turbo boost 101 problems
12-31-2002, 02:08 PM
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Track Day
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turbo boost 101 problems
Hello porsche fans,
greetings, I just bought a "bargain" -yeah heh heh... 951 and am trying to get it on the road. Here's my dilemna, any suggestions would be great... I just put in a "new" used engine, as well as a "new" used turbocharger. Hooked everything up, started it, but there's no boost. I want to get this fixed before I take it off the jackstands. Here's what I've tested so far.... please help!!!!1.Wastegate...cold to touch after engine is warm. clamping off hose to wastegate does nothing. 2.Exhaust leaks...nothing that I can feel with my hands. feels like no warm air is leaking from around the manifolds when the engine is cold and running. It also has new exhaust ring seals. 3.boost gauge... reads 1 bar when the ignition is in the "run" position but the engine is off.. (atmospheric pressure) and quickly goes left down to ,4 bar when the engine starts (as the manifold develops vacuum). Also, disconnecting the banjo bolt to the turbo computer lets the gauge go back up to 1 bar, and then you can hear the vacuum sucking into the hose. 4.Blow off valve... new. taking off vacuum line on top makes no difference...5. turbocharger. (new to me) spins freely. I took off the intake "J" boot to it and started the engine and it only sputtered, but there was enough exhaust pressure to get the turbo spinning freely. There's no screwdriver or something stuck there.6.cat converter...my next project will be to disconnect the cat to make sure it isnt clogged.
But what else could it be??? If I unhook the TPS sensor while the car is running, it makes absolutely no difference in how the car runs (which is fine, except for no turbo pressure. The car runs like a 944 N/A). Should disconnecting the TPS make "no" difference in engine running, or is that messed up??? Also would that interfere with boost pressure? Does the computer have any other ways to cut boost other than triggering the cycling valve or cutting fuel? I stuck the car in gear and "spun" up the rear axle to 50 miles an hour to make sure the computer wasn't somehow cutting pressure because the car wasn't under load...but that wouldnt matter cause I had the wastegate line clamped off anyway. Anyway, any thoughts would be helpful. I'm about to pull my hair out. By the way, how in the heck do you bleed the clutch slave valve. I've tried it 12 ways to sunday and it wont bleed right on hold pressure. I thought I'd be clever and replace the slave cylinder since i was in there. what a mistake!
I am drowning in a sea of brake fluid....Advice would be great. Come by and fix it if you want. Come by and take it if things dont start gettin better quick!!!!
Sincerely, Ron
greetings, I just bought a "bargain" -yeah heh heh... 951 and am trying to get it on the road. Here's my dilemna, any suggestions would be great... I just put in a "new" used engine, as well as a "new" used turbocharger. Hooked everything up, started it, but there's no boost. I want to get this fixed before I take it off the jackstands. Here's what I've tested so far.... please help!!!!1.Wastegate...cold to touch after engine is warm. clamping off hose to wastegate does nothing. 2.Exhaust leaks...nothing that I can feel with my hands. feels like no warm air is leaking from around the manifolds when the engine is cold and running. It also has new exhaust ring seals. 3.boost gauge... reads 1 bar when the ignition is in the "run" position but the engine is off.. (atmospheric pressure) and quickly goes left down to ,4 bar when the engine starts (as the manifold develops vacuum). Also, disconnecting the banjo bolt to the turbo computer lets the gauge go back up to 1 bar, and then you can hear the vacuum sucking into the hose. 4.Blow off valve... new. taking off vacuum line on top makes no difference...5. turbocharger. (new to me) spins freely. I took off the intake "J" boot to it and started the engine and it only sputtered, but there was enough exhaust pressure to get the turbo spinning freely. There's no screwdriver or something stuck there.6.cat converter...my next project will be to disconnect the cat to make sure it isnt clogged.
But what else could it be??? If I unhook the TPS sensor while the car is running, it makes absolutely no difference in how the car runs (which is fine, except for no turbo pressure. The car runs like a 944 N/A). Should disconnecting the TPS make "no" difference in engine running, or is that messed up??? Also would that interfere with boost pressure? Does the computer have any other ways to cut boost other than triggering the cycling valve or cutting fuel? I stuck the car in gear and "spun" up the rear axle to 50 miles an hour to make sure the computer wasn't somehow cutting pressure because the car wasn't under load...but that wouldnt matter cause I had the wastegate line clamped off anyway. Anyway, any thoughts would be helpful. I'm about to pull my hair out. By the way, how in the heck do you bleed the clutch slave valve. I've tried it 12 ways to sunday and it wont bleed right on hold pressure. I thought I'd be clever and replace the slave cylinder since i was in there. what a mistake!
I am drowning in a sea of brake fluid....Advice would be great. Come by and fix it if you want. Come by and take it if things dont start gettin better quick!!!!
Sincerely, Ron
12-31-2002, 02:31 PM
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What about the "recycling valve" otherwise known as dump valve. If it is constantly open you will get these symptoms.
You must empty the brakefluid reservoir before you disconect the hydraulics on the clutch cylinders, if not you get all the brake fluid in your face.
Eirik Kvello-Aune
<a href="http://www.diateam.no/porsche" target="_blank">www.diateam.no/porsche</a>
You must empty the brakefluid reservoir before you disconect the hydraulics on the clutch cylinders, if not you get all the brake fluid in your face.
Eirik Kvello-Aune
<a href="http://www.diateam.no/porsche" target="_blank">www.diateam.no/porsche</a>
12-31-2002, 02:44 PM
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[quote] but there's no boost. I want to get this fixed before I take it off the jackstands. <hr></blockquote>
[quote] I stuck the car in gear and "spun" up the rear axle to 50 miles an hour to make sure the computer wasn't somehow cutting pressure because the car wasn't under load...but that wouldnt matter cause I had the wastegate line clamped off anyway. Anyway, any thoughts would be helpful. <hr></blockquote>
The car needs to be under a load to register boost. I don't think just drivetrain load would be enough either. The engine will just rev quicker and never build any boost pressure without a load.
[quote] By the way, how in the heck do you bleed the clutch slave valve. <hr></blockquote>
The clutch is a pain to get bled properly. You either need a power bleeder or have the back end of the car much higher than the front if you are doing it the old way. The reason, take a look at where the fluid fill from the brake master cylinder is.
Good luck,
Rob
[quote] I stuck the car in gear and "spun" up the rear axle to 50 miles an hour to make sure the computer wasn't somehow cutting pressure because the car wasn't under load...but that wouldnt matter cause I had the wastegate line clamped off anyway. Anyway, any thoughts would be helpful. <hr></blockquote>
The car needs to be under a load to register boost. I don't think just drivetrain load would be enough either. The engine will just rev quicker and never build any boost pressure without a load.
[quote] By the way, how in the heck do you bleed the clutch slave valve. <hr></blockquote>
The clutch is a pain to get bled properly. You either need a power bleeder or have the back end of the car much higher than the front if you are doing it the old way. The reason, take a look at where the fluid fill from the brake master cylinder is.
Good luck,
Rob
12-31-2002, 05:10 PM
#5
Race Director
Yeah, you won't have enough exhaust gases flowing to build much boost unless you've got the throttle open quite a bit, like over 60-70%. Not a good idea on jackstands!
Also by default, the CV is fully open, sending pressure to the wastegate and dumping boost. Proper computer control then cycles the valve on & off like a fuel-injector and diverts the pressure back around to the intake. So if there's something wrong with the CV (stuck open, no electrical signal, etc.), then the failsafe mode dumps boost automatically.
Most likely your car's boosting just fine, just have to drive on the road.
Also by default, the CV is fully open, sending pressure to the wastegate and dumping boost. Proper computer control then cycles the valve on & off like a fuel-injector and diverts the pressure back around to the intake. So if there's something wrong with the CV (stuck open, no electrical signal, etc.), then the failsafe mode dumps boost automatically.
Most likely your car's boosting just fine, just have to drive on the road.
01-01-2003, 09:14 AM
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Track Day
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Dear everyone!
Thanks for the advice. I was so sure the fix was going to take weeks and cost thousands. I feel like a Moron!!! I had been putting the car in gear and spinning, occasionally lightly hitting the brakes to build a resistance but there was no boost. There's something very unerving about powerbraking at full power on top of three foot tall jackstands (even without the tires on..no odd spinning syntrypical forces, or perhaps moreso because there werent any wheels mounted...no landing gear) Last night I came to the conclusion that if it aint broke, it's gotta work... and if it dont work, It's worthless and can smash the ground for all I care, so after throwing some wrenches and throwing down some beer, I said screw it, ignored my friends ominous "remember what happened in ferris beuler's day off movie" and really loaded the engine up with resistance (hit the brakes way hard) and loaded the engine, and guess what, boost galore.... Obviously, I've never played with turbos before. After my victory I then proceeded to ring in the new years by dumping more brake fluid onto my face trying to bleed the clutch....Stuff works great for hair jel...adds lots of body. Ive tried disconnecting the slave cylinder and bleeding it from several different angles to make sure that its not trapping air. I'd really like to drive this thing now I hear they are pretty fast (im used to a 944na, a 924 n/a, a 66 912 and 68 911 with 130 whopping hp. Now if I can just get this darn clutch to work... I've never driven a 951 before. Tell me they're fast. Fast like the whooshing sound of money leaving my wallet in the last two months...
Thanks again,
Ron
Thanks for the advice. I was so sure the fix was going to take weeks and cost thousands. I feel like a Moron!!! I had been putting the car in gear and spinning, occasionally lightly hitting the brakes to build a resistance but there was no boost. There's something very unerving about powerbraking at full power on top of three foot tall jackstands (even without the tires on..no odd spinning syntrypical forces, or perhaps moreso because there werent any wheels mounted...no landing gear) Last night I came to the conclusion that if it aint broke, it's gotta work... and if it dont work, It's worthless and can smash the ground for all I care, so after throwing some wrenches and throwing down some beer, I said screw it, ignored my friends ominous "remember what happened in ferris beuler's day off movie" and really loaded the engine up with resistance (hit the brakes way hard) and loaded the engine, and guess what, boost galore.... Obviously, I've never played with turbos before. After my victory I then proceeded to ring in the new years by dumping more brake fluid onto my face trying to bleed the clutch....Stuff works great for hair jel...adds lots of body. Ive tried disconnecting the slave cylinder and bleeding it from several different angles to make sure that its not trapping air. I'd really like to drive this thing now I hear they are pretty fast (im used to a 944na, a 924 n/a, a 66 912 and 68 911 with 130 whopping hp. Now if I can just get this darn clutch to work... I've never driven a 951 before. Tell me they're fast. Fast like the whooshing sound of money leaving my wallet in the last two months...
Thanks again,
Ron
01-01-2003, 10:07 AM
#7
Race Director
"Tell me they're fast."
Dooooude, I've like... heh, heh, had my car for like 5-years, ye know... and it STILL scares me!
I mean, this is one bad-*** car you always gotta respect and always keep an eye on it, even in your sleep! If you relax for just a moment, it will sense it and smack you!
I always approach it gingerly, like coming up to a wild thoroughbred, you don't want to make any sudden movements or noises. As you get nearer, you can feel the ominous presence. You know, like that deep rumble you could feel but not hear? It's just bristling with power, ready to pounce in an instant! As you make the final approach, you can sense the energy, it's kinda like static and you can feel it raising the hairs on the back of our neck.
Never, ever take it for granted. When you're driving it, keep a tight grip on the steering wheel and always feather the throttle, like you've got an egg between your foot and the gas-pedal. Always be prepared to slam on the brakes. This car has a mind of it's own, and it wants to go!
One time, must've have been a cold day or my plugs were fouled or something. But I go to pass a guy and gave it a little gas, and it hesitated for a fraction of a second. So I impatiently gave it a little more gas and it cleared its throat and just HOWLED! It leapt forward with such viciousness like it wanted to devour the Corolla that was trolling in the fast lane in front of us. I just barely got full on the brakes just in time or else we would've been one with the Corolla.
Another time, I get out from behind another guy creeping along at 80mph, and I see there's a straightaway. So I foolishly gave it full gas. The car jumped into the air, it must have been at least 3-feet, and changed 2-lanes at the same time! Luckily, we cleared the car next to us and landed on the shoulder.
So be careful driving this monster! Be afraid, be very afraid...
Dooooude, I've like... heh, heh, had my car for like 5-years, ye know... and it STILL scares me!
I mean, this is one bad-*** car you always gotta respect and always keep an eye on it, even in your sleep! If you relax for just a moment, it will sense it and smack you!
I always approach it gingerly, like coming up to a wild thoroughbred, you don't want to make any sudden movements or noises. As you get nearer, you can feel the ominous presence. You know, like that deep rumble you could feel but not hear? It's just bristling with power, ready to pounce in an instant! As you make the final approach, you can sense the energy, it's kinda like static and you can feel it raising the hairs on the back of our neck.
Never, ever take it for granted. When you're driving it, keep a tight grip on the steering wheel and always feather the throttle, like you've got an egg between your foot and the gas-pedal. Always be prepared to slam on the brakes. This car has a mind of it's own, and it wants to go!
One time, must've have been a cold day or my plugs were fouled or something. But I go to pass a guy and gave it a little gas, and it hesitated for a fraction of a second. So I impatiently gave it a little more gas and it cleared its throat and just HOWLED! It leapt forward with such viciousness like it wanted to devour the Corolla that was trolling in the fast lane in front of us. I just barely got full on the brakes just in time or else we would've been one with the Corolla.
Another time, I get out from behind another guy creeping along at 80mph, and I see there's a straightaway. So I foolishly gave it full gas. The car jumped into the air, it must have been at least 3-feet, and changed 2-lanes at the same time! Luckily, we cleared the car next to us and landed on the shoulder.
So be careful driving this monster! Be afraid, be very afraid...
