knock sensor and cycling valve
10-04-2015, 09:45 PM
#1
Drifting
Thread Starter
knock sensor and cycling valve
Still learning about the turbo version of the 944, I offer the following questions:
How do you know if your Knock Sensor is bad?
What are the symptoms of a defective cycling valve? While I was putting the engine externals back on and adding a Lindsey Boost Enhancer I started thinking about these components and how they affect the engine.
How do you know if your Knock Sensor is bad?
What are the symptoms of a defective cycling valve? While I was putting the engine externals back on and adding a Lindsey Boost Enhancer I started thinking about these components and how they affect the engine.
10-05-2015, 03:30 AM
#2
Rennlist Member
Do you suspect both items to be original to the car? If so, replace them.
If the knock sensor failure mode is false-positive, the DME/KLR will [unnecessarily] pull timing and the car will be down on power [not a big deal]. If the failure mode is false-negative, the DME/KLR will not pull timing during pre-ignition/detonation and, over time, damage to the pistons, rods, bearings, and crankshaft will grenade your motor [big deal].
The CV has three vacuum connections: a reference input taken from the J-boot, a pressure input taken from the compressor discharge hard pipe [where the LBE connects], and a pressure output to the wastegate. If the plastic output nipple breaks off, no pressure signal goes to the wastegate, you enjoy a few seconds of boost nirvana, then a ka-boom, followed by a cacophony of clunking sounds as you begin depositing parts of pistons, connecting rods, and cylinder walls on the open road [big deal]. If the CV has an internal failure, the pressure signal to open the wastegate could/would go unrestricted, allowing the wastegate to vent exhaust prematurely, indicated by a lower-than-expected boost pressure in the manifold [not a big deal].
In order to maintain the factory overboost protection, aka "limp mode", the system needs to have a [fully-functioning] CV.
If the knock sensor failure mode is false-positive, the DME/KLR will [unnecessarily] pull timing and the car will be down on power [not a big deal]. If the failure mode is false-negative, the DME/KLR will not pull timing during pre-ignition/detonation and, over time, damage to the pistons, rods, bearings, and crankshaft will grenade your motor [big deal].
The CV has three vacuum connections: a reference input taken from the J-boot, a pressure input taken from the compressor discharge hard pipe [where the LBE connects], and a pressure output to the wastegate. If the plastic output nipple breaks off, no pressure signal goes to the wastegate, you enjoy a few seconds of boost nirvana, then a ka-boom, followed by a cacophony of clunking sounds as you begin depositing parts of pistons, connecting rods, and cylinder walls on the open road [big deal]. If the CV has an internal failure, the pressure signal to open the wastegate could/would go unrestricted, allowing the wastegate to vent exhaust prematurely, indicated by a lower-than-expected boost pressure in the manifold [not a big deal].
In order to maintain the factory overboost protection, aka "limp mode", the system needs to have a [fully-functioning] CV.
10-05-2015, 01:45 PM
#4
Basic Sponsor
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That kaboom is entirely fictional, there won't be parts on the road, the first thing to blow from overboost typically is the head gasket and there is no kaboom just a lot of steam.
Do you suspect both items to be original to the car? If so, replace them.
If the knock sensor failure mode is false-positive, the DME/KLR will [unnecessarily] pull timing and the car will be down on power [not a big deal]. If the failure mode is false-negative, the DME/KLR will not pull timing during pre-ignition/detonation and, over time, damage to the pistons, rods, bearings, and crankshaft will grenade your motor [big deal].
The CV has three vacuum connections: a reference input taken from the J-boot, a pressure input taken from the compressor discharge hard pipe [where the LBE connects], and a pressure output to the wastegate. If the plastic output nipple breaks off, no pressure signal goes to the wastegate, you enjoy a few seconds of boost nirvana, then a ka-boom, followed by a cacophony of clunking sounds as you begin depositing parts of pistons, connecting rods, and cylinder walls on the open road [big deal]. If the CV has an internal failure, the pressure signal to open the wastegate could/would go unrestricted, allowing the wastegate to vent exhaust prematurely, indicated by a lower-than-expected boost pressure in the manifold [not a big deal].
In order to maintain the factory overboost protection, aka "limp mode", the system needs to have a [fully-functioning] CV.
If the knock sensor failure mode is false-positive, the DME/KLR will [unnecessarily] pull timing and the car will be down on power [not a big deal]. If the failure mode is false-negative, the DME/KLR will not pull timing during pre-ignition/detonation and, over time, damage to the pistons, rods, bearings, and crankshaft will grenade your motor [big deal].
The CV has three vacuum connections: a reference input taken from the J-boot, a pressure input taken from the compressor discharge hard pipe [where the LBE connects], and a pressure output to the wastegate. If the plastic output nipple breaks off, no pressure signal goes to the wastegate, you enjoy a few seconds of boost nirvana, then a ka-boom, followed by a cacophony of clunking sounds as you begin depositing parts of pistons, connecting rods, and cylinder walls on the open road [big deal]. If the CV has an internal failure, the pressure signal to open the wastegate could/would go unrestricted, allowing the wastegate to vent exhaust prematurely, indicated by a lower-than-expected boost pressure in the manifold [not a big deal].
In order to maintain the factory overboost protection, aka "limp mode", the system needs to have a [fully-functioning] CV.
10-06-2015, 10:53 AM
#6
Drifting
Thread Starter
Before I started taking the engine apart (not the core) the engine didn't run without spraying a little starter fluid into the intake. It wouldn't get over 1800 rpm and struggled to do that. So I decided to take the whole mess apart and start from zero. The engine was running real rich (black plugs). I found two disconnected vacuum lines, one broken temp sensor, bottom screw on distributor cap not connected and leaking oil from steering rack (not germain to engine issue) and other areas. So far I've changed the vacuum lines, pulled the rack and the turbo and had both totally rebuild, replaced badly leaking AOS seals, replaced leaking intercooler, replaced temp sensor, ISV rubber mounts, rebuilt injectors, entire ignition system, fuel lines, fuel damper and regulator, reoriented wiper on AFM, new intake gaskets, O2 sensor (fried), new boost gauge and Innovate AFR system to A pillar, added fuel pressure gauge to fuel rail, replaced frayed throttle cable, removed jumper PO placed in the cooling fan connector (fans on continuously), DME relay, total brake and rotor rebuild, etc, etc. Planning to give the engine a start today.
One thing....I noticed when I turned the ignition switch on and then off, the aux water pump (which was replaced as well) didn't come on as it previously did. I'm wondering if there's an issue or if the engine needs to run before it comes on. Something else to check out....
One thing....I noticed when I turned the ignition switch on and then off, the aux water pump (which was replaced as well) didn't come on as it previously did. I'm wondering if there's an issue or if the engine needs to run before it comes on. Something else to check out....
10-06-2015, 10:48 PM
#7
The ka-boom might be fictional, but possible damage to the pistons and rings is probably not. My track 951 was loosing power, coming up on boost erratically, sometimes little or no boost. I replaced the wire harness and in the process discovered a broken wire at the knock sensor. Unfortunately, for me, I had continued running the car as I chased the problem. My compression went from 145 to 120 on all cylinders, and the leak down from 98% to 92%. I suspect ring/cylinder wall damage due to it running very rich. It was spitting raw gas out the tailpipe. I hope the former and not the latter. Will find out when I take it apart this winter.
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10-07-2015, 07:40 PM
#8
Drifting
Thread Starter
Before I started taking the engine apart (not the core) the engine didn't run without spraying a little starter fluid into the intake. It wouldn't get over 1800 rpm and struggled to do that. So I decided to take the whole mess apart and start from zero. The engine was running real rich (black plugs). I found two disconnected vacuum lines, one broken temp sensor, bottom screw on distributor cap not connected and leaking oil from steering rack (not germain to engine issue) and other areas. So far I've changed the vacuum lines, pulled the rack and the turbo and had both totally rebuild, replaced badly leaking AOS seals, replaced leaking intercooler, replaced temp sensor, ISV rubber mounts, rebuilt injectors, entire ignition system, fuel lines, fuel damper and regulator, reoriented wiper on AFM, new intake gaskets, O2 sensor (fried), new boost gauge and Innovate AFR system to A pillar, added fuel pressure gauge to fuel rail, replaced frayed throttle cable, removed jumper PO placed in the cooling fan connector (fans on continuously), DME relay, total brake and rotor rebuild, etc, etc. Planning to give the engine a start today.
One thing....I noticed when I turned the ignition switch on and then off, the aux water pump (which was replaced as well) didn't come on as it previously did. I'm wondering if there's an issue or if the engine needs to run before it comes on. Something else to check out....
One thing....I noticed when I turned the ignition switch on and then off, the aux water pump (which was replaced as well) didn't come on as it previously did. I'm wondering if there's an issue or if the engine needs to run before it comes on. Something else to check out....
10-08-2015, 01:31 AM
#9
Rennlist Member