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Do i have a vacuum leak? Vacuum testing 

 

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 Post subject: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 6:25 pm 
Tyre Shredder
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hey guys,

My hunt to find a solution as to why my car is running so ritch continues...

Today i got a vacuum gauge to check for vacuum leaks..

Im not sure what im looking for exactly. If there was a leak would the vacuum pressure fluctuate? or remain low?

I dont know what pressure it should be at. i fit it all up, started the car and the pressure was steady on just under 0.5 bars at idle, and the pressure would rise when i revved the engine.

So have i got a vacuum leak?
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 6:40 pm 
Getting Side Ways
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the pressure should drop with revs im fairly sure

 

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 6:42 pm 
Tyre Shredder
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well i pushed the throttle sightly, and my revs rose up to about 1500, like usual lately.. and the gauge went up to about 0.6 bars
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 6:43 pm 
Getting Side Ways
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at idle the vacuum should be steady. -0.5 bar
then when you rev the engine the vacuum should rise at maximum RPM the vacuum should be pretty much 0 bar.

If you are boosting your engine it will go into positive pressure.

you say -0.5bar ? thats about -50kpa which my cammed AU idles at.
not sure what exactly your vacuum should be at but it seems a bit low to me.

Last edited by MMD on Wed Sep 15, 2010 6:53 pm, edited 1 time in total.

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 6:46 pm 
Tyre Shredder
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if i have a leak, would the needle jump around at idle? or just sit there?

Anyone know what pressure idle is meant to be at in EL?

Mind you my revs at idle are sitting slightly higher than what they are meant to be
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 6:52 pm 
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I didn't think a vac leak would cause it to run rich...

Have you had a code reader on it to make sure no sensors are out of range or anything?

Cheers,
Tim

 

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 7:00 pm 
Tyre Shredder
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you say that the pressure should drop when you accelerate, then why does mine rise?

As for faults, i havnt checked it myself, but i have had it checked at ultra-tune, and at CVE, no faults came back, the only one i got was power steering switch at ultra and that got changed.
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 7:12 pm 
Getting Side Ways
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yeah pressure should rise
your car is Naturally aspirated, which means your vacuum should be a "vacuum" meaning Negative Pressure
as an example at idle it should read -100 and when at 6,000RPM it will read 0
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 7:33 pm 
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yeah when the butterfly is closed (idle) the engine is sucking air in still hence creating a low pressure inside the manifold which is less than atmospheric... Commonly called vacuum...

When at WOT then there is no separation between it and the atmosphere so pressure will be almost indentical inside and and outside the manifold so the negative pressure (vacuum) must rise to be equal with the atmosphere...

Other thing that causes cars to run rich and wont show up as a code the the fuel reg... With a pressure gauge on the fuel line I think from memory you're looking for around 200 to 250kpa... if its much higher then there is too much pressure and hence too much is squirting in on each injector pulse... Tried swapping it out if you can't test it? if you block the return line off and with the motor running the std fuel pump will reach 600 kpa of pressure (they don't last long if the run at this pressure for months on end)...

Cheers,
Tim

 

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 7:35 pm 
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on second thoughts... If you do have no vacuum then this is the same as being at high revs (no vac at WOT) so the fuel reg will be lifting pressure to accommodate with the added load/speed of the motor... So I can see how too high manifold vac at idle and low revs could be making it rich...

Cheers,
Tim

 

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Performance: Complete AUII VCT Wiring & Power Train, Pacey Headers, 2.5" Exhaust, Exedy Clutch, DBA Rotors
Visuals: FG XR Wheel, XR Front, 17's, BA 5 Spd Shifter, BA Ghia Window Switches, NL Cluster
Tunes: 8" Pioneer Sub, JBL Speakers, Clarion Double DIN Headunit

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 7:36 pm 
Tyre Shredder
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as by request of MMD i will be making a video of the gauges behaviour tomorrow to show you guys whats going on
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 10:42 pm 
Tyre Shredder
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Come to think of it. I was thinking about fuel regs. I now recall when I changed my welsh plugs I found the hose on top of the fuel reg was split. And even after changing that hose, Nothing had noticably improved(bad idle, running ritch) reckon the fuel reg has died??
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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 10:55 pm 
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I've seen it before...

 

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Performance: Complete AUII VCT Wiring & Power Train, Pacey Headers, 2.5" Exhaust, Exedy Clutch, DBA Rotors
Visuals: FG XR Wheel, XR Front, 17's, BA 5 Spd Shifter, BA Ghia Window Switches, NL Cluster
Tunes: 8" Pioneer Sub, JBL Speakers, Clarion Double DIN Headunit

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Wed Sep 15, 2010 11:00 pm 
Getting Side Ways
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timmytimtim wrote:
I've seen it before...



The rubber inside them eventually tears & the reg doesn't do much at all....

Cheers

ToranaGuy

 

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 Post subject: Re: Do i have a vacuum leak? Vacuum testing
Posted: Thu Sep 16, 2010 12:11 am 
Parts Gopher
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yep not uncommon
mines done it
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