Power FC PFC Knock Protection Device
06-19-06, 01:03 AM
#1
Junior Member
Thread Starter
PFC Knock Protection Device
I had the idea to build an inexpensive, and easy-to-duplicate knock protection device for the PFC.
Here's the theory:
Use the knock warning light ouput for the exhaust overheat sensor to open a selected circuit upon exceeding user defined knock threshold.
The $5 version:
The warning light output is connected to a relay set up in a 'self latching' configuration. Since the light is set to blink, this is required to generate a constant output from a knock warning. A momentary switch is used as a reset. In the software, the knock warning value is the actual value where knock protection is initiated.
Now, what to do with the output? From here, there are a whole host of techniques to protect the engine. These could range from harsh, but effective, techniques such as cutting coil or igniter power -- to more elaborate techniques such as forced sensor values. As an example, it was a comman practice with a certain standalone to either max out the coolant sensor to Vref or GND to fetch a desired timing change -- using the sensor extreme that was least likely to be encountered in everyday useage. This was often used with nitrous to retard timing on demand, and could similarly retard timing with the PFC. I'm sure we could find a nice effective solution with the tools we have available. Take a peek at your CLT sensor values at the lowest temp setting. Probably 15 degrees of retard, and lots of fuel enrichment. A second relay grounding the sensor might be a nice solution, as the default map seems to have enough fuel and timing changes to stop a knock event.
The $25 version:
Sure, hitting a reset button after your car knocks is an inconvenience. Set the knock number to a reasonable value, however, and you might save your engine. The more expensive version involves the use of a timer relay in place of the reset switch. Duration is your choice, but 1 second sounds reasonable. In this time, the map will drop to a lower load point -- and you will be aware that something is amiss! This could be much like the built-in fuel cut for overboost in the PFC. The device set up in this manner would be fully automatic.
But what about injector duty cycle warning? Since this triggers the same output, you could either defeat it by setting it to 100%, or elect for the identical protection from the same circuit. I'd rather saturate the injectors and see it in the log rather than loose a race -- besides, if it goes lean enough to knock I would be under protection. I'm willing to loose a race over knock protection, however. Beats trailering home, and a new engine.
This could all be connected at the ECU location, with just a few wires. A piggyback connector version could be built for those unwilling to cut / tap wires. Add a buzzer for $5 more.... a piezoelectric igniter from a grill in your seat to make you feel the same thing your engine is experiencing...
This is simple stuff. Not advanced like ECU controlled protection, with incremental timing chages, etc -- just solid protection from knock. Could even be used as a temporary tuning tool in case false triggers from mechanical noise are an inconvenience in everyday driving.
Any interest? Really, if you know how to wire a couple of relays you have everything you need to get started. I'd like to hear other's comments.
Here's the theory:
Use the knock warning light ouput for the exhaust overheat sensor to open a selected circuit upon exceeding user defined knock threshold.
The $5 version:
The warning light output is connected to a relay set up in a 'self latching' configuration. Since the light is set to blink, this is required to generate a constant output from a knock warning. A momentary switch is used as a reset. In the software, the knock warning value is the actual value where knock protection is initiated.
Now, what to do with the output? From here, there are a whole host of techniques to protect the engine. These could range from harsh, but effective, techniques such as cutting coil or igniter power -- to more elaborate techniques such as forced sensor values. As an example, it was a comman practice with a certain standalone to either max out the coolant sensor to Vref or GND to fetch a desired timing change -- using the sensor extreme that was least likely to be encountered in everyday useage. This was often used with nitrous to retard timing on demand, and could similarly retard timing with the PFC. I'm sure we could find a nice effective solution with the tools we have available. Take a peek at your CLT sensor values at the lowest temp setting. Probably 15 degrees of retard, and lots of fuel enrichment. A second relay grounding the sensor might be a nice solution, as the default map seems to have enough fuel and timing changes to stop a knock event.
The $25 version:
Sure, hitting a reset button after your car knocks is an inconvenience. Set the knock number to a reasonable value, however, and you might save your engine. The more expensive version involves the use of a timer relay in place of the reset switch. Duration is your choice, but 1 second sounds reasonable. In this time, the map will drop to a lower load point -- and you will be aware that something is amiss! This could be much like the built-in fuel cut for overboost in the PFC. The device set up in this manner would be fully automatic.
But what about injector duty cycle warning? Since this triggers the same output, you could either defeat it by setting it to 100%, or elect for the identical protection from the same circuit. I'd rather saturate the injectors and see it in the log rather than loose a race -- besides, if it goes lean enough to knock I would be under protection. I'm willing to loose a race over knock protection, however. Beats trailering home, and a new engine.
This could all be connected at the ECU location, with just a few wires. A piggyback connector version could be built for those unwilling to cut / tap wires. Add a buzzer for $5 more.... a piezoelectric igniter from a grill in your seat to make you feel the same thing your engine is experiencing...
This is simple stuff. Not advanced like ECU controlled protection, with incremental timing chages, etc -- just solid protection from knock. Could even be used as a temporary tuning tool in case false triggers from mechanical noise are an inconvenience in everyday driving.
Any interest? Really, if you know how to wire a couple of relays you have everything you need to get started. I'd like to hear other's comments.
06-19-06, 08:25 AM
#2
I don't believe anyone, in the US, as gotten the knock or injector warning to go off with a PFC. I think that would be the first milestone. I haven't had the time but there was a recent thread on the rewiring but I don't believe anyone actually had it go off because of a warning only came on at startup. I would love to have a buzzer, light or something to indicate knock without looking at a computer screen.
06-19-06, 08:31 AM
#3
RX-7 Bad Ass
iTrader: (55)
I agree - good idea, but we need to figure out why the light doesn't come on in the first place. I did the writeup on how to light the check engine light instead of the overheat light a while back.
I'm sure there's a way to make that system work properly. I'd LOVE to get my hands on a Japanese shop manual and decipher the wiring diagram.
Dale
I'm sure there's a way to make that system work properly. I'd LOVE to get my hands on a Japanese shop manual and decipher the wiring diagram.
Dale
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