scan tool vs boost guage

[syon99]

I own a scan tool that lists boost. Do I need to buy and install a boost guage or can I rely upon the scan tool for boost information?

[Hubert]

A full time boost gauge will help diagnose problems during daily driving. The scan tool should read boost fine if you want to leave it hooked up. The recommended guages are EGT, boost, fuel pressure, and transmission temp if you tow for good real time continuous (and easily read) monitoring and diagnosis.

I think PCM measures boost in actual pressure not gauge pressure so value/units might be a little different than what is typically posted-talked about.

[Robyn]

You really need a boost gauge and a pyro to know whats going on. The Pyro will let you see whats happening before you melt it.

The boost gauge/Pyro mounted in/on the dash somewhere is a must if these engines have seen any chip upgrades or mods to the turbo controls.

Max boost without an aftercooler 12 PSI Max EGT 900 Post turbo and 1100 preturbo (Close to the exhaust ports)

Several companies make nice sets. Banks offers a nice set and most all the gauge makers have just about anything you could want in the way of gauges.

Stuart Warner, VDO, Isspro, Auto Meter and so on

I personally have the Banks set as it came with the exhaust kit.

Hope this helps

Robyn

[syon99]

Thanks for your help. I believe I got my answer. Scan tool reads boost as a percentage e.g. 105% at idle. 150% at WOT which is about 15psi boost given barometric pressure is about 30psi. (more info: PSI = inch of HG x 0.49118)

I'll also consider some additional gauges.

Thanks again for you replies.:)

[DmaxMaverick]

Thanks for your help. I believe I got my answer. Scan tool reads boost as a percentage e.g. 105% at idle. 150% at WOT which is about 15psi boost given barometric pressure is about 30psi.

I'll also consider some additional gauges.

Thanks again for you replies.:)

NOT barometric pressure. PSIA, or Atmospheric pressure. At sea level, it's ~14.7 PSI (something Biblical about driving around AT sea level). Your scan tool is reading the percentage of atmospheric pressure, not barometric. Unless you drive all the time at sea level, you'll need a slide rule, barometer, thermometer, altimeter, and who-knows-what-else, to know what your actual intake charge air pressure is, every time you look at it. PSIG (the "boost gage") is a measure of the intake charge air pressure, compared to the actual atmospheric pressure where you have the gage (or sender, if it's digital) located. This is why it takes considerably more boost pressure (as indicated on a gage) at higher altitude to make the same amount of power as at sea level.

All that said, NO (analog or digital) gage, sender, sensor, etc. you install into your truck is calibrated, and certainly, not all them, calibrated with each other. A boost gage, as with any electronic/mechanical measuring device on your truck, is best for setting bench marks, and tracking trends. Having a device dedicated to measuring a parameter (such as intake charge air pressure) is close enough to do this. You're not driving around in the space shuttle.

[syon99]

I should have stayed awake in math class. When the scan tool reorts 150% boost at sea level I should have about 6psi boost reported on a boost gauge. I will install the boost gauge at my earliest opportunity.

Thanks for helping me sort this out.