Hi, I've got a 2009 HHR SS that's equipped with an interceptor digital gauge in place of the factory boost gauge on the A-Pillar and I've noticed for the last year that when I shut the car off that the gauge would give me a reading of about -1 psi or so.

I never gave it much thought, but recently I've been seeing -2 to -3 psi on the digital readout after shutting the car down and I'm starting to wonder if the whatever sensor supplies info to the gauge is bad. I've also seen some issues with the car not holding boost very well over 5 psi (slow bleed off to 0) and am curious if this might be related.

Some background: The car has 108k miles on it now and I bought it used two years ago with about 76k on it. The previous owner was a member here, Dr. Jekyll, and had the GM PP stage kit installed and then a custom tune done at some point as well although I don't know when or at what mileage so the car has the 3 bar map sensors. The intercooler and hot side piping was replaced in the last month after I found a leak in the intercooler due to a wrench coming through the lower grille and leaving a nice wrench shaped impression (there's probably a good story behind this, but it happened before I had the car). Post intercooler replacement the intake seemed to hold pressure when I did a pressure test up to 10 psi with a compressor.

 

No ideas?

Should I just start unplugging sensors to see when I don't get a gauge readout? Is there any way to test a MAP sensor for functionality?

 

Unplugging sensors might help pin point which one is the problem, but it could cause more problems!
Perhaps a battery lobotomy will rest the whole system if the one at a time method shows no results.
You could clean the MAP sensor, if it is not working it should throw a code!

 

I know nothing about turbo. Sounds to me like a air leak somewhere.