Wur regulator

Are you saying that you are actually measuring the control pressure, and it drops suddenly occasionally (and then restores itself suddenly), or is this just your suspicion of what might be happening?

What version 1985 308QV?

 

What version? (Euro version use a WUR that senses changes in the intake manifold vacuum and intentionally reduces the control pressure to add enrichment under acceleration; whereas, a US version uses a different WUR and has a separate differential pressure switch to sense changes in the intake manifold vacuum and electrically "squirts" the cold start injector to add enrichment under acceleration).

Smoking black is good convincing evidence of too rich (and has rarely been reported). The choke injector (usually called the cold start injector) is an electric gizmo, but it could also just leak mechanically. One easy thing you can do is just unplug it when the problem occurs (to see if it's an electrical problem), but, to eliminate it as having a mechanical/sealing issue, it would have to be physically removed (and then the hole blocked if you wanted to run the engine). Still could be the WUR, but there you are left with measuring the control pressure to see if it drops when you have the problem.

 

I had my WUR rebuilt 2 years ago, for a Euro 84 QV. It's a bit more complicated than changing the o-rings, one of the critical failure points is the bimetallic strip, which is specific to each variant of the WUR (and there are dozens of variants for the various 308s and other cars with K-Jet fuel injection) and they can't be easily interchanged (and Bosch no longer sells individual bimetallic strips). Some are close in spec to each other and can be used, but it's a very careful process to select an alternate spec and then the cold/warm control pressures have to be adjusted to compensate. The bimetallic strip had failed in mine, and we were very lucky to find a bimetallic strip from a 1978-79 SAAB 99 had very similar temperature curve to the -116 WUR in my Euro QV.

Once verified that your bimetallic strip is OK, diaphragm is OK, o-rings are OK, you need a pressure test rig to adjust/set the control pressures in the rebuilt WUR, first the warm control pressure is set with the height of the large cylinder, followed by cold control pressure by adjusting the height of the smaller plug. You also need the specific WUR pressure chart for your variant to know the pressure ranges you need to set.

Here's an example of the significant differences in WUR settings - the -116 variant is used on my 84 Euro QV, the -033 is used by another 308 model (I don't recall if it's the US QV, or a 2 valve Euro or US). The combination of the bimetallic strip and the cold and warm control pressure adjustments are what ensures the WUR provides pressures within the appropriate pressure map.

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Here's a thread from a couple of years ago talking about WUR rebuilds: https://www.ferrarichat.com/forum/threads/wur-rebuild.547525/

 

The WUR is primarily a mechanical (not electrical) device that uses temperature and its affect on bimetalluc strip to vary the control pressure and hence mixture. Before you spend money on rebuilding the WUR have you tested the control pressure and compared to the chart for your model year?


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