scope103

Holy Cow! This is pretty impressive.

But I get the sense that you're not reading the truck's OBD I directly, but rather you have installed a handful of sensors (or are reading voltages) directly. True?

My '94 (OBD I) does have a "proprietary" OBD signal that is an inverted serial at (so far as I can tell) 110 baud. (My storage scope got pinched before I could get farther on measuring.) One of the measurements in that stream is the injector "open" time in milliseconds. Since the pressure drop through the injectors is constant (thanks to the fuel pressure regulator) the open time should be pretty close to fuel volume. With a suitable calibration factor, you can get gals/hour. Another avail. measurement is miles per hour, so your microchip can determine mpg directly from that.

Reading 110 baud on a modern computer is harder than you would think, but a talented chip programmer like yourself could bit-bang it and then resend it at some more modern baud-rate. That would still leave you with "time" to measure the things your are measuring currently. (One of the pins on the diagnostic connector is an analog voltage that indicates the gear (and lockup) of the automatic transmission; that's one I'd like to monitor.)

Thanks for the writeup, and I for one would like to hear more.

Cyberman

I looked a little closer at all this. Looks like you're getting all the inputs from the ECU, like you said. It also looks like you are just measuring voltages (and frequencies), which in turn will be coded into "real" values (i.e. TPS open %)?

Personally, I'm not sure how all this helps at a glance, it is cool to be able to pull those values. Of course, I'm not a tuner, so those values would mean nothing to me anyway. What I did find interesting is that the speedometer converts the mechanical cable into an electronic speed signal for the ECU.

ahickman

Cyberman: Beyond just being a novel display of voltages and frequences, it is indeed a useful diagnostic tool. If you read through the postings in YT, you will see that a large percentage of issues (oxygen sensor, oil ECT sensor, VAF and TPS sensors) result in the use of a voltmeter or similar tool. By having these various parameters displayed realtime, you can more easily narrow the troubleshooting steps. For instance, if you see that the O2 sensor stays high (0.9V), you might first look at the cold start switch. With a flip of the dial, you can look directly at the state of the cold start switch to determine if it is in the open/close position.

Scope103: I feel a little embarrased and may not have done all my homework. The OBD-I output from the ECU, does this give real time information beyond the diagnostic codes? Can you get the discrete values of the individual sensors from this stream? No sense in re-inventing the wheel if it is already round

gte718p

I was working on something fairly similar before I deployed. I was using an AVR chipset on the ardurino board.

For MPG I found a fairly accurate flow meter on Fleabay. One sensor on the pressurized line one on the return. I'm simply measuring flow, and input to the speed. A quick little numerical integration and I get a decent number.

One of my other plans that never got implemented was to use a relay to short the ECU test jumper and read in the flash pattern and have it spit out english. It seems fairly trivial but would be alot nicer then counting the flashed.

Sparkfun has some fairly cheap accelerometer. I was also thinking about building my own gtech to measure HP and to see if my mods actually did anything.

My project start b/c I was trying to use an RFID chip as a key like the new luxury cars are doing. That was fairly simple and I had all these spare inputs that I decided to do something with.

Cyberman

Ya, I wasn't knocking your project. I haven't dug deep into the electronic diagnosis of this truck yet. I'm sure what you're doing is useful.

scope103

a. Don't feel embarrassed; you're miles ahead of me, even if on the parallel road.

b. Homework isn't the issue; I couldn't find any direct documention of this (there's nothing in the FSM). I found a drawing of the service tool (Toyota brand OBD-I) showing the display screen, and went forward from there.

c. The information is real time, but it's 90s tech. At 110 baud, it repeats about every 2-3 seconds. (110 baud is only about 12 bytes/second). Unfortunately, I never got to the point where I was able to decode the byte positions. But I'm 95% sure that it contains miles per hour, temp, and injector-open time. I'm pretty sure it contains the fuel trim info and the state of some of the off-on sensors. Beyond that I can't help (yet).

d. Because you'll get the data only every 2-3 seconds, it will never replace what you've done (imagine watching the O2 sensor at that update rate). It you want instantaneous mpg and will accept a slow update rate, there you go. Or, you could tap the injector signal directly and measure the length of EVERY pulse. But I'm sure a very big part of your task was picking each of those wires off the ECU connector, vs. taking what Toyota has already served up.

Good luck, and please keep us posted!

ahickman

If anyone is interested, I have finally tweaked this project enough that I spent a few dollars to have the circuit board fabricated. The final version is pretty solid and I have been running it on my 94 truck for several weeks without a problem. It is capable of displaying individually the following sensors:

1. Oxygen sensor
2. Intake manifold pressure (vaccuum)
3. Vta
4. Vs
5. Battery
6. Thw (engine coolant)
7. Tha (air intake temp)
8. Ne ( units of Hz and RPM)

The LCD display is backlit and is easily viewable day or night. The real power of this logger is the RS-232 output. You can spit the data out real-time to a laptop and plot it using Excel or similar application.

If there is anyone out there that is interested, I will sell them for little more than the cost of the components. PM me if interested.

Aaron


http://i303.photobucket.com/albums/n.../OBDTool01.jpg

http://i303.photobucket.com/albums/n...s_Edge/thw.jpg

bigtrucknwheels

I'll be buying one from you, simply because I envy your programing skills!

Bravo my friend, Bravo.

gte718p

That is nice. I wish my board was anywhere close to that clean and well packaged.

ahickman

Thanks. I had to get away from the breadboard version because it got to be a mess to troubleshoot. On a couple of occassions, I shut down the vehicle when replacing jumper wires into the wrong ports. Scarey, but did not end up hurting anything.

Matt16

That is truly remarkable.

I would love to have a read out that monitors the instantaneous fuel economy so I could "tune" my driving style for maximum fuel economy. I certainly wouldn't complain if I could see the voltages produced by the tps, afm O2 sensor etc.

ahickman

Currently, this tool does not give you fuel economy (e.g. MPG). It is only a diagnostic tool which reports to you the various sensors individually. It is most useful in indicating either a malfunctioning sensor or set of sensors. For example, the O2 sensor voltage is displayed real-time. You can see the exact voltage and watch it swing through rich/lean conditions either via the voltage value or the moving bargraph.

abecedarian

Have you considered including the offset the ECU includes for determining fuel mix?
I'd have to google around, but there is a terminal on the diag port that reports how far the ECU is compensating the fuel mixture.

And what are you expecting / contemplating selling this for, whether assembled or loose parts?

ahickman

Abe,

The more I played with this project, the more potential I saw it having. Its real purpose for me was to eliminate the need to constantly have to pull out my volt meter and connect/disconnect wiring harnesses when troubleshooting common problems. It is not always fun or feasilble to spend the evening pulling of the TPS or VAF to see if it is the root of a miss, stumble or hesitation. There is so much more that can be done with this project, but I have learned over the years about project "creep" and decided to reach a functional stopping point.

Having said that, I have already started to add to this design a few more features. I was hoping to get it in the hands of a few people such as yourself and Thook and get feedback for additional features or improvements. My ears are open to improvements if you or anyone else suggest any.

I only want to recoupe the cost of the materials and shipping plus 5 or 10 dollars for my time invested. Should be about $100. Most of this is owing to the printed circuit board. I had not thought of sending out the boards unassembled, but hey, if that is a preference I would do so.

abecedarian

all I was getting at was taking advantage of the facilities provided for by the factory diagnostic port. you've done a fantastic job reverse engineering things. I really wish I was dedicated enough to do what you've done / are doing.

From what I've gleaned, nearly everything the ECU does is available in some way from the diagnostic port. I'll go through some of the things I've come across and compare to the features you're offering and see if there's anything I can offer to help.

People have tried developing VAFM to MAF conversion systems and haven't produced as much as you have.

ahickman

Hey, anything you can suggest or improve upon would be great. I personally would be interested in knowing how to calculate/determine the A/F ratio and even how the MPG is determined on most vehicles. Any thoughts?

Also thought about adding a port that would "listen" to the MIL indicator and then interpret the codes as they flash out. It would be convenient to have it displayed as decimal numbers on the LCD rather than having to remember each set of numbers if you have more than one error condition.

86blue4runner

hey man, i know the newer chevys do this and display it in real time. if you want me to i can get a hold of some of my buddies who know a lot about the GM electronics and such, and ask them about it and see if they have any input. BTW great work, wish i could get one for my 86 keep the good work going.

mt_goat

Your truck doesn't have the wide-band O2 sensor needed to accurately read the A/F ratio, but you can add one to the exhaust stream and add a gauge for the read out.

space-junk

iTrader: (1)

thats a nice set up dale, is that yours?? and how much would a set up like that run??

mt_goat

Yeah, here is one similar: http://www.urdusa.com/product_info.p..._id=1260518598