Overboosting after K27 & by-pass install
02-01-2005, 10:01 PM
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Overboosting after K27 & by-pass install
I've noticed it's a lot easier to overboost now that the cat is gone and the 3LDZ has been replaced with a K27-7200. I've attached compressed air to the IC hose to the waste gate, and noticed nothing flowing into the gate. All the air seems to just go right thru the other blow off to ambient hose (the place where the air get forced out when the diaphragm inflates).
so, does that mean the rubber diaphragm is shot? valve frozen shut? both? I assume this is the correct method to troubleshot the wastegate?
so, does that mean the rubber diaphragm is shot? valve frozen shut? both? I assume this is the correct method to troubleshot the wastegate?
02-01-2005, 10:08 PM
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If you blow air into the w/g and the valve doesn't open, your diaphragm is either shot or your valve guide is worn out. It's easy to take apart and check.
If you are over boosting though, then it sounds like your w/g is stuck in the closed postion and not bypassing the overboost....
Just a few thoughts...
Jim
If you are over boosting though, then it sounds like your w/g is stuck in the closed postion and not bypassing the overboost....
Just a few thoughts...
Jim
02-01-2005, 10:53 PM
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Jim-
so the valve could be just stuck/ frozen closed, and the rubber diaphram could be OK? this car sat (NY) for about a year before I bought it according to the registration papers. maybe that's when it froze... rust/ moisture/ non-use.
I think I always had this problem (not written up at PPI time), but it wasn't as easy to overboost before with the old turbo and junk cat... too much pressure behind the turbo to get it to spool fast. before, and now after these mods, I've never heard the gate dump; it would just launch the pump shut down relay after pinning the gauge and violently back-off.
I'll plan another cold evening in the garage... thanks.
so the valve could be just stuck/ frozen closed, and the rubber diaphram could be OK? this car sat (NY) for about a year before I bought it according to the registration papers. maybe that's when it froze... rust/ moisture/ non-use.
I think I always had this problem (not written up at PPI time), but it wasn't as easy to overboost before with the old turbo and junk cat... too much pressure behind the turbo to get it to spool fast. before, and now after these mods, I've never heard the gate dump; it would just launch the pump shut down relay after pinning the gauge and violently back-off.
I'll plan another cold evening in the garage... thanks.
02-02-2005, 12:58 AM
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Gino,
I think you'll need to isolate the problem further first...
If your WG was stuck close, I think you'll also have overboost with the original turbo. If you blow air into the WG slowly, you should be able to hear exactly when it starts to open.
Having said that, with the K27-7200, I think its also possible that it pushes enough air that you see overboost. But I'd still first ensure the state of the WG...
Good luck.
I think you'll need to isolate the problem further first...
If your WG was stuck close, I think you'll also have overboost with the original turbo. If you blow air into the WG slowly, you should be able to hear exactly when it starts to open.
Having said that, with the K27-7200, I think its also possible that it pushes enough air that you see overboost. But I'd still first ensure the state of the WG...
Good luck.
02-02-2005, 12:36 PM
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PT-
I did have the problem before w/ original turbo, just didn't recognize the source as the w/g and the overboosting didn't happen often. When I give the control line pressurized air, I can hear it just bleed out of the other line. In fact, I unclamped that line and felt it. Again, no valve opening, nor sound or leaking out the dump muffler.
JHunt-
sender is in the standard stock location... the pop-off valve housing. I'm using the standard VDO mini-meter in the RPM gauge.
It seems to me that interior inspection of the w/g is required. Damn!, more rusty bolts. Do I actually have to remove the w/g from the car? Can I remove the w/g head and access the diaphragm and valve and guide w/o removal from the exhaust system?
I did have the problem before w/ original turbo, just didn't recognize the source as the w/g and the overboosting didn't happen often. When I give the control line pressurized air, I can hear it just bleed out of the other line. In fact, I unclamped that line and felt it. Again, no valve opening, nor sound or leaking out the dump muffler.
JHunt-
sender is in the standard stock location... the pop-off valve housing. I'm using the standard VDO mini-meter in the RPM gauge.
It seems to me that interior inspection of the w/g is required. Damn!, more rusty bolts. Do I actually have to remove the w/g from the car? Can I remove the w/g head and access the diaphragm and valve and guide w/o removal from the exhaust system?
02-02-2005, 01:31 PM
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Does your overboost switch cut off your fuel pumps? Or do you just see it on the boost gauge?
Does it overboost briefly, or say in 3rd gear for extending periods?
And finally, what spring do you have in it? Stock, 1 bar gold, or 1 bar silver?
Does it overboost briefly, or say in 3rd gear for extending periods?
And finally, what spring do you have in it? Stock, 1 bar gold, or 1 bar silver?
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02-02-2005, 04:51 PM
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Gino,
I just rebuilt my w/g and replaced my turbo with a K27 too. It sounds like your w/g is not opening and it could be all of the things that have been mentioned. Having said that , you will have to remove the entire w/g. I tried to remove only the top but it is not worth the effort required. Before you try to remove the w/g, you MUST use penetrating oil on the bolts for several days before you try to remove the bolts. It helps to heat them up the first time with a torch and then put the first application of penetrating oil on. Then every day for a few days add more oil. I broke one of my studs off but they can be replaced. Ace hardware sells them. If you need a new boot I have a new one for sale as well as a 0ne bar spring. As I have said in the past lists, I used a pistol grip bar clamp from Sears to hold the top of the w/g on when assembling or removing the top. Don't believe the people that say you can hold it with one hand while you remove the last nuts. Put the clamp on before you remove the last two nuts. It,s not that tough but the nuts are a potential problem. If you have access to a die grinder or rotary cutter you can just cut the nuts off.
Good luck,
Rudy
I just rebuilt my w/g and replaced my turbo with a K27 too. It sounds like your w/g is not opening and it could be all of the things that have been mentioned. Having said that , you will have to remove the entire w/g. I tried to remove only the top but it is not worth the effort required. Before you try to remove the w/g, you MUST use penetrating oil on the bolts for several days before you try to remove the bolts. It helps to heat them up the first time with a torch and then put the first application of penetrating oil on. Then every day for a few days add more oil. I broke one of my studs off but they can be replaced. Ace hardware sells them. If you need a new boot I have a new one for sale as well as a 0ne bar spring. As I have said in the past lists, I used a pistol grip bar clamp from Sears to hold the top of the w/g on when assembling or removing the top. Don't believe the people that say you can hold it with one hand while you remove the last nuts. Put the clamp on before you remove the last two nuts. It,s not that tough but the nuts are a potential problem. If you have access to a die grinder or rotary cutter you can just cut the nuts off.
Good luck,
Rudy
02-02-2005, 05:03 PM
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jhunt-
the cut-off works, or at least I believe that's what the violent reaction is when the boost goes WAY past the 1.0 mark. at that point, the whole car almost seems to stop... rpms drop, boost stops and driver/ passenger are almost thrown into the windshield! this whole thing lasts just a second or 2, then normal engine operation continues.
I can get it to overboost easiest in 2nd and 3rd. before the changes, it took longer to spool, so full boosting did come in until 5000 rpm if I punched it at 3 grand in 3rd. now if I did the same, it's pinning the boost meter before 4000 and launching the 'safety relay'...
the car was bone stock before I did the K27-7200 and cat by-pass. I assume 0.8 bar spring as it's not been opened.
the cut-off works, or at least I believe that's what the violent reaction is when the boost goes WAY past the 1.0 mark. at that point, the whole car almost seems to stop... rpms drop, boost stops and driver/ passenger are almost thrown into the windshield! this whole thing lasts just a second or 2, then normal engine operation continues.
I can get it to overboost easiest in 2nd and 3rd. before the changes, it took longer to spool, so full boosting did come in until 5000 rpm if I punched it at 3 grand in 3rd. now if I did the same, it's pinning the boost meter before 4000 and launching the 'safety relay'...
the car was bone stock before I did the K27-7200 and cat by-pass. I assume 0.8 bar spring as it's not been opened.
02-02-2005, 06:10 PM
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Yeah that sounds like your overboost circuit works. I have teeth marks in my steering wheel from mine.
So just to make sure we are all on the same page;
The car has stock exhaust except for the cat bypass. And you changed the turbo to the K27.
Don't assume on the spring, a previous owner may have changed it. I think I have a spare stock spring you are welcome to if you want to try it.
Check the hose from the intercooler to the wastegate. Make sure it is in good shape and solidly connected.
It isn't unusual for cars with 1 bar to spike then settle down to 1 bar boost (quickly settles down). But this is more often associated with having headers. If the spike triggers the overboost then it doesn't have a chance to settle down.
So just to make sure we are all on the same page;
The car has stock exhaust except for the cat bypass. And you changed the turbo to the K27.
Don't assume on the spring, a previous owner may have changed it. I think I have a spare stock spring you are welcome to if you want to try it.
Check the hose from the intercooler to the wastegate. Make sure it is in good shape and solidly connected.
It isn't unusual for cars with 1 bar to spike then settle down to 1 bar boost (quickly settles down). But this is more often associated with having headers. If the spike triggers the overboost then it doesn't have a chance to settle down.
02-02-2005, 08:26 PM
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jhunt-
Sure I'll take you up on the spring. Will it have markings on it so when I open mine, I'll know? I'll PM you with my address, thanks.
My car has the factory system w/ heat exchanger w/ stock muffler. I just recently changed out the 3LDZ to the K27 and by-pass, but held on to the cat (although I can't see it doing anything... when I shake it, it sounds like loose rocks inside) to pass emissions. The IC-W/G hose is fine, checked that, again, when I did the compressed air thing.
I wouldn't call the overboosting a spike. If I were to use an analogy... to a math graph, the boost slope is expediential. The boost build seems linear, but them it comes on in a big rush 'up the slope', and then a straight line down to zero. I can hold the boost at around 0.7-.8 if I don't give it too much pedal. But, any lift from that pedal eliminates the boost (that's another question...)
how come the boost completely disappears when the driver ever so lightly lets up on the pedal? Is this what I read dual port wastegates are supposed to fix? Applying pressure from both sides of the diaphragm so it's not on-off?
Sure I'll take you up on the spring. Will it have markings on it so when I open mine, I'll know? I'll PM you with my address, thanks.
My car has the factory system w/ heat exchanger w/ stock muffler. I just recently changed out the 3LDZ to the K27 and by-pass, but held on to the cat (although I can't see it doing anything... when I shake it, it sounds like loose rocks inside) to pass emissions. The IC-W/G hose is fine, checked that, again, when I did the compressed air thing.
I wouldn't call the overboosting a spike. If I were to use an analogy... to a math graph, the boost slope is expediential. The boost build seems linear, but them it comes on in a big rush 'up the slope', and then a straight line down to zero. I can hold the boost at around 0.7-.8 if I don't give it too much pedal. But, any lift from that pedal eliminates the boost (that's another question...)
how come the boost completely disappears when the driver ever so lightly lets up on the pedal? Is this what I read dual port wastegates are supposed to fix? Applying pressure from both sides of the diaphragm so it's not on-off?
02-02-2005, 09:27 PM
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Turbos require pressure to work, let off the gas and the required pressure dissapears and with it the boost. This is generally a good thing as you don't want/need boost when slowing down.
If you are on the freeway, on maybe a slight upgrade and floor it in 3rd gear, will it spike and cause the overboost circuit to come on?
I'll send the spring that I have. I bet that will fix it.
If you are on the freeway, on maybe a slight upgrade and floor it in 3rd gear, will it spike and cause the overboost circuit to come on?
I'll send the spring that I have. I bet that will fix it.
02-02-2005, 10:53 PM
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Well, if your WG is working properly, it should not be bleeding air out until the designated pressure point is reached. Your comments seem to indicate its constantly leaking thru?
Now, if you are using the stock gauge - I would not trust that. Get a mechanical gauge.
Now, if you are using the stock gauge - I would not trust that. Get a mechanical gauge.
02-03-2005, 11:27 AM
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jhunt-
yes to your question. on a slight incline, you can see the boost gauge react and come on to maintain the power to sustain mph up the grade... maybe reach 0.4-.5 bar. if I depress the gas, not even to the floor, I can get it to pin the gauge and launch the safety system.
PT-
I don't think the W/G is working at all. I have never heard anything coming out of the muffler on the dump pipe. even when I put compressed air at 20psi through the control hose, it leaked out the other ambient relief hose, not the W/G dump pipe. I had a friend on the floor to listen for it. That to me, and others, that the valve is not open and perhaps the diaphragm is compromised not allowing it to pressure up and accuate the valve.
yes to your question. on a slight incline, you can see the boost gauge react and come on to maintain the power to sustain mph up the grade... maybe reach 0.4-.5 bar. if I depress the gas, not even to the floor, I can get it to pin the gauge and launch the safety system.
PT-
I don't think the W/G is working at all. I have never heard anything coming out of the muffler on the dump pipe. even when I put compressed air at 20psi through the control hose, it leaked out the other ambient relief hose, not the W/G dump pipe. I had a friend on the floor to listen for it. That to me, and others, that the valve is not open and perhaps the diaphragm is compromised not allowing it to pressure up and accuate the valve.
02-03-2005, 11:59 AM
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From the "For what it's worth" department.......
Porsche states in their shop manuals that the engine should running when testing the wastegates on 930's. I don't know if this is because of the additional exhaust backpressure working on the valve makes the test more accurate, or what, but it's been written.
"It's in the Bible, it's in the Bible!!" (Monty Python's-"Life of Brian")
Porsche states in their shop manuals that the engine should running when testing the wastegates on 930's. I don't know if this is because of the additional exhaust backpressure working on the valve makes the test more accurate, or what, but it's been written.
"It's in the Bible, it's in the Bible!!" (Monty Python's-"Life of Brian")