22 MPG in the city!!
The next thing to do, besides my action items below, is to implement the fuel cut-off feature. I just read that it can save up to 4 MPG.
If that's truth, I will finally be better in fuel economy than the old days when my car was stock and gave me 24 MPG.
Power is nothing without control
Originally Posted by Buzo
When it gets below freezing you will need a LOT of extra fuel to get it going. Closed loop fuel control won't work because the mixture needs to be so rich that it's beyond the useful range of the O2 sensor. The O2 sensor also won't read properly until it warms up. It will also take quite a bit of air too. You'll need enough air to get the idle up to 2000RPM or so and enough fuel to get the AFR up to 12:1 or so.
Hot restart problems are common. Probably the IAT sensor is getting heat soaked when the hot engine sits without running for a bit. The ECU then thinks the air temp is higher than it is and injects less (not enough) fuel. Also the fuel stuck to the intake manifold walls evaporates and has to be replaced, which makes the lean condition worse. Moving the IAT sensor to a cooler location usually helps.
C|
This is how the fuel cut-off looks like:
The injector gets shut off when the TPS is released and the RPMS are higher than 1500, and restarted when the RPMS get below 1500.
In this case I am leaving the injector open with 1% of PWM. It will save fuel per sure.
Power is nothing without control
I found the solution for this:
If the IAC position is more open than the position at Idle, I add 5 points of extra fuel, independently of the tables and the calculated fuel. Assuming IAC=150 when Idling, then.
if(tpsoff)
{ if(IAC>151)
PWM_Sent+=5;
if(IAC>152)
PWM_Sent+=5;
if(IAC>153)
PWM_Sent+=5;
if(IAC>154)
PWM_Sent+=5;
if(IAC>155)
PWM_Sent+=5;
if(IAC>156)
PWM_Sent+=5;
}
The program cycles counter only decreases when the TPS is released, so it depends of how many "stops" you make in the beginning of your trip, as more time the TPS is released (i.e. in a stop light) the 9000 program cycles will end sooner. That's the reason why it sometimes was not enough. So I will put a bigger counter that is not dependent of the TPS but the time elapsed after startup.
Power is nothing without control
This is the Oxygen Sensor Log during my trip this morning.
It is the best Closed Loop Control for the air/fuel mixture I have ever reached.
I added a line in yellow indicating where the O2 stoichiometric target for a Narrow Band (0.5 V) is at.
I set a target of 0.6V so that's why the average is slightly up from the 0.5V, first of all I wanted to make sure the software was able to stay around any given target. Then I can set it to any value I need.
Most of the trip was highway cruising at 60 MPH and 2500 RPM.
Dam! I should stick with this software revision for a while! Because I am already thinking in improving something else...
Power is nothing without control
The only one thing that is holding me to test this system in another car is the cold start.
The problem seems to be how the IAC motor responds to the commands, it looks like there is some inertia in the motor that makes the IAC to loose a few pulses or something. There is no other feedback but the engine speed to assure the IAC is actually moving. And for the time the engine responds, the IAC is too much open that leans the mix out so the engine can't accelerate any more, then the IAC opens even more until the engine dies...
Any suggestion is welcomed.
Power is nothing without control
The IAC should be closed-loop controlled just like the fuel. The control loop needs to be tuned to the IAC such that it won't try to adjust it too quickly. This would involve a PID loop like I mentioned before for fuel control. It also sounds like maybe the fuel control is not reacting fast enough either to keep up with the extra air. Using PID loops would allow for tuning the short and long term response.
It's also possible that the IAC doesn't like the type of control signal you are sending it. Have you checked to make sure your PWM frequency is correct for it?
C|
I found a bug in the software. I was commanding the next turn of the IAC before it finished the current turn. That's why I was loosing the number of "ticks" sent.
A simple if IAC_moving then wait... has solved the last issue I had. Still need to test the car tomorrow morning. I know where IAC must be according to the ambient temperature and the software is ready to execute it. The problem was the tick counter was lying to me so I assumed it was in certain position when it actually was in a different position.
Thanks again for your response. I'll let you guys know how this works.
Happy thanksgiving day!
Power is nothing without control
I knew it shouldn't be that hard to get the car started in a cold morning.
It was cold and raining today - two factors that affect the air density - and the car fired up at the first attempt.
So some time ago when I checked the IAC for correct traveling, correct frequency, etc., I removed the TBI from the engine to look at the opening and created a table of Ticks vs IAC Position, but once you put it back you can't longer see if the IAC is moving. Except for the response of the engine speed. Somehow I changed the code and removed the "wait for the IAC to finish the current adjustment" it was in place when I created the table.
Just did a little more work with the after-crank enrichment this morning and that was it. Now just need to wait for the one-digit temperatures and I should be all set.
Power is nothing without control
The semi-autotune function I created works pretty good.
What I did was to start with a flat table of 100% and take the car for a ride in a highway, then the autotune will correct each table address according to the O2 response, while everything is being logged with the laptop.
At the end of the ride the table must be manually updated (that's why I called it semi-automatic). One ride is enough to fill the whole table. Even the O2 could be disabled after that and it will work much better than any de-vacuum'd carb.
Currently I am working in improving the period where we don't have the feedback of the O2, because the car is slightly rich in that period of 5 minutes, at the point that I can see a black mark in the floor right below the exhaust pipe. But I consider that as a part of the tuning process and not part of the development process.
One option I am thinking of at this time is to replace the stock O2 with a electrically heated O2 sensor, so I can reduce that time in a half at least...
Power is nothing without control
This is how the fuel cut-off looks like:
The injector gets shut off when the TPS is released and the RPMS are higher than 1500, and restarted when the RPMS get below 1500.
In this case I am leaving the injector open with 1% of PWM. It will save fuel per sure.
Just by adding this feature improved from 22 MPG to 28 MPG.
And still the car is too rich during the warming up time, so there is still chance for improvement.
I am trying to monitor a signal other than the O2 to do the closed loop while the O2 is warming up.
I am thinking in the RPM, so I'll start with a 20% of PWM, then reduce it one by one until I detect a change in the RPM, then stop there, wait a few seconds and reduce the PWM once again, and so on and stop just before the engine dies. OK, let's do it!
Power is nothing without control
I never bought the idea of paying 50 USD for the conic shape air filter, (remember I paid 35 for the TBI and sensors) so ended up with the following design for only 5 bucks...
Power is nothing without control
Cont'd...
Power is nothing without control
By reading over the internet I found that the EMCs from GM have one Idling target RPM table vs. coolant temperature for Park/Neutral and another for Idling vs. coolant temp for Drive.
As of today I have one single table for both, P/N & D so I usually wait until the RPMS go down to ~1200 to start my drive in the mornings. I don't have to do that if I just implement a second table of target RPMS specifically for D.
It will take me a couple of extra lines of code, and a couple of cold mornings to test it!
I don't know if someday I am going to really finish this project though. But for now, It's been 7 months of lot of fun since I started it.
Power is nothing without control
I passed the cold start test today.
It's snowing and the car fired up just like a new car. It is very interesting to see how the IAC motor needs to open double the length to reach the same Idle Speed than at hot temperature.
That brings me an Idea of connecting the hot air hose that goes from the muffler to the filter cover of the stock carb. Certainly warming up the manifold air will same some extra fuel.
Power is nothing without control
That air filter is epic! Glad to see you making progress.
Dr_Snooz
"I like to take hammers, and just break stuff, just break stuff." - Beavis
1989 Honda Accord LX-i Coupe, 240k miles, MT swap, rear disc swap
Shop manual downloads available here: CLICK TO VIEW
Just noticed that your cam pulley is rather unusual looking. I haven't seen one like that before.
C|
It is a piece of sheet metal that i put in front of the stock pulley. It was from the days when I was trying to generate the 7x signal for the GM ECM. So I cut some holes to get 7 pulses each crankshaft turn 6 even and 1 uneven pulse for sync. It didn't work. The idea is good but needs more refined machining skills.
Thanks Dr., Just saved 45 USD and my engine is well protected from the elements!That air filter is epic! Glad to see you making progress.
Power is nothing without control
The issue I described above is still present. I just got a heated wide band O2 sensor so its time to install it. I just didn't expect so many wires coming out of the sensor.
Step 1) how it works?
Power is nothing without control
Which one did you get?
C|
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