Boost Pressure Loss

[RichB]

I was watching my boost pressure while I was driving in to work this morning and noticed that it was only holding at 11 psi with 13 psi spikes. The car feels fine but I usually see it spike to around 16 PSI.

The last time I looked at boost this closely was while I still lived in Virginia. Now I am in Denver, so I am wondering if the altitude difference has anything to do with it. It shouldn't but I could be wrong.

The other thing it could be is my Aeroforce Interceptor Scan Gauge. I am wondering if there is some kind of calculation error in the ECU at altitude.

Other than that, are there any suggestions on what hoses to check?

Thanks in advance!

 

[Jackis]

As far as I know, altitude defference really does the job. 18 to 11 psi is rather huge difference, but I've heard about people who has 1.25 bar (18 psi) at sea level and not more then 1 bar (14 psi) at 1-2 km above sea.
Check your coldpipe (compressor to intercooler) and hotpipe (intercooler to throttle body) for t-bolts are proper tightened and no leaks there.
Check your bypass valve it is holding boost well (I decided to add 2 shims to my blue spring Forge just to be sure it holds boost nicely) and all vacuum lines are properly connected.
And the ver last - somebody over here said that intake manifold gasket may also leak. But it's very seldom I believe.

 

[RichB]

Thanks for the reply. So 4 PSI is possible just based on Altitude?

I have a PG FMIC. Could that have some kind of effect?

Also, I think I found a nick on my vacuum line from my BPV. I didn't think it went all the way through but if it did, could that be messing my readings up? It would be weird since my car is fine at Idle.

Thanks again!

 

[Kain]

Holy crap, when did you move?

 

[RichB]

Holy crap, when did you move?

A little over a month ago

 

[Kain]

Fail.

 

[RichB]

Fail.

Fail for what? Moving?

 

[Jackis]

May be, fail for moving to less dense air???
Nick in vacuum line could cause boost leaking (it could force spring to be partially opened).
Also, FMICs usually takes 0.5-1.5 psi of boost because of more long and bended route.
As a last, check your wastegate actuator is working so the gate isn't partially opened.

 

[RichB]

May be, fail for moving to less dense air???
Nick in vacuum line could cause boost leaking (it could force spring to be partially opened).

So with the vacuum line nick, I could be idleing fine but have a loss up top?

 

[Jackis]

When you idling - you can just disconnect vacuum line, because there is no pressure over atmospheric in the boost contour and the valve is fully shut. But when you revving - nick may cause boost leak.

 

[RichB]

When you idling - you can just disconnect vacuum line, because there is no pressure over atmospheric in the boost contour and the valve is fully shut. But when you revving - nick may cause boost leak.

wouldn't disconnecting that line cause the manifold pressure to rise making the idle rough?

 

[Jackis]

When I disconnected it on my vehicle on the fly, nothing changed and nothing had to You can also try it

 

[RichB]

I just thought of something else, they only have 91 octane here in Denver. Could the ECU be dialing back boost to compensate?

 

[RichB]

Ok, I think I figured something out. The manifold pressure reading that is going to my aeroforce gauge is not actually gauge pressure (Absolute - Atmosphere). What is measured is Absolute - 14.7 psi.

As a result, this screws up my high altitude readings. The measured atmosphere pressure while I was checking out my guage this morning was about 11.8 psi. This means that I would be reading 2.9 psi lower than I would at sea level for the same boost.

So, the 11 psi constant with the 13 psi spikes I was seeing here in Denver this morning would be the same as seeing 13.9 psi constant with 15.9 psi spikes in Virginia. Since I was just on surface streets this morning and I couldn't slam on the gas, these numbers make sense.

I am glad I researched this a little more.

 

[RichB]

UPDATE: It took me a while, but I figured out that my Aeroforce Interceptor has an altitude setting. When I pulled it up, it was at 1000 ft. This number is wrong for both Virginia and Colorado (more wrong in Colorado). So I have been reading the wrong numbers ever since this gauge went in!

I set the altitude to 6000 ft which is the altitude where I live. I will see what things look like on my drive home.

 

[RichB]

Everything looks normal now!