Transition From Vacuum to Boost
Transition From Vacuum to Boost
Suxks. If I give the car partial throttle, it bucks and kicks now. It never did this until I cleaned up the ECU codes and now I have more problems. If I give it hard gas, it hesitates, pops, then boosts fine. If I tootle around off boost, the car is fine. If I want to pass someone, it gives me crap. Any ideas? I have checked the vacuum lines several times, but nothing seems wrong. COuld it be spark plugs?
.-
KaZ (VaBch)
- Posts: 418
- Joined: Tue Dec 02, 2003 10:34 am
A pressure tester is your friend...
You need a pressure valve, with male/female ends on each side, that you hook to a correctly sized PVC fitting, and put it in the intake hose where the MAF would be. You then hook the other side of the pressure valve to an Air Compressor and adjust the pressure valve to 10 PSI and listen for leaks... Works great.
I put a TTZ together for a guy that was running barely 6psi of boost (should have been more). Hooked up the pressure tester and found all sorts of leaks (hoses that had cracked on install, but that I couldn't see, clamps that were loose etc). Also if you're having trouble finding the leak, get something soapy, like windex or something, and spray around the questionable area and look for bubbles... works great.
What's required:
- PVC fitting correctly sized for your intake where the MAF connects (turbo side, not the intake side).- Adjustable air line pressure valve w/ pressure gauge (any gauge will work fine, you won't be going past 10psi with this setup anyway).- Male and Female air line adapters. You'll need the female end on the air compressor side, and the male end on the fitting side (or if you wanted to put a male fitting into the PVC fitting, put two females on the pressure valve, just make sure you hook it up in the right direction).- Air Compressor (anything will do, but holding constant 10psi will cause a average sized movable tank to RUN to keep the pressure up).
I've got this thing (5 Peak HP, 17 Gallon Husky Compressor creates 5.1 SCFM @ 90 psi. The compressor has a max pressure of 150 PSI and is perfect for the DIY'er) and at 8-10psi, I'll go from 120psi down to 60psi in a matter of minutes... and when the compressor kicks back on, its harder to hear the leaks. Thankfully I had a LONG hose setup, so I had the compressor around in front of the car I had sitting in front of the car I was working on (blocked some of the noise).
I can take some photos of my setup tonight for anyone interested.
Later,
You need a pressure valve, with male/female ends on each side, that you hook to a correctly sized PVC fitting, and put it in the intake hose where the MAF would be. You then hook the other side of the pressure valve to an Air Compressor and adjust the pressure valve to 10 PSI and listen for leaks... Works great.
I put a TTZ together for a guy that was running barely 6psi of boost (should have been more). Hooked up the pressure tester and found all sorts of leaks (hoses that had cracked on install, but that I couldn't see, clamps that were loose etc). Also if you're having trouble finding the leak, get something soapy, like windex or something, and spray around the questionable area and look for bubbles... works great.
What's required:
- PVC fitting correctly sized for your intake where the MAF connects (turbo side, not the intake side).- Adjustable air line pressure valve w/ pressure gauge (any gauge will work fine, you won't be going past 10psi with this setup anyway).- Male and Female air line adapters. You'll need the female end on the air compressor side, and the male end on the fitting side (or if you wanted to put a male fitting into the PVC fitting, put two females on the pressure valve, just make sure you hook it up in the right direction).- Air Compressor (anything will do, but holding constant 10psi will cause a average sized movable tank to RUN to keep the pressure up).
I've got this thing (5 Peak HP, 17 Gallon Husky Compressor creates 5.1 SCFM @ 90 psi. The compressor has a max pressure of 150 PSI and is perfect for the DIY'er) and at 8-10psi, I'll go from 120psi down to 60psi in a matter of minutes... and when the compressor kicks back on, its harder to hear the leaks. Thankfully I had a LONG hose setup, so I had the compressor around in front of the car I had sitting in front of the car I was working on (blocked some of the noise).
I can take some photos of my setup tonight for anyone interested.
Later,
-
KaZ (VaBch)
- Posts: 418
- Joined: Tue Dec 02, 2003 10:34 am
That definitely sounds like a leak...
Basically, a vacuum leak is a boost leak, and a boost leak is a vacuum leak. Just the direction of the air flow based on the speed of the turbine... =) They're one and the same on a turbocharged car. If it leaks vacuum at a vacuum state, it will leak boost at a boost state.
The fact that its worse when cold states its probably a hose, as its a lose seal when cold, and when hoses heat up they expand and normally seal better.
Boost won't necessarily stay "low" but it will be lower than it should.
Say your wastegate is set to 9psi... well if you have a minor leak, say a pound or so... the wastegate still won't open until it SEES 9psi... so... with a 1lb leak, the turbo may actually be producing in excess of 10psi, but the engine/gauge never sees that due to the leak. It can be hard to describe, but the way the vacuum actuated wastegates work is they stay closed under spring tension until the pressure being given to the wastegate via the vacuum lines exceeds the spring tension. So if you have a leak somewhere, the boost won't exceed the spring tension at normal levels... so the turbo will continue to create MORE boost as its not releasing the excess exhaust pressure through the wastegate to slow it down.
Hope that made sense... Definitely check it. A leak is bad for performance, bad for fuel economy, and can be bad for the motor (lean moments can develop because fuel pressure is based off vacuum/boost levels as well). =(
Later,
Basically, a vacuum leak is a boost leak, and a boost leak is a vacuum leak. Just the direction of the air flow based on the speed of the turbine... =) They're one and the same on a turbocharged car. If it leaks vacuum at a vacuum state, it will leak boost at a boost state.
The fact that its worse when cold states its probably a hose, as its a lose seal when cold, and when hoses heat up they expand and normally seal better.
Boost won't necessarily stay "low" but it will be lower than it should.
Say your wastegate is set to 9psi... well if you have a minor leak, say a pound or so... the wastegate still won't open until it SEES 9psi... so... with a 1lb leak, the turbo may actually be producing in excess of 10psi, but the engine/gauge never sees that due to the leak. It can be hard to describe, but the way the vacuum actuated wastegates work is they stay closed under spring tension until the pressure being given to the wastegate via the vacuum lines exceeds the spring tension. So if you have a leak somewhere, the boost won't exceed the spring tension at normal levels... so the turbo will continue to create MORE boost as its not releasing the excess exhaust pressure through the wastegate to slow it down.
Hope that made sense... Definitely check it. A leak is bad for performance, bad for fuel economy, and can be bad for the motor (lean moments can develop because fuel pressure is based off vacuum/boost levels as well). =(
Later,
-
float_6969
- Moderator
- Posts: 17366
- Joined: Mon Aug 26, 2002 1:55 pm
- Car: CA18DET swapped 1995 Nissan 240sx (too many mods to list)
2015 SV Leaf w/QC & Bose (daily) - Location: Topeka, Kansas
- Contact:
-
KaZ (VaBch)
- Posts: 418
- Joined: Tue Dec 02, 2003 10:34 am
My friend tried a similar setup... problems with that are:
#1, there is no way to "regulate" the pressure. Yeah you can get it to 10psi, but then you disconnect... But that would be very easy to "over pressurize" and also leads to problem #2
#2, if you have a BAD leak, you're not going to be able to keep pressure up... You'll barely get it to 10PSI and it will leak right out. We tried that setup on my buddy's Supercharged M3. It wouldn't hold pressure for 2 seconds... Couldn't begin to find the leak without hearing the "hiss" of the air going through the tire fitting.
Now when we hooked it up like the setup I described above... it will hold air, and its MUCH quieter... you barely hear anything other than the leak. I'll take pictures tonight and post them.
Later,
#1, there is no way to "regulate" the pressure. Yeah you can get it to 10psi, but then you disconnect... But that would be very easy to "over pressurize" and also leads to problem #2
#2, if you have a BAD leak, you're not going to be able to keep pressure up... You'll barely get it to 10PSI and it will leak right out. We tried that setup on my buddy's Supercharged M3. It wouldn't hold pressure for 2 seconds... Couldn't begin to find the leak without hearing the "hiss" of the air going through the tire fitting.
Now when we hooked it up like the setup I described above... it will hold air, and its MUCH quieter... you barely hear anything other than the leak. I'll take pictures tonight and post them.
Later,
Could someone post pics of all the vac ports off the plunum? I have removed everything but the PCV (everything runs off that now) and the line on the passengers side that I have routed to wastegate. I am wondering if we forgot to cap something...
Also, I am seeing 20in. Hg on my boost gauge at idle and when deceleratng with the throttle closed I see about 22in. Hg
Also, I am seeing 20in. Hg on my boost gauge at idle and when deceleratng with the throttle closed I see about 22in. Hg
Yeah, if you have throttle off, but in gear declerating it puts more vacuum on it because the engine its doing work to match the car but your not putting any throttle in. But, i went through this yesterday to get the car to run smooth, all i did was go over the ENTIRE plenum and follow every line and check for leaks. I eventualy found my whole leak problem to be the throttle body gasket to plenum.
-
KaZ (VaBch)
- Posts: 418
- Joined: Tue Dec 02, 2003 10:34 am
20 in vacuum is the norm for Nissans. My Z would read ~17-19 in of vacuum at idle, and up to ~23 in during in gear deceleration. But every car is different. Also, you boost gauge may not be 100% accurate. Does it zero out when its off? Some don't zero completely... they kinda sit near 1 to begin with...
Ahh, I'll definitely give yours a goKaZ (VaBch) wrote:My friend tried a similar setup... problems with that are:
#1, there is no way to "regulate" the pressure. Yeah you can get it to 10psi, but then you disconnect... But that would be very easy to "over pressurize" and also leads to problem #2
#2, if you have a BAD leak, you're not going to be able to keep pressure up... You'll barely get it to 10PSI and it will leak right out. We tried that setup on my buddy's Supercharged M3. It wouldn't hold pressure for 2 seconds... Couldn't begin to find the leak without hearing the "hiss" of the air going through the tire fitting.
Now when we hooked it up like the setup I described above... it will hold air, and its MUCH quieter... you barely hear anything other than the leak. I'll take pictures tonight and post them.
Later,
and smoke likes crazy... im just gonna wait for my 2 good intercooler couplings.-
KaZ (VaBch)
- Posts: 418
- Joined: Tue Dec 02, 2003 10:34 am
I was trying to get my S12 to run right last night... didn't get a photo of my pressure tester setup, sorry.
Basically, at the moment I've got a bad backfire if i let it decelerate in gear (as soon as I pull it out of gear to shift after decelerating in gear, it pop backfires) and the idle is hunting, the Wideband O2 reading bounces from 13 to 17 and back and forth constantly and you can audibly hear the hunting...
Had to pull out my DET fuel rail as it would not fit at all on the ET manifold setup. It was off like 1mm in stagger for the injector locations and cause me to blow the upper Oring on #1 (I blew #4 previously, then blew #1 last night spraying fuel all over the front of the motor). I went and put the CA20E non turbocharged rail back in that I had before. She ran fine with the 450cc injectors I had in it before, but now with the 370cc injectors, it seems to run worse... argh. I'll pressure test it tongiht and see what I find... =(
Later,
Basically, at the moment I've got a bad backfire if i let it decelerate in gear (as soon as I pull it out of gear to shift after decelerating in gear, it pop backfires) and the idle is hunting, the Wideband O2 reading bounces from 13 to 17 and back and forth constantly and you can audibly hear the hunting...
Had to pull out my DET fuel rail as it would not fit at all on the ET manifold setup. It was off like 1mm in stagger for the injector locations and cause me to blow the upper Oring on #1 (I blew #4 previously, then blew #1 last night spraying fuel all over the front of the motor). I went and put the CA20E non turbocharged rail back in that I had before. She ran fine with the 450cc injectors I had in it before, but now with the 370cc injectors, it seems to run worse... argh. I'll pressure test it tongiht and see what I find... =(
Later,