is TBI an option for our cars?

[Buzo]

After struggling with the morning starts section of my code & hardware, I found out that the problem was due to the battery voltage getting as low as 7V when cranking.

So 7V divided between the 5 ohms resistor and the 4 ohms injector resistance results in not enough voltage to open the injector.

I made a lot of changes to the hardware and software during the last two weeks and could not explain myself why everything worked fine if forcing the input signals, but as soon as tryed to start the car, the injector just won't open.

Reading the megasquirt manual I learned how the 'peak and hold' circuit works and just implemented it in my code and removed the series resistor.

Problem solved. The peak and hold runs at 60% duty cycle when cranking and 30% duty cycle when running.

The red line in the picture shows the coil pulse and the blue one shows the peak and hold function. 1 ms peak of full voltage and then 8 ms of 30% duty cycle (4 volts)

[Buzo]

Start up at High Idle - Done
Smooth decceleration until Idle - Done
TPS Enrichment - Done. Almost perfect, in fact.

I still don't quite understand how the MAP will compensate for the load of the engine.

All I know is that the Value when the engine is not running is 255
The value when idling is 125 (half of above)

So the question is what happen with the vacuum during different acceleration schemes. I have some MAP data captured before but it looks too noisy. (Captured before I fixed my vacuum leak in the distributor)

Does somebody have a chart of MAP vs RPMs that can share with me, please?

[Buzo]

This is the only MAP chart I could rescue from all the data logs I made. It doesn't say much but the following:

When the engine is off, the MAP reading is at Maximum, as the engine fires up the MAP readings goes down. That's why I put the cranking pulse as reference, to tell when the engine got fired up.

With every pedal acceleration (3 TPS pulses) the MAP reading increases. (but then there is this noise that I don't think its normal)

Need help to understand what happen with the vacuum (MAP) at constant TPS position but when the load is being increased - lets say by climbing a hill in the road.



I'm affraid I need to redo this log just as I said, when climbing a hill, just looking here for some clue. This MAP thing works in logic inverse (always happen to me with vacuum things) so my brain can not process it very well haha.

[cygnus x-1]

So, I think to understand the significance of MAP (or Manifold Absolute Pressure) it helps to think about what is actually happening in an engine. You can think of an engine as a sort of air pump, that pulls air in through the intake and pushes it out through the exhaust. The purpose of the throttle plate is to control the rate of air flow into the intake manifold and thereby control air flow into the engine's cylinders. In order to have proper engine function (combustion in the cylinders) the fuel injection system needs to figure out how much air is going into the cylinders so that it can inject the proper amount of fuel. A popular way to do this is to measure the pressure and temperature of the air in the manifold and use those to calculate the mass of air that will end up in the cylinders during the intake cycle; assuming that when the valves close the pressure in the cylinders will be roughly equal to the manifold pressure. Once you know the air temperature and pressure, you can calculate the total air mass using the volume of the cylinders and the density of air at the measured temperature and pressure. Once you have the air mass you can calculate the required fuel based on the stoichiometric ratio (air to fuel) for whatever fuel you intend to use.

So, essentially the MAP is what determines how much fuel needs to go into the cylinders during each engine cycle. A consequence of this is that the throttle position really doesn't matter that much. Once you know the MAP the throttle position is largely irrelevant, because it's the manifold pressure that determines how much fuel is needed, not throttle position. The throttle position is also not a very good indicator of how much air mass gets into the cylinders because the flow through the throttle is dependent on the pressure differential between the atmosphere and the inside of the manifold, which changes depending on engine RPM, air temperature, engine load, and other things like plenum volume and intake manifold resonance effects. It's a very complicated system to model.


If you haven't already, it would be good to check out the Megasquirt documentation where they describe the theory of operation, e.g. the fueling equation. The fueling equation is really the heart of what a fuel injection system is trying to do. That is to determine how much air is going into the engine, and then inject the proper amount of fuel based on the air going in.


One other thing that I found useful in understanding this stuff is to forget about "vacuum". Vacuum is an artificial number that is dependent on whatever the atmospheric pressure is, not to mention it's backwards. What you really want to know is the absolute pressure. No air at all (full vacuum) would be an absolute pressure of 0 and normal atmospheric pressure (at sea level) is 14.7PSI, or 100kPa, or 760 mm Hg. So more air pressure means more air will go into the cylinders, which then means more fuel needs to go in as well.


Hopefully the above will help to explain things and not just add more confusion.


C|

[Buzo]

Thanks a lot, the explanation helped me out to put things in order in my mind. I was kind of cycled into this. Thanks for the advise of forgeting the vacuum, so suddenly the MAP became a positive logic I can better process. That was key.

I added today two "new" features to my ECM:

1) Acceleration pump emulation based on TPS's (and/or MAP's) sudden change, so more fuel is injected when sudden TPS changes are detected. Just like the carb's accel. pump.

2) If the engine gets overflooded, I only need to press the pedal 80% of WOT while cranking and the fuel will be cut off, so it gives me the chance to restart the car after a flooded engine(a common thing for me in these days)

The problem I am working on right now is the after crank enrichment value.

If I control it by time, it works OK when cold, but stays too long in a hot restart.

If I control it by coolant temperature, it gets to zero too soon, before the engine can keep up.

So its obvious I need a combination of the two above. This is the best hobby I have ever had. (I left the other (women) hobby behind since I got married)

[Buzo]

If you haven't already, it would be good to check out the Megasquirt documentation where they describe the theory of operation, e.g. the fueling equation. The fueling equation is really the heart of what a fuel injection system is trying to do. That is to determine how much air is going into the engine, and then inject the proper amount of fuel based on the air going in.
C|

I have this figured out already. I do not have issues when the engine has already run for 10 minutes or more.

Right now as I said in my post below, the task is to define the logic between the first start of the day and the restart after a quick stop in the road.

Its just a matter of getting to the right code that makes desicions based in start up cooling temp to determine the lenght of the after-cranck enrichment.

I really prefer to stay rev'd up for long time than needed, than having my engine killed due to lack of fuel when cold.

I am also thinking in adding a couple of TEMPORAL push buttons to increase/decrease the after crank enrichment, until I can get good numbers for each temp condition. That would be something easy to implement...
I can use my laptop, but somethimes I just get lazy to hook it up to the car.

[cygnus x-1]

The temperature compensation stuff can be a challenge. My car doesn't go out when it's cold so I've never bothered to tune for colder temperatures.

The MS method for cold starts (all starts actually) is to use a time based after start enrichment. The time can be anywhere from a few seconds to a minute and changes based on temperature. So there are two tables, one to determine how much fuel to add during the ASE period, and another to determine the length of the ASE period. cold starts will use a long ASE period and hot starts use a short period. So it's pretty much what you were describing as a combination of time and temperature.


C|

[Buzo]

The temperature compensation stuff can be a challenge. My car doesn't go out when it's cold so I've never bothered to tune for colder temperatures.

The MS method for cold starts (all starts actually) is to use a time based after start enrichment. The time can be anywhere from a few seconds to a minute and changes based on temperature. So there are two tables, one to determine how much fuel to add during the ASE period, and another to determine the length of the ASE period. cold starts will use a long ASE period and hot starts use a short period. So it's pretty much what you were describing as a combination of time and temperature.


C|

This was my personal fix for cold start and Hot-restart

The Car always starts at the same IAC openning, but the cooling temperature when the key is first open defines the lengh of the step for the IAC to close. This chart was taken in the car. Started in the morning, wait for the fans to come on, and an immediate restart.

I believe this has been my most brilliant idea for my ECM...

[Buzo]

I captured some RPMs vs MAP charts to better understand how they react at different conditions


Chart #1.- Taken at start up. Its 2 seconds long.

Chart #2.- Shift in D, brake pressed and accelerating at the same time, The car didn't move, so I just simulated some load in the engine.

Chart #3.- Parking, then moved the shift to D, and back to Parking

Chart #4.- Getting out of my neighborhood. The computer got slow and couldn't take more good data, like hard accelerations, climbing hills or so.

Note that I changed the scales from one chart to another to separate one line from another. The RPMs scale to the left is accurate, while the MAP may have an offset...But the real MAP values are from 0 to 255.

[Buzo]

This is how I am emulating the Mechanical acceleration pump of a carb.

The rate of change of the TPS is monitored around 50 times per second. If the change from the current value to the next is bigger than (tuneable value) then open the injector by (tuneable value) extra time

You can see the PWM OUT little squares. They apear only when there is a positive and sudden slopes.

[2ndGenGuy]

Dude, this is a ton of work! I love reading through this thread. I wish I had something more constructive to contribute. But please keep posting the updates!

[Buzo]

Dude, this is a ton of work! I love reading through this thread. I wish I had something more constructive to contribute. But please keep posting the updates!

Wow, your coment got just in time, I was asking myself before posting the next graphs if this information would be useful or not, or if I was just filling the forum with some sh...

Thanks for posting, and based on your comment I will keep posting what I have found, so the data is documented in some place other than my computer haha.


Here is a chart of the engine RPMs vs TPS vs MAP in a short trip I made today.





And here is the same period of time, but only MAP and TPS.
Honestly I don't see any difference other than the MAP changing a lot faster when accelerating than the TPS.

I know Cygnus has told me before that fuel compensation using MAP is more accurate than using TPS, but in reality they are very similar to each other...

[Warren 88 Accord]

Dude, this is a ton of work! I love reading through this thread. I wish I had something more constructive to contribute. But please keep posting the updates!

^^What he said^^

[Buzo]

I believe a short video of the TBI working in the car would be nice at this point of time, right?

Even though its toasting outside, I will take a short videoclip during the weekend and will upload it here for your reference.

[Buzo]

^^What he said^^

Thanks for your comment Warren!

[cygnus x-1]

Wow, your coment got just in time, I was asking myself before posting the next graphs if this information would be useful or not, or if I was just filling the forum with some sh...

It's definitely interesting watching you go through this, and quite inspiring. You've made enormous progress in a short period of time.

And here is the same period of time, but only MAP and TPS.
Honestly I don't see any difference other than the MAP changing a lot faster when accelerating than the TPS.

That's big part of it actually. The MAP is a lot more sensitive than TPS, especially at low throttle. At higher throttle levels there isn't as much difference. But...

I know Cygnus has told me before that fuel compensation using MAP is more accurate than using TPS, but in reality they are very similar to each other...

Unfortunately when you look at the physics of what is going on (why acceleration/deceleration compensation is REALLY needed), it's far more complcated than just TPS and MAP. At all times there is fuel sticking to the intake manifold walls and also evaporating from the walls. Under static conditions the amounts of evaporation and sticking are the same, so there is no difference in how much fuel is injected vs how much gets into the cylinders. But when you open the throttle, the MAP increases, which makes the fuel evaporate as a slower rate, so for a short period of time there is more fuel sticking to the walls than is evaporating, so you need an extra shot of fuel to make up for this until the sticking/evaporation rates equalize again. Changing engine RPM changes the air flow rate through the manifold, which also affects the evaporation/sticking rates.

Much of the time, you can get pretty good results by using a combination of MAP and TPS based enrichment. But to really get it nailed down you need to use a wall wetting compensation scheme, like what the MS guys call X-tau, or EAE. These methods actually keep track of the fuel on the manifold walls (based on MAP, RPM, and the amount of fuel injected, with some adjustable curves that determine sticking and evaporation rates) so that the injected fuel can be compensated. It's a bitch to tune but when you do get it tuned right it works VERY well.


C|

[Buzo]

I stole the Megalogviewer software from the megasquirt website and I am using it to view my own logs. Hope they don't care...

I captured a moment where there is a HUGE difference between TPS and MAP

The red circle shows how the TPS remains flat while the MAP starts high, and decreases as the RPMs increases.

With this, I am ready to write the code to add compensation based on MAP changes.

[Buzo]

...But to really get it nailed down you need to use a wall wetting compensation scheme, like what the MS guys call X-tau, or EAE. These methods actually keep track of the fuel on the manifold walls (based on MAP, RPM, and the amount of fuel injected, with some adjustable curves that determine sticking and evaporation rates) so that the injected fuel can be compensated. It's a bitch to tune but when you do get it tuned right it works VERY well.


C|

Thanks for your comments, everything you said is accurate as usual.
However your last statement is too advanced for me. I only want my car to fire up every time without me pressing the pedal. I want the car to be at the same RPMS always, don't care if it is in P or D or if it is cold or hot, or if I had drove it for 5 minutes or 45 minutes. I want to be able to switch from fuel economy mode to power mode depending on how many beers I have had. That's something my carb was not giving me and I got by switching to my own EFI version. I have also had a lot of fun with this project and I am glad somebody is interested in what I have done so far, and in what's going to happen at the end...

[Buzo]

I believe a short video of the TBI working in the car would be nice at this point of time, right?

Even though its toasting outside, I will take a short videoclip during the weekend and will upload it here for your reference.

Too short video but enough to show you guys the TBI working in the car.


http://imageshack.us/clip/my-videos/17/etqx.mp4/

[Buzo]

Edit, I said today I worked fine tuning the acceleration algoritm, but it is actually the CRUISE algoritm...

I am writing my code in Assembler, so instead of making tables which is a little complicated in this language, I am assigning PWM/MAP values a little below from stoichiometric, then just let the O2 to add whatever PWM points are needed to reach the stoich line.

In the first chart, I am not using the O2 Signal to control, (but its being recorded for reference) so you can see how the O2 goes almost to zero when accelerating wich means the engine gets too lean. And it is too rich when idling in a stop sign.

In the second chart, I already added the code for the O2 to compensate the required PWM above and below the stoich line (0.5 Volts) and see how it stays in such mid line in average.

In both charts the O2 readings are in the Secondary (right) axe.



Above readings were taken in the same route through the streets of my neighborhood. The first chart with the O2 control disabled and the second with it enabled.

[Buzo]

I need to fix a couple of problems,

1) There is a Purge Pulse sent each time the key is open. This is useful when starting up in the morning. The Manual says the pulse must be done before start cranking, so I am having fuel odor due to this pulse because sometimes I open the ign key just to open/close the windows and the purge pulse is send to the TBI.

I think I am going to send it at the first cranking pulse instead of at the ignition key open pulse.

2) Having problems to keep the stoich at Idle. For some reason my algorithm (or the engine response) is too slow, so I can feel the engine slightly rev'ing up and down while the closed loop is trying to control the stoich value.

I am going to play with delays, make and adjustment and wait a second until the engine responds.

Besides those two problems everything else is working great. I've been into several rush hours and the car has responded perfect. I will wait until the next tank refill to capture the new fuel economy, whatever it is.

[Buzo]

It was raining today and took my car for a ride. It ran different at IDLE w/load, almost wanting to die, even though I made a pretty long drive this afternoon with no issues.

I believe its time to work in the Manifold Air Temperature compensation...

Done the purge pulse change I described below, by the way.
The engine is not purged until the first pulse from the coil is received so I am free to open the key at any time. No more fuel odor...Certifyed by my daughter who was the one that detected the fuel smell.

[Buzo]

The following chart is an XY scatter of the Engine Speed vs the MAP sensor.

This helps a lot to manually build the VE table, since it defines the area where the car will be at at any given time/engine speed, and the areas where it will never be at. So the effort of tunning can be concentrated in such area while the surronding area can be just estimated.

I found a way (a painful way) to make a 16x16 table for the VE in assembler, so its what I am working at right now.

[Buzo]

It was raining today and took my car for a ride. It ran different at IDLE w/load, almost wanting to die, even though I made a pretty long drive this afternoon with no issues.

I believe its time to work in the Manifold Air Temperature compensation...

This is the behavior of the Manifold Air Temperature and the Coolant Temperature Sensor during my 20 minutes trip this morning.
It was at 30 C when I fired the car up. Need to think a little bit what would be the best algorithm for MAT compensation and avoid what happened in a raining day

[Dr_Snooz]

That video is awesome! Nice work.