Homebrew OBD / diagnostic display
09-23-2008, 09:10 PM
#1
Homebrew OBD / diagnostic display
Both of my Toyotas are pre OBD-II so troubleshooting requires a bit of patience and a volt meter. I decided to invest a few evenings in the construction of a sudo OBD-II meter which monitors and displays some of the more common sensors of interest (oxygen, VAF-Idle, TPS-Vta, VAF-Vc, Vs, Injector dwell time, Ne cycles, etc.). It has worked out rather well. Below are a few pictures of the display as it cycles through the various sensors:
http://i303.photobucket.com/albums/n...rs_Edge/02.jpg
http://i303.photobucket.com/albums/n...dge/IGN-Ne.jpg
http://i303.photobucket.com/albums/n...ge/TPS-Vta.jpg
http://i303.photobucket.com/albums/n...dge/VAF-Vc.jpg
In particular, the O2 sensor is invaluable. In addition to the actual voltage, a bargraph slides back and forth proportional to the voltage. Kinda like watching the heartbeat of the engine. Absolutely valuable diagnostic for determining whether your O2 sensors are working as expected.
In addition to being displayed, the data is spit out through an RS232 cable at 9600 baud and can be captured by a laptop using Hyperterminal or any other similar software.
Hoping that others out there can makes suggestion on what other sensors would be of interest or useful in troubleshooting either 22re's or 3VZE's. Only other parameters I typically am concerned with are fuel pressure, oil pressure, coolant temperature and EGR temperature. Any suggestions or positive input would be appreciated.
Thanks,
Aaron
http://i303.photobucket.com/albums/n...rs_Edge/02.jpg
http://i303.photobucket.com/albums/n...dge/IGN-Ne.jpg
http://i303.photobucket.com/albums/n...ge/TPS-Vta.jpg
http://i303.photobucket.com/albums/n...dge/VAF-Vc.jpg
In particular, the O2 sensor is invaluable. In addition to the actual voltage, a bargraph slides back and forth proportional to the voltage. Kinda like watching the heartbeat of the engine. Absolutely valuable diagnostic for determining whether your O2 sensors are working as expected.
In addition to being displayed, the data is spit out through an RS232 cable at 9600 baud and can be captured by a laptop using Hyperterminal or any other similar software.
Hoping that others out there can makes suggestion on what other sensors would be of interest or useful in troubleshooting either 22re's or 3VZE's. Only other parameters I typically am concerned with are fuel pressure, oil pressure, coolant temperature and EGR temperature. Any suggestions or positive input would be appreciated.
Thanks,
Aaron
09-23-2008, 09:22 PM
#3
Hah! I only wish I could get to the preventive maintenance on these two frames. Seems I fix one thing and then something else craps out. Good thing I enjoy tinkering.
Got any suggesions on what other parameters would be useful to monitor or log? I have no experience with ODB-II excepting the equivalent used on my Mercedez. Looks like they are full of both userful and useless diagnostic features.
Got any suggesions on what other parameters would be useful to monitor or log? I have no experience with ODB-II excepting the equivalent used on my Mercedez. Looks like they are full of both userful and useless diagnostic features.
09-23-2008, 10:34 PM
#4
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very impressive... did you actually mfg. the "scanner" or did you just macguyver an OBD1 plug onto an oBD2 scanner? just curious... would like to have something like this myself to check the engine periodically...
09-24-2008, 04:34 AM
#6
Total homebrew. I used a microcontroller to read, calcualte and then display the meansurements. Added a few discrete analog components to ensure I buffered the voltages tapped off the ECU and so far nothing has gone up in smoke.
Getting close to the point of having the board fabricated but wanted to get input from others like yourself that know much more about troubleshooting common issues on the pre-ODB toyotas. Before I send off the CAD drawing for the board, I want to make sure I maximize the diagnositc features. Working right now on monitoring the fuel pressure at the fuel rail, the coolant and block temperature, the pressure (vaccum) at the intake, the cold start switch and the oil pressure.
Anything you can suggest would be appreciated.
Aaron
Getting close to the point of having the board fabricated but wanted to get input from others like yourself that know much more about troubleshooting common issues on the pre-ODB toyotas. Before I send off the CAD drawing for the board, I want to make sure I maximize the diagnositc features. Working right now on monitoring the fuel pressure at the fuel rail, the coolant and block temperature, the pressure (vaccum) at the intake, the cold start switch and the oil pressure.
Anything you can suggest would be appreciated.
Aaron
So what is this, OBD 1.8 upgrade?
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09-24-2008, 08:10 AM
#8
Contributing Member
The things I look at most with OBDII is coolant temp and whether or not the ECU is in open or closed loop, and if in closed loop what the fuel trims are. Not sure how to help you with those but you asked for input. 
09-24-2008, 08:16 AM
#9
mt_goat, what are fuel trims exactly? I don't know if I reall seeing an output on the ECU that identifies whether it is in closed or open loop. However, the O2 sensor seems to be a good indicator. For example, when I fire up the engine cold, the O2 voltage is flat (does not change). As well, when I push in the clutch to and let the RPM's drop, it goes flat. These instances would be ideally when the ECU goes into closed loop (ignores ECT, O2, etc., correct?
09-24-2008, 08:37 AM
#10
Contributing Member
mt_goat, what are fuel trims exactly? I don't know if I reall seeing an output on the ECU that identifies whether it is in closed or open loop. However, the O2 sensor seems to be a good indicator. For example, when I fire up the engine cold, the O2 voltage is flat (does not change). As well, when I push in the clutch to and let the RPM's drop, it goes flat. These instances would be ideally when the ECU goes into closed loop (ignores ECT, O2, etc., correct?
It should be pretty easy for you to come up with some way to tell when you are in open or closed loop, like you said maybe by the front O2 sensor, or maybe something else. I can usually also tell by looking at my A/F gauge. The ECU should go into open loop at cold start-up and during hard decelerations and of course hard accelerations (anything over about 80% throttle). Knowing when you're in closed loop would be of benefit for you because you'll get the best MPG in closed loop.
EDIT: This is a lot more info than you probably wanted, but it does explain fuel trims and open/closed loop very well:
http://www.gadgetonline.com/U-Tune.pdf
Last edited by mt_goat; 09-24-2008 at 09:07 AM.
09-24-2008, 06:07 PM
#12
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Something else to bear in mind some trucks only have one o2 sensor before the cat [like my japan built 94]...
fuel trims might be worth knowing...
basically I'd like to be able to track those things you're looking at right now like intake vacuum pressure and so forth...
fuel trims might be worth knowing...
basically I'd like to be able to track those things you're looking at right now like intake vacuum pressure and so forth...
09-24-2008, 07:48 PM
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out of curiosity, how are you planning on obtaining some of the readings considering the toy doesn't have sensors to accomodate them... intake vacuum, fuel pressure, cold start switch operation, engine temp (as opposed to coolant temp), etc.?
09-24-2008, 08:52 PM
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Ambient air temp (partial to those who like to not just know the air-fuel, but also how hot or cold it is outside.)
Mileage/Fuel Calcs.
Voltage. (*even though on the dash, dash meter's fluctuate in quality.)
Great Idea...sow license and sell it to the public!
Kelley
p.s. daytime pics would be cool also to see how it looks.
(realizing there is probably some secrecy to it until released)
Mileage/Fuel Calcs.
Voltage. (*even though on the dash, dash meter's fluctuate in quality.)
Great Idea...sow license and sell it to the public!
Kelley
p.s. daytime pics would be cool also to see how it looks.
(realizing there is probably some secrecy to it until released)
09-25-2008, 04:59 AM
#17
Bigtruckinwheels: I am using Microchip's PIC16F877 controller.
KellyC: Air temp and battery voltage are in progress, just need to find a location on the truck that is relatively unaffected by engine temperature. Fuel/mileage calcs are something I have considered, but I can't quite wrap my head around how they are calculated accurately. Any suggestions?
Abecarian: manufacturers like Motorola, Analog Devices and Linear Tech. all have discrete components that are highly accurate and very inexpensive. Some of the sensors (like cold start switch) don't even require a separate sensor. They are either "on" or "off" and can be determined simply by detecting the state using a digital I/O pin from the microcontroller. The fuel pressure sensor is somewhat difficult owing to the fact that the pressure sensors are >$100 because of the harsh environment (fuel). I am tinkering with using an oil pressure sensor since it can handle the fuel contact and measure the high pressures. When I said engine temp, I should have said coolant temp. Sorry.
KellyC: Air temp and battery voltage are in progress, just need to find a location on the truck that is relatively unaffected by engine temperature. Fuel/mileage calcs are something I have considered, but I can't quite wrap my head around how they are calculated accurately. Any suggestions?
Abecarian: manufacturers like Motorola, Analog Devices and Linear Tech. all have discrete components that are highly accurate and very inexpensive. Some of the sensors (like cold start switch) don't even require a separate sensor. They are either "on" or "off" and can be determined simply by detecting the state using a digital I/O pin from the microcontroller. The fuel pressure sensor is somewhat difficult owing to the fact that the pressure sensors are >$100 because of the harsh environment (fuel). I am tinkering with using an oil pressure sensor since it can handle the fuel contact and measure the high pressures. When I said engine temp, I should have said coolant temp. Sorry.
09-25-2008, 08:40 AM
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Bigtruckinwheels: I am using Microchip's PIC16F877 controller.
KellyC: Air temp and battery voltage are in progress, just need to find a location on the truck that is relatively unaffected by engine temperature. Fuel/mileage calcs are something I have considered, but I can't quite wrap my head around how they are calculated accurately. Any suggestions?
Abecarian: manufacturers like Motorola, Analog Devices and Linear Tech. all have discrete components that are highly accurate and very inexpensive. Some of the sensors (like cold start switch) don't even require a separate sensor. They are either "on" or "off" and can be determined simply by detecting the state using a digital I/O pin from the microcontroller. The fuel pressure sensor is somewhat difficult owing to the fact that the pressure sensors are >$100 because of the harsh environment (fuel). I am tinkering with using an oil pressure sensor since it can handle the fuel contact and measure the high pressures. When I said engine temp, I should have said coolant temp. Sorry.
KellyC: Air temp and battery voltage are in progress, just need to find a location on the truck that is relatively unaffected by engine temperature. Fuel/mileage calcs are something I have considered, but I can't quite wrap my head around how they are calculated accurately. Any suggestions?
Abecarian: manufacturers like Motorola, Analog Devices and Linear Tech. all have discrete components that are highly accurate and very inexpensive. Some of the sensors (like cold start switch) don't even require a separate sensor. They are either "on" or "off" and can be determined simply by detecting the state using a digital I/O pin from the microcontroller. The fuel pressure sensor is somewhat difficult owing to the fact that the pressure sensors are >$100 because of the harsh environment (fuel). I am tinkering with using an oil pressure sensor since it can handle the fuel contact and measure the high pressures. When I said engine temp, I should have said coolant temp. Sorry.
you could measure engine temp all you need is a simple stick-on transducer attached to the block someplace away from the manifold... say opposite side for a 4cyl and on top underneath the intake runner for a 6/8... just an idea not sure what you'd be able to infer operation wise from that measurement if anything, but if you wanted to know...
