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Discussion Starter · #1 ·
Hey all,

I have a 98 GS with a GenV supercharger and intake upgrade that was running great for a while, but now seems to Only be maxing out at 3psi boost. It used to intermittently do this once in a while but would correct itself and then it became more often and would only correct itself once in a blue moon... now it never corrects itself and stuck at 3psi. Fuel mileage is pretty brutal. I did notice the boost bypass valve under idle conditions is stuck down (no bypass) where it used to be up (bypass) and I think that the actuator is not functioning properly. I replaced it with another one and seems to have the same issue. I think it may be in the wiring. If I unplug the BBV (Haha as a side note my phone changed BBV into BBC autocorrect... Definitely not BBC Lol) there is no difference in the way the car runs or the way the valve acts at idle. If I spike the throttle the valve stays down for the split second that it is raving up but as the throttle is released it swings up slightly then slowly rests back down. From what I used to remember it would rest in the up position and when you would spike the throttle it would spike the valve down and then return to up position. Is this correct? I am gonna try once more changing out the actuator and if that doesn't work looks like I am gonna be tracing some wiring short somewhere. Hopefully it will just be the connector and not some obscure place deep in the harness. Is there any other place somewhere that could be causing this issue? I get an occasional bank 2 fuel lean error code (from what I remember) and my long term fuel trims are quite high around 16-18% constantly but the short term is seeming to be normal. Especially at idle long term fuel is high.

Am I right thinking it is the BBV? Or could it be something else causing this?
 

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You should remove the solenoid and disable DTC P0234, I believe it is (only for traction control/torque management, etc. purposes that have plenty of other help from other systems), and the only vacuum line left connected should be the one running to the tree on top of the M90, with lower one open to air. This is how most people have typically setup their upgraded S/C with this type of bypass.

You may also want to look over everything you've personally worked on, and see if there's vacuum leaks. They would have to be huge to cause 75% of your boost to bleed off, so that's more likely bypass operations. I can go in my garage and take photos of my spare GenV with the bypass and it's blade in different spots, but I'm pretty sure a Google search can get you that quicker.
 

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Discussion Starter · #3 ·
Thanks for the reply. The thing is it was working fine for a long time. Then this condition became intermittent... now its progressively gotten worse to the point it is now permanent. So something must have given out.

...and I just figured it out. It was the actuator. I put on a third spare I had sitting around and instantly the valve went full bypass. Now it works properly and I'm getting around 7-8psi. Hope I get some gas mileage back too. I just went thru a full tank of gas in 100 miles...

But tell me more about that mod you were talking about. Do what to what for how many green jellybeans??? So what vacuum lines do i need to connect to What? I will take few pics with my potato of a camera on my phone later today... I will show you what I got connected to where.
 

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Basically, run it like this (without the M90 cut-away... or do that, too, for science):

11096
 

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Discussion Starter · #5 ·
Ok well... this is what I gots... sorry for the Crappy pics n stuff but I hope you understand what I did...
11110


So this is how the vacuum lines are connected. The three split off the top of the supercharger goes big one to the connector at firewall. One little one goes to the top of the bypass plunger then to the actuator then the other side of the actuator to the t on the top of the fuel pressure regulator. The other small one goes all the way around the back of the engine bay towards the passenger side then follows along the passenger side of the engine bay to:
11111

A t piece that has a check valve with the bottom connector to a line that goes into the main wire harness looming in through the firewall into the cabin. The line that is towards the front of the engine bay goes all the way to the vacuum canister.

11112

The line circled in green is a line connected to the side and plugged off. Then this big vacuum line outlined in red goes from the bottom of the throttle body adapter plate to:
11113

This connection on the back of the supercharger. Also note the other connection to the left of the red outline.
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Here's where it goes from the back of the actuator to a T piece that goes to the top of the fuel pressure regulator and then to the next T piece that goes to the intake and:
11115

Around the back to the MAP sensor. Note the line at the top of the pic. This is the one that goes to the passenger side I mentioned earlier.

So is this as clear as pea soup to you? Is it correct? Anything I should change? Can you explain which connections I need to change to do what you're talking about?
 

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Yep. The top tree connects to the boost bypass top, the brake booster, and the center one takes a long path to the HVAC system under the glove box to help control the vents.

The line running around under the s/c snout is getting a reference from the end of the lower intake, which supplies this to the MAP in the back, then fuel pressure regulator and solenoid under the boost bypass on the front.

The line running to the fuel regulator would end there with an elbow, and everything going on at the bottom of the boost bypass would be removed to make it look like the one in my previous post. If you're not familiar enough to do this, then leave it be.

The line coming up vertically from the GenV behind the TB is PCV, which runs to the TB to access a port that opens just ahead of the blade.

Someone did a little work to get things connected after a GenV swap, so it "should" work fine, but needs a scan and some physical checks to see what's going on.
 

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Discussion Starter · #7 ·
That's all me. I did the swap and know just enough about the setup to be dangerous lol. I will give what you said a try and see how it goes. I run only 94 octane gas so knock isn't usually an issue. At least not at these boost levels. I seem to only get a maximum of like 7-8 psi of boost no matter what. The torque app shows about 2psi less than the boost reading off of the dash. You would think that since both of them more than likely get the readings from the same sensor should show the same readings but whatever. I'm just not sure which one to believe more.

Fast forward to now... (forgot to post this reply)
So I did the mod that you suggested. I think i picked up an extra psi or 2. Butt dyno seems faster and the stock boost display shows a high of like 9ish psi. Couldn't log or verify with torque because stupid me left my Bluetooth dongle in my buddy's car the other day and haven't got it back yet. However like I said seems faster for sure. I am gonna log a 0-60 pull and see what the actual difference is between the two configurations. I also checked my spark plugs and wires and one of the connections at the plug (back passenger side) I believe had a bad connection there so I fixed that with a new plug wire.
 

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Good luck, hope all is well.

Not sure how accurate the Regal displays are, as I've only used for some random occasions, while the turbo setup goes past it up top. Torque should be a good direct reading of the MAP, just converting the kPa value above 0psi atmosphere (100kPa) as it goes from -1bar/0kPa to +1bar/200kPa (+14.5 psi).
 
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