vacuum readings + installation gauge
#1
Rennlist Member
Thread Starter
vacuum readings + installation gauge
Hi,
can anybody tell me what the correct vacuum readings should be of the engine
when cold and when hot?
And where should I install my permanent vacuum gauge? Just before my WUR?
My engine is M28.12 , 4.7L 300 HP Kjetronic CiS
928S of 1980
thnx in advance
can anybody tell me what the correct vacuum readings should be of the engine
when cold and when hot?
And where should I install my permanent vacuum gauge? Just before my WUR?
My engine is M28.12 , 4.7L 300 HP Kjetronic CiS
928S of 1980
thnx in advance
#2
Instructor
Hi GerritD .
Vacuum "pressure" at idle speed must be near 500 mbar (+/- 50 mbar ) cold or hot no difference .
The best , praticale , position for the vacuum tester is donwn the vacuum plug on the WUR .
When you accelerate , the vacuum pressure go down .
Vacuum "pressure" at idle speed must be near 500 mbar (+/- 50 mbar ) cold or hot no difference .
The best , praticale , position for the vacuum tester is donwn the vacuum plug on the WUR .
When you accelerate , the vacuum pressure go down .
#3
Rennlist Member
Connect anywhere BELOW the throttle plate - line to brake booster, WUR etc. Most such gauges read inches of Mercury, when you should see 17-21 at idle, less with throttle open, more backed off against the engine. Usually gauge is connected with a fine bore tube, to avoid seeing reading flutters at low revs.
jp 83 Euro S AT 57k
jp 83 Euro S AT 57k
#5
Rennlist Member
Thread Starter
Connect anywhere BELOW the throttle plate - line to brake booster, WUR etc. Most such gauges read inches of Mercury, when you should see 17-21 at idle, less with throttle open, more backed off against the engine. Usually gauge is connected with a fine bore tube, to avoid seeing reading flutters at low revs.
jp 83 Euro S AT 57k
jp 83 Euro S AT 57k
#7
Instructor
This electro valve can make trouble sometime .
His fonction is to down the WUR's pressure when , only during cranking , at hot start to help to start and can be leak all the time .
When it leaks , the WUR pressure is to low ... The electric command of this one is a thermocontact .
His fonction is to down the WUR's pressure when , only during cranking , at hot start to help to start and can be leak all the time .
When it leaks , the WUR pressure is to low ... The electric command of this one is a thermocontact .
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#11
Rennlist Member
Thread Starter
#13
Rennlist Member
Thread Starter
Vacuum at idle of about 1000rpm is 220 mBar (165 mmHg)
After 2 minutes when engine warms up, it already rises to 260 mBar (195 mmHg)
WHen revving to 2000 rpm the vacuum goes to about 500mBar (375 mmHg)
Is this OK ? (My fuel pressure is still 2.7 Bar (39Psi) after 1 hour not running the car )
Last edited by GerritD; 12-14-2018 at 05:45 PM.
#14
Instructor
The position of the vacuum tester is at a good place .
May be I made a mistake about "no difference with cold and warm vacuum pressure" ...
Because , it's possible with auxiliary air valve open when cold , minimise the vacuum .
Try to see with warm engine , when the AAV is close, after 6 or 7 minutes at 20°C , more at less temperature , if you have the right vacuum .
When the engine is warm , you must find 3,4 to 3,8 bar with WUR pressure and when you disconnect the WUR vacuum , near 0,6 bar less .
2,7 bar of fuel rest pressure after stop engine during 1 hour is very good !
May be I made a mistake about "no difference with cold and warm vacuum pressure" ...
Because , it's possible with auxiliary air valve open when cold , minimise the vacuum .
Try to see with warm engine , when the AAV is close, after 6 or 7 minutes at 20°C , more at less temperature , if you have the right vacuum .
When the engine is warm , you must find 3,4 to 3,8 bar with WUR pressure and when you disconnect the WUR vacuum , near 0,6 bar less .
2,7 bar of fuel rest pressure after stop engine during 1 hour is very good !