Stock Boost Gauge

[aquariuz6]

hi im new to my skyline

what does this stock boost gauge mean?

doesnt +7 supposed to be 14psi?

mine only goes over the "0" just a tiny bit even though i did that mod where you can undo and leave your car running 2nd stage stock boost all the time

so is mine supposed to be like that on the stock boost gauge or is there something wrong?

[shif_tea]

ummm something seems to be wrong. 7psi should be in the middle (which is what you should be running if you've bridged the solenoid to leave it permanently high boost) of 0 and 7mmHg.

You're right, 7mmHg = 14psi. Boost leak somewhere??

[aquariuz6]

anyone know where i could start to try and fix this?

i have no ideas... all new to the turbo side

[Craved]

start with checking the hose to the boost guage.. it is located in the drivers side rear of the engine bay, right in the corner. hose comes from the back of the plenum.

if thats ok, check all the hose clamps on the intercooler piping.

try to test with an aftermarket guage.

[aquariuz6]

cool thanx..

i'll get back and to see what the problem is

[blind_elk]

ummm something seems to be wrong. 7psi should be in the middle (which is what you should be running if you've bridged the solenoid to leave it permanently high boost) of 0 and 7mmHg.

You're right, 7mmHg = 14psi. Boost leak somewhere??

0 is "atmospheric" pressure. -7 is vacuum , +7 is boost. And I'm sure there are posts around suggesting that the scale on the gauge is "x 100mm Hg", so the range is from -700mm Hg - 700mm Hg (760 is 1 bar or 14.7 psi)

ALL engines cruise under vacuum, so your car should always have the boost gauge sitting between -7 & 0 under normal driving conditions. Only when you hit boost should the gauge indicate a reading > 0.

Now back to the original problem - if the car feels like boost is working, then it is obviously a leak between the manifold and the gauge. If it feels like boost is not happening, but you can here the turbo working, then it is a problem with the plumbing between the turbo and the inlet manifold (slipped connection usually). If it feels like boost is not happening and you can't hear the turbo, then it's likely a dead turbo (probably blown exhaust wheel).

[TTT]

buy new boost gauge.

VDO make good accurate gauges and are very cheap

[Mr Italy!]

ALL engines cruise under vacuum, so your car should always have the boost gauge sitting between -7 & 0 under normal driving conditions. Only when you hit boost should the gauge indicate a reading > 0.

I've always wondered, is it best to cruise with more vacuum (closer to -7) then it is to cruise closer to 0... Will more fuel be consumed under less vacuum?

Just been wondering that for a while... anyone?

[paulr33]

fuel consumption is based on the stock ecu using its factory closed loop feedback. it doesnt have anything to do (that i know of) with boost pressure. as the fuel injection values off the maps are based on engine RPM and airflow meter load, not boost pressure.

[Mr Italy!]

fuel consumption is based on the stock ecu using its factory closed loop feedback. it doesnt have anything to do (that i know of) with boost pressure. as the fuel injection values off the maps are based on engine RPM and airflow meter load, not boost pressure.

Wouldnt more vacuum mean theres greater flow past the Air flow meter?

I dont have a clue when it comes to this, just making wild guesses

[blind_elk]

The vacuum is behind the throttle plate. The air flowing in past the throttle plate to "fill" the vacuum is controlled by the position of the throttle plate. At a high vacuum - closer to -7 - less air can flow past the throttle plate (small throttle opening), so less air is flowing through the AFM.

Less vacuum actually equates to more AFM airflow due to the wider opening of the throttle plate.

You can only cruise at a given vacuum given the condition of the engine - to vary the vacuum, you need to change the throttle plate position, so you change speed, so you aren't "on cruise".

If you study the maps in any programmable ECU (PFC, etc) you will notice that the injector times at low loads (high vacuum) are much shorter than those at higher loads (less vacuum, or boost).