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Old 08-02-2004, 07:42 PM   #1
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Default Boost Gauge problem

Always had this, but not too big of a deal because the Autotapping showed a 12.7 psi before rockers and I'm running decent times...however, the boost gauges is not steady. Sometimes while waiting at a stoplight the needle will flunctuate a few millimeters and under acceleration it may do the same if I hold a steady foot. No surging or performance problems, just a wierd gauge. What lines feed the gauge? I'd like to give them a glance and check for a leek of some kind.
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Old 08-06-2004, 11:33 AM   #2
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I too have the same problem...

BUMP TTT..

P.*. Would this be moved to the "forced induction thread"
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Old 08-06-2004, 03:42 PM   #3
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That'll be your map sensor. If you pull the vacuum line to it the boost gauge should go straight to 0. As far as I've found its normal to have it bounce a little above -10 stopped when in drive..
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Old 08-06-2004, 03:50 PM   #4
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Especially with a smaller pulley and/or a cold day.
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Old 08-06-2004, 03:59 PM   #5
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Mine'* quite steading actually, pinned at the end ( :P just kidding). I don't really see any fluctuations. I presume the 97 to 99 are the same for the L67, there are 2 MAP sensors on mine. One for the PCM to read and the other for the boost guage...neat huh?

Cheers,
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Old 08-06-2004, 04:24 PM   #6
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Quote:
Originally Posted by DrJay
That'll be your map sensor. If you pull the vacuum line to it the boost gauge should go straight to 0. As far as I've found its normal to have it bounce a little above -10 stopped when in drive..
What about driving? Where'* the MAP sensor (got pics?) and if the MAP sensor is going.. will it throw a code?
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Old 08-06-2004, 04:40 PM   #7
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Ya know I browsed my pics and I have one of the map sensor but its a little too zoomed in to make out where it is. Its easy to find though. Its a rectangular box about 1/2" thick mounted just above your rear valve cover (towards the firewall). Its got a somewhat large 3 prong plug going into it and its got a vacuum line that goes to the FRP and branches off to attach to the vacuum splitter on the supercharger.

Look at the vacuum splitter on the supercharger. Its on the top of the */c at the rear (Towards the TB) and has 3 vacuum lines attached to it. Follow the middle one to the back of the car. It splits and one goes to the FPR the other goes to the Map sensor. I pulled that from my memory but I'm pretty sure its the middle one


If you still can't find it I'll go take some pictures, its just raining now .
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Old 08-06-2004, 04:58 PM   #8
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Quote:
Originally Posted by DrJay
Ya know I browsed my pics and I have one of the map sensor but its a little too zoomed in to make out where it is. Its easy to find though. Its a rectangular box about 1/2" thick mounted just above your rear valve cover (towards the firewall). Its got a somewhat large 3 prong plug going into it and its got a vacuum line that goes to the FRP and branches off to attach to the vacuum splitter on the supercharger.

Look at the vacuum splitter on the supercharger. Its on the top of the */c at the rear (Towards the TB) and has 3 vacuum lines attached to it. Follow the middle one to the back of the car. It splits and one goes to the FPR the other goes to the Map sensor. I pulled that from my memory but I'm pretty sure its the middle one


If you still can't find it I'll go take some pictures, its just raining now .
Thanx Doc.. will look for it later tonight... hopefully there'* still light by the time I get to my car. ( Tamara has it right now to get a new tire valve installed )
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Old 08-10-2004, 04:56 PM   #9
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Quote:
Originally Posted by DrJay
That'll be your map sensor. If you pull the vacuum line to it the boost gauge should go straight to 0. As far as I've found its normal to have it bounce a little above -10 stopped when in drive..
OK.. I found both of them.. I cant see the one that thats closest to the middle if there'* a vacuum line attatched to it or not.. but the one closest to the fender I do see a vacuum hose going to the bottom of it
So when you say to pull it and it shoudl read zero.. is that with engine running or not? Will this cause issue with it?
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Old 08-10-2004, 05:13 PM   #10
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Quote:
Originally Posted by Drifter420
So when you say to pull it and it shoudl read zero.. is that with engine running or not? Will this cause issue with it?
Yes with the engine running, inspect all the vacum lines, a small crack can cause it to bounce as well.
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