worf928

I thought about trying to do that. But, it is difficult if not impossible to get both the ports and the taps in the same pic. Besides, the mapping from ports to taps is very straightforward. On the air pump side there's one port and one tap. On the other side the top tap is the top port and the bottom port is the lower tap. So, it's easy to trace.

mark kibort

Did you read, even on these documents, that the pressure is controlled by the line fuel pressure. The more fuel you use, the more the diaphram closes the return line, keeping the pressure constant? Now, The KEY POINT , you are referring to, is that the vacuum could be an Atomospheric adustment fine tuning element. Did you miss the part where they talk about a constant pressure differential, based on "Absolute" pressure accross the injector? What this means, is when you are at WOT at 10,000feet, the absolute pressure differential will be less at WOT, so the vacuum will try and pull back pressure to keep the mixture the same as it was at sea level. it also has the same effect at any throttle position. Its a fine tuning mechanism. It's the reason there is no noticable difference with me not using it . I have the fuel presure so high that it is not that effective anyway. remember, Im at 70+psi.
Again, i dont use the vacuum line and my car runs great!

I got us way off on a tangent with the "binary"control of the vacuum line. yes, it has a slight effect, for my uses, it's just an idle pull-back fuel pressure feature that has some additional benifits of fine tuning mixture and fuel pressure for other conditions. the reality of the situation , is that the fuel pressure is brought back by about 5-7psi at idle. anytime after idle, the change of pressure with and without the vacuum connected is very slight.


MK

Bill Ball

Yes, I think that's true. No load really doesn't tell much. The throttle was not opened much. So, sorry I didn't get out of the garage. I'll have more useful information after I get to work.

BrianG

That would be it....... sorry, I missed that it wasn't a road test.

Do try to get some range of load/throttle opening data. Like flat road 1/4, 1/2, 3/4, WOT, each at 1500 RPM, then at 2000 RPM, then at 3000RPM, etc; and then on a really steep hill at these same throttle positions and RPMs.

Bill Ball

OK, I did a bunch of vacuum observations on the way to work. I couldn't do the kind of testing Brian describes driving to work, but here's what I got, for what it is worth:

- idle in neutral: 18 cold, 19 warm
- idle in gear (AT): 16
- engine braking maximum: 26
- cruise on level ground, any speed up to 75: 18 (throttle just barely off-idle)
- WOT from any speed: 0; but as the car accelerates and the RPM increases, the vacuum heads towards 18 smoothly.
- steady 70 MPH on Sunol grade (?percent): 11; 1/3rd throttle
- If you push the pedal down at just about any speed, the instant vacuum drops to near zero at anywhere more than 1/3 throttle. If the load is such that the car does not accelerate (i.e., the RPM stay fixed), the vacuum reading will stay at the instant level. As the RPMs increase the vacuum heads back towards the cruise level of 18. So, it appears as more air is pumped at any throttle opening, the vacuum increases.

Mark and guys, have fun with the physics of this.

mark kibort

Thanks Bill.

That's what i had tested a few years ago.

Its key to understand, and correct me if im wrong, is that the numbers you are using , like "11", are 11" Hg. This equates to .36bar and near 5psi. 5psi acting on the diapham controlling 40-70psi, hardly makes a dent. But, as you noticed at a steady state load of 1/3 throttle, vacuum is actually "0" as you tested, until the rpms start to go up and then vacuum starts to build. this is because of the venturi effect of the position of the Fuel regulator port and the fact that the mass air speed is increasing . its one of the reasons that the torque of an engine goes down with speed. (pressure drops in the intake)

so, the point is, for any throttle position above 1/3 , vacuum is reduced almost to nothing at this particular port. However the instant value, "stays there if the rpm doesnt change"

Now, the other main point i had made is if you measured this vacuum at the manifold, the values, besides at idle, would be higher (more vacuum measured), and act more proportional to throttle position, even though it too will drift according to rpms as well.

The biggest single point of all this, is that the vacuum line on the fuel regulator is a fine tuning device primarily pullinig back fuel pressure at idle. the fuel pressure at cruise speeds, only fights with the 02 sensor, making it fight to keep the mixtures in the 14.7:1 average range, hunting from full rich to rull lean. The higher the pressure, the faster the rate the system has to turn on and off. Under WOT, conditions, you can see that the fuel pressure is ONLY dictated by the fuel regulator itself, and that demand of fuel changes with RPM.

Mk




wht

mark kibort

just did the comparison of the vacuum on the throttle body vs on the intake (as measured on the manifold where the vacuum booster is fed)

as i mentioned, its different.

throttle body feeding the fuel regs, 9.5psi idle and near this at 3000rpm idle, then, on the road, 5-7psi light throttle, .5 to 1psi under less than half throttle, near 0 at WOT.

vacuum at the manifold, 12.1 psi idling and 10psi at 3000rpm.

So, you can see, clearly, the vacuum measured at near the throttle plate is different vs the vacuum at the manifold. i have pictures of the very accurate sensor read out. Compared to the cheapo vacuum gauge from Kragens, which is no where near as accurate, still read , 25"Hg idle on the manifold and 22"Hg idle measured at the throttle body.

Mk

mark kibort

Here is the sensor read out in the driveway.

vacuum at the fuel regulator at idle and then 3000rpm
vacuum at the manifold at idle and at 3000rpm

under load, both are very near nothing, in otherwords, there is no real effect on the fuel regulators. even part throttle on the throttle body vacuum port is so low at 50% throttle, its less than 2psi, and of course, near 0 as you push it to the floor.
mk

worf928

I'll trust your math and BB's metrics.

For us 'normal' folks that run the stock S4 ~45-55 PSI pressure, 5 PSI is a significant correction. That's 10% more-or-less. For 85/86s where the stock pressure is far lower (IIRC ~32 - 42) it's closer to 15%.

As for the rest, in several cases your cause and effect descriptively reversed. But, I give up.

What originally started out, at least for me, as a quest for the answer to why we see numerous cautions about 'lean running' has gotten run over by the 'physics of the pressure regulator.'

I still believe that there must be some truth, in very specific contexts, to those cautions. But, clearly, this thread's not going there.

mark kibort

you have to remember, that 5psi is just a little more than idle speeds and loads. I was on the road today, and under constant load, vacuum doesnt change and its near .5 to 1psi vacuum. (almost nothing) as i mentioned in the beginning. the entire point was that the fine tuning is really for part throttle conditions,and anything under load or as you start to accelerate, the tiny vacuum present for the fuel regulators, doesnt do much, if anything. if you look at fuel pressure, you can see that after part throttle, the pressure rises and pretty much stays constant for most loads and rpms.

my " cause and effect" never reversed. its always stood the same. the fuel regulator doesnt react much with any thing other than idle vacuum levels. after that, it is still pressent, but not really effective. AND it is a different level than the vacuum you see in the manifold, which is generally 30% higher.

dont trust my math, these are pretty easy conversions. plus im using a very accurate gauge. 1 bar = 29.92"Hg= 14.7psi

as far as the "lean" issue. as we talked about here, its a gross misconceptions, as the temps of the exhaust and heads go WAY down with lean mixtures. the only thing to worry about, IS the just a little lean of the perfect mixture. stoich and a little leaner than stoich is BAD. (high temps, chance for detonation , knock, etc) after that, lean of this stoich area actually reduces temps even farther than running real rich would do. No thats the point of this discussion .

here is a shot of the sunx sensor with a very part throttle push, and its still under 1psi. thats the answer you were looking for. notice that the ARM sensor is still hunting and not full lean.

MK

worf928

One chart versus numerous other references with 'lean' cautions. Sorry. Doesn't pass muster. There's definitely important context missing when it comes to the cautions. Until that context is at least somewhat understood, it is faulty to attribute gross misconception to numerous authors on the basis of a discussion of running 'rich' or 'lean' of stoich with fuel/air mixtures that are well within the spark-ignition range in a well-controlled lightly-modified (or not) system.

Note that I'm not questioning the discussion of the regions of operation discussed in this thread. I do, however, refute your conclusion that the warnings are bunk for any and all operating conditions. There are air/fuel ratios that are outside the ability of a spark to ignite. It is possible for these ratios to occur in a motor if the control system (or controlled system) is broken. Broken in that context could refer not only to system faults but to poor control response to a highly modified system.