Boost Guage question

[Andrewkb]

I've just DIY instaleld my Boost Guage and is tapped onto the Fuel Pressure Regulator line.

 

Everything worked fine, except one repeatable problem.

 

When the engine is started from cold, the guage worked perfectly.

 

However, when the engine is shutted down and started while hot, the boost guage register "0" !!! It stays at "0" for ~30sec to 1min then jumped to life !

 

It is repeatable which make me rule out a faulty guage.

 

One possibility is that the fuel pressure regulator probably has a valve that shuts the vacuum from the hose when engine is started hot .... it then has something that gotta do with the injectors right ?

 

Should I tap another line instead?

[Dwoon]

???? Wei..... its fuel pressure or boost??? They're different.....

[Andrewkb]

Yes, it's recommended to tap boost signal from fuel pressure regulator vacuum line

[Dwoon]

Errrr..... sorry.... can't visualise how tapping the fuel pressure works in determining boost. Mine is tapped from after the turbo but before the intercooler where it is "T-off" to the wastergate solenoid.

 

Another method where I've heard for more accurate boost signal/control is to tap from after the intercooler instead which is more indicative of the pressure downstream and closer to what the engine is experiencing.

[Elfenstar]

look for the line that comes out of your plenneum (same one that runs to the fuel reg, brake booster etc) and tap it as close to the pleneum you can get or at least before all the T pieces.

 

Alternatively tap the vacuum line that goes to the wastegate actuator. If you have a boost controller, tap it between the nipple and the boost controller and not between the boost controller and wastegate actuator.

 

The readings with these 2 locations will be slightly different. One has the boost that the turbo is putting out, the other one the pressure at the plenneum (usually a lil lower coz there is a slight pressure loss with an intercooler).

Edited April 10, 2006 by Elfenstar

[Andrewkb]

OK, as I've a top mount intercooler, the area near the intake manifold/plenneum is quite inaccessible as I've to remove the intercooler. So I actually tap the otherside of the hose as it runs nearer to the side of the engine. Does that matters ? There's quite a few vacuum hoses around.

 

One thing though, a few website I visited recommended using the vacuum hose from the fpr as it's also help to monitor the vacuum to the fpr. Though, it's not the safest, as a leak there will cause improper functioning of the fpr

[Elfenstar]

Its the same set of hoses. by right yours should work but some cars have a vacuum tank and a control switch before the FPR so the reading might not be accurate. this hose is usually at the back of the pleneum, near to or facing the firewall.

 

try following the hose you tapped back towards the pleneum.

 

If you really want to monitor how well your fueling is, then i suggest you get a fuel pressure gauge.

Edited April 11, 2006 by Elfenstar

[Andrewkb]

OK, i suspect the hose I'm using (those clear hose) is not strong enough. So when engine is off while hot, the hose collapse. So when I next switch the car on, it takes a while before the hose is expanded (after collapse) to read accurately.

[Elfenstar]

possible. definately heard of

[Andrewkb]

OK, got myself a proper thick silicone hose and connect to the boost guage. Problem still persisted.

 

The Fuel Pressure Regulator vacuum hose is connect to a electronical device. I tap the hose inbetween this 2 devices.

[Elfenstar]

tap it between the device and the plennum.

[Adawang]

simple, just connect to intake manifold will do

I did that, but choose the right one as some outlet will cause your

meter needle to "bounce"

[Normal_aspirated]

Yes, it's recommended to tap boost signal from fuel pressure regulator vacuum line

.....there is a solenoid valve in series, could be the cause?

[Andrewkb]

Exactly which one did you tap ? There's way too many hoses there

[S2P2]

bro!!!! where are u now, disappear liao ah.....germans dun allow msn issit

[Andrewkb]

Yah loh ! Yahoo only ! You got my Yahoo acct right ?

Edited April 12, 2006 by Andrewkb

[Andrewkb]

That's what I suspect. It's a electrical solenoid, so it must have detected engine hot, and closed the valve for 1min ..... why ? I dunno .... maybe to give the injectors full duty cycle ?

[Normal_aspirated]

nope, i was refering to the vacuum side.......