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Old 05-05-2006, 06:52 PM   #1
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Default Low Boost - 36 inHg MAP sensor reading + spercharger noise

I just took my car for a test drive with my scanner and the maximum reading the MAP sensor gave me at full throttle was 37 inHg. That'* only about 3.5 lbs of boost, and I thought the Series II L67s ran in the neighborhood of 8 psi stock, so I should be seeing 46-47 inHg. Am I correct?

When thinging about what would cause low boost, the only things I could come up were:
- a clogged air filter (it'* a stock paper element in stock air box, but its clean)
- slipping belt (belt is only months old and I don't hear any squeeking)
- damaged supercharger lobes (although I don't know how that would happen)

When running with the hood open and engine cover off, there'* a weird sort of noise coming from the supercharger. My friend has a supercharger LSS with 180,000 miles on it and it doesn't have any noise coming from the supercharger, so that leads me to believe that something might be wrong. It'* definatly coming from the lobes of the supercharger because I can hear it very clearly with my ear directly above the blower. When I do the same to my friends car, I only hear one sweet motor purring at idle. The sound definatly isn't the coupler, as it isn't a knocking. The noise honsetly sounds like the valvetrain on a OHC engine, as weird as that seems. It'* not exactly a growling, like the gears were bad, but it'* sort of like, well, an OHC engine'* valvetrain. I'm stumped. Does anyone have any ideas as to what could be the problem? Do you think there'* a problem? Maybe I just need a new blower with a ported inlet and outlet.

Oh yeah, I've already done the supercharger bypass valve mod, so it'* not that. (that little thing snaps closed with any little blip of the throttle)
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Old 05-08-2006, 02:01 AM   #2
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After doing more snoooping around the forums (and realizing this would have best been posted in Forced Induction (moderator?)) I think the problem could be that the teflon coating on the rotors has begun to (or already has) come off. (Like the guy with the M62 on the BMW) That'* the only logical explination for the really low boost I'm seeing (3 psi vs 8 psi) (But it doesn't explain the sound???)

Has anyone ever had this happen to them or known of this happening to someone else'* car? What would it take? I mean, with only 71K miles, and the fact that blowers with 200K miles on them don't have this problem, it makes me wonder........
It was a junkyard engine (or should I say salvage yard engine) from a '99 Park Avenue w/71K on it (or so they say), so I guess anything'* possable. However, the place I got the motor from is supposed to be really reputable (my uncle owns an ind. raepair shop and has used them to save many a customer'* pocketbooks), so I would be suprised if they lied (I even got the VIN of the car it came out of)

It really frustrates me because I went through all the time, effort, and money to swap in the boosted 3800, and now I don't have any boost!!!!!! I might as well still have the N/A motor.

Any thoughts on the issue would be helpful.
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Old 05-08-2006, 09:33 AM   #3
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I don't think it'* anything you've posted so far.

How about disconnecting the TOP vac line on your boost control actuator on the front of the supercharger? When you do this at idle, does your BCA go to full travel? If so, drive and scan again.

The BCA is the black thing on the front of the SC with two vacuum lines going to it. One at the top, one on the side. The top vac line goes back to manifold vac, the side (lower line) is switched by the BCS (boost control solonoid) by the PCM to control boost.

The car is normally in 'bypass' at idle, and will only supply boost in driving conditions based on driver demand. A bad or weak BCS or BCA, or a vacuum leak in either can cause your symptoms. The S2 is also known for cracking/breaking the vac line that runs under the nosedrive of the SC.

Don't rule out a bad MAP sensor or a leak at that point either. I'll move this for you.
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Old 05-08-2006, 09:53 AM   #4
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The S2 BCA actually has it'* vacuum lines on the sides. The one Willwren mentions on the top..is located on the passenger side of the BCA can. (S1 is on top)

As for the noise, have you removed the belt and checked the amount of play? The noise could be a coupler.

Low boost and coating. Oh..I've got experience here. Peeled coating entirely from a SC will yield you about 5-6 lbs of positive pressure when WOT.
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Old 05-08-2006, 10:10 AM   #5
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The coating doesn't have a habit of coming off without ALOT of chemical help. If you've never had it apart, and never injected anything, my gut tells me your coating is fine.
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Old 05-08-2006, 11:56 AM   #6
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Quote:
Originally Posted by willwren
The coating doesn't have a habit of coming off without ALOT of chemical help. If you've never had it apart, and never injected anything, my gut tells me your coating is fine.
Agreed...mine took a beating with harsh chemicals before I was able to peel it.
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Old 05-08-2006, 08:04 PM   #7
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I just took the belt off and there is ZERO play in the coupler. I rocked the pulley back and forth a tiny tiny bit to feel any play, then tried rocking it quickly from side to side, and, still no play. I'm sure the noise isn't a coupler.
It also spun relativly smoothly and easily, so I'm pretty sure that it couldn't be a binding issue with the rotors caused by worn bearings.

I also took the vacuum line off the top-side of the BCA and it snapped to full closed without a second thought. I've still got to scan the car with the vacuum line dissconected (maybe later tonight when traffic subsides)

I also checked all vacuum lines, and they were all ship-shape. The lines are all plactic slipped into rubber Ts, so I don't know how the plastic would break. The T under the nose drive on the LIM started to crack when I tried to pull it off, but it cracked after it went over the hump on the fitting, so I'll be OK for now (one more thing to add to the list)

I'm still stumped.
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Old 05-08-2006, 08:06 PM   #8
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We need to know if you get full boost on your scan with that vac line forcing the bypass closed.

This is why I strongly encourage any car without a boost gauge to install one. It'* often your first indication something is wrong.
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Old 05-08-2006, 09:10 PM   #9
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I just did a test drive. The BCA was full closed when I did it, and I'm still only seeing 36 inHg. It'd go 35.6, 36.2, 35.9, etc. and would hover around 36. It could just be a bad MAP, but it'* a 99 motor with a 99 MAP, so what are the chances of it failing? At idle, it reads the proper 9-10 inHg.

I don't know. I was really hoping it was a simple issue with the BCA staying open, but alas. Where has my boost gone and who'* stolen it?
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Old 05-08-2006, 10:53 PM   #10
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According to my calculations, 36 inches of mercury is 17.68155psi.

I'd like to know how big that turbo is.

Can you check your math please?
I strongly suggest piping in an aftermarket boost gauge. Instructions are in Techinfo.
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