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Howto read vcds group 77

2899 Views 5 Replies 4 Participants Last post by  caglare
I measured group 77 in vcds the emission reduction (secondary air injection bank 1).
The engine is warm, sai is off. I get the following readings
Engine speed: 720 rpm
Maf g70: 1.89
Air mass from sec air inj bank 1: 7.8%.

What does the last value mean? Btw, in several examples of vcdc it shpuld also be in g/s, but in mine it is in percentage. Is this the value the system has calculated when doing the test?
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I try to find a vacuum leak. I tested the sai system, that works fine. By doing this I found the measure 077 block. I cannot find any explanation on the sai percentage. Just curious.

I'm still on my vacuum quest.

VW recommended to exchange the maf, since it had a low reading. I exchanged it for a new bosch oem maf, same values. So placed the old one back.

When I squeeze the rubber hose between intake manifold and Y link to brake and pcv line on top of the engine I hear a hissing sound and when measuring vacuum on intake manifold at the same time I see the vacuum decreasing, but it settles back after a while. However I cannot find any cracks in this rubber.

Also when I press the brake pedal I loose some vacuum on the intake manifold, I'm not sure if that is normal.

Another potential issue i noticed is at the valve cover. I don't seem to have a vacuum there. I have slight vacuum however in carter. When i remove dipstick the STFT and LTFT changes, but not much happens if I remove oil filler cap.
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Have you looked at your fuel trim readings?

Fuel trim readings

Pencilneck, yes I did.
After reset 20-25% lean stft, results in 6% lean ltft at idle and 0% at medium power.
You better to change the maf sensor or you can go to chip tuner and they can cancel the maf sensor and let the engine reads always the same number which will be more easy and less cost :)
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