installed new boost gauge, not reading right?

[JiveMasterT]

i just installed a new boost gauge and it doesnt seem to be reading right and i want to know if what im getting is normal. the air around here is about 20-30 degrees right now and the gauge is reading about 12-14 vac at idle, and when i hit full boost it reads about 14-16psi. that doesnt sound to outlandish to me, but what does concern me is that when the car is off, the gauge needle isnt in the center of the square on the gauge. i posted some pics from my camera phone.

when the car is off.....

 

[JiveMasterT]

and now, when the car is on for a few min and there is nothing else on in the car (no radio, lights, not pressing the brake, etc)......

 

[92tsiawd84]

Gauge looks at 0 to me. Check out the spacing on the vac side. It gets cut off. I would say that you have some vaccum leaks. You should get ~18 vaccum. Do a boost leak test.

 

[FrostbyteTalon]

If its reading positive on the pressure side when the motor is off that could mean that the readings will all be about 1 to 2 higher... or it could mean the gauge is defective completely. I would definitely do a leak down test and check for boost leaks. Oh and by the way... I have never found that having anything on in the car like radio, headlights, etc would effect the reading on the boost gauge. If it was electronic or digital, I could understand... maybe........ but not with a mechanical gauge like boost. I think either you have a bad gauge (which isn't uncommon with autometer) or you have a vac leak. Are you sure that where you "T"'d the vac line you have a good seal. Also... I know this may be a pain... but check to make sure you have a good seal in the back of the gauge. If that nylon hose isn't into the back of the gauge securely, you could lose some vac pressure. Check those things out...

 

[JiveMasterT]

the seal to the back of the gauge is good, cause i used teflon tape and tightened it with a wrench. the t-fitting is good cause it feels really snug and i used cable ties to clamp the fitting together. i guess i might have a boost leak.

the other interesting thing though is that the gauge reads 15psi when it hits full boost and then it drops back down to 13psi right after that. its weird and i dont know what the hell to do. maybe i should just send the thing back and see what happens with the new one.

 

[Red1]

Your gauge is fine. You might have might have a vac leak though. Those readings are kinda low.

 

[Defiant]

Vacuum can be lower with accessories running, as the engine's throttle is opened further to run the alternator.

Make sure there aren't any crimps or kinks in the sensing line.

 

[92tsiawd84]

Originally posted by JiveMasterT
the other interesting thing though is that the gauge reads 15psi when it hits full boost and then it drops back down to 13psi right after that. its weird and i dont know what the hell to do. maybe i should just send the thing back and see what happens with the new one.

That has nothing to do with the boost gauge. It is the crappy t25 turbo. They cannot hold boost to redline. It always dies off. Your vac readings are low unless you have cams in there of something. Should be ~18 hg.

 

[FrostbyteTalon]

He's lucky his only drops to 13psi. Before I did the 17psi Actuator my boost dropped from 15 to 11.5-11 at about 5.3k rpm. Yeah.. the t25 sux!

 

[Defiant]

Originally posted by FrostbyteTalon
Yeah.. the t25 sux!

...at boosting over five grand. However, for boost between 2800 and 5000, it spools up quickly and efficiently. It's a street car turbo, not a racer.