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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 |
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 . |
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 |
So you mean the bottom vacuum connection on the WUR, not the one on top ?
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Originally Posted by jpitman2
(Post 15496091)
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 |
Top of the WUR is just to "atmosphere" , "mise à l'air" in French .
I found this , may be help you ... https://cimg2.ibsrv.net/gimg/rennlis...8e5cfd6ab6.jpg https://cimg7.ibsrv.net/gimg/rennlis...e27e041530.jpg |
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 . https://cimg6.ibsrv.net/gimg/rennlis...2ef8300f28.jpg |
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On later 928 , they don't have this syteme .
https://cimg8.ibsrv.net/gimg/rennlis...6e719d02b.jpeg In the 928 orner's notice , they tell to press throttle pedal when you crank in hot start . |
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Originally Posted by allan29
(Post 15496769)
Top of the WUR is just to "atmosphere" , "mise à l'air" in French .
I found this , may be help you ... https://cimg2.ibsrv.net/gimg/rennlis...8e5cfd6ab6.jpg https://cimg7.ibsrv.net/gimg/rennlis...e27e041530.jpg |
Originally Posted by allan29
(Post 15496838)
https://cimg3.ibsrv.net/gimg/rennlis...4fa062072f.jpg |
Originally Posted by allan29
(Post 15495582)
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 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 ) https://cimg7.ibsrv.net/gimg/rennlis...22526f3808.jpg https://cimg8.ibsrv.net/gimg/rennlis...655fbd1e74.jpg |
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 ! |
I can't test on my car now because I "rebuid" my fuses panel and many wires , modified my CIS and put new parts on my car ...
https://cimg9.ibsrv.net/gimg/rennlis...f3f7858735.jpg https://cimg9.ibsrv.net/gimg/rennlis...8bc1bb5c46.jpg https://cimg2.ibsrv.net/gimg/rennlis...375bba465e.jpg https://cimg6.ibsrv.net/gimg/rennlis...cdb0df28a3.jpg https://cimg8.ibsrv.net/gimg/rennlis...5b9c6a9a0e.jpg |
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