Boost figures

[tcf]

Scangauge is showing -6.9psi boost at idle. Normal low speed running sees it at around 0psi. Car seems to run as normal. Cleaned the MAP sensor and reset ecu from battery disconnect. Still no change. Turbo hoses (Samco) are all good.

Anyone had this issue? Any ideas?

(JKU 07 CRD auto)

[Paul-JK]

Is the scangauge set for the correct altitude? From memory boost pressure is the difference between the internal pressure and the estimated ambient outside pressure. When you set it up you need to set the altitude you're basing it at as the external air pressure changes with altitude. Your's sounds like it's set for the top of Everest!

[layback40]

Originally Posted by tcf

Scangauge is showing -6.9psi boost at idle. Normal low speed running sees it at around 0psi. Car seems to run as normal. Cleaned the MAP sensor and reset ecu from battery disconnect. Still no change. Turbo hoses (Samco) are all good.

Anyone had this issue? Any ideas?

(JKU 07 CRD auto)

Your figures are what one expects from a turbo. -6.9 shows the turbo has not spooled up. You dont get boost until you have it working. See what you get at the RPM for max torque when going up a long hill.

[Paul-JK]

Originally Posted by layback40

Your figures are what one expects from a turbo. -6.9 shows the turbo has not spooled up. You dont get boost until you have it working. See what you get at the RPM for max torque when going up a long hill.

Really? Mine shows about 0 at idle running up to about 20 pulling up steep hills.

[tcf]

Paul-JK, it has only changed in the last week or so to the negative value. Previously it showed approx zero at idle. I will try reset the scanguage and reprogram it. Sounds like this could be the issue.

layback40, I'm not sure it should be showing negative pressure? Boost should just add to the pressure of what would otherwise be normal aspiration. Negative boost would mean the turbo is is doing opposite to what it should. My boost range is showing ~ -6.9psi - 13.0psi. Normally it shows ~0.0psi to 21.0psi.

[Grahame]

You haven't accidentally selected MAP instead of BST have you? BST is a compensated value whereas MAP is absolute. When BST is zero the pressure is actually 14.7 psi if you're at sea level on a standard day. This is why you will sometimes see a negative value at idle when it's cold. Older firmware versions of the SG2 didn't have the BST gauge and you could adjust the MAP gauge to compensate for your height ASL. If you haven't selected MAP by accident select it and see if you have about 14 psi difference. This might give you a lead as to whether or not you have a software problem.

[tcf]

Hi Grahame

I have a newer version so I couldn't find any Sea level settings to change. I selected MAP and get figures in the range ~ 14.9 - 35.0. This corresponds to what would be normal BST figures of 0.0 - 21.0. However when I set it to BST it still shows ~ -6.9 - 14.0. Still got me buggered and I'd really like to have BST showing all the time on my gauge