Adjusting the Cartech fmu
10-21-2004, 07:40 AM
#1
Adjusting the Cartech fmu
This isn't quite finished yet, but as there were several questions recently concerning adjusting the Cartech fmu, I'll post what I have and update later.
Bell Engineering has a website with information on tuning with the Cartech fmu. You probably should read that instead of this, but maybe this will help some, too.
Bell engineering website
Bell's fmu instructions
Basic operation of the Cartech fmu
The Cartech fmu has two adjustments. One is for the fuel pressure at onset of boost (as manifold pressure passes through zero). This is controlled by the center screw. If the screw is all the way out, then the fmu does not affect fuel pressure at zero manifold pressure, rather it is controlled by the fpr. The more the center screw is screwed in, the higher the fuel pressure will be as manifold pressure transitions from vacuum to boost. In fact, the center screw can be used to increase fuel pressure before onset of boost. This is useful if you want to lower the afr at partial throttle settings when you are at low manifold vacuum but are not boosting. Of course, this will only work at a throttle setting high enough to cause the ecu to go into open loop.
The other adjustment is the rise rate of fuel pressure referenced to the boost pressure. This is controlled by the bleeder valve. If the bleeder valve is all the way closed, you get the maximum rise rate. Minimum rise rate occurs with the valve all the way open.
The Cartech fmu does not have an adjustment for base fuel pressure at idle. You need a separate adjustable fpr in order to make that adjustment. The fpr should be installed in-between the fuel rail and the fmu in the fuel circuit.
In theory, the Cartech fmu allows you to adjust both fuel pressure at zero manifold pressure and the rise rate of fuel pressure as a function of manifold pressure. If you think of the equation of a line, these two settings allow you to set the y-intercept and the slope of the line:
y = mx + b
where: y is fuel pressure as a function of manifold pressure, x,
m is the slope, or rise rate, controlled by the bleeder valve,
b is the y-intercept, or fuel pressure at onset of boost, controlled by the center screw.
Tuning with the Cartech fmu
It is best to tune with a wideband O2 sensor, and all examples I give were done with O2 sensor data collected with an Innovate LM-1 system.
The purpose of tuning by adjusting fuel pressure is to enrich or lean out the afr by controlling how much fuel goes through the injectors during wide-open-throttle (WOT) conditions when the ecu is in open loop. In open loop mode, the ecu is programmed to produce an injector duty cycle based on rpm and maf voltage. Injector duty cycle is simply the fraction of time the injector is open and delivering fuel. The ecu controls duty cycle by pulsing the injectors with a voltage over a calculated time interval. Lookup tables have been programmed into the ecu which tell the ecu how long the pulse width needs to be for a given engine rpm and maf voltage. The injector pulse widths were programmed assuming the fuel pressure is constant.
Since the ecu thinks the fuel pressure is constant, and since the ecu does not adjust afr based on O2 sensor information in open loop mode, we can make adjustments to the afr by changing fuel pressure without the ecu trying to readjust back to what it thinks is right, such as would happen at partial throttle in closed loop mode.
Figure 1. below shows data collected for a second gear run at WOT, using a JWT ecu. For this run I have the fmu disconnected so that it is not affecting fuel pressure during the run. Fuel pressure rise is due solely to my adjustable fpr. I have the base fuel pressure set to 37 psi, which gives 46 psi at onset of boost.
Figure 1. Baseline WOT run in 2nd gear with Cartech fmu disconnected. JWT ecu.
From figure 1 we see that the fuel pressure rises gently from about 46 psi at onset of boosting to just over 51 psi at 6800 psi. This is only a rise of 5 psi, even though boost pressure is about 10 psi at 6800 rpm, which makes me think my cheapo fpr isn’t doing it’s job adequately, but we’ll ignore that for now. Notice that the JWT tune starts out in the low 13’s, and transitions to the mid 12’s at 5000 rpm.
Effect of bleeder valve
Figure 2 shows another 2nd gear WOT run, this time with the Cartech fmu connected. The center screw is backed all the way out, and the bleeder valve has been screwed in about 1.5 turns.
Figure 2. WOT run with Cartech fmu connected, center screw all the way out, bleeder valve 1.5 turns in.
With the center screw backed all the way out the fmu is not affecting fuel pressure at the onset of boost, but the fmu is causing the fuel pressure to rise with increasing boost pressure. So instead of 51 psi fuel pressure at 6800 rpm, we have 56.5 psi, a rise of 10 psi from 46 psi at onset of boost, and we see a concomitant lowering of afr to the high 11’s by the end of the run. The afr at the beginning of the run is unchanged and still in the mid 13’s. If the bleeder valve was turned in more than the 1.5 times used for this run, fuel pressure would increase at a faster rate and the afr at the end of the run would be even lower.
Effect of center screw
The center screw adjusts fuel pressure at onset of boost, thus raising the fuel pressure throughout the rpm range at WOT. Figure 3 shows the 3rd WOT run, this time with the bleeder valve in 1.5 turns and with the center screw turned in to give 53 psi of fuel pressure at onset of boost
Figure 3. WOT run with Cartech fmu connected, center screw turned in to give 53 psi fuel pressure at onset of boost, bleeder valve 1.5 turns in.
This time we see fuel pressure starting out at about 53 psi at onset of boost and rising from 53 psi to 68 psi by the end of the run, a rise of 15 psi. The afr at onset of boost is now lowered from the mid 13’s to the mid 12’s, transitions to the mid 11’s at 5000 rpm and keeps lowering to the high 10’s by the end of the run. Thus the afr has been lowered throughout the rpm range.
Bell Engineering has a website with information on tuning with the Cartech fmu. You probably should read that instead of this, but maybe this will help some, too.
Bell engineering website
Bell's fmu instructions
Basic operation of the Cartech fmu
The Cartech fmu has two adjustments. One is for the fuel pressure at onset of boost (as manifold pressure passes through zero). This is controlled by the center screw. If the screw is all the way out, then the fmu does not affect fuel pressure at zero manifold pressure, rather it is controlled by the fpr. The more the center screw is screwed in, the higher the fuel pressure will be as manifold pressure transitions from vacuum to boost. In fact, the center screw can be used to increase fuel pressure before onset of boost. This is useful if you want to lower the afr at partial throttle settings when you are at low manifold vacuum but are not boosting. Of course, this will only work at a throttle setting high enough to cause the ecu to go into open loop.
The other adjustment is the rise rate of fuel pressure referenced to the boost pressure. This is controlled by the bleeder valve. If the bleeder valve is all the way closed, you get the maximum rise rate. Minimum rise rate occurs with the valve all the way open.
The Cartech fmu does not have an adjustment for base fuel pressure at idle. You need a separate adjustable fpr in order to make that adjustment. The fpr should be installed in-between the fuel rail and the fmu in the fuel circuit.
In theory, the Cartech fmu allows you to adjust both fuel pressure at zero manifold pressure and the rise rate of fuel pressure as a function of manifold pressure. If you think of the equation of a line, these two settings allow you to set the y-intercept and the slope of the line:
y = mx + b
where: y is fuel pressure as a function of manifold pressure, x,
m is the slope, or rise rate, controlled by the bleeder valve,
b is the y-intercept, or fuel pressure at onset of boost, controlled by the center screw.
Tuning with the Cartech fmu
It is best to tune with a wideband O2 sensor, and all examples I give were done with O2 sensor data collected with an Innovate LM-1 system.
The purpose of tuning by adjusting fuel pressure is to enrich or lean out the afr by controlling how much fuel goes through the injectors during wide-open-throttle (WOT) conditions when the ecu is in open loop. In open loop mode, the ecu is programmed to produce an injector duty cycle based on rpm and maf voltage. Injector duty cycle is simply the fraction of time the injector is open and delivering fuel. The ecu controls duty cycle by pulsing the injectors with a voltage over a calculated time interval. Lookup tables have been programmed into the ecu which tell the ecu how long the pulse width needs to be for a given engine rpm and maf voltage. The injector pulse widths were programmed assuming the fuel pressure is constant.
Since the ecu thinks the fuel pressure is constant, and since the ecu does not adjust afr based on O2 sensor information in open loop mode, we can make adjustments to the afr by changing fuel pressure without the ecu trying to readjust back to what it thinks is right, such as would happen at partial throttle in closed loop mode.
Figure 1. below shows data collected for a second gear run at WOT, using a JWT ecu. For this run I have the fmu disconnected so that it is not affecting fuel pressure during the run. Fuel pressure rise is due solely to my adjustable fpr. I have the base fuel pressure set to 37 psi, which gives 46 psi at onset of boost.
Figure 1. Baseline WOT run in 2nd gear with Cartech fmu disconnected. JWT ecu.
From figure 1 we see that the fuel pressure rises gently from about 46 psi at onset of boosting to just over 51 psi at 6800 psi. This is only a rise of 5 psi, even though boost pressure is about 10 psi at 6800 rpm, which makes me think my cheapo fpr isn’t doing it’s job adequately, but we’ll ignore that for now. Notice that the JWT tune starts out in the low 13’s, and transitions to the mid 12’s at 5000 rpm.
Effect of bleeder valve
Figure 2 shows another 2nd gear WOT run, this time with the Cartech fmu connected. The center screw is backed all the way out, and the bleeder valve has been screwed in about 1.5 turns.
Figure 2. WOT run with Cartech fmu connected, center screw all the way out, bleeder valve 1.5 turns in.
With the center screw backed all the way out the fmu is not affecting fuel pressure at the onset of boost, but the fmu is causing the fuel pressure to rise with increasing boost pressure. So instead of 51 psi fuel pressure at 6800 rpm, we have 56.5 psi, a rise of 10 psi from 46 psi at onset of boost, and we see a concomitant lowering of afr to the high 11’s by the end of the run. The afr at the beginning of the run is unchanged and still in the mid 13’s. If the bleeder valve was turned in more than the 1.5 times used for this run, fuel pressure would increase at a faster rate and the afr at the end of the run would be even lower.
Effect of center screw
The center screw adjusts fuel pressure at onset of boost, thus raising the fuel pressure throughout the rpm range at WOT. Figure 3 shows the 3rd WOT run, this time with the bleeder valve in 1.5 turns and with the center screw turned in to give 53 psi of fuel pressure at onset of boost
Figure 3. WOT run with Cartech fmu connected, center screw turned in to give 53 psi fuel pressure at onset of boost, bleeder valve 1.5 turns in.
This time we see fuel pressure starting out at about 53 psi at onset of boost and rising from 53 psi to 68 psi by the end of the run, a rise of 15 psi. The afr at onset of boost is now lowered from the mid 13’s to the mid 12’s, transitions to the mid 11’s at 5000 rpm and keeps lowering to the high 10’s by the end of the run. Thus the afr has been lowered throughout the rpm range.
10-21-2004, 10:51 AM
#4
Originally Posted by IceY2K1
Hot damn...nice.
I think this is backwards though..."The afr at onset of boost is now lowered from the mid 13’s to the mid 14’s".
I think this is backwards though..."The afr at onset of boost is now lowered from the mid 13’s to the mid 14’s".
It's been corrected.
10-21-2004, 11:16 AM
#5
Supporting Maxima.org Member
iTrader: (54)
Join Date: Feb 2001
Location: Northern Jersey
Posts: 10,166
So if you have a JWT, it would be best to keep the Cartech hooked up, and dialed to 53 psi at idle for onset and bleeder 1.5 turns in ??
or with the JWT would it be best just to ditch the Cartech ?
-matt
or with the JWT would it be best just to ditch the Cartech ?
-matt
10-21-2004, 11:37 AM
#6
Originally Posted by matty
So if you have a JWT, it would be best to keep the Cartech hooked up, and dialed to 53 psi at idle for onset and bleeder 1.5 turns in ??
or with the JWT would it be best just to ditch the Cartech ?
-matt
or with the JWT would it be best just to ditch the Cartech ?
-matt
I have found that the original tune provided by JWT, maybe adjusted downward just a couple of points (which I accomplished by raising base fuel pressure to about 37 psi with the adjustabe fpr), is totally acceptable.
I still am not sure why my afr is in the mid 12's as produced by the JWT ecu, since JWT said they were going to tune to 11.5:1. I suspect the reason is that a supercharged engine will always show leaner than it actually is due to a certain amount of unburned air/fuel blowing through the cylinder and into the exhaust due to valve overlap. Turbocharged engines don't have that problem since the turbo produces more backpressure than boost pressure.
10-21-2004, 12:22 PM
#9
Matt - Yes, that is why you pay JWT the big $$$$ and that is the PROVEN route.
Although, you might keep it incase you happen to need a little more fuel up top, so don't go selling it until you get everything tuned.
Although, you might keep it incase you happen to need a little more fuel up top, so don't go selling it until you get everything tuned.
10-21-2004, 05:29 PM
#13
Supporting Maxima.org Member
iTrader: (54)
Join Date: Feb 2001
Location: Northern Jersey
Posts: 10,166
Originally Posted by IceY2K1
Matt - Yes, that is why you pay JWT the big $$$$ and that is the PROVEN route.
Although, you might keep it incase you happen to need a little more fuel up top, so don't go selling it until you get everything tuned.
Although, you might keep it incase you happen to need a little more fuel up top, so don't go selling it until you get everything tuned.
-matt
10-21-2004, 06:01 PM
#14
Matt - Cartech or any FMU for that matter are really for coarse, ie large, adjustments in fuel pressure to get you in the safe ballpark range.
The AFC is for fine-tuning and IMHO only for REMOVING fuel, say 0.5-1.0 AFR, not adding. So, I'd use the JWT and AFC together, but if you find you're getting lean up top and need more fuel, I'd use the Cartech NOT the AFC to add some.
The AFC is for fine-tuning and IMHO only for REMOVING fuel, say 0.5-1.0 AFR, not adding. So, I'd use the JWT and AFC together, but if you find you're getting lean up top and need more fuel, I'd use the Cartech NOT the AFC to add some.
10-22-2004, 05:50 AM
#16
Originally Posted by matty
Ill have to buy an AFC..I didnt think I would need mine so I sold it like 2 months ago 
-matt
-matt
10-22-2004, 10:40 AM
#18
Originally Posted by ChristheNite
I'm getting the impression that I am going to have to dynotune to make the best outta the SAFC2...
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