DIY Fuel Cut Defender - Update
#92
Datasheet says LM393 input common mode voltage range V+ -1.5V. Input voltage may be larger than V+ without damage.
V1 setpoint works OK
V2 gets to about 4V then freezes - doesn't go to low output until about 5.6V is applied
I think we need a different comparator if we want to keep 5V supply, which ideally we do.
V1 setpoint works OK
V2 gets to about 4V then freezes - doesn't go to low output until about 5.6V is applied
I think we need a different comparator if we want to keep 5V supply, which ideally we do.
#96
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I don't think to process a signal which can potentially go within 0.5V of the rail is easily possible without reducing the signal (which causes problems with V1). So I think running the comparator at more than 5V is required.
#97
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So, I think we are here then? Typo - the 10K in parallel with the zener should be 5K (for a 50% divider - down to 6-7.5V and zener will pull down the rests) as the two pots are in parallel!
[Edited by john banks - 2/24/2002 5:05:23 PM]
[Edited by john banks - 2/24/2002 5:05:23 PM]
#98
I tried running it off 12V, also with feedback resistor on V2 (I used 470K - all I had). It made no difference at all. OP2 still will not snap to low at the V2 setpoint. I've checked my build up for errors and can't see any.
When the input voltages are where you would expect the output to drop, the output "wobbles" to about 10V and the voltage at the input FALLS. Weird.
I'm using a PP3 & pot to fire voltages in & an wondering if the resistance of the pot is upsetting it?
When the input voltages are where you would expect the output to drop, the output "wobbles" to about 10V and the voltage at the input FALLS. Weird.
I'm using a PP3 & pot to fire voltages in & an wondering if the resistance of the pot is upsetting it?
#99
Meanwhile - unrelated to the above circuit -
This circuit works effectively:
http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm
Note that this is a fuel cut ONLY. It is NOT a lifter.
Looks like this and costs less than £5:
The output tracks input very closely, here is the plot:
[Edited by Paul_H - 2/25/2002 1:30:47 AM]
[Edited by Paul_H - 2/25/2002 1:42:28 AM]
This circuit works effectively:
http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm
Note that this is a fuel cut ONLY. It is NOT a lifter.
Looks like this and costs less than £5:
The output tracks input very closely, here is the plot:
[Edited by Paul_H - 2/25/2002 1:30:47 AM]
[Edited by Paul_H - 2/25/2002 1:42:28 AM]
#101
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http://www.national.com/pf/LM/LMC6772.html
This is about £2 from Farnell and is a rail to rail single supply dual comparator with open collector outputs. Seems ideal for running off 5V supply?
This is about £2 from Farnell and is a rail to rail single supply dual comparator with open collector outputs. Seems ideal for running off 5V supply?
#102
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The above is as far as I have got based on some suggestions sent to me from Xavier from the French Subaru board. I have emailed him with the above attempt so far and await his reply.
"I think you only need 1 comparator, 1 amp OP and a variable voltage
regulator (LM317 for example). I explain : The ampOP is used at G=1 and
powered with the variable voltage regulator. Adjusment of the first
threshold is done through the the variable voltage regulator (you tune the
output voltage with a varistor) so that the AmpOP saturates at the desired
input level. The second threshold is made by the comparator on the input
signal (threshold is tunes with a resistor bridge, one of the resistor is a
varistor). The comparator output drives the variable voltage regulator so
that when the comparator's output switches to high level, the voltage
regulator outputs a higher voltage, then the ampOP no more saturates and
its output goes to the input signal, which is over the ECU's cut threshold.
As you can see, it's very simple and no switches are needed.
You have to choose a rail-to-rail ampOP which accepts input voltages higher
than its power supply (most of the AmpOP accept this)."
#104
john banks,
have not read all the pages so forgive me if it's been suggested, but would putting a restrictor in the line to the map sensor not do the same?I noticed that cosie convert was running a second Dawes type valve to the map sensor at crail allowing him to run higher boost but shut down if it went too high.I just wonder if your restrictor valve would do the same.
have not read all the pages so forgive me if it's been suggested, but would putting a restrictor in the line to the map sensor not do the same?I noticed that cosie convert was running a second Dawes type valve to the map sensor at crail allowing him to run higher boost but shut down if it went too high.I just wonder if your restrictor valve would do the same.
#105
John
Compare these two circuits - this one I know this works well:
Compare with this:
When comparator output is low D4 is reverse biased.
Comparator output is high at new fuel cut only, when D4 conducts.
Op-amp U1-2 follows voltage at pin 5 when defending.
When D4 conducts, output of FCD rises - triggers new fuel cut.
R5 sets new fuel cut level. R6 sets supply voltage for comparator.
FCD output will follow supply voltage when comparator goes high. This voltage must be sufficient to trigger a new fuel cut, but below 5V.
LM358 needs more than a 5V supply (input range supply -1.5V) which limits defend point to about 3.5V. Works well at 12V although I'm going to try a 7806.
All this is theory only - any comments before I try it?
Compare these two circuits - this one I know this works well:
Compare with this:
When comparator output is low D4 is reverse biased.
Comparator output is high at new fuel cut only, when D4 conducts.
Op-amp U1-2 follows voltage at pin 5 when defending.
When D4 conducts, output of FCD rises - triggers new fuel cut.
R5 sets new fuel cut level. R6 sets supply voltage for comparator.
FCD output will follow supply voltage when comparator goes high. This voltage must be sufficient to trigger a new fuel cut, but below 5V.
LM358 needs more than a 5V supply (input range supply -1.5V) which limits defend point to about 3.5V. Works well at 12V although I'm going to try a 7806.
All this is theory only - any comments before I try it?
#106
T-uk
A bleed valve or similar will work but will result in MAP sensor giving wrong info to the ECU all the time with possible implications for ignition advance. We only want to feed it duff info part of the time
A bleed valve or similar will work but will result in MAP sensor giving wrong info to the ECU all the time with possible implications for ignition advance. We only want to feed it duff info part of the time
#107
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Sounds good.
Consider though that the voltage supply to the comparator will depend on its state as the current it draws will vary - I have the same issue with the last circuit I posted and Xavier suggested another buffer, with the modification below.
You could also consider using rail to rail comparator/op amps.
Keeping the component count down and the need for a reference would be nice.
John - Andy's system uses a ball-spring T'd off the map line as a relief valve, but the amount it can bleed is limited by a restrictor as well. The disadvantage is that you have to find the new fuel cut to work out where it is and it will also vary with temperature, as well as being considerably more expensive as a DIY project, although certainly easier than coming up with the right circuit.
Consider though that the voltage supply to the comparator will depend on its state as the current it draws will vary - I have the same issue with the last circuit I posted and Xavier suggested another buffer, with the modification below.
You could also consider using rail to rail comparator/op amps.
Keeping the component count down and the need for a reference would be nice.
John - Andy's system uses a ball-spring T'd off the map line as a relief valve, but the amount it can bleed is limited by a restrictor as well. The disadvantage is that you have to find the new fuel cut to work out where it is and it will also vary with temperature, as well as being considerably more expensive as a DIY project, although certainly easier than coming up with the right circuit.
#109
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I think our designs are converging together.
Your comparator would have to be a "beyond the rails" input type if you are changing the supply voltage.
I struggled enough to find the LMC6772 to go up to the rails.
An op amp to go beyond the rails seems to be easier to find.
Keep us posted - we WILL get there and it will be worth it! 18 PSI does make it rather a beast.
[Edited by john banks - 2/28/2002 10:45:54 PM]
Your comparator would have to be a "beyond the rails" input type if you are changing the supply voltage.
I struggled enough to find the LMC6772 to go up to the rails.
An op amp to go beyond the rails seems to be easier to find.
Keep us posted - we WILL get there and it will be worth it! 18 PSI does make it rather a beast.
[Edited by john banks - 2/28/2002 10:45:54 PM]
#110
Paul
T uk was referring to a Dawes valve not a bleed valve. With a Dawes 'type' valve in the MAP line the pressure is only bled off above the valve set point ie 15 psi.
The MAP will see true pressure up until 15 psi and thereafter it will only see a percentage of the additional pressure rise, this percentage can be pre set by fixed restrictors.
My unit is set up for 20% ramp post 15 psi.
Therefore when true manifold is 15psi, MAP sensor input to ECU is 15psi
16 = 15.2
17 = 15.4
18 = 15.6
19 = 15.8
20 = 16.0 (Boost I'm using)
21 = 16.2
22 = Fuel Cut
All very simple and reliable although maybe not as much fun as electronics
cc
T uk was referring to a Dawes valve not a bleed valve. With a Dawes 'type' valve in the MAP line the pressure is only bled off above the valve set point ie 15 psi.
The MAP will see true pressure up until 15 psi and thereafter it will only see a percentage of the additional pressure rise, this percentage can be pre set by fixed restrictors.
My unit is set up for 20% ramp post 15 psi.
Therefore when true manifold is 15psi, MAP sensor input to ECU is 15psi
16 = 15.2
17 = 15.4
18 = 15.6
19 = 15.8
20 = 16.0 (Boost I'm using)
21 = 16.2
22 = Fuel Cut
All very simple and reliable although maybe not as much fun as electronics
cc
#112
CC
Wouldn't the ball in a Dawes stay closed until the setpoint - so MAP sensor would see no pressure until the valve opened? and how would it cope with vacuum in the manifold e.g. on the overrun..
I would love you to convince me, then I can just go throw all these electronics in the skip
Wouldn't the ball in a Dawes stay closed until the setpoint - so MAP sensor would see no pressure until the valve opened? and how would it cope with vacuum in the manifold e.g. on the overrun..
I would love you to convince me, then I can just go throw all these electronics in the skip
#114
Cheers John, yes - inputs transposed
Plan "B" (or should that be "F") here, with input to comparator after the buffer.
I think a rail to rail comparator will be OK e.g. if new fuel cut required at 20 PSI, set R5 to 4.36V and set R6 to just a little more. Anywhere up to 5V in fact. I'll let you know!
Plan "B" (or should that be "F") here, with input to comparator after the buffer.
I think a rail to rail comparator will be OK e.g. if new fuel cut required at 20 PSI, set R5 to 4.36V and set R6 to just a little more. Anywhere up to 5V in fact. I'll let you know!
#116
John
I've been following this with interest for a while, and am impressed with the progress that you are making. Well done.
Am I right in thinking that although this is aimed at doing what it says in the title - stopping the fuel cut - it could also be used to cure the MY01's aversion to boost pressure. IIRC effectively the MY01 PPP (ignoring the mechanical changes) is "just" (a simple but effective solution as a more complicated one was not required) a boost clamp on the MAP signal to the standard ECU map preventing the ignition being retarded excessively and a revised boost controller that takes the correct signal. If this is correct, presumably combining both the Fuel Cut Defender and a separate boost controller would achieve the same effect?
Duncan
I've been following this with interest for a while, and am impressed with the progress that you are making. Well done.
Am I right in thinking that although this is aimed at doing what it says in the title - stopping the fuel cut - it could also be used to cure the MY01's aversion to boost pressure. IIRC effectively the MY01 PPP (ignoring the mechanical changes) is "just" (a simple but effective solution as a more complicated one was not required) a boost clamp on the MAP signal to the standard ECU map preventing the ignition being retarded excessively and a revised boost controller that takes the correct signal. If this is correct, presumably combining both the Fuel Cut Defender and a separate boost controller would achieve the same effect?
Duncan
#117
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Duncan, the PPP on the MY01 is a smaller restrictor along with alteration of the MAP signal. There is no separate boost controller - it relies on the ECU aiming for a higher target as the MAP sensor output has been altered. However, the MAP sensor is remapped by RPM too, whereas the above design with a restrictor would presumably give you a bit more across the range. The boost controller seems superflous.
#118
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Yet another circuit. Cost about £2.34. Damn, I had better actually try one of these! Just throwing in lots of ideas!
See below for latest.
The comparator has open collector output and when activated lets the zener clamp the voltage. All runs of 5V. Both ICs are rail to rail input/output and 8 pin DIL packages. Any ideas on how the zener will work?
[Edited by john banks - 3/2/2002 11:22:38 PM]
See below for latest.
The comparator has open collector output and when activated lets the zener clamp the voltage. All runs of 5V. Both ICs are rail to rail input/output and 8 pin DIL packages. Any ideas on how the zener will work?
[Edited by john banks - 3/2/2002 11:22:38 PM]