boost problem

[junya1985]

OK i'm having a problem when i hit full boost my boost gauge is reading between 7-9 psi it bounces back and forth really fast i thought it was my wastegate because it was bad before than i replaced that and put on a FMIC so i took it for a test drive and noticed its still doing and my VAC is sitting at 18 at idle so i'm not sure if i have a vac leak but if any suggestions let me know

[SteelWarrior]

not sure if it helps but my vacum NEVER goes under 20, always 20+

[Velocifero]

yeah, briefly it sounds like a leak of some type. Does the car buck?

[low_psi]

Did the gauge just start reading this way?

[junya1985]

no under full boost doesnt seem to have any problems

[junya1985]

Did the gauge just start reading this way?

no its been like this but i thought it was just because of my bad wastegate so i finally replaced it and its still like it

[Velocifero]

does the car feel like it is actually performing at 7psi then 9psi? does it feel slower faster slower faster? Any chance you can try someone else's boost gauge? What kind do you have? Just searching for more info to see if we can solve this.

[Jaysanooch]

Are you running a Profec b ebc? I had a similar situation with my profec trying to tune it at 10psi..it was nightmare so we went with a JoeP mbc and it ran smooth.

[MSP_03_FL]

Now I have the same problem. It bounces back in forth between 5-6 psi. I checked the lines and re tighten them but it still does it. Might not be the gauge since it's brand new.

[Velocifero]

My biggest question is... If you are not looking at the boost gauge, can you tell the car isn't running correctly? Does it feel like you are bouncing between two different pressures?

[MSP_03_FL]

My biggest question is... If you are not looking at the boost gauge, can you tell the car isn't running correctly? Does it feel like you are bouncing between two different pressures?

No, the car is running smoothly and correct.

[junya1985]

i got an autometer sport comp but it doesnt feel like its running to top shape i was thinking it should be faster than what it feels i dont have a boost controller on it at
all but its not stock
cp pistons 8.5:1 k1 rods
injen intake
Corksport TBE
JDM cam 626 intake manifold

[Noel]

when mine idles apparently its sitting at 10 vac and my greddy ebc says so to, however when I go into boost or full boost my boost gauges and ebc increase at the same rate and show the same readings, So when I hit 7 psi it shows that on both units, 10 psi same thing. this low vac is a problem? I was once told your vac should be what your boosting?

[MSP_03_FL]

I don't think your vac should be the same as what your boost. I could be wrong because I'm still new to this but I'm running 20 vac on idle and only 6-7 psi on full boost since it keeps bouncing and i can't tell. lol

[Noel]

HMMM ..how can you tell theres a vac leak and how can you fix it? like im running boost and not running boost everything seems fine?

[Velocifero]

Your vac wont equal your boost, for starters they are measured in different units that are not a 1psi:1inHg aspect. Our cars generally run 20-24inHg and boost is whatever you have it set at.

[MSP_03_FL]

Hey Velocifero, is it normal for my gauge to be bouncing from 6-7 psi at full boost? The car is running correctly and I don't feel anything out of sync. I checked the lines and nothing wrong.

[Velocifero]

Hey Velocifero, is it normal for my gauge to be bouncing from 6-7 psi at full boost? The car is running correctly and I don't feel anything out of sync. I checked the lines and nothing wrong.

sounds fishy if it is going back and fourth. If it was going to 7 then creeping down to 6 I could see that, but I can't say it is normal to bounce back and fourth unless you are modulating the throttle, but if you have it pegged at WOT, it should hit a max psi then bleed out.

[MSP_03_FL]

sounds fishy if it is going back and fourth. If it was going to 7 then creeping down to 6 I could see that, but I can't say it is normal to bounce back and fourth unless you are modulating the throttle, but if you have it pegged at WOT, it should hit a max psi then bleed out.

Damn then I have no idea whats going on with my boost gauge. Anyone have suggestions?

[Velocifero]

Damn then I have no idea whats going on with my boost gauge. Anyone have suggestions?

What source is your gauge seeing pressure from?

[MSP_03_FL]

What source is your gauge seeing pressure from?

From the U-shaped vacuum hose on the top right hand side of the intake manifold.

[yashooa]

Make sure that there is not a kink in the line anywhere.

[MSP_03_FL]

I guess I'm gonna have to double check it again. Thanks

[ChopstickHero]

my vac in my area is -20 at idle. when i go up into the mountains (8000 ft above sea level), my vac is -16 to -18. when i go to the beach, it is -22 at idle. so i think elevation has something to do with it. but generally, it should be around -20.

[junya1985]

Ok i finally got around to getting another gauge to try and it fixed my problem its not bouncing around anymore it just holds steady boost

[Velocifero]

that's good to hear, it sounded like that was the problem since the car didn't feel like it was bouncing between two boost levels.