What criteria activates bypass valve solenoid?

**J57ltr** · 04-11-2015

Well pretty much what the title says. Under what conditions force the solenoid to keep the bypass open? I keep having an issue where if the car does go into boost (05'GTP) then the pressure will drop back to 0. Even downshifting it will not go into boost for less than a second. I have noticed that sometimes I will ease into it and see 2-3 psi then I'll push it a little more and get it to 7-8, then it just drops to 0 and I can slow and punch it and it runs like it's NA and the gauge won't go past 0.

Thanks.

Jeff

**industrialfish** · 04-11-2015

Sounds like you have a cracked vac line blowing out when it goes from vacuum to boost.

**J57ltr** · 04-11-2015

I think you are right, but I also have something else going on. I bypassed the solenoid and damn near killed the engine, caused the engine to go to reduced power and traction control. Never got into boost and even cut all throttle control. It also gave me a P0068 and I got a data freeze of the info shut the car off reconnected everything started it back up and drove home. I also went up a pulley size before this.

Jeff

**industrialfish** · 04-11-2015

That's caused by a leak/open line going from the snout T to the bypass. To bypass the solenoid you have to unplug it and cap the line going into it from the passenger side.

**J57ltr** · 04-11-2015

You're talking about the line that runs from the solenoid to the bypass? I took the line that tees under the snout to the solenoid and attached it to the bypass valve.

i covered all the other vacuum lines I did here:
http://www.grandprixforums.net/threa...kicking-my-xxx!

I just replaced the line going from the bypass solenoid to the bypass valve and go the same result.

Jeff

would having the data help?

**industrialfish** · 04-11-2015

Make sure the line coming off the T has no cracks in it on both lines coming off the T. I believe the other half of the T goes into the Boost Gauge sensor on the firewall which all become pressurized under boost but are pulling a vacuum when not under boost.

**industrialfish** · 04-11-2015

Take the skinny line that runs from the snout T and disconnect it from the solenoid, and plug the line. Unplug the electrical connector from the solenoid (optional). Leave everything else alone.

The bypass is only activated by TCS, ABS, and Reverse, not much else.

**J57ltr** · 04-11-2015

What about this 0068 and shutting throttle control from me?

Jeff

**J57ltr** · 04-11-2015

Disconnected as you said, still no change. No boost.

**Turbocharged400sbc** · 04-11-2015

as these cars get to over 120k ive come across several that carbon buildup has prevented the bbv flap from closing/rotating.

ive also seen the lines run improperly for the dual MAP cars which would also give the appearance of low/no boost but may well be boosting

**J57ltr** · 04-11-2015

On the gen V did they finally used sealed ball bearings are they still bushings?

I had thought about reversed sensor cables, but my MAP and BAro readings would be swapped on my scanner.

Jeff

**Turbocharged400sbc** · 04-11-2015

bushings. most seizing ive come across has been after a spray can or lube joint "cleaning" that disolves the carbon and it rinses down into the shaft area's and the solvent evaporates leaving carbon where it normally wouldnt be

**J57ltr** · 04-11-2015

Well I cleaned the TB off the car and didn't worry about the inside of the blower. I thought that the TB was sticking.

i have noticed if the engine is at idle and I force the valve closed it doesn't pop back easily. If I goose it it will open again.

what are the suggestions for cleaning the bypass?

**Turbocharged400sbc** · 04-11-2015

pull the blower off, scrape the carbon off, and use a solvent/brake cleaner/gas soaked rag to wipe out the assembly and use a brake cleaner can with a straw to flush out the sides of the shaft while working it open/closed. with the blower set/propped on a bench with the tb side down and the pulley straight up youll keep all the crap flowing out towards the TB flange and onto the bench. hang it from a ladder over a bucket/garbage can even. (make sure to remove your evap solenoid on gen5's (do this before removing blower/etc as the evap hose snout is easily broken off, exceedingly common and quite annoying as your not likely to find an intact one in the junkyard.))

then just wipe out the inlet side and i toss a few drops of sc oil on the shaft to help lubricate and displace any future carbon buildup (plus you always have a couple drops in the bottom of those damn gm oil bottles, might as well use it)

**J57ltr** · 04-12-2015

Ok, maybe I'll just wire it shut and see if I can build any boost. The last time I saw a blower without boost the snout shaft failed at the splined end that drives the coupler. Need to check the fluid as well. Do you guys us a gasket or rtv? There's 1 05+gtp in the
junkyard I probably should pull.

thanks for the tips.

Jeff

**Booba5185** · 04-12-2015

I've never seen or heard of that on an M90. The coupler would go first, like it's designed to. I think there's a vacuum leak somewhere, these are some pretty odd ball situations you are hunting down now. You can move the BBV by hand to see if it's moving or watch it while the car is running to see if it'll move. If it moves it's not your problem. It's possible the BBV isn't sealing completely but that would cause NO boost, it'd cause low boost.

If you end up pulling the supercharger off, then I'd use RTV to seal it to the LIM again. I don't any reason to replace the supercharger though...at all. If the oil leaked out it'd stink to high heaven, be dirty as hell, and the heat would destroy the coupler at minimum. If the oil leaked out it's be possible that the snout would lock up, and the belt would squeal really bad since the pulley would no longer turn.

**J57ltr** · 04-12-2015

Well, I've seen a lot of things happen to M90's I've been playing with them since they were freshly installed on GM engines. I'll have to see if I can dig up some carnage photos. Basically we had a couple of people that had that happen where the coupler drive is splined onto the shaft and it failed at that point. You could spin the blower by hand and it didn't make any noise like there was a problem. When you spun it with the belt it would sound weak and not make boost. It might have made noise, but the OP never said and it wasn't until he switched blowers and removed the snout and found it. Another thing is since we had intercoolers we had a lot higher drive ratios so we spun the blowers much faster than the GM crew did our "10%" pulley was 2.85" and stock our boost levels were 12-13psi and we had to deal with Gen 3 M90's and didn't get the Gen 4 until 94'.

The BBV moves, so what would cause a no boost situation?

i know I'm not leaking SC oil, but I do need to check the level anyway

Thanks,

Jeff

**Booba5185** · 04-12-2015

Have you tried a smoke test for vacuum leaks? A cheap way is to pull the brake booster hose with the check valve still attached, and put a clean hose on the check valve. Then pull the air intake tube off of the throttle body and put a latex glove over the throttle body, sealing it off. Spark up whatever smoking device you see fit (cigar, cigarette, etc.) and blow it into the clean hose. After 4 or 5 puffs, you'll see smoke coming from somewhere if there is a leak.

Another possibility is your MAP sensor, it could be reading incorrectly and not picking up the boost. Rare, but possible.

**J57ltr** · 04-12-2015

Well I have done the propane torch test using an unlit propane torch and a small bit of hose to Go around all the fittings to see if there is a vacuum leak.

also this is a mechanical gauge I am reading, but it follows the MAP

Jeff

**J57ltr** · 04-12-2015

Here is one instance that I could remember. Hopefully by now it's no longer an aluminum hub.

[COLOR=rgba(0, 0, 0, 0.701961)]http://www.sccoa.com/forums/showthread.php?106201-Lost-boost-today[/COLOR][COLOR=rgba(0, 0, 0, 0.701961)]

Jeff

[/COLOR]