is within the specified tolerance
5. wait (several hours) for the bi-metal to cool down and bend back downwards
6. adjust the cold pressure by knocking the CPP down in the housing until the cold control pressure is within the specified tolerance
7. apply 12V to the heating coil circuit an re-check warm pressure.

Tripster's modification simply allows the cold control pressure to be raised (A/F leaned) w/o disassembling the WUR. I remember hearing about a puller that attached to the fuel fittings and allowed the adjustment of warm pressure w/o disassembly, but I've never seen one.

A couple of points about WUR's:
- Knocking the WPDP down in the housing increases spring pressure from below thus increasing control pressure and making the AF ratio leaner. Knocking the CPP down decreases the spring pressure on the WPDP thus decreasing control pressure and making the AF mix more rich
- Basically all K-Jet WUR's are the same. Completely different part #'s usually denoted different housings (vents, etc.). There are also WUR's with a base plate containing a vacuum diaphragm and a plug that the spring rests on. Applying more or less vacuum increased or decreased spring pressure and thus allowed for a simple full-throttle enrichment. Differing last digits usually denoted different heating coils/bi-metal strips for faster or slower cold start cycles.

Hope this has helped.

[stevemfr]

Originally Posted by Gunter

It is my understanding that knocking the plug down will lower the pressure but make the mixture richer.

Control pressure pushes against the metering plate in the airflow meter. The higher the control pressure, the less the metering plate can rise and the less fuel is injected. Higher control pressure = leaner, lower control pressure = richer.

[Paulporsche]

Thanks for that valuable info, Steve. Slowly the mysteries of CIS become unravelled...

Funny, yesterday I was looking @ my spare WUR and thinking, "looks like that large plate is also a press fit. I wonder what would happen if it gets pushed in?"

[bkreigsr]

maybe I'm not as bright as I look.
is it wrong to assume that the WUR only enters into the mixture equation during warm-up?
thanks
Bill K

[RarlyL8]

"Warm Up Regulator" is a misnomer. It should be called a Control Pressure Regulator. The WUR affects all ranges of operation from cold start to boost enrichment.

[stevemfr]

Originally Posted by bkreigsr

maybe I'm not as bright as I look.
is it wrong to assume that the WUR only enters into the mixture equation during warm-up?
thanks
Bill K

Need a pic to answer that question - JK

As rarly says, it should actually be called a control pressure regulator or the like. Read my first post above- warm control pressure is whenever running a warm engine which is nearly all the time.

[HansW]

Dear members

Even though i am not a Porsche owner, but have a Volvo instead, it is the same K-jetronic and the same questions.

Did anyone play around with the full throttle enrichment? I wan thinking in terms of replacing the smaller spring to a harder One, so that the pressure drops further, --

Greetings from ireland, Hans (used to live 10 miles from zuffenhausen)

[jrcook320]

I'm new here but have some input. On non vacuum WUR's you can move the entire valve body in and out to change warm control pressure. Here is my setup, it's a little crude but it works for me:


A little CAD diagram I drew up to help understand:


On vacuum WUR's you can drill a hole in the brass plug to gain access to a small hex screw to adjust the position of the secondary spring perch, which is an easier method to adjust warm control pressure. I suspect this is what Brian Leask does with his though I haven't seen one yet.

[MikeBogue]

What would be the advantage of having an adjustable warm control pressure on the WUR? Doesn't this adjustment have the same effect as adjusting the mixture screw then the cold control pressure on the WUR, or am I missing something?

[jrcook320]

adjusting control pressure lets you bring a WUR that is out of spec back into spec. It also allows you to adjust control pressure of a WUR to meet the needs of a heavily modified engine, or to adjust a WUR from one vehicle to meet the needs of another vehicle. It can also allow you to compensate for running higher system pressure.

Both the mixture screw and control pressure will have an effect across the board on mixture, but changing control pressure has an effect on how freely the sensor plate moves. It also changes teh relationship between system pressure and control pressure, adjusting the mixture screw does not.

[jrcook320]

Edited to hopefully make more sense... in fact, looking back I'm not sure why I posted this at all. It was a copy/paste from a discussion on another forum that seemed relevant to the discussion here at the time. Oh well.

I am running a volvo 240 turbo WUR. Both the Volvo and Audi 5000s use a WUR with 2 ports, one above the diaphragm and one below it. The lower port uses a check/delay valve that blocks boost and positive pressure change into the lower chamber. I've been wondering why they are plumbed like instead of a single vac/boost line above the diaphragm like the 930 uses.

From what I have observed, I think there is a difference between a vacuum WUR and a boost sensing WUR, both in the range of travel of the diaphragm but also in the "preload" of the diaphragm. The home position of a the Volvo and Audi turbo WUR's diaphram is at the top stop, which means it must be preloaded in that direction. This also means that if it were plumbed with a single vac/boost line it wouldn't provide any change in control pressure until there is positive pressure applied.

I observed this top stop home position on an audi 5000s WUR off the car (with NO fuel pressure) and watched the diaphram move from top stop at 0 psi to the lower stop under pressure. I then tested the volvo WUR on my car plumbed with a single line, with fuel pump jumpered and observing control pressures while applying pressure, then vacuum. I only noticed a drop in CP under "boost", but CP did not raise under vacuum.

With it plumbed with a check valve on the lower port, I get immediate drop in CP (which means better throttle response & less turbo lag). I need to take my spare audi 5000s WUR appart and see if my theory of diaphragm preload is correct.

Here are my findings:
1 Vacuum/boost line to top port of WUR (similar to the 911)
WCP @ 0" Hg = 54 psi (fuel pump jumpered)
WCP @ idle, 19" Hg = 56 psi
Throttle blip to 5" Hg = no change, 56 psi
AFR @ idle, closed loop = 13.2 - 13.4

Vacuum/boost line to top port, vacuum line w/ delay valve on bottom port (volvo plumbing):
WCP @ 0" Hg = 54 psi (fuel pump jumpered)
WcP @ idle, 19" hg = 47 psi
Throttle blip to 5" Hg = CP dropped to 30 psi
AFR @ idle, closed loop = 12.6 - 12.8

In the second test, what is happening is the diaphragm is pulled down some by equal vacuum on both ports. Once vacuum drops (on throttle tip in), the delay valve (like a check valve to keep boost from reaching the lower port) holds vacuum under the diaphragm while pressure rises above the diaphragm, allowing the diaphram to drop to give instant drop in control pressure and excellent throttle response. This works much like an accelerator pump on a carb would. Under boost, the top port sees full boost pressure, the lower port sees nothing.

I realize this stuff probably doesn't apply to most 930 guys...

[MikeBogue]

I had not thought about how the WUR could be adjusted for the different motors and that makes sense to me, but I thought that the mixture adjustment was an engine temperature independant adjustment of the control pressure. If this is the case, and the proper WUR is on the proper motor, then shouldn't it be possible to adjust the warm pressure with the mixure adjustment and then the cold pressure with the WUR? I am just trying to understand better, because I am installing a '74 motor into my car this Saturday and it has not been started in 10 years, so I may need to do some work on it.

[Paulporsche]

Mike,

I brought up a similar question in a recent thread. Some CIS-knowledgeable guys told me that you may not be able to actually get the correct "curve" reqd for your engine unless the WUR is set correctly. OTOH you just might. I'm using an old Audi 5000 one on my car and I don't know what my control pressures (cp) are (or my CO for that matter) yet the car starts and runs well. Although I must admit, now that the warm weather has arrived, my warm running is a little rich. I think a little plug knocking to get my ccp down for a richer start is in my near future. Then I can slightly lean the overall setting.

The warm adjustment and cp setting don't seem to be a problem for these cars, maybe since they are adjusted for CO and for proper running when warm. It seems that the amount of adj in the mixture control unit is plenty to get around any wcp issues. It seems also that there is sufficient available to handle the cold as well, you just have to be able to get both in line for the engine to operate properly over its entire range. If you have the correct cps, warm and cold, then one adjustment when warm should do it.

[MikeBogue]

Paul,
I think that you may be right about the curve, because while the bimetallic strip is heating it will have a different curve if the warm CP is set in the WUR. However I suspect that this change only occurs over a short time and ahould have a minor effect as starting should be controlled by the cold CP and the CP when the engine is fully heated can be controlled with the mixture adjustment. Thanks for the info.

[jrcook320]

Originally Posted by MikeBogue

I had not thought about how the WUR could be adjusted for the different motors and that makes sense to me, but I thought that the mixture adjustment was an engine temperature independant adjustment of the control pressure. If this is the case, and the proper WUR is on the proper motor, then shouldn't it be possible to adjust the warm pressure with the mixure adjustment and then the cold pressure with the WUR? I am just trying to understand better, because I am installing a '74 motor into my car this Saturday and it has not been started in 10 years, so I may need to do some work on it.

The mixture adjustment screw only changes the positiong of the plunger rod in relation to the sensor plate lever arm, which changes the mixture only. It has no effect on control pressure. Control pressure is a near 0 flow counter pressure over the plunger rod that acts as a damper to erratic motion and also restricts travel.

Warm control pressure is somewhat temperature independant as well, meaning once the bimetallic spring warms up to the point of non-contact it has no further effect on control pressure. This means the warm control pressure is the warm control pressure no matter what the ambient or engine temp is.

Originally Posted by HansW

Dear members

Even though i am not a Porsche owner, but have a Volvo instead, it is the same K-jetronic and the same questions.

Did anyone play around with the full throttle enrichment? I wan thinking in terms of replacing the smaller spring to a harder One, so that the pressure drops further, --

Greetings from ireland, Hans (used to live 10 miles from zuffenhausen)

I am running a Volvo 240 turbo WUR on my system which currently consists of a volvo 240 turbo fuel distributor and a volvo 260 AFM.

Replacing the secondary spring with a harder one will increase control pressure thus leaning your mixture out. To increase full throttle enrichment on the volvo WUR the first thing I would suggest is to remove the thermastat valve on the vacuum/boost line going to the wur. This will allow enrichment to function at all engine temps rather than just below 120*f. If that is not enought, you can move the lower stop on the vacuum diaphragm to allow the control pressure to drop further under boost.

[47silver]

I was wondering how the plug worked up and down and now i realize that the plug is tapped and that the bolt is threaded into the plug to allow up and down adjustments while the friction keeps the plug in the bore of the wur. Nice and looks pretty simple.

[47silver]

I was wondering how the plug worked up and down and now i realize that the plug is tapped and that the bolt is threaded into the plug to allow up and down adjustments while the friction keeps the plug in the bore of the wur. Nice and looks pretty simple.