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Forced Induction All questions and problems regarding Superchargers, Turbos, NOS, ZEX, intercoolers, water injection, etc.

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Old 08-26-2007, 10:08 PM   #1
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Default Low Boost

While driving today I had the opportunity to "floor it" for the first time in a while. I noticed however, my Boost PSI did not go much past 2 or 3. After attempting to get more boost several times I still could not get the guage to move past 3 PSI. Of course I checked the common problems sticky and found the Boost Solenoid to be one of the common problems. I would like the try and do it myself to save a little money for a change, but the link given in the sticky doesn't work anymore. Could anyone give me a little instruction in regard to changing out the solenoid? Thanks.

P.*.: I will also be getting a scan tomorrow to see if there are any trouble codes.
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Old 08-26-2007, 11:02 PM   #2
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IIRC, if the solenoid is bad, you won't get into boost (past 0) at all. Check for a vacuum leak, first. Check in particular the T under the supercharger snout, and the capped off vacuum port on top of the supercharger.

I think the solenoid is held on with one nut...maybe 2. Remove the nut(*), 2 vacuum lines, and the electrical connection.
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Old 08-27-2007, 12:15 AM   #3
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The solenoid or actuator could both cause low boost, as well as the PCM limiting boost for some other reason.

At idle, remove the top vacuum line from the boost control actuator (the large round black thing on your supercharger):

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See the round black thing? With the vac line that goes from the center top of the pic to the left (the left end has a splash of white on the boot)?

Pull the line as it comes out of the BCA (center of pic). As you pull it and reinstall it at idle, the BCA should pull the bypass valve full travel up and down. If it doesn't go fully, 'help' it. Does it go farther? Look at the marks on the BCA shaft to see how far it should go. There should be wear marks.

If that checks out ok, look at this pic:
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Disconnect the yellow vacuum line (yours isn't yellow) at idle. Plug whichever end 'sucks'. Go for a drive. do you have full boost? (don't drive like this long-term, damage may come bite you in the arse).

Let us know.

I'll move your topic to the right section in the meantime.
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Old 08-27-2007, 12:48 AM   #4
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Thanks for the detailed information. I'll give this a try tomorrow night after work. The funny thing is I don't really notice too much lose of performance...seems almost normal to me, except the supercharger whine is quite absent. I'll let you konw what happens.
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Old 08-27-2007, 12:50 AM   #5
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The supercharger spins at the same rpm'* regardless of any of what I posted, and as such, the sound will be unchanged.

Other things to consider are:

Accurate boost reading? A vacuum leak to the MAP sensor can affect this.
Slipping belt? It can limit boost.
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Old 08-27-2007, 11:34 AM   #6
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The vacuum T from under the supercharger runs to the MAP sensor on one side, and to the fuel pressure regulator and boost control solenoid on the other. The vacuum port on top of the supercharger has 3 sections...one is capped off, and one of the others runs to the boost control actuator. (The 3rd runs to the brake booster.) Those are frequent problem areas.

A sticky or leaky actuator, that round cylinder that Bill pointed out (yours will look slightly different), could also cause the problem but has been much less of a problem in the 00+* than those vacuum lines. This is a quick overview of the diagnostics.

Quote:
Under most conditions, the PCM commands the boost control solenoid to operate at a 100 percent duty cycle (ON) to allow full boost pressure upon demand. However, if reverse gear is selected or the PCM detects rapid deceleration or engine load is extremely high, reduced boost pressure is desired. Under these conditions, the PCM commands the boost control solenoid to operate at a 0 percent duty cycle (OFF), which opens the bypass valve. With the Bypass valve open, boost pressure is reduced by recirculating intake air back through the supercharger inlet.

DIAGNOSTIC AIDS
If the Boost Control System Check has been performed and no electrical or vacuum related fault is found, check for the following conditions:

* A misadjusted or sticking bypass valve actuator. Refer to Bypass Valve Actuator Replacement.
* Any binding in the bypass valve or the bypass valve linkage. Refer to Boost Control System Description.

An intermittent may be caused by a faulty connection, rubbed through wire insulation, or a wire broken inside the insulation. Check for the following conditions:

* Inspect the PCM harness connector for backed out terminals, improper mating, improperly formed or damaged terminals, faulty terminal-to-wire connections, and a damaged harness. Use a corresponding mating terminal to test for proper terminal tension.
* Test for intermittents. Disconnect the PCM and use a DMM to monitor the voltage between the control circuit of the boost control solenoid at the PCM connector and ground. With the key on, observe the voltage while manipulating the related connectors and the wiring harness. If the failure is induced, the voltage display will change. This may indicate the location of the fault.
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Old 08-27-2007, 12:00 PM   #7
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I'm not sure if this has anything to do with it, but I saw somewhere on the site a while back about the AC compressor making a lot of noise when the Air is turned off. Something about the clutch plate rubbing against something. Sounds like a high pitched whistling sound...well, mine has been getting worse and worse of late. Any way that could cause a problem like this? Otherwise all of the belts are new and slippage only occures when they get wet from a deep puddle.
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Old 08-27-2007, 12:01 PM   #8
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Archon, his BCA will look identical to that one. I posted pics of the M90 setup, not my own.
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Old 08-27-2007, 02:22 PM   #9
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Sorry, Bill, but there are some minor differences from the one that you posted, and the 2000 BCA. Perhaps better wording would be that the look of the area will be different. First the 2000 BCA has the top and bottom vacuum ports directly across from each other, and the top hose is a regular vacuum hose. It doesn't have the 90* elbow or the plastic hose. The other thing I didn't want him looking for as reference, is the vacuum port shown right near the BCA. The 2000+* do not have that. These are pictures from my car.
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Just trying to clarify the setup for him...and yeah...my engine could use a cleaning.
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Old 08-27-2007, 02:41 PM   #10
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Awesome, Dick. I had no clue they were different. Can you upload those to the GH PB account also?
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