Since we had a lot of extra pneumatic equipment at work (gauges, fittings, hoses etc) I decided to set up a permanent vacuum gauges in place of my non functional fuel gauge.
Idle is around 17" vacuum. 60mph on level ground is 12" 70mph is 10".
A couple of things surprised me. It takes very very little throttle input when accelerating to drop the vacuum to 3-5". At about 1/3 throttle vacuum drops to 0 at up to 4000rpm. At 6000rpm there is zero vacuum at 1/2 throttle. Moral of the story? Because the car has a light throttle and smooth engine I don't realize how fast I'm accelerating and how much gas I'm burning. When I tried driving by the vacuum gauge by keeping vacuum at 10" or more, the car is just plain slow. Acceleration felt more like the 240.
Another fun experiment was using cruise control and watching the vacuum bounce up and down. On pretty level freeway with the cruise set at 60mph, the vacuum gauge moved wildly between 20" and no vacuum. The cruise control seems to over compensate throttle input over the smallest hills just to keep the speedometer from moving 1 mph down. Very inefficient.

Next experiment will be to use a gauge that shows both vacuum and positive pressure in order to see if the ram air intake has any effect. Finding out is half fun. Stay tuned.

Where are the 2 knock sensors located on the engine block? Are they beneath the intake manafold? What other parts do you remove in order to get to them?
I just ran the OBDI tests on all the systems and no fault codes came up. This does not mean the knock sensors are not lazy. Did a little bit of research and the consensus seems to be after 100k miles the knock sensors are toast.

Both knock sensors are located on the driver's side of the block under the intake manifild. You can get to the front one by taking off the air intake hose. Poolman will have to tell you how he got to the rear one without taking off the intake. I replaced both when I had the intake off.

On our 95 (OBD1) the knock sensors won't set a code (and neither will the Power Stages).

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

Both our 2.3L LH-Jet cars show 19-20 inches at idle, the K-Jet a little less. Idle vacuum is highly dependent on valve timing, but I would expect your 960 to be a solid 20in. Sounds like it may have a leak or some adjustment is off.

I too have used a vacuum gauge to watch cruise control action, and even on our 4-cyls it does not swing wildly on level highways, it increments up and down in very small amounts. Are you saying yours shows the throttle is going between nearly closed and one-third open on a level road? Something's wrong.

But it is interesting to see how the cruise control works - in discrete steps, not a smooth and gradual movement of the throttle.

You will see no 'ram air' effect (positive intake pressure) at any speed you can realistically maintain on a highway. By the time the airflow gets through the filter, the AMM, the throttle plate, while following the several bends in the intake ducting, the miniscule amount of speed-generated pressure is gone. Actually, you would need a gauge that measures inches of water column (not inches of Mercury or psi) to even see the "pressure" at the front edge of the grille at, say, 70 MPH.
--
Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and numerous old motorcycles)

Where did you connect the vacuum hose to your engine? It sounds to me like you're not getting the best readings, especially if you're dropping to zero with just a little throttle.

I connected to the brake booster hose. Im sure I don't have any leaks. I think the throttle body on the 960 is really large for a 3 litre engine. Also my TB as well as the intake in front of it has been modified. I expect to see positive presssure on the highway at full throttle.

Hey tjts1- I'm wondering if you are getting all the vacume thats available, the specs on these engines call for 20lbs on a good engine, When mine was down to 17 I got to wondering what was retarding my ignition, installed two new knock sensors and the vac jumped up to 19.5. I have checked with a couple of diff vac gauges and get the same readings. After I found my timing belt off on the intake cam, the vac jumped to 21, where it is now.
Also note that when the knock sensors start going bad they do not send a code to let you know.
When I check my vac readings I take them from the vacume block(for the want of a better word) that is located next to the intake. This block has a number of lines running from it and a couple of ports that are capped off. I have a line installed in one of the unused ports that I use when checking vac readings.
Good Luck
Poolman

Poolman
Thanks for the info on the knock sensors. Is there any way of checking the sensors like for example the way you check an O2 sensor? How many miles did you have on the engine when you changed the knock sensors? Im at 109k miles right now. I have noticed that my fuel economy is down of late. On highway trips im doing 21-22 mpg where I used to get 23-25. I might be able to atribuit this to the poor california winter gas. I don't know. I have repeated the results multiple times now so i know its not a fluke.
The 92-94 vs 95+ could also have different vacuum reading at idle. Just speculating. On to the fun stuff.

Heh again--- car had about 165k on her before I started to take notice of the knock sensors, also I had just gotten rid of my prize 66 7 litre 427 side oiler ford ( galaxie with a 427 AC Cobra engine from the factory 2 four carbs pushing 527 horse with 535 ft lbs of tourqe) that car was sold to keep my young son out of her and the Volvo is going to be his this year. I don't know how far the car had gone like that, but when I didn't have my ford to stay into I had for some reason to look for other avenues to keep my interest.
I've got to say though that selling the bad ass Ford did help me to go to working into areas that I had thought I never would, Fuel injection is really simple in some regards to fully tuining multiple carbs and the brickboard has helped a great deal in that education.
In total responce to your question though, the knock sensors can go bad from a number of problems, over tourque,contamination from petrol or byproducts or just old age.
If you do replace them Dewfpo has stated that they have positional chariteristics to be taken into play, if I remember the back sensor must be placed at 3 oclock and the front one at 5 oclock ,both tourqued at 12 ft lbs
I've also read that the sensors can be disabled sometimes by a faulty alternater, giving off magnetic interference that will throw the sensors off. What was said there, was that, there would need to be some type of sheild to keep the alternater from disrupting the knock sensor. There is a magnetic feild that causes this and belive it or not the use of small gauge screen mesh will stop this from happening by cutting it just large enough to cover the sensor and then grounding it. I don't know any more, hope that helps, the burbon is taking over now, one last note , bought the new sensors from FCPGroten at about 40bucks each. Burbon has a good hold now for sure--------------------
Poolman

Knock Sensors....

One goes on in the 5 o'clock position and one in the 9 o'clock position. They are torqued to 15 Ft. Lbs.

I paid $75.56 (including shipping) on 12/16/04 from http://www.autohausaz.com/. They are Bosch parts and are exactly the same.


DEWFPO
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1998 S90 071,245 and 1995 964 154,100

Thanks for the information.

I'm thinking about how to add another temperature sensor like the ambient sensor to the air filter box so I can see that on the outside air temperature gauge by fliping a switch. Need to spend some time with the wiring diagram. I'm thinking of a relay actuated by the switch so the filter sensor can be substituted for the ambient sensor near the front of the engine compartment. I don't want to go behind the instrument panel!
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'96 965, 16' wheels, rear 18mm bar & Koni + 204HP cams at 122K. Had '85 745 Turbo Diesel for 200K.