boost gauge not reading what it "should" - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

superhoss37 · 12-22-2003, 10:19 PM

well i got my boost gauge finally hooked up tonight and my wastegate spring is set for .4 bar which im pretty sure is 5.6 psi roughly. when i go WOT on it, the boost gauge only reads like 3 psi at most( from what i can tell by glancing at it while driving). What do you guys think is wrong? a boost leak maybe? i dont hear any hisssing from my pipes or anything like that. Thanks!

when my car idles it reads 20 vacuum...is this a normal #?

Evil S14 · 12-23-2003, 11:39 AM

the vacuum seems normal, usually 18-22 for a normal car. As for the boost issueits possile you have a pinhole leak, but this would also cause bad idle and running rich as a mofo, its also possible that the gauge is messed up or you kinked the air line going into the gauge

superhoss37 · 12-23-2003, 07:25 PM

well as far as i know, i just have a little leak on the #4 runner on the exhaust manifold. would this cause this kind of problem? oh, and yea, i have very bad idle problems sometimes
once the car is warmed up fairly good, it idles around 700rpm or so but sometimes it likes to fluctuate down to like 550rpm. out my tailpipe, ihave some liquid that drips out but im not too sure if it's gasoline.

klattr1 · 12-23-2003, 08:15 PM

a boost leak would cause a lower number than you expect

Evil S14 · 12-23-2003, 09:19 PM

i say its a boost leak, take your dipstick out and see if your oil is really thin and smell like gas. if it does ur running rich as a mofo.

the small exhhaust leak shouldnt affect anything related to your boosting problems

chek all pipes for leaks, make sure all hoses are tight and pressure test the whole system

uiuc240 · 12-23-2003, 10:36 PM

Where is the source for your boost gauge signal? If the wastgate spring is set to 5.6 psi, and the signal line for the gauge is all the way on the OTHER side of the intercooler by the throttle body (like most are), you could very easily see 2 psi of pressure drop (if you have a big IC and lots of piping).

True, this is not a good thing, but it's not out of the realm of possibility.

Build an Intake Pressure Tester if you want to find boost leaks.

Exhaust leaks will affect spool-up (it'll be slower), but won't affect the boost pressure.

20 in-Hg of vacuum is good.

Autometer gauge? They are notorious for reading about 1 psi low from the factory (all I've seen sit at the low end of the "0" box). You can adjust it with a little creativity and a small screwdriver...take the bulb out and probe around in the back until you figure it out...be careful though.

Eric

uiuc240 · 12-23-2003, 10:40 PM

Here is the website I was thinking of:

http://www.vfaq.com/mods/ICtester.html

Eric

12-22-2003, 10:19 PM	#1
superhoss37 Join Date: Sep 2003 Location: TN Posts: 23 Trader Rating: (0) Feedback Score: 0 reviews	boost gauge not reading what it "should" well i got my boost gauge finally hooked up tonight and my wastegate spring is set for .4 bar which im pretty sure is 5.6 psi roughly. when i go WOT on it, the boost gauge only reads like 3 psi at most( from what i can tell by glancing at it while driving). What do you guys think is wrong? a boost leak maybe? i dont hear any hisssing from my pipes or anything like that. Thanks! when my car idles it reads 20 vacuum...is this a normal #?

12-23-2003, 11:39 AM	#2
Evil S14 Zilvia Addict Join Date: Dec 2001 Location: Indianapolis/Bloomington Age: 41 Posts: 610 Trader Rating: (0) Feedback Score: 0 reviews	the vacuum seems normal, usually 18-22 for a normal car. As for the boost issueits possile you have a pinhole leak, but this would also cause bad idle and running rich as a mofo, its also possible that the gauge is messed up or you kinked the air line going into the gauge __________________ image exceeds forum limit -Moderation

12-23-2003, 09:19 PM	#5
Evil S14 Zilvia Addict Join Date: Dec 2001 Location: Indianapolis/Bloomington Age: 41 Posts: 610 Trader Rating: (0) Feedback Score: 0 reviews	i say its a boost leak, take your dipstick out and see if your oil is really thin and smell like gas. if it does ur running rich as a mofo. the small exhhaust leak shouldnt affect anything related to your boosting problems chek all pipes for leaks, make sure all hoses are tight and pressure test the whole system __________________ image exceeds forum limit -Moderation

12-23-2003, 10:36 PM	#6
uiuc240 Nissanaholic! Join Date: Apr 2002 Location: Naperville, IL Age: 46 Posts: 2,093 Trader Rating: (0) Feedback Score: 0 reviews	Where is the source for your boost gauge signal? If the wastgate spring is set to 5.6 psi, and the signal line for the gauge is all the way on the OTHER side of the intercooler by the throttle body (like most are), you could very easily see 2 psi of pressure drop (if you have a big IC and lots of piping). True, this is not a good thing, but it's not out of the realm of possibility. Build an Intake Pressure Tester if you want to find boost leaks. Exhaust leaks will affect spool-up (it'll be slower), but won't affect the boost pressure. 20 in-Hg of vacuum is good. Autometer gauge? They are notorious for reading about 1 psi low from the factory (all I've seen sit at the low end of the "0" box). You can adjust it with a little creativity and a small screwdriver...take the bulb out and probe around in the back until you figure it out...be careful though. Eric __________________ 2002 Mazda Protege5 1989 S13 w/SR20DET (sold)

12-23-2003, 10:40 PM	#7
uiuc240 Nissanaholic! Join Date: Apr 2002 Location: Naperville, IL Age: 46 Posts: 2,093 Trader Rating: (0) Feedback Score: 0 reviews	Here is the website I was thinking of: http://www.vfaq.com/mods/ICtester.html Eric __________________ 2002 Mazda Protege5 1989 S13 w/SR20DET (sold)

12-23-2003, 07:25 PM	#3
superhoss37 Join Date: Sep 2003 Location: TN Posts: 23 Trader Rating: (0) Feedback Score: 0 reviews	well as far as i know, i just have a little leak on the #4 runner on the exhaust manifold. would this cause this kind of problem? oh, and yea, i have very bad idle problems sometimes once the car is warmed up fairly good, it idles around 700rpm or so but sometimes it likes to fluctuate down to like 550rpm. out my tailpipe, ihave some liquid that drips out but im not too sure if it's gasoline.

12-23-2003, 08:15 PM	#4
klattr1 Leaky Injector Join Date: Dec 2002 Location: SC and NC Age: 42 Posts: 112 Trader Rating: (0) Feedback Score: 0 reviews	a boost leak would cause a lower number than you expect __________________ KA24DER.com - Buy your supercharged KA24DER kits here!