6K rpm bog? Need help!
11-14-06, 11:46 PM
#1
6K rpm bog? Need help!
Now that the winter is here i noticed that at night, when the air temp is low, the car bogs going WOT at about 6K rpm. The hesitation lasts about one second and then it boosts right up till redline. I'm no expert, but could i be hitting fuel cut? OR boost spiking due to cold air and semi-open exhaust? I am stock besides apexi intakes, catback, and midpipe. Still have the precat. (I know, its retarded, its how i baught it ). Also, the bog mainly happens in 3rd or 4th gear when the car really starts to pick up. Any 1 know what it could be? Thanks for the help.
Last edited by prescription 7; 11-15-06 at 12:14 AM.
11-15-06, 01:29 AM
#3
Will do, i'll buy 1st thing tomorrow (need 1 anyway). Now from what you just posted, im gathering that its possible to creep and then hit fuel cut? I think thats the prob. Cold air causing high boost and the ecu is reacting with fuel cut. Does that sound right? I'll try to get the boost numbers asap
11-15-06, 01:31 AM
#4
Originally Posted by prescription 7
Will do, i'll buy 1st thing tomorrow (need 1 anyway). Now from what you just posted, im gathering that its possible to creep and then hit fuel cut? I think thats the prob. Cold air causing high boost and the ecu is reacting with fuel cut. Does that sound right? I'll try to get the boost numbers asap
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11-15-06, 02:51 AM
#8
There are tons of people who don't understand it. Or they found they could afford $75 to add a midpipe, but somehow lost their finances and mechanic skills when they found they needed to install a boost controller and port the wastegate.
Boost creep is a limit to a simple system in your car: to control boost, you need to divert exhaust around the turbo. That's what the wastegate opening is for, and the door is the control. So if you install a higher flowing exhaust behind the turbo, air flows more easily through that opening, meaning the wastegate needs to open further, more of the time. On the stock ecu with stock boost control, about 2-3 flow mods is the limit before the boost increases. (Yes, modded FDs need a boost gauge, and this is why). It needs to stay at 10-11psi, which is why the stock ECU is often recited to live by the "10 psi rule". If it goes higher, you install an adjustable boost controller, manual or electronic, and you can adjust it back down to happy land at 10psi. You'll see some other using a PFC to adjust the stock boost control solenoids, which can work on mildly modded cars. So by keeping the boost adjusted down we've negotiated that issue. That's all ok, up to a point. For most FDs, installing the full exhaust is this breaking point. (I suspect you may in fact have a gutted precat.)
However, air flow is like increasing traffic on a highway. There is a point where more cars simply can't get through without slowing down. In fluid mechanics terms this is called choked flow, and choked flow is what causes boost creep. The wastegate flow starts to stack up, and even though your boost controller maxes out and holds the door 100% open, not enough exhaust goes around through the wastegate, which means too much of the exhaust finds its way through the turbine and creates too much boost. Just like a traffic jam, the longer you stay in the gas, the more the exhaust stacks up and the boost just climbs higher.
Yeah, you can watch your boost gauge and take your foot off the gas whenever it creeps, but personally I like the view through the windshield better, and the faster you drive it becomes more ABSOLUTELY NECESSARY to focus as far ahead as you can see. I only advise this solution for the time being to get the car fixed. Which shouldn't be long.
Some people will tell you that you need to upgrade the ECU and fuel system to handle the extra boost. Yes, this is true, because as long as you deliver enough fuel, and your maps can handle the boost, you're ok. But 1) this is expensive and 2) remember how the boost never stops creeping higher? So we're delaying the problem but not solving anything - your boost can still creep higher than the limits of your fuel system. This sounds like I'm getting unrealistic, but in fact you can produce a LOT of boost for a LONG time in 5th gear on a cool day. All it would take is one long highway pull or long uphill in 5th, and boom.
The problem is that the restriction of the wastegate path and turbo/exhaust are too far out of balance. You can either increase the restriction in the exhaust by installing less aggressive components (I suggest a high-flow cat, with downpipe, cat-back, and boost controller), or open the wastegate by enlarging it. (the procedure is called 'porting' the wastegate). These are both real, solid, permanent answers. For maximum performance, porting the wastegate is best because you can't flow enough exhaust through the turbos to creep. Now the flow will not choke at the wastegate, and the wastegate door won't need to be opened 100% ever, which means the boost controller can always control it.
Well enough allergy-medicine induced insomniac typing for tonight. Most of the time I would have stopped at 'search' and 'faq'. Read this again and again until it's clear, or just pay a rotary shop to check out your car and fix it.
Boost creep is a limit to a simple system in your car: to control boost, you need to divert exhaust around the turbo. That's what the wastegate opening is for, and the door is the control. So if you install a higher flowing exhaust behind the turbo, air flows more easily through that opening, meaning the wastegate needs to open further, more of the time. On the stock ecu with stock boost control, about 2-3 flow mods is the limit before the boost increases. (Yes, modded FDs need a boost gauge, and this is why). It needs to stay at 10-11psi, which is why the stock ECU is often recited to live by the "10 psi rule". If it goes higher, you install an adjustable boost controller, manual or electronic, and you can adjust it back down to happy land at 10psi. You'll see some other using a PFC to adjust the stock boost control solenoids, which can work on mildly modded cars. So by keeping the boost adjusted down we've negotiated that issue. That's all ok, up to a point. For most FDs, installing the full exhaust is this breaking point. (I suspect you may in fact have a gutted precat.)
However, air flow is like increasing traffic on a highway. There is a point where more cars simply can't get through without slowing down. In fluid mechanics terms this is called choked flow, and choked flow is what causes boost creep. The wastegate flow starts to stack up, and even though your boost controller maxes out and holds the door 100% open, not enough exhaust goes around through the wastegate, which means too much of the exhaust finds its way through the turbine and creates too much boost. Just like a traffic jam, the longer you stay in the gas, the more the exhaust stacks up and the boost just climbs higher.
Yeah, you can watch your boost gauge and take your foot off the gas whenever it creeps, but personally I like the view through the windshield better, and the faster you drive it becomes more ABSOLUTELY NECESSARY to focus as far ahead as you can see. I only advise this solution for the time being to get the car fixed. Which shouldn't be long.
Some people will tell you that you need to upgrade the ECU and fuel system to handle the extra boost. Yes, this is true, because as long as you deliver enough fuel, and your maps can handle the boost, you're ok. But 1) this is expensive and 2) remember how the boost never stops creeping higher? So we're delaying the problem but not solving anything - your boost can still creep higher than the limits of your fuel system. This sounds like I'm getting unrealistic, but in fact you can produce a LOT of boost for a LONG time in 5th gear on a cool day. All it would take is one long highway pull or long uphill in 5th, and boom.
The problem is that the restriction of the wastegate path and turbo/exhaust are too far out of balance. You can either increase the restriction in the exhaust by installing less aggressive components (I suggest a high-flow cat, with downpipe, cat-back, and boost controller), or open the wastegate by enlarging it. (the procedure is called 'porting' the wastegate). These are both real, solid, permanent answers. For maximum performance, porting the wastegate is best because you can't flow enough exhaust through the turbos to creep. Now the flow will not choke at the wastegate, and the wastegate door won't need to be opened 100% ever, which means the boost controller can always control it.
Well enough allergy-medicine induced insomniac typing for tonight. Most of the time I would have stopped at 'search' and 'faq'. Read this again and again until it's clear, or just pay a rotary shop to check out your car and fix it.
Last edited by dgeesaman; 11-15-06 at 02:59 AM.
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