TVS, vac @ idle?

OX1

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I got my Roush Phs 3 and VMP tune in.
Thinking I might have a problem with the bypass
valve.

Upon startup, vac will be 10 in HG (and not waver even slightly).
After blipping the throttle, it goes to what I consider normal, 18-20
in HG (depending upon exact idle RPM, which settles a bit after first
startup).

This normal?
 

46addict

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You need to compare readings at the same rpm, because vac will drop with more throttle/rpm. If there was an issue with the BPV (stuck open or something), you would have issues building boost. BPV movement should not affect vacuum.
 

redfirepearlgt

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If the Bypass Valve was stuck (I HAD THAT PROBLEM ON A SALEEN TWIN SCREW BTW) you will have no issue with vacuum but will have ZERO, ZILCH, NODDA boost. That is if the BPV is stuck in the vacuum held position. On the other side if the vacuum hose is not hooked up and the bypass valve is failed closed (normal position with key off or WOT when properly working) boost will not be relieved properly when letting off the throttle which is not a good thing either over the long haul.

So again the BPV (short of a leak on the vacuum line feeding the device) has nothing to do with vacuum level and everything to do with boost only. Been there.......done that. In fact I still have one at the house.

On a Coyote 302, 15+ at idle with my tune and stock cams. At initial start vacuum is around 10" with the idle hovering around 1200 RPM until it decays and settles into normal idle after initial startup and going closed loop and reads 17" Hg.


Cams will also effect vacuum level at idle. For reference with Detroit Rocker cams my 2005 Saleen twin screw setup generated about 10-11" vacuum at idle after settling on cold start.
 
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OX1

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You need to compare readings at the same rpm, because vac will drop with more throttle/rpm. If there was an issue with the BPV (stuck open or something), you would have issues building boost. BPV movement should not affect vacuum.

If the Bypass Valve was stuck (I HAD THAT PROBLEM ON A SALEEN TWIN SCREW BTW) you will have no issue with vacuum but will have ZERO, ZILCH, NODDA boost. That is if the BPV is stuck in the vacuum held position. On the other side if the vacuum hose is not hooked up and the bypass valve is failed closed (normal position with key off or WOT when properly working) boost will not be relieved properly when letting off the throttle which is not a good thing either over the long haul.

So again the BPV (short of a leak on the vacuum line feeding the device) has nothing to do with vacuum level and everything to do with boost only. Been there.......done that. In fact I still have one at the house.

On a Coyote 302, 15+ at idle with my tune and stock cams. At initial start vacuum is around 10" with the idle hovering around 1200 RPM until it decays and settles into normal idle after initial startup and going closed loop and reads 17" Hg.


Cams will also effect vacuum level at idle. For reference with Detroit Rocker cams my 2005 Saleen twin screw setup generated about 10-11" vacuum at idle after settling on cold start.

Funny you mention that. The first time I drove it, it had almost no more power than stock. Could barely spin a tire. Went home and put in a vac/boost guage in the next day. Took it out for a drive and it instantly hit 10 PSI and spun the tires until I backed out of it.

My thought is, it was stuck completely open at first, and now sticks (partially closed maybe) only @ initial start up until I blip throttle and create boost for just a second. Roush's suggestion was to go drive the crap out of it and see if it frees up. Never had a vac/boost on a NA coyote, so not sure what it did stock.

I'll try it again and just let the idle settle on it's own and engine warm up without driving anywhere, see if the vac climbs (increases) to normal levels.

A/F seems right, about 14.6 @ idle and mid-high 11's under boost.
 

46addict

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If it's a spring loaded BPV like the ones I'm thinking of, you may want to see if it shuts completely on its own when the engine is off. Some valves allow you to adjust spring tension to fix issues like this.
 

redfirepearlgt

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If it's a spring loaded BPV like the ones I'm thinking of, you may want to see if it shuts completely on its own when the engine is off. Some valves allow you to adjust spring tension to fix issues like this.

It's not adjustable.
 
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redfirepearlgt

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Funny you mention that. The first time I drove it, it had almost no more power than stock. Could barely spin a tire. Went home and put in a vac/boost guage in the next day. Took it out for a drive and it instantly hit 10 PSI and spun the tires until I backed out of it.

My thought is, it was stuck completely open at first, and now sticks (partially closed maybe) only @ initial start up until I blip throttle and create boost for just a second. Roush's suggestion was to go drive the crap out of it and see if it frees up. Never had a vac/boost on a NA coyote, so not sure what it did stock.

I'll try it again and just let the idle settle on it's own and engine warm up without driving anywhere, see if the vac climbs (increases) to normal levels.

A/F seems right, about 14.6 @ idle and mid-high 11's under boost.

11.4-11.6 is a happy spot for PD setups. Roush runs so rich they burn your eyes out at 11.0 WOT. One thing you don't have to worry about is the support with the VMP tune as long as you have data logged and done as they have asked you to do. Even at that I'd run their tune unverified before I'd waste my time with anything Roush calls a tune. It makes a number and that is about it.

If the BPV is sticking in such a manner that you don't make boost, first off you will def know it. Pull over, and shut off the car. Reach back behind the SC to get to the BPV and wiggle the actuator rod to see if it is sticking. It will snap closed if it is. From there if it is you will need to determine if it has to do with realigning the BPV so that the actuator and linkage attached to the BPV shaft aren't binding and make sure it isn't over stroking when it opens into bypass when vacuum is present.

Speak to VMP about tune concerns. They are great guys with much more to offer than Roush IMHO. Roush is overly proud of a mediocre product. If I had been better educated on VMP products when i made my purchase I would have gone VMP all the way. As it currently stands I run a VMP tune on this car as well as the previous, VMP triple pass HE, VMP BAP, and VMP recommended JLT 123 CAI. I hope to source a VMP GEN II housing and do that swap soon enough along with their recommended 56 # injectors to complete the metamorphosis.
 
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OX1

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11.4-11.6 is a happy spot for PD setups. Roush runs so rich they burn your eyes out at 11.0 WOT. One thing you don't have to worry about is the support with the VMP tune as long as you have data logged and done as they have asked you to do. Even at that I'd run their tune unverified before I'd waste my time with anything Roush calls a tune. It makes a number and that is about it.

If the BPV is sticking in such a manner that you don't make boost, first off you will def know it. Pull over, and shut off the car. Reach back behind the SC to get to the BPV and wiggle the actuator rod to see if it is sticking. It will snap closed if it is. From there if it is you will need to determine if it has to do with realigning the BPV so that the actuator and linkage attached to the BPV shaft aren't binding and make sure it isn't over stroking when it opens into bypass when vacuum is present.

Speak to VMP about tune concerns. They are great guys with much more to offer than Roush IMHO. Roush is overly proud of a mediocre product. If I had been better educated on VMP products when i made my purchase I would have gone VMP all the way. As it currently stands I run a VMP tune on this car as well as the previous, VMP triple pass HE, VMP BAP, and VMP recommended JLT 123 CAI. I hope to source a VMP GEN II housing and do that swap soon enough along with their recommended 56 # injectors to complete the metamorphosis.

Thanks for the info. I let it just idle from dead cold, to a stable idle. Fast idle seems much higher than I remember, but not ridiculous. Anyway, started @ 9 and made it's way to 18ish after idle settled down.

I wish I could get to that valve, but I don't see how. I can only even see it (barely) from the opposite side of intake/TB. Might hook a separate vac/boost guage into that line for valve and see what it is doing (or commanded to be doing anyway).

I picked Roush for only one reason. Possible visual emission inspection (I also bought the closed air box top if I ever need it). My plan was TT until NJ changed their emission inspection. If you fail @ state for any reason, you have to go to a shop for re-inspection. Figured my luck I'd fail for something fluky and then have to find a shop that would look the other way.
 

redfirepearlgt

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Thanks for the info. I let it just idle from dead cold, to a stable idle. Fast idle seems much higher than I remember, but not ridiculous. Anyway, started @ 9 and made it's way to 18ish after idle settled down.

I wish I could get to that valve, but I don't see how. I can only even see it (barely) from the opposite side of intake/TB. Might hook a separate vac/boost guage into that line for valve and see what it is doing (or commanded to be doing anyway).

I picked Roush for only one reason. Possible visual emission inspection (I also bought the closed air box top if I ever need it). My plan was TT until NJ changed their emission inspection. If you fail @ state for any reason, you have to go to a shop for re-inspection. Figured my luck I'd fail for something fluky and then have to find a shop that would look the other way.

Gotcha. Makes sense. Thankfully there are no hoops to jump through in my state. If that should happen I will simply register the car in my father's name (same as mine) in his state which has no emissions laws and keep it there during the winter months.

As for the BPV it is very simple. It is hold open (in bypass) with the presence of vacuum. When at static pressure or boost the BPV spring releases closed when boost is made. Let of the gas, engine is back in a vacuum state and the bypass valve opens releasing the excess buildup of pressure still in the manifold area. It does nothing else. In bypass the engine remains in vacuum state. You can probably use a mirror to look at the position of the actuator rod back there. I forget that it is tight where Roush put that thing. The Saleen was right out in broad view on the passenger side for access. Man that was a sweet, sweet little SC.

There are other concerns with regard to low boost other than a sticky bypass valve, but there really is no need to go into that unless you verify you actually find the car intermittently making low boost AND running rich @ WOT.

Last question. Have you properly data logged the car per VMP instructions and sent the logs back to Justin and the guys for review? If not do so. They will see trends if there are concerns with functionality and tell you to address them before they would make any tuning corrections if any would be needed.

Good luck.
 
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OX1

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There are other concerns with regard to low boost other than a sticky bypass valve, but there really is no need to go into that unless you verify you actually find the car intermittently making low boost AND running rich @ WOT.

Last question. Have you properly data logged the car per VMP instructions and sent the logs back to Justin and the guys for review? If not do so. They will see trends if there are concerns with functionality and tell you to address them before they would make any tuning corrections if any would be needed.

Good luck.

Boost seems fine now. I've only driven it twice and the second time I was easily getting 10 PSI (and I haven't taken it near redline yet) with the closed airbox (VMP said OK to run that for now if desired, it would just lower boost and HP slightly, but tune is OK with it).

Anyway, have not datalogged for Justin yet as I wanted to make sure this BPV was OK and car was sitting since fall. I wanted to burn up old gas before datalog. I asked for very conservative tune to start with. I'm now down below 1/4 tank, so I can get fresh gas and start to play. :smiley-face-popcorn
 
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