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Old 11-12-2007, 10:13 PM   #1
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Default Boost gauge gone crazy

I've search all the forums and can't find a fix. Here'* my problem.

When I start my car in the morning and drive, the boost gauge works fine. After driving for a while the boost needle starts jumping irradically and finally pegs out on +10. The needle then stays there until the car is turned off, then on a restart the needle goes to zero and stays there for the remainder of the day no matter how many shutoffs and restarts. The needle does not correct itself until sitting all night and then the same thing happens the next day, and every day.

I just recently installed new nose drive bearing and coupler. And that didn't fix anything, but it needed them anyway, it was rattling pretty bad.

Any help would be appreciated.
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Old 11-12-2007, 11:01 PM   #2
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Old 11-12-2007, 11:43 PM   #3
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That article won't help much.

This sounds like either a guage or MAP sensor issue. You'll need a scantool to determine the most likely cause.

There'* no way you can be pegging the gauge at idle or off, so it has to be one or the other. This is where I'm a little 'gray' though. The S1 L67 doesn't use the MAP signal for 'pcm functions'. It'* only for a boost indication. So the question is, does the MAP signal get split in the sensor, or is it like the ECT'* on the S2 with two different sensors in one?

If it'* ONE signal being split, we need to know what the PCM sees. If the PCM is getting a good read on the MAP data, it would be a wiring or gauge problem.
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Old 11-13-2007, 08:20 AM   #4
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Originally Posted by willwren
If it'* ONE signal being split, we need to know what the PCM sees. If the PCM is getting a good read on the MAP data, it would be a wiring or gauge problem.
Close..

it'* two individual MAP sensors side by side. Unplug one and you'll unplug the PCM'* input, unplug the other and you'll get the gauge input. I would assume since the car isn't running oddly that it'* the gauge sensor.

With the recent work, first thing to do is check the small plastic line that runs from under your nosedrive, behind the alternator and then over to the two map sensors on the rail attached back behind the supercharger. Those two T'* can get pretty brittle.
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Old 11-13-2007, 09:00 AM   #5
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I don't see a broken vacuum line causing a pegged gauge. It would be quite the opposite. If the two MAP sensors are the same, try swapping them. If the car runs like crap, but the boost gauge reads correctly, your problem is a sensor.
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Old 11-13-2007, 09:53 AM   #6
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Correctamundo .. I meant to say check the T'* as well as the electrical connectors. The default might be pegged to ensure extra fuel is added and a lean condition is not induced by a faulty sensor. Although that would need to be checked in the FSM.
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Old 11-13-2007, 10:04 AM   #7
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Default mode of failure on a MAP sensor is atmospheric pressure. His boost gauge would read 0.

I suggest concentrating on the sensor swap for the time being.
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Old 11-15-2007, 10:25 AM   #8
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I don't suppose anyone has a pic of these map sensors. As to where they are? Do you have to physically remove these to swap or are the wires long enough to just swap plugs?
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Old 11-15-2007, 12:56 PM   #9
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Remove the engine cover if you don't already have it off. Look at the top rear of the engine (facing the motor from the front of the car). Just behind the supercharger will be a bracket coming up from the LIM/rear Cylinder head. It should have two rectangular sensors on it. Each sensor should have a vacuum line and an electrical connector.

Swap connectors if possible. I don't know if they're keyed the same, or if the harnesses are long enough to swap between them. If you swap them, and the boost reading works right, the car will probably run like ****. If that'* the case, we need to figure out which is which for replacement. That can be done by disconnecting them one at a time to determine which is the boost gauge MAP sensor, and remembering whether the 'bad' one was intstalled in that location or not. Make sense?

Carefully inspect the vacuum fittings at the same time.
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Old 11-15-2007, 04:02 PM   #10
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The sensor wires should be long enough and are not keyed. They can easily have the tab broken off from rear manifold heat.

As for the vacuum lines, they are underneath and nearly impossible to see w/o unbolting the sensors or bracket the sensors are bolted onto.
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