![]() |
|
|
|
Writer/Teacher
|
Losing Boost Pressure?
Well, my first mechanical problem with my 951 came up today (oh yay).
I noticed today that there seems to be a pretty abrupt drop-off in boost (and hence accelleration) at about 5000-5500ish rpm, which didn't exist before tonight. It also doesn't feel like the car is making the same kind of max boost/hp it did before, but this may be in my mind because i'm concentrating on the problem. I am not yet very familiar with turbo systems, so I can only tell you what it "feels" like. It actually feels like turbo pressure is "escaping" somehow - I'm not sure WHY it feels like that, but it does. It also seems to be a problem that varies in severity - sometimes the boost drops off, comes back, and drops off again, sometimes the car pulls harder than others, and sometimes the drop-off is more severe. These facts together with how it "feels" leads me to believe that I am losing pressure somewhere - either at the wastegate, at the turbo, or from one of the lines/pipes/hoses. Just a guess though. The only modification or work I've done on this car is to install a Lindsey Racing Boost enhancer. It was installed for just over 24 hours, and I drove on it for about 2 hours total, but I removed it because I was told that it actually increases boost slightly, so if I use the LBE without compensating for the fuel somehow I would run the risk of going lean and blowing a head gasket. So I removed it and went back to stock setup until I get chips or a bigger FPR. This was about 3 days ago. I have driven the car once since then (Wed.), and everything seemed fine then. Yes, I checked the tightness/security of the hoses and banjo bolt that were tampered with in order to install/uninstall the LBE. Everything seems kosher here. Any ideas what's going on?
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
Join Date: Sep 2006
Location: In my office
Posts: 337
|
It definitely sounds like a leak somewhere, or it could also be your blow off valve, or bypass valve. When you're looking down from the front to your right you'll see a J shaped rubber boot/hose going from the input side of the turbo under the intake over to the AFM, AFM then connects to air box. On the J-Boot is a maybe 2 inch diameter canister looking thing. It goes into the J-Boot, and has a thick hose going to an intercooler pipe, and a small vacuum line on the back side of it. If you have a piece of vacuum line laying around, disconnect it and put your other piece on there, suck on the vacuum line and then hold your finger/thumb over it. It should hold the suction. If it does not, it is bad. That's just a simple test. The two big pipes running to the front of the car are the intercooler pipes, they are notorious for coming loose. And if you've been running slightly higher boost, that will make them loose. Just go over ever hose clamp in the front of the car you can see. And I mean make them TIGHT. Have spares on hand should you break one, they are old. The intercooler pipe that the banjo bolt is on where you connected the LBE before goes directly into the turbo output side, see if you can wiggle it or turn it. If you can, get at that clamp somehow and tighten or replace it. You'll probably have to take the airbox off to do that. If you haven't taken the airbox off before it's easy. First take the two screws holding the snorkel on out and move it out of the way, then there are two scres in front and two in the rear that hold the cover on where you change the filter, and also one screw in the back that holds a bracket over the intercooler pipe. Once that's off there's one hex head bold on your left/bottom and one on the right/bottom holding the box in place. When those are all out there's a vent hose connected to the box in the back.
Those are the first things to check. And here are some questions... Do you hear any strange sounds when the boost goes away, like a fluttering or cycling sound? Do you ever hear a loud ticking/clicking sound coming from the passenger side floorboard? Does the car 'buck' at all prior to loss of boost? What did you have for dinner? This will get you started, welcome to Porsche land... Regards, Russell |
||
![]() |
|
Writer/Teacher
|
Thanks for the quick response, Rusell. In all honesty, when this started happening my first thought was pressure escaping from somewhere. First thing I did when I got home was re-check the lines around the banjo bolt.
I have worked on 944s before, so I can navigate an engine bay pretty well. If I have time tomorrow I will start checking things out. Now to answer your questions: No strange sounds when boost goes away. No clicking sound. No bucking, just a sudden lack of accelleration. Annie's brand Mac&Cheese (can you tell I'm a bachelor?) Haha and I am a serious veteran of Porsche land... welcome to turbo land is more like it. Thanks for your help, I'll check back once I get a chance to get into the engine bay.
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Writer/Teacher
|
Russell (or whoever):
The vaccuum line for the bypass valve is on top of the valve, right? Well, assuming that this is the vacuum port, I did a little test. I didn't have any actual vacuum line lying around, but I DID have an extra rubber vacuum "Y-joint", which, after trying it out, fit snugly around the vacuum port. I snipped off one arm of this joint (so there's only two openings), and did your test. The BOV does NOT appear to be holding pressure. Let me know if this is an acceptable test. Is there any more detailed way of figuring out if it is this valve that is faulty? I know that the OEM BOV is notorious for failing.
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Writer/Teacher
|
Ok, another update.
Just for ha-has, I removed the BOV itself in order to visually inspect it. Not that I'd know what to look for, but couldn't hurt. ![]() I attempted the suction test on the BOV itself, sucking on the vacuum port on top (after cleaning it off, of course). If I just do this while holding the BOV, it does NOT hold suction. However, if I put my hand over the side port (the one that attaches to the intercooler pipe, I think), it DOES hold suction. What do you make of this? Is my BOV bad?
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
|
thats a Bosch BOV for you. We had those come on Mitsubishi Eclipses, from 95-99. They were terrible...13psi or more and it would split the plastic top off, and it would leak. Sometimes it would split noticably, sometimes youd have to dump it in water to see where it was leaking.
If you want a real mans blow off valve, get a 1st generation DSM one..from 90-94. Made of metal and by far one of the best factory bovs ever made. We used to do a simple mod where you put it in a vise, and compress the head of it a little, to clamp down on the spring. It would effectively keep the bov from pushing open after 14psi, and depending on how much you crushed it, i've had them hold 20psi or more. The only thing that bests it is a Nissan Skyline GTR bov, which is practically the same design, but just a lot larger. A popular import mag way back did a test on factory ones and aftermarket ones, showing the pressure spike as the valve opened, and the 90-94 bovs and the GTR ones had almost no pressure spike, and and no interruptions as it vented. The worst one was one made by HKS, as it opened it would spike multiple times as the air was let out...miniature compressor surges. Due to that model, it killed my friends turbo after 3 years of use. Which is why he runs a DSM one now.
__________________
1985 944 / 2007 335i / 1987 325is / 1985 535i / 1999 528iT / 2006 X5 |
||
![]() |
|
![]() |
Writer/Teacher
|
Quote:
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
Join Date: Jul 2006
Posts: 574
|
Quote:
![]() The previous owner didn't install the LBE (pre-previous owner did) , and he had it for about a year. I suppose my BOV could be on the verge any day now, it could be a run of luck.... I guess the chip could have something to do with it, but logic seems to say no... The 13 psi is 13 psi whether the computer adapts to it or not... The bov still has to hold it regardless of the chip. Hopefully someone with more exp will come around and correct me... -poz [edit] Here's lindseyracing's blow off valves -- 3 styles, OEM for $41, a performance one for $120, and super performance for $150 http://www.lindseyracing.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=LR&Category_Code=BYPASSVALVE
__________________
My cars for sale, due to move 1986 944 turbo - For sale. 1987 944 N/A - For sale. Last edited by pozican; 11-20-2006 at 10:05 AM.. |
||
![]() |
|
Writer/Teacher
|
Well, it's possible that if mine was worn out the extra 2 or 3 psi might have pushed it over the edge
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
Join Date: Sep 2006
Location: In my office
Posts: 337
|
When you loose boost, is it very abrupt, like the car falls on its face abrupt? I'm wondering if your car is hitting overboost protection for some reason. Could be that there is gunk in the KLR line causing a false overboost reading to the computer. The behavior of overboost protection is like you just turned the fuel off, very abrupt, then it won't build more than 6-7 psi until it gets out of the limp mode until the car is shut off for a bit and restarted. Are you experiencing this?
|
||
![]() |
|
Writer/Teacher
|
Nah, it's not "flat on your face" abrupt, but it's noticeable if you are used to what these cars can usually do.
Russell, does it sound like my BOV has failed?
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
|
to me it sounds like it has. Boost cut In most cars is somewhat severe (my friends mx6 turbo, and DSM) usually it will buck, accompanied by a backfire, as the AFM tries to sort things out, but that usually only happens when you free up the car a lot (intake system, intercooler hardpipes, no cat and a full 3 inch exhaust).
Pretty much boost cut goes like this (in a dsm at least). AFM reads x Hz reading at y rpm. The car isnt supposed to see x Hz at y rpm, its supposed to see y Hz at y rpm, but since you added all these mods to increase the airflow in and out of the car, it changes how fast the air comes into the car. When it sees x Hz at y rpm, the computer thinks 'wait a minute somethings not right, the AFM is asking for 100% duty cycle on the injectors at y rpm, and y rpm is not redline.' So what does it do? It shuts the car down as a safety measure. But in import cars its quite abrupt, almost like you dropped ignition or fuel in a cylinder or two (or all). I have a feeling your bov was leaking out of it, or it was bypassing air back into the turbo, which will not cause any jerking or studdering, just cause slower acceleration. Since there is air leaking out of the BOV into the charge pipe, that air takes up space that would have normally been occupied by an incoming charge from the AFM. Since the new air is coming in at a slower pace because of the air coming out of the bov, the AFM will read a lower reading, and consequently pull the injector duty cycle down. We used to run into that problem all the time with the 1st generation DSM bovs...a simple press in the vise would cure the leaking problem.
__________________
1985 944 / 2007 335i / 1987 325is / 1985 535i / 1999 528iT / 2006 X5 |
||
![]() |
|
![]() |
Writer/Teacher
|
Quote:
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
Join Date: Sep 2006
Location: In my office
Posts: 337
|
Another possibility is the cycling valve, it's under the back of the intake and a bear to get to. However, bypassing it is easy. You can run a line directly from the banjo bolt to the wastegate, and plug the line the banjo bold was connected to test it. The cycling valve was designed to fail open. So either the BOV, or cycling valve are the most likely culprits.
Regards, Russell |
||
![]() |
|
Writer/Teacher
|
Well, I did the "suction test" and it did not hold suction. As a matter of fact, I pulled the BOV off and I could blow or suck (hold the dirty jokes please) the vacuum port freely, unless i put my hand over the intercooler pipe port.
Bad BOV, non?
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
Join Date: Sep 2006
Location: In my office
Posts: 337
|
Quote:
This thread is starting to take a turn to the gutter I fear... blowing, sucking, nipples, diaphragms.... ![]() |
||
![]() |
|
Writer/Teacher
|
It was the BOV. Bluebullet fabricated a DSM unit for me, and it's working great. Thanks to all for your help.
__________________
Current Stable: Black 07 Porsche 987 Cayman S: Long-Tube Headers; FabSpeed Exhaust; VividRacing ECU Tune; IPD Plenum; 997GT3 Throttle Body. Blue 1983 Porsche 928S. 1985.5 Porsche 944 Rat Rod. 2011 Acura MDX. 2008 Mazda 3. Gone But Not Forgotten:Garnet Red 86 Porsche 951("The Purple Pig"). Alpine White 83 Porsche 944 ("Alpine Wolf"). Guards Red 84 Porsche 944. |
||
![]() |
|
Registered
|
glad to be of service
![]()
__________________
1985 944 / 2007 335i / 1987 325is / 1985 535i / 1999 528iT / 2006 X5 |
||
![]() |
|