My stock boost gauge is not going over 10 psi with a GM Stage 2 w/ 2.8 pulley. What is the most likely cause between bad gauge, map sensor, actual low boost? Car runs ok but this gauge is making me think i'm missing out on some power.

 

Boost is just a measurement of restriction

 

it is, however its also an indicator something is wrong as a 2.8" pulley should be making 15-16psi on a typical lsj.

it could be a number of things. first off, did this just start happening, or did you make ome changes and now its the result?

check for belt slip, make sure your bypass valve is fully closing, air filter is clean. if all that looks ok id get a mechanical boost gauge on it and see what it says.

 

I bought the car about 6 months ago and it has always been like this. I just didn't know if it was common for the gauge to be off by 5psi. I guess i'll have to buy a mechanical gauge to know for sure. I just hope my Map sensor is not sending the wrong info to the pcm because my car is running lean and i've already fixed all the vacuum leaks and a bad evap purge solenoid.

 

Gauges are used as an indicator that it's working. When it drops to 5 you will know it before you look at the guage. Make sure your bypass valve is not sticking and it hits the stop when you blip the throttle. A few drops of oil on the butterfly shaft fixed mine right up. Fwiw I see 10-11 psi with a 2.9 when I first nail it. It may go higher but it's all I can do to drive when I'm WFO so I only see it for a second. Do they go higher as it revs?

 

I am also running a 2.8 and I see anywhere between 11-13psi. I also have a header and a 3" downpipe, if you're running any exhaust mods, you should expect to see slightly less than a stock lsj would make boost wise .

 

Where are you at in fl?

 

I make 13 psi with 2.8" ZZP also using Vibrant headers and Vibrant 3" exhaust. Needs a resonator, super loud. Have both aeroforce and autometer mechanical gauges with same result.

 

Close to Plant City which is between Tampa & Orlando.

I just had a new Thrush turbo muffler put on and the exhaust shop found several exhaust leaks at the header, collector, and two mid pipe flanges. I suppose those are contributing to the lower boost # and making the car lean.

 

My old LSJ is in Orlando. Sees 14-16psi on the 2.8 and it is catless.


Check your bypass valves and intercooler pumps.


Let me know if you want to tune them

 

I've been reading up on the bypass valve and will try to unplug the bypass solenoid connector to see if the pcm is bleeding off my boost for some reason and check to make sure the solenoid is not stuck open. There is a LOT of conflicting info on the bypass valve.