Boost Reading Accuracy

deenasty

Member
Joined
Feb 10, 2007
So I recently installed my Lorenz Boost Controller, along with my injector and chip combo from Eric. I upgraded my ECU with t powerlogger, and installed the Scan Master 2.2 chip.

My scanmaster is reading 15-16lbs, however my VDO boost gauge is showing 20lbs! At first, it scared the crap out of me. Is it safe to say that the scanmaster/powerlogger combo is more accurate than the VDO gauge? Any information is greatly appreciated. Thank you for reading.


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I would believe the stock map over the gauge but stock maps have been know to.leak as well.

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I would believe the stock map over the gauge but stock maps have been know to.leak as well.

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Ha! I didn't see your reply saying basically the same thing until after I posted........

We need to make the private track rental happen.

Sorry OP, Back to our original programming...........;)
 
Rubber, from a local auto parts store. :cool:

Take the old one off, take it to your parts store, buy only what you need. You won't need top replace it again for a long time.
 
Rubber, from a local auto parts store. :cool:

Take the old one off, take it to your parts store, buy only what you need. You won't need top replace it again for a long time.

So I checked the hose, and the nylon hose is in great shape. The boost gauge “T’s” into that hose. Is this type of discrepancy “normal” from gauge to what the computer is seeing? I am still using the factory MAP. Thanks!


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I suggest replacing what "looks good" anyway.

I'll let Boost231 elaborate.
 
I've seen some crazy reading from both sensors. Gauges can be off but they can be accurate. Same as the stock map sensor. I would personally trust the map sensor over your cheap style gauge. Another thing I would fix how its plumbed.. you need to have a dedicated line to the map sensor. For what your doing it's not a end all be all since your not using it for SD. But I still don't like seeing it T into anything. Run your gauge off another line or port.

Only sensor I trust is a ssi or a good quality and calibrated gauge. Vdo and autometer is not.

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I've seen some crazy reading from both sensors. Gauges can be off but they can be accurate. Same as the stock map sensor. I would personally trust the map sensor over your cheap style gauge. Another thing I would fix how its plumbed.. you need to have a dedicated line to the map sensor. For what your doing it's not a end all be all since your not using it for SD. But I still don't like seeing it T into anything. Run your gauge off another line or port.

Only sensor I trust is a ssi or a good quality and calibrated gauge. Vdo and autometer is not.

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I went ahead and replaced the line from the plenum to the MAP sensor that “looked good” and it was so brittle, the plastic tube cracked in half, and appeared to have some other small cracks in it. So I ran a dedicated new rubber line.

I went ahead and ran the boost gauge line to the vacuum line that connects into the charcoal canister. Does this sound ok?


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There's a check valve going to the canister, so it only gets vacuum, not boost. If you see pressure on the canister hose, the check valve is defective. You shouldn't use that hose to run a gauge.
 
The stock 2-bar MAP sensor only reads to 15psi, so it's maxed and will never read higher. Normally people put a 3 bar MAP sensor to read more boost.
 
The stock 2-bar MAP sensor only reads to 15psi, so it's maxed and will never read higher. Normally people put a 3 bar MAP sensor to read more boost.

Thank You for pointing that out! I will order up a new 3 bar MAP from you today.


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There's a check valve going to the canister, so it only gets vacuum, not boost. If you see pressure on the canister hose, the check valve is defective. You shouldn't use that hose to run a gauge.

Where do you suggest?


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Didn't even think he was running a 2 bar.

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The stock 2-bar MAP sensor only reads to 15psi, so it's maxed and will never read higher. Normally people put a 3 bar MAP sensor to read more boost.
Help me understand why that is.... if 1 bar is 14.7 psi (at sea level) wouldn't a 2 bar sensor theoretically read up to 29.4 psi?
 
Help me understand why that is.... if 1 bar is 14.7 psi (at sea level) wouldn't a 2 bar sensor theoretically read up to 29.4 psi?

14.7 psi, or 1 bar, is ambient outside pressure. When you add 14.7 psi of boost on top of ambient, you get 2 bar. But it's still only 14.7psi getting into the engine.

A 3 bar map sensor will read up to 29.4psi.

-Patrick-
 
14.7 psi, or 1 bar, is ambient outside pressure. When you add 14.7 psi of boost on top of ambient, you get 2 bar. But it's still only 14.7psi getting into the engine.

A 3 bar map sensor will read up to 29.4psi.

-Patrick-
Makes perfect sense.... thanks for the explanation.
 
Just FYI, the factory boost gauge will no longer read correctly with a 3-bar MAP sensor. You could add the 3-bar separately if you wanted to keep that reading, but most guys don't care.
 
Just FYI, the factory boost gauge will no longer read correctly with a 3-bar MAP sensor. You could add the 3-bar separately if you wanted to keep that reading, but most guys don't care.

Thank You Eric, but the car has aftermarket GNX style VDO gauges, no more factory boost gauge. Just want to make sure the gauge and the MAP are reading as accurately as possible.


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