I am the very happy owner of my first cossie saph (wife wouldn't let me get a 3door/escos) the problem is kids. No seriously when i got the car it would boost to 30psi an hold it but i can't remember what the boost gauge said on idle at that time now the car will only boost to 20 or so psi but i have noticed the boost gauge reads -9psi on idle not sure but think it read 0psi on idle before any help would be great thanks

 

thanks for help guys or lack of
sorted it myself ,is it worth paying gold membership fee's for this?
will what awhile and see

 

Hi m8.

can you tell me what you did to fix your car.?

 

Would read minus on idle m8.

 

Chill out like

Not all questions get answered straight away

Its supposed to read in the minus (-)whilst on idle, what was the problem then

Bri.

 

It reads VACUUM(negative) on idle and BOOST on boost(positive).
tabetha

 

Had this listed for nearly a week no replies reposted when fixed it now loads of replies not jumping the gun just coudn't understand why no one could reply sooner to what i thought was an easy question to answer to anyone with a boost gauge and ok running car


the repair consisted of replacing the dump valve (slight leak)
washed the air filter (precaution)
and 2 loose connections on the intake plenum (vac pipes)

spent most of my childhood in garages as my father was a mechanic/mot tester but he's no longer with us so could not ask his advice

 

Very easy as basic engine principals here, but I did not see it ?, and I answer a few million on here!!
I have had one or two mysteriously disappear.
tabetha

 

 

HG and PSI is merely a different type of measurement, like lbs and kilo's.
Most testing type kit measures in HG, as they traditionally used MERCURY MANOMETRES but this is not the case witha lot of newer kit, when ther gas engineer services your boiler he uses a MERCURY MANOMETRE, but this is down to regulations.

tabetha

 

In the cossie manual it says that the vacum at idle should be between 40/60 cm/hg if you multiply mg/hg by 0.1937(roughly can't remember exact figure) it will give you a psi value


i.e 50cm/hg x 0.1937=9.685psi

 

I realise that, but my comment was 'trying' to point out that the gauge is almost certainly going to show the vacuum as a measure of mercury, therefore if they wish to use it for a reference they need to realise that it is a measure of mercury and not Psi............

Since somebody believing the -30 represented psi would not realise it was in fact 1551mm.Hg or mercury...........

 

But as he says the guage is MARKED in PSI, it does not measure "IN" anything it measures pressure, positive and negative, the markings are then applied after the scale is calibrated to read correctly in WHATEVER SCALE THEY USE, on cars it is PSI/BAR, but just the same as a mercury scale just not as it is choisen by the manufacturer to mark in PSI/BAR.
tabetha

 

 

DUH, he mentions PSI so we must assume it has PSI writte on it.
They are connected to the VACUUM side of the engine and consequently show the VACUUM or boost state ot play.
If you have never seen a boost guage iof the type talked about here you really need to get out more.
Are you even looking at the same as everyone else ?
I am not going to continue this waste of time with you, clearly you must be referring to another "LETTER"
If you want to get techy, they are incorect anyway even the MONOMETRES as they do not register the normal air pressure first!!,ie add 14 or so psi.
tabetha
ps what the hell are you reading ?

 

Well, I was with your for a while, then curiosity won me over and I had to have a look


You can clearly see in.Hg on the vacuum side, and PSI on the boost side

Went out and checked my Ford Racing boost gauge and it's the same.

So I thought, maybe they are both measures of the same pressure, just different units

Well, to convert in. Hg into psi, you need to multiply in.Hg by 0.4912.

Do boost gauges indeed convert pressure/vacuum into two different units depending on which side of 0 they are

It's a genuine question, not trying to stir things up

 

 

Checked my boost gauge and it has no makers logo but reads -15psi to +30psi if this makes any difference, sorry no way of posting a pic at the mo..

 

My boost gauge took awhile but got there in the end

 

I think the reason its not in Mercury is probably to do with the fact it has No makers logo on it..........