[17txcamaross]

I am having some trouble with my LT1 to LT4 swap build and hoping someone may have some insight. I have been posting under IAT Logs in order to correct the heat issue I was having. I have figured out that the heat is due to the bypass valve not being operational, but now have questions on why my bypass valve is no longer operational.

First, a description of the build: LT4 blower (blower base PCV welded shut), 2.3 upper pulley, Rotofab intake and ported stock TB. Also have headers/xpipe which I don't think would have any effect.

I recently purchased new and replaced my supercharger bypass valve as it was not operating correctly to allow for the bypass valve to open at idle and cruising speeds when the system should be under vacuum and not compressing air. Since replacing the valve it is still not operational and under further inspection both PCV lines going from the blower to the bypass valve diaphragm have suction/vacuum on them at idle. If I remove the line going to the electronic solenoid the bypass valve opens, but immediately upon reconnecting the valve closes.

From my understanding this valve should be open at idle and cruise allowing the blower to run cooler and allow for better MPGs. I have double and triple checked that the PCV lines are all correctly run and cannot hear any vacuum leaks with the naked ear when the engine is running.

Would having the blower base welded shut have any effect on bypass valve operation? This weld was used instead of replacing the valleycover PCV on the front with a plug. I believe the valley cover still has the stock PCV in it and is possibly venting directly into the engine bay.

Thanks for your help...again.

[XXX ZL1]

Your lt1 doesnt have the electronics for bypass and without power the valve is open. Only make about 4 lbs in this situation assuming stock pulley. Just bypass the bypass.

[17txcamaross]

Originally Posted by XXX ZL1

Your lt1 doesnt have the electronics for bypass and without power the valve is open. Only make about 4 lbs in this situation assuming stock pulley. Just bypass the bypass.

Thanks for the reply. I understand that the LT1 does not have the electronics for the PCM to force the valve open, however, the bypass valve should still function based on vacuum from my understanding. Right now the valve is stuck shut (essentially bypassing the bypass). This is a problem as the bypass being open at idle and cruising speeds allows for the blower to stay cooler and the engine to get better MPG.

I also know this valve should operate properly off of vacuum after watching the ADM Performance dyno video on their LT1 to LT4 conversion. You can see in the video that the bypass is open at idle and closes as they go WOT. It then reopens once off the throttle. A link to that video is below.

[17txcamaross]

I should also add that even removing the solenoid and putting the PCV lines direct from the blower to the diaphragm has the same results...so this does not have anything to do with running through the electronic solenoid.

[BMWM.D.]

So just to clarify: you do or do not have the electric control solenoid from the ZL1? I’m guessing not, as I don’t see how it would be controlled. But your prior posts are a little confusing on this.

Without bringing home my vacuum pump and doing some testing (or knowing exactly where both ports on the blower go) I can’t be totally sure, though I think I know what your problem is:

The bypass valve solenoid is sprung closed. So it’s closed when the engine is off or at WOT (no vacuum). At idle and cruise, high manifold vacuum should pull it open. A normal bypass valve is very simple in operation. Now, the dual ports on the LT4 bypass valve are your issue, IMO. They are located on different sides of the diaphragm. This is so it can be controlled via the electric valve. Vacuum applied to both sides (like your car) is going to result in zero vacuum effectively being applied to the diaphragm. Logic says you are only going to want a line connected to the rear fitting on the bypass. The other should be plugged.

If you are running an electronically controlled vacuum valve for the bypass, then we need more info on that.

[17txcamaross]

Originally Posted by BMWM.D.

So just to clarify: you do or do not have the electric control solenoid from the ZL1? I’m guessing not, as I don’t see how it would be controlled. But your prior posts are a little confusing on this.

Without bringing home my vacuum pump and doing some testing (or knowing exactly where both ports on the blower go) I can’t be totally sure, though I think I know what your problem is:

The bypass valve solenoid is sprung closed. So it’s closed when the engine is off or at WOT (no vacuum). At idle and cruise, high manifold vacuum should pull it open. A normal bypass valve is very simple in operation. Now, the dual ports on the LT4 bypass valve are your issue, IMO. They are located on different sides of the diaphragm. This is so it can be controlled via the electric valve. Vacuum applied to both sides (like your car) is going to result in zero vacuum effectively being applied to the diaphragm. Logic says you are only going to want a line connected to the rear fitting on the bypass. The other should be plugged.

If you are running an electronically controlled vacuum valve for the bypass, then we need more info on that.

Thanks for the response again. This was the next thing I planned on trying. It sounds completely logical that if the electronic solenoid was powered that it could block itself off and allow for vacuum to be applied to the back side of the diaphragm. Then the PCM could electronically control how quickly the valve closed under acceleration and effectively open the bypass under whatever predetermined circumstances GM programs.

As for the electronic solenoid...I do have the part on the car, but it is not wired and as such doesn't do anything. If plugging that port on the diaphragm and the blower solves this issue then I will have an electronic solenoid for sale along with the vacuum lines.

[EDFHOBBIES]

Can you just replace the actuator with an aftermarket 1 then adjust rod for throw? Looks like the aftermarket ones are integrated.

My solenoid was a pain to mount when I upgraded to the 2650.

Wifes SS 1 vacuum line actuator 1st pic
My 2 line 2650 actuator 2nd pic
Solenoid from my Zl1 to run the actuator

BTW what did you do with the hole on the bottom of the blower? Run a LT4 valley cover or plug?

If you plugged it where did you get it I need to plug mine so when I sale it or I need a new seal I had to reuse my seal so just popped it out..


You took care of this correct?

[BMWM.D.]

Originally Posted by 17txcamaross

Thanks for the response again. This was the next thing I planned on trying. It sounds completely logical that if the electronic solenoid was powered that it could block itself off and allow for vacuum to be applied to the back side of the diaphragm. Then the PCM could electronically control how quickly the valve closed under acceleration and effectively open the bypass under whatever predetermined circumstances GM programs.

As for the electronic solenoid...I do have the part on the car, but it is not wired and as such doesn't do anything. If plugging that port on the diaphragm and the blower solves this issue then I will have an electronic solenoid for sale along with the vacuum lines.

This is 100% your problem. The GM tech literature mentions that the electric valve is commanded at 99-100% duty cycle during normal driving. This closes the electric valve (i.e. no vacuum), and lets the bypass be controlled by natural manifold vacuum. So your valve being installed in a non-powered state is not good. Get rid of it. It is actually doing something by default, as it’s sprung open.

[17txcamaross]

Thanks everyone! Problem solved!

For those with an LT1 to LT4 swap during install you CANNOT install all vacuum lines to the bypass valve diaphragm assembly. As BMW noted above you must install only the rear vacuum line and plug the other line.

[EDFHOBBIES]

Glad u got it going did you buy a lt4 valley cover or plug lowers pcv hole?

[17txcamaross]

Originally Posted by EDFHOBBIES

Glad u got it going did you buy a lt4 valley cover or plug lowers pcv hole?

I have the LT4 valley cover, but the second blower I got has the lower PCV blocked off on the blower case. I then removed the nipple on the valley cover.

[BlueCamaro6]

I know this is an old post, but it has wrong information about the vacuumm solenoid for the bypass valve. I have all the stock lines hooked up to mine and have for over 20k miles without an issue. I wired the solenoid to the ecm when I did the install and it works great. Did this when I wired IAT2 in as well.

[Eldi Z]

Originally Posted by BlueCamaro6

I know this is an old post, but it has wrong information about the vacuumm solenoid for the bypass valve. I have all the stock lines hooked up to mine and have for over 20k miles without an issue. I wired the solenoid to the ecm when I did the install and it works great. Did this when I wired IAT2 in as well.

Old post indeed and raising it back again.
Can you describe how you wired the solenoid for the bypass valve to the ECM? I.E. which wire / pin at the ECM did you tap into (or did you even have to go into the ECMs loom and locate a specific wire)?
Same question about the IAT #2...

[biker2k]

Originally Posted by BlueCamaro6

I know this is an old post, but it has wrong information about the vacuumm solenoid for the bypass valve. I have all the stock lines hooked up to mine and have for over 20k miles without an issue. I wired the solenoid to the ecm when I did the install and it works great. Did this when I wired IAT2 in as well.

I have an eforce 2300 and am trying to figure out if there is a way to make the lt4 bypass work on my setup. my vacuum bypass is too much like a switch and I wonder if the electronically controlled lt4 setup would work better, if so how would I make it work....