is TBI an option for our cars?

[Buzo]

I did a quick search and found nothing about somebody trying a carb to TBI conversion. Need to say the following first:

1) I'm really happy with my carb performance. But I'm getting bored.
2) Not interested in the $600 USD aftermarket TBI.
3) Not interested in a FI donor car.
4) I know the advantages of a multi port FI over the single port FI. But I also know the advantages of the single port FI over the carb.
5) I will build my own ECU. I'm most worried about the mechanical portion of the system than the electronics.
6) I'm thinking this may be my next project.

I owned a chevy monza some time ago with the Single Port or TBI system (sold only in Mexico, I think), honestly, I never though about the fuel system it has, because it never gave any problem.

I have on hand an in-tank Fuel Module with a pump, filter and regulator, everything integrated in a bucket that fits my fuel tank. So check mark to this part of the project.

Then I'll need to:

a) Adapt a TPS and a Mass AirFlow Sensor to the Carburetor, and start collecting data while its still carbed. So when I start writting my code I know the range of the input values at all drive conditions.

b) Get a Chevy Throttle Body Asm from a JY, make and adapter plate and throw it into the OEM intake manifold.

The plan is to start writing the "default" program which every single ECU runs when any input goes bad, which estimates the missing signals just to keep the car running.

If that part of the project works, then I can think in compensate for temperature, altitude etc.

[Buzo]

This picture tryes to explain what I just said below:

To begin, only the Throttle Position Sensor will drive the amount of fuel dispensed in the intake manifold. If that works, the other sensors will be added later, one at the time.

[cygnus x-1]

I would recommend looking for an older Megasquirt, like an MS1 or MS2, for the following reasons:

1) Can be had for cheap now that MS3 is out.
2) Supports TBI or port injection and ignition if you decide to tackle that later.
3) VERY hackable since all schematics and source code are available.
4) There are some excellent tuning tools available for free.
5) You will NOT get bored.

At the very least check out the online manuals for MS as they have a wealth of information on how fuel injection works in general.


If you still want to try and roll your own ECU, the bare minimum information the ECU needs to run the engine is load and RPM. On a stock type engine load is best determined with a MAP sensor, not throttle position. You could also use MAF but those are more tricky to setup. To start the engine cold you'll also need a coolant temp sensor. Then if you want to play around with acceleration enrichment you can add a TPS, although you can do better by looking at the rate of change of the MAP instead.


Seriously, at least look into MS. It's well worth the effort.


C|

[Dr_Snooz]

Didn't some of the older Civics have dual port fuel injection? They might provide some of the hardware you're looking for.

[Buzo]

Didn't some of the older Civics have dual port fuel injection? They might provide some of the hardware you're looking for.

Thanks, i'll start looking for these civics as well as citations, cavaliers, etc. around the 1992 MY.

[Buzo]

I would recommend looking for an older Megasquirt, like an MS1 or MS2, for the following reasons:

1) Can be had for cheap now that MS3 is out.
2) Supports TBI or port injection and ignition if you decide to tackle that later.
3) VERY hackable since all schematics and source code are available.
4) There are some excellent tuning tools available for free.
5) You will NOT get bored.

At the very least check out the online manuals for MS as they have a wealth of information on how fuel injection works in general.


If you still want to try and roll your own ECU, the bare minimum information the ECU needs to run the engine is load and RPM. On a stock type engine load is best determined with a MAP sensor, not throttle position. You could also use MAF but those are more tricky to setup. To start the engine cold you'll also need a coolant temp sensor. Then if you want to play around with acceleration enrichment you can add a TPS, although you can do better by looking at the rate of change of the MAP instead.


Seriously, at least look into MS. It's well worth the effort.


C|

I alredy read some stuff about the Megasquirt and all the FI theory they have in their site. If something fails, I will 100% follow your recommendation.

[forrest89sei]

Yeah the 88-91 Civics with the D15B2 Came with DPFI, I've always wondered about adapting one of those TBI Setups to work on a A20

[Buzo]

I found a TBI from a 4 cylinders Cavalier in a very small package that I believe will fit under hood.
The guys in the JY were supposedly to dismount it for me tomorrow because I went a little late today. The cost was 35 USD with all sensors, hydraulic connections and harnesses. So another check mark for the hardware.

I modified mi OBDZ by adding a Transistor that will drive the injector.
It can monitor 8 analog inputs at the same time at a clock speed of 20MHz, so speed or memory resources are not a problem.
It also can generate 0-100% PWM signal in 255 steps which I believe will give me enough resolution for the control of the fuel.
Check mark for the computer, the material cost of this thing is 50 USD If I remember correctly. (Check mark anyway)

The only pending so far is the software (almost nothing haha), I have written the basics already that should allow me to keep the engine idling.
Then from there it will be test, and retest, and retest (how do you say "prueba y error" in english?)

[Buzo]

"The Computer"

[2oodoor]

brilliant idea, has been discussed before but never has anyone here done it that I have read.

I would thinik that a small v6 would be a better donar for the hardware. Something that is capable, but hey I guess one from an old long stroke GM four banger would suffice. I would explore the likelyhood of other electronics donars such as AMC Jeep, VW, Escorts, something that is more retrofitted to keep up with the other makes would have more isolated wiring harness I would guess.
Getting it to work with OBD2 interfaces would be awesome since most oem TBI are not. I guess you are going to use a carbed distributor or what are your thoughts there for electronic ign advance?

[cygnus x-1]

I really like this kind of pioneering work. Will be interesting to see how this works out!

For that TBI, you'll need the fuel pump from that car as well, or something similar. TBIs use a higher fuel pressure than carburetors, but lower than standard port injection. You *may* also have to run a return line back to the tank, but I'm not sure if the TBIs did that or not.

Looks like you have the electronics under control, but I'll throw out some random thoughts anyway. I think you'll need a heat sink on that driver transistor. Can't tell from the picture, is it a MOSFET? The injector will have quite a lot of inductance so you'll want a flyback diode on there.

Have you sorted out which sensors you'll be using yet? I have some voltage curves for the stock Honda MAP sensor and I think one of the temp sensors if you're interested. You actually don't need an O2 sensor to run although it will be helpful for tuning. If you have a wideband O2 it would be MUCH easier and more useful than a narrow band (stock type) sensor.


C|

[Buzo]

I got the TBI from the 89 Cavalier with a 4 cyl 2.2L from the JY, barely above our Honda's 2.0L.

It has the Map Sensor, the TPS, and the Air Temp Sensor. It also has the air idle control solenoid which I don't know exactly what it does.

I am going to collect data from all sensors, even the stock ones, but to start really controlling the fuel I am going to use only the TPS signal as a first step. I have read that there are some racing cars that uses only the TPS to determine the quantity of the fuel. That will be to probe myself I am in the correct direction.

This is the little guy. Sorry for the quality of the picture, looks like my cel strugles to focus when there is some sun light in the pic frame.

[Buzo]

I really like this kind of pioneering work. Will be interesting to see how this works out!

For that TBI, you'll need the fuel pump from that car as well, or something similar. TBIs use a higher fuel pressure than carburetors, but lower than standard port injection. You *may* also have to run a return line back to the tank, but I'm not sure if the TBIs did that or not.

Looks like you have the electronics under control, but I'll throw out some random thoughts anyway. I think you'll need a heat sink on that driver transistor. Can't tell from the picture, is it a MOSFET? The injector will have quite a lot of inductance so you'll want a flyback diode on there.

Have you sorted out which sensors you'll be using yet? I have some voltage curves for the stock Honda MAP sensor and I think one of the temp sensors if you're interested. You actually don't need an O2 sensor to run although it will be helpful for tuning. If you have a wideband O2 it would be MUCH easier and more useful than a narrow band (stock type) sensor.


C|

Thanks for pointing out your observations.
The fuel pump and the filter I got is from a returnless system, it means no return line is required since the pressure regulator and filter are in-tank type. I believe it has a working pressure of 400 kPa, but I can easily get a 350 kPa regulator (or lower) if needed.

From the electronics, you are right, there is a diode alread in the solder side. I am going to drive a coil that will damage the NPN transistor (TIP41) if the diode is missing. I will look for a heat sink as well.

In the near future, after I can control my engine with the TPS, I will add everything else, including the MAP sensor, Cololant and Air Temperatures, and of course our stock O2, which is a narrow band I know, but once you get it hot it will tell you if the mix is rich or lean. Good enough for me.

Forgot to say that any voltage curve you have that can share with me will be very helpful. Thanks a lot for your interest. I know this is going to work better and the project done faster than I expected. At this time I have everything but the adapter plate that I will take to the machine shop on saturday.

[Buzo]

brilliant idea, has been discussed before but never has anyone here done it that I have read.

I would thinik that a small v6 would be a better donar for the hardware. Something that is capable, but hey I guess one from an old long stroke GM four banger would suffice. I would explore the likelyhood of other electronics donars such as AMC Jeep, VW, Escorts, something that is more retrofitted to keep up with the other makes would have more isolated wiring harness I would guess.
Getting it to work with OBD2 interfaces would be awesome since most oem TBI are not. I guess you are going to use a carbed distributor or what are your thoughts there for electronic ign advance?

The plan so far is to leave the carbed distributor.

For the momment I just want to hear it Idling. Then I can think in adding more and more capabilities.
A friend of mine works in a local company that makes the hand held OBDII diagnostics devices, so he has all the communication protocols and everything, I can get him engaged in this project and take us to the OBDII world with his help.

[Buzo]

As a side note, I went tho the JY today and as expected the guys had not removed the TBI from the engine. They were told by their boss to fire up the engine first before removing the TBI, so they can clasify the engine as a good or bad.

You won't believe this but they connected a battery and fired it up (using a "direct" of course because they couldn't find the key) did put some gas directly in the throttle and the engine started and kept idling immediately. Of course there were dust everywhere, but It idled nicely. They got surprised that there was still some fuel in the tank.

Tell me if ANY carbed engine can do that without sputtering, vibrating and needing several tries, well this is going to be the great advantage if we can make the carb conversion to TBI to work.

After this quick test they could finally remove it and sell it to me!

[Buzo]

The TBI height compared with the stock carburetor.

Yeah, its really dirty, I plan to clean it through before installing it.

[Buzo]

The adapter plate I built myself. Not bad uh?
At this time I am ready to begin with the instalation tomorrow morning!

[Buzo]

A visual aid of how the software in my home made ECU will work.
There is an Idle Air Solenoid in the TBI that I don't quite understand how it works (if it needs PWM or is only a on/off signal), so I am sure I need to add some code for such solenoid. But its easy in any case, not worried at all.

[cygnus x-1]

The idle solenoid probably takes a PWM signal. It acts as a sort of computer controlled throttle to help keep the idle stable. You can do without it.

Your control scheme is missing a critical variable, RPM. Engine fueling varies significantly with RPM so you will need that to run. Probably the easiest way to do that is to get a signal off the tach line and count the pulses. The signal may not be very nice though so you might want it optically isolated. If your MCU has any hardware counters you could use those, or you could add a frequency to voltage converter and sample the voltage.

That's cool that the TBI has all the sensors included. It's a nice compact package.


C|

[Buzo]

I removed the stock carb and emissions stuff and checked my adapter plate against the manifold.



Then removed some material to match the new TBI, also changed the 4 screws for a short ones



And this is the first wiew of the TBI installed, after adapting the "disc" for the accelerator taken from the stock carb. This was the most time consuming activity.



More pics later...

[2oodoor]

wow, you are on task dude!

I am surprized the tbi throttle plate clears the partition plenum on the factory intake.

[Buzo]

[Buzo]

The pump and filter assembly. These guys are going to help me to fire it up...

The fuel pressure regulator is integrated to the TBI, so I have to add a return line. But in the other hand I don't have to guess which is the working pressure of the injector. Everything is OK to run the first functional test tomorrow.

[Buzo]

Could a Moderator help me to add this pic to my signature Please? I tried in the edit signature option but I couldn't. For some reason none of the smilies to the right or the buttons above work in any screen of the forum. It is only to motivate myself, OK? because this project still can fail...



Thanks.

[Buzo]

The first task today will be to acquire the TPS values at several throttle openings, so I can plot the TPS response from Idle to Wide Open Throttle.

The second, which finally includes some fuel, will be to apply a PWM % to the injector, fire up the engine and manually open the throttle until the engine is starving for fuel (just like in the old days when adjusting the mix screw). Capture the TPS and the engine RPMs vs the PWM % applied. Create a table and use it in the software. AND THAT'S IT, hahaha, sure. We'll see.