MAF Adjuster

[VL400 Member Find all posts View Profile Close VL400]

Myself and a mate both have the early model petrol 90 series Prado that run no cats or oxy sensor. A month or two ago I finally got the shits with fuel economy, well lack of, so started looking at ways to improve it. AFAIK the ECU uses a OTP custom MCU so gaining access would not be worth it, couldnt see a way to log data either. Chucked a wideband oxygen sensor on it using an Innovate exhaust clamp and it said it was running pig rich - 11:1 cold start, 13.5-14 at cruise and 10.8 WOT. I have since found that the Innovate clamp mounted WB reads totally different to what a WB in a bung further up the exhaust reads (at cruise with 14:1 on the clamp was 15:1 using a bung, but WOT is identical). I will be doing some more testing with this but looks like the Innovate clamp is useless - and on a car with no cats it really should work ok.

Anyway, before finding out the clamp read wrong I made this little device up...




It takes the 0-5v MAF signal and can modify the output +-50% to trim the airflow signal that the ECU uses - which in turn changes what fuel gets injected, but still need to be careful as the spark advance is also changed. It has a few other inputs to make it more tunable - RPM, vehicle speed, injector pulse, throttle position and wideband. It has USB for logging and uses TunerPro (http://www.tunerpro.net/) to edit the tables and data log. At the moment it just has a big 3D table of MAF voltage and RPM with the required adjustment, but will have lean cruise and a few other things eventually. It can do instant fuel economy in L/100km, which can be used when trimming the fuel but it sure does have some big numbers.

Am still playing with the firmware but its getting there slowly. Its happy making changes to the MAF voltage, engine runs identical with 0% adjustment and get no check engine light. Will post up more info as I start to use it more and also what gains in fuel economy I can get but thought some of the 90 series members might be interested.

[ianafloat Junior Member Find all posts View Profile Close ianafloat]

Holy shit, I am going to need someone to explain what you just said, other than crap fuel economy. Just from the picture of the electronics, well done, I look forward to seeing how it goes.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Yeah I'm a bit confused as well.
But my truck drinks too much, like it's owner. If this gizmo can fix this I'm interested.

[Jeepster Junior Member Find all posts View Profile Close Jeepster]

Sounds promising, keep us posted! I'm sure a few of us 90 owners will be interested in how this turns out!!

[letsgoplaces Advanced Member Find all posts View Profile Close letsgoplaces]

I'm watching too

[humphrey Junior Member Find all posts View Profile Close humphrey]

I'll be watching too..........just to see if anyone can explain what it all means.

[VL400 Member Find all posts View Profile Close VL400]

Well it basically means the MAF ends up lying to the ECU, as we are wanting around 15 parts air to 1 part fuel if you lie to the ECU about how much air is really being consumed you can change how much fuel the ECU injects.

Here are some screen shots of the sort of info you get to see. A sample of the dash monitor, there are heaps of other things to view though..




And the table to make adjustments with...

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Will be very interested to see the end product, is there any power loss when you lean out the fuel, and does the engine temp rise.

[williade Avid PP Poster! Find all posts View Profile Close williade]

Could this be used on a late model with oxy sensor and hot wire MAF?

I wonder if a passive circuit could be made to do the same thing, or is your AVR chip taking input from other sources to calculate the maf adjustment on the fly?

[VL400 Member Find all posts View Profile Close VL400]

Will be very interested to see the end product, is there any power loss when you lean out the fuel, and does the engine temp rise.

If there is a loss of power its too lean and you will prob end up using more fuel - will take more throttle to maintain the same speed. Engine temp shouldnt rise as the exhaust gas temp will be a little cooler but will be keeping an eye on it. I have not made much of a change yet but will be over the next few weeks so will see how it goes. Lean cruise has been used for years on other cars.

Could this be used on a late model with oxy sensor and hot wire MAF?

I wonder if a passive circuit could be made to do the same thing, or is your AVR chip taking input from other sources to calculate the maf adjustment on the fly?

Originally I was just going to use a simple resistive divider, but kinda got carried away. The AVR chip calculates the correction on the fly, so its not just an accross the board adjustment. Its possible to have diffent correction factors for all different load points and RPM - so can lean off just where it sits at 90-110KPH cruising but once you get to a hill or overtake it will go back to 0% correction (or can add fuel if the factory is too lean) as your in a different part of the map.

[MidLifeCrisis Out of control poster! Find all posts View Profile Close MidLifeCrisis]

I will be watching this thread intensely as I have noooo idea what this all means but the overwhelming sense of confusion makes my day to day problems just fade away.

Peoples knowledge levels in certain areas amaze me!

[williade Avid PP Poster! Find all posts View Profile Close williade]

Do you plan on releasing the schematics and the hex code for the AVR? If so I have an AVR ISP and would be happy to be a test guinea pig for the project.

[VL400 Member Find all posts View Profile Close VL400]

I will see how it all works out first - it has only been installed for a few weeks and am still making code changes. But if it ends up working well and helps improve fuel economy I have a few spare boards so can make some more up or send out blank boards for people to buy the components themselves. Hex code will be released and prob the source too. If you (or others) want to give it a go anyway, PM me and can send you over a board that you can build up yourself.

[09PradoGXL Junior Member Find all posts View Profile Close 09PradoGXL]

Also going to follow this. I don't have a 90, but the project looks interesting.
Nice work.

Scott.

[wanderingoz Junior Member Find all posts View Profile Close wanderingoz]

I have a few spare boards so can make some more up or send out blank boards for people to buy the components themselves.

Just adding my name to the list of followers. I almost choked when I read this piece. The only spare boards I have are left over from making the drawers in the back and are made of ply

WOz