How Much Vacuum?

[montez]

How much vacuum should my boost gauge be showing when the engine is idling?

[GazzaG60]

stock engine?

[montez]

It has been super-chipped and has a decat scorpion exhaust

[Rusty]

Superchips - not that it should affect idle.

At rest 15-20 in Hg, when driving on overrun something in the 20-25in Hg region.

[montez]

15 Hg that's getting on towards half a bar of vacuum, cheers for that ill try it in a bit to see what I get, It is my suspicion that I have a vacuum leak somewhere

[Rusty]

In which case it's likely that you have a boost leak too! Not many hoses are vac. only. Check all of the stuff under the dash and back seat for the diff lock, often overlooked. A boost leat test of the whole system will highlight most leaking vac hoses.

[montez]

I have connected it with a T piece by the ECU so I am guessing that will show both boost and vacuum, the N75 valve is shot I have a new one to install today so that may make a difference. I have a load of pipes coming tomorrow as I am going through replacing all the vacuum/boost ones.

[Rusty]

It's those little pipes that make the difference when you're trying to get the whole thing boost tight. If you have got a small leak and it gets solved with this, the car will fly

Seeing what the ECU sees is a good idea when trying to problem solve or diagnose any leaks etc.

[Smiley]

I doubt that you can guess a small air leak just from reading the boost gauge. Unusual poor MPG is a good hint for me.
I recommend doing a proper pressure test when you're in doubt.
Just my 2c

[montez]

I have just re-checked the gauge, I must have slightly kinked the pipe when I installed it it now sits at -1/2 a bar on idle and just under -1 bar when on overrun. The car is only boosting to 0.5 bar though on full throttle, but I am guessing this is down to the WGFV as it is reading something like 4000 ohms when its is supposed to be 35

[Rusty]

Sounds about right, had to re-read teh bit about just under -1 bar tho

Boosting to 0.5 bar will be stock WG spring boost and could be down to a number of things, best to check the fault codes really although swapping the N75 is a quick starting job...

[montez]

The fault codes were read the other week, the only other thing that came up was the Air Intake Manifold sensor which has since been replaced. I will fit the N75 and see if it is making a difference.

[montez]

Just changed the N75 valve for one of those uprated ones that have been for sale over the last few weeks. The car is now boosting to around 0.8 bar of boost I think this is getting on towards more normal for a stock car. Not sure how much extra boost it would be running with the superchip though? Silicon hose should be here tomorrow as well as the fittings for my new fuel pump, will be interesting to see if any difference has been made. When I change gear now you can hear the BOV more how audible are they stock?

[Rusty]

Better off going back to stock WG spring and chip, IIRC superchips fitted a stronger WG spring.

Thinking about it, 0.8bar is stock 3B boost dropping to 0.6/0/5 at redline. When you had the problem, 0.5bar is nearly stock WG spring boost (usually ~0.4bar), doesn't sound like it's chipped

[montez]

I have the receipts from Van Aaken Developments (which now has gone bust) who did a superchip conversion in the late 90s, don't know if it is the "superchip" though?