logray

What's your intake vacuum at 680 rpm idle?

Measurement taken at 1800 feet elevation. 1999 996 C2 M96-01 3.4L. Hijacked throttle body fuel vapor vacuum hose for the gauge.

edit: ambient temp 92F, engine oil temp 195F.

Macster

IIRC one source is 0.4 to 0.6 bar. In IN of HG @ 32F this works out to 11.8 to 17.7.

Not sure what effect elevation has on this reading.

Why do you ask?

Sincerely,

Macster.

logray

That's a pretty big range if you ask me, but you've been around longer than I, so who am I to say that.

FWIW my Ford F150 reads rock solid steady at 17.5 bar IN Hg.

I've read that elevation can affect the reading (starting around 2000 feet), since atmospheric pressure affects how many inches of mercury drawn by vacuum.

I'm taking some measurements to ascertain the health of my engine after top end rebuild and backing up other measurements such as crank case vacuum using slack tube manometer, leakdown and compression, and spark plug examination.

For example, there are numerous ways one can use intake vacuum pressure to determine various engine issues such as timing, valves, piston rings, vacuum leaks, etc.

Here is a slack tube manometer crank case vacuum reading at 680 rpm idle 93F ambient temp engine temp 197F 1800 feet elevation, appx. Pacific time, 2:30pm, waning crescent moon.

5 inches of water drawn from the crank case (and steady).


Oh, and THANKS for the reply, as always.

Macster

I've used a vacuum gage, sometimes more than one, up to 4 at a time, to set carbs, 1, 2 or more barrel carbs like Holley and Webers (2 2 barrel side drafts) and 4 individual cars on my Honda CB750 motorcycle, and other brands I've long forgotten.

You have to be a bit careful relying upon vacuum with these engines. The VarioCam system can render the vacuum readings while not meaningless, confusing.

The proper range of vacuum can vary depending upon the state of the VarioCam system and I believe if a vacuum reading wants to be taken the tech can command the VarioCom system to deactivate (or activate) and the factory engine manual will give him a vacuum reading or range of permissible readings.

Just a naked reading might be well, not all that useful.

Also, the engine controller will give you are clue as to the health of the engine by when it is operating performing a variety of tests some over a long period of time and others over a very short period of time. In the case of the latter, misfires.

If the engine controller doesn't detect any misfires the odds are high the engine's in pretty good health.

Sincerely,

Macster.

logray

I too, with my "Porsche Service Tool 2" (a.k.a. PST2) or "Durametric" computers can instruct the vehicles computer to activate or deactivate variable camshaft timing at will (should I so chose to using those test functions).

With the 3.4L 1999 C2 996 M96-01 engine, there are two operating functions of variocam. On or off.

Without human intervention (below ~1500 rpm or above ~5500rpm) it is off or not grounded. At 680 rpm idle, one should expect static operation and affects of variocam operation, correct? (thereby assume that variocam operation is not affecting vacuum gauge readings - aside from perhaps a faulty ground, DME, wiring loom, voltage, exhaust issue, valve guide, actuator, solenoid, map, timing, leak, breech, NVRAM, or otherwise?).

https://rennlist.com/forums/996-foru...-a-primer.html

Mother

Just from the engine sound did not hear any abnormalities and real time data from say a Durametric gives you some good eng health.