89 328 Fuel Pressure Regulator vacum supply...

My 86 hasthe port directly under throttle plate. Actually quite a large hose for vac supply. looks to be about 3/8 or 12 mm. This travels under the intake to the top of the warm up regulator.. No vac to fuel distributor. How did you lose yours??Cant imagine the engine would run correctly with the hose off,as it would create large leak.

 

If you mean the Warm Up Fuel Pressure Regulator vacuum port, then the other end of that hose goes into the port right below the big hose.
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A minor nit, but that port on a US 328 (K-Jet with Lambda), being upstream of the throttle plate, really isn't a "vacuum port" -- it's an "atmosphere port" (of clean, filtered air). On the K-Jet without Lambda systems (which use a different type of WUR), the WUR port is connected to a vacuum port (i.e., a port downstream of the throttle plate).

 

Although the Euro version does still have that same upstream connection. The downstream conection is a second small port on the side of the WUR.

 

Yes, your description is better -- K-Jet with Lambda WUR (...132) only senses the atmospheric pressure; K-Jet without Lambda WUR (...033,...083,...116, etc.) senses both the atmospheric pressure and the engine manifold pressure.

 

I had assumed the port is just a breather so not really sensing as such. Sorry, now I'm being picky!

The Probst book does not seem to show the versions on the US cars. Steve does the lambda version have the large enrichment diaphragm in the bottom? I assume not, as the port on the top does not go to manifold vacuum. So it is the same as the K-basic but with a breather in the top?

 

I haven't come across a good detailed description of the inner workings of the various WURs, but the US 328 WUR specs definitely show that changes in the ambient pressure alter the control pressure -- but since there is no other pressure connection to compare the ambient pressure to (and deflect a diapraghm and/or spring or something) I'm not sure how it works internally -- but there is definitely no connection to the engine intake manifold. A "vent" is essentially the same as a "connection to the atmosphere" so I don't see a difference there.

I believe that the Figure 5-4 on Page 16, Chapter 6 of the Probst book may be mislabeled, and that one should be described as being "altitude compensation" only (like used on US 328). Also, it says "vacuum connection is on top", but that doesn't seem right to me (and it should say "ambient pressure connection (or vent ) is on top". If you look at the US 328 SPC figures, the WUR drawing exactly matches Fig 5-4 down to the special mounting slot that Probst noted as an identifying feature of this type.

 

Agree completely.

Fig 5-3 shows the Euro type.
Strangely on this type the connection on the side (vacuum) and the connection on the top (vent) both go to the same internal space. But the vent has a very small restriction in the tube. So I guess that gives a partial vacuum inside when the lower port has vacuum as this has no restriction.

 

More minor senseless nitpicking.. A vacuum port ,regardless of its location, in front or behind throttle plate, will have identical vacuum as the intake manifold when the engine is running, until the throttle plate is closed.The same amount of air is moving past the port, creating the vacuum.The volume and speed of the air creates the vacuum.The vacuum port on the WUR enriches the mixture. It wants to monitor the vacuum of the engine in front of the throttle plate when the engine may need more air... Not when throttle plate is closed, or decelerating. Which will create excessive intake manifold vacuum.The ambient pressure is monitored by a chamber inside, or on the bottom of the WUR.Hence vac port on top of WUR.

 

But the WUR leans the mixture when vacuum is applied not enriches it. At least thats what Probst states, and what I can confirm having dismantled a Euro style WUR.
Its possible that the US cars WUR works in a way not documented by Probst though. Anyone dismantled one and have pics?
Here is the Euro type, although ours does not have the front connection to manifold, only the rear one (which is actually at one end!):
When vacuum is applied, the lower diagpragm is forced up, which closes the control pressure valve which increases the control pressure and leans the mixture.

If, on the US version, the top port is a vacuum port rather than a breather, I would think it would work in the opposite way to above. When the butterfly is almost closed, the air speed through the small gap will be greater than when its open, thus creating more vacuum on the port by the venturi effect.
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I'm happy to agree that at very large throttle plate openings the difference in pressure upstream and downstream of the throttle plate will be small, but I want to challenge these statements:

Assuming a 100% filling efficiency (which is too good to be true), a 3.0l engine at 6000 RPM would have an airflow velocity of 45.2 m/sec (101 mph) thru its 65mm diameter throttle body. Assuming incompressible flow (since the Mach number is only ~0.1 and the references say that this is a good assumption for a compressible fluid if the Mach number is below ~0.3), the pressure of such moving air is only 0.012 Bar less than the same air at rest. This is a miniscule pressure difference that is insignificant to the kind of pressure changes that the WUR can sense -- feel free to argue your own set of numbers...

 

Agree, simple picture is worth a thousand words:
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I agree that the way Tepps explained it cant be correct. But what about the opposite way? What would the air speed be for the flow through the almost-closed throttle at 1000 RPM? Pretty fast. If the port on the throttle body were correctly shaped (not looked at it) this fast (but relatively low volume) air moving over the top of the port might create a vacuum in the connection. Thats assuming the US style WUR actually has any vacuum sensing at all, which does not seem to be certain.

Air speeds in a closed-throttle situation are definitely fast, incidentally this is one problem with trying to use carbs in an emissions-compliant situation. During normal driving droplets of fuel accumulate on the throttle body in a carb, but as soon as the throttle is closed the whole lot is blown off the sides into the engine thus infringing emissions. Thats one reason carbs had to be ditched for emissions purposes (although there are ways around the problem).

 

I don't have any information on that, but the port would have to be very small and be located exactly adjacent to the throttle plate edge. AFAIK, the port locations are very much like shown in your sketch -- and inch or two away from the throttle plate's closed position so they wouldn't detect that.