bleeding boost - BOV or WG?
03-05-2009, 06:50 PM
#1
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bleeding boost - BOV or WG?
I think I've got a boost creep issue. Whenever I get into the boost quick and hard, the car farts and bleeds power. But the problem does not occur when I roll onto the throttle slowly and build boost progressively. The problem occurs every time I stand on the gas in 1st/2nd gear at high RPM's (I cannot make more than 12PSI in 1st/2nd, when previously I could hit 15-16PSI). The power loss is noticeable, but not dramatic...it feels a little like a misfire, but more subtle. In higher gears, this problem does not occur at all and I can make 18PSI all day long.
MBC is hooked-up correctly and I don't have any boost or vacuum leaks (recently smoke tested). I suspect a faulty BOV or WG. Which is a more likely culprit based on what I've described? The only way I know how to test the WG and BOV is to disconnect them, which makes me nervous (for a number of reasons). Any other suggestions? Has anybody had a similar experience? How do I isoalte the problem? TIA.
MBC is hooked-up correctly and I don't have any boost or vacuum leaks (recently smoke tested). I suspect a faulty BOV or WG. Which is a more likely culprit based on what I've described? The only way I know how to test the WG and BOV is to disconnect them, which makes me nervous (for a number of reasons). Any other suggestions? Has anybody had a similar experience? How do I isoalte the problem? TIA.
03-05-2009, 08:09 PM
#2
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I think I've got a boost creep issue. Whenever I get into the boost quick and hard, the car farts and bleeds power. But the problem does not occur when I roll onto the throttle slowly and build boost progressively. The problem occurs every time I stand on the gas in 1st/2nd gear at high RPM's (I cannot make more than 12PSI in 1st/2nd, when previously I could hit 15-16PSI). The power loss is noticeable, but not dramatic...it feels a little like a misfire, but more subtle. In higher gears, this problem does not occur at all and I can make 18PSI all day long.
MBC is hooked-up correctly and I don't have any boost or vacuum leaks (recently smoke tested). I suspect a faulty BOV or WG. Which is a more likely culprit based on what I've described? The only way I know how to test the WG and BOV is to disconnect them, which makes me nervous (for a number of reasons). Any other suggestions? Has anybody had a similar experience? How do I isoalte the problem? TIA.
MBC is hooked-up correctly and I don't have any boost or vacuum leaks (recently smoke tested). I suspect a faulty BOV or WG. Which is a more likely culprit based on what I've described? The only way I know how to test the WG and BOV is to disconnect them, which makes me nervous (for a number of reasons). Any other suggestions? Has anybody had a similar experience? How do I isoalte the problem? TIA.
If stock = $69
WG = $400+
seems straight forward enough to me, replace the pop-off, plus it is far easier to get to...
03-05-2009, 10:03 PM
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I have an aftermarket recirc valve...it appears generic and it not labeled with a brand or model number. It was on the car when I bought it. If this is the problem, I'll replace it with a Forge or Synchronic BOV. I just want to be sure it's money well spent. My WG is a Tial 38mm and controlled by a MBC. Less than 10K miles on both.
03-05-2009, 10:19 PM
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Maybe take the BOV off and test it.
Depending on how it is built it should be easily taken apart and inspected.
What kind of WG do you have?
Depending on how it is built it should be easily taken apart and inspected.
What kind of WG do you have?
03-05-2009, 10:32 PM
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What's the best way to test the BOV? I disassembled it once and greased it up a little bit...nothing appeared wrong. The spring seemed a little weak to me...but I really have no idea how much resistance is normal.
My WG is a Tial 38mm.
My WG is a Tial 38mm.
03-05-2009, 11:50 PM
#6
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(I can't believe you're even getting enough traction in first or second gear to able to just stand on the gas.)
So if it's in a higher gear, standing on the gas, the problem doesn't occur?
You would think if it's the wastegate or the BOV, the problem would occur in any gear.
So if it's in a higher gear, standing on the gas, the problem doesn't occur?
You would think if it's the wastegate or the BOV, the problem would occur in any gear.
03-06-2009, 10:52 AM
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(I can't believe you're even getting enough traction in first or second gear to able to just stand on the gas.)
So if it's in a higher gear, standing on the gas, the problem doesn't occur?
You would think if it's the wastegate or the BOV, the problem would occur in any gear.
So if it's in a higher gear, standing on the gas, the problem doesn't occur?
You would think if it's the wastegate or the BOV, the problem would occur in any gear.
Everything seems fine until about 4k RPM and 12PSI...then it farts. I really thought is was a misfire at first...but it's more subtle than that (the car doesn't fall on it's face, it just stumbles a little and loses power). The probmem occurs when the boost spikes suddenly...but when I roll onto the boost nice and easy I get no symptoms of the problem. This is why it doesn't happen in higher gears...when you are cruising at 60mph and dump the throttle in 4th gear, the boost doesn't kick on like a light switch (like it does in 1st/2nd gear). If not the BOV or WG, what else might cause these symptoms?
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03-06-2009, 11:00 AM
#8
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I was getting a slight stumble myself when I hit the throttle hard. Yet it did not occur when I progressively increased the throttle. I found that I actually had a coupling that seemed tight but, wasn't quite fitted exactly perfect. Under hard instant load acceleration it was obviously opening up enough to cause a leak.
I would get a stumble and then it would go away. Took a minute to track down but,once I did the car ran fine regardless of the amount of throttle used. I'd say sounds like you might have a very simple problem on your hands in terms of fix/money but, could be hard to trace down. I'd go over ever single vac line in the engine bay and double check to make sure you don't see anything.
btw my vac at idle was fine and partially throttle was fine. If I hadn't known everything else on the car was brand freggin new I might have thought it was something else.
I would get a stumble and then it would go away. Took a minute to track down but,once I did the car ran fine regardless of the amount of throttle used. I'd say sounds like you might have a very simple problem on your hands in terms of fix/money but, could be hard to trace down. I'd go over ever single vac line in the engine bay and double check to make sure you don't see anything.
btw my vac at idle was fine and partially throttle was fine. If I hadn't known everything else on the car was brand freggin new I might have thought it was something else.
03-06-2009, 11:01 AM
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Knock?
Could the ECU/KLR/Knock Block be pulling timing because of Knock?
Do you have any way to read AFR's?
As John said it could be a Vacuum leak. I have seen the fittings on the intake manifold come loose. Mine were loose but I have seen them pop out on the track. I pulled mine and stuck them back in with fresh loctite.
Could the ECU/KLR/Knock Block be pulling timing because of Knock?
Do you have any way to read AFR's?
As John said it could be a Vacuum leak. I have seen the fittings on the intake manifold come loose. Mine were loose but I have seen them pop out on the track. I pulled mine and stuck them back in with fresh loctite.
03-06-2009, 11:47 AM
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I was getting a slight stumble myself when I hit the throttle hard. Yet it did not occur when I progressively increased the throttle. I found that I actually had a coupling that seemed tight but, wasn't quite fitted exactly perfect. Under hard instant load acceleration it was obviously opening up enough to cause a leak.
I would get a stumble and then it would go away. Took a minute to track down but,once I did the car ran fine regardless of the amount of throttle used. I'd say sounds like you might have a very simple problem on your hands in terms of fix/money but, could be hard to trace down. I'd go over ever single vac line in the engine bay and double check to make sure you don't see anything.
btw my vac at idle was fine and partially throttle was fine. If I hadn't known everything else on the car was brand freggin new I might have thought it was something else.
I would get a stumble and then it would go away. Took a minute to track down but,once I did the car ran fine regardless of the amount of throttle used. I'd say sounds like you might have a very simple problem on your hands in terms of fix/money but, could be hard to trace down. I'd go over ever single vac line in the engine bay and double check to make sure you don't see anything.
btw my vac at idle was fine and partially throttle was fine. If I hadn't known everything else on the car was brand freggin new I might have thought it was something else.
03-06-2009, 11:52 AM
#11
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Knock?
Could the ECU/KLR/Knock Block be pulling timing because of Knock?
Do you have any way to read AFR's?
As John said it could be a Vacuum leak. I have seen the fittings on the intake manifold come loose. Mine were loose but I have seen them pop out on the track. I pulled mine and stuck them back in with fresh loctite.
Could the ECU/KLR/Knock Block be pulling timing because of Knock?
Do you have any way to read AFR's?
As John said it could be a Vacuum leak. I have seen the fittings on the intake manifold come loose. Mine were loose but I have seen them pop out on the track. I pulled mine and stuck them back in with fresh loctite.
03-06-2009, 06:48 PM
#12
I have an aftermarket recirc valve...it appears generic and it not labeled with a brand or model number. It was on the car when I bought it. If this is the problem, I'll replace it with a Forge or Synchronic BOV. I just want to be sure it's money well spent. My WG is a Tial 38mm and controlled by a MBC. Less than 10K miles on both.
If you have a stock BOV, you might want to put it back in for a test drive to isolate the issue.
03-06-2009, 07:09 PM
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I had the same problem after going to a full 3" exhaust and Synapse wastegate. Turned out it was the chips - are your's stock or aftermarket? I was lucky to be at a shop that had another 951, and they swapped stock maf, FPR, and DME with no luck, while I was there and watching the dyno results. They installed Lindsey/Russell's chips and the problem was gone. I also had a dip in HP/Torque around 4K RPM which was cured with the chips. Hope this helps.
Rick
'86 951
Rick
'86 951