General engine tach. electrical characteristics?
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
|||||||||||||
|
Posted by on May 23, 2005, 3:38 pm
Please log in for more thread options Hi there, I'm considering designing a data aquisition/storage box for some personal use on my car. The car in question is a 1992 Nissan 240sx, pre-ODBII. Because I don't have a working scope at my disposal(long story), I'm looking for general information on the tachometer signal. The car is a distributor-based 4cylinder, with an external coil and power transistor. There is a crank position sensor(I assume it to be a hall-effect type), integrated into the distributor housing. The tach signal to the gauge cluster is supplied by the ECM/ECU. I'm basically looking for general information about this signal: what I can expect. I'm assuming it will be fixed-pulse width, 5V(TTL) or 12V peak-to-peak signal, with varrying frequency. What is the upper range for the frequency? Is the frequency a *direct* indication of the crank/engine RPM, or is it divided up/down? Thanks for any insite: I'll need to get my scope working eventually, but I just need to know about the tach signal to select an apropriate microprocessor(capable of timing the signal, and if need be, reduce the pk-pk voltage). Regards, -Jamie | |||||||||||||
|
Posted by Mike Deskevich on May 23, 2005, 4:41 pm
Please log in for more thread options if you're going to be making a daq for your car, your best bet is to get a factory service manual. they're usually pretty cheap on ebay. i'm working on the same project as you are for my 1989 toyota (also pre-OBDII) and the FSM has really helped. it has pinouts for the ECU and all the info on voltages and everything. one place you might want to check out is www.autoshop101.com. they have tech manuals on all kinds of neat stuff. their manuals are primarily toyota, but i wouldn't be surprised if the ECUs were similar (toyota and nissan use aisin as a parts supplier). but to answer your question about the CPS, here's what i do know. it's a +5 (or maybe -5) signal that happens once per revolution (no multipling or dividing of the signal). it's primary use is to tell the ECU when to fire the injectors. my toyota (4cyl) has multiport injection, however all 4 injectors are fired at the same time, so the CPS only needs to give the signal once. i remember that my '95 nissan had TBI injection, so i wouldn't be surprised if your '92 also used TBI. so it's the same principle, the CPS just tells the ECU when to fire the injector. from your question, it seems like you want to read the tach signal coming from the ECU to the gauge. i can't help you there, but my guess is that it's an analog signal and the tachometer is just a voltmeter (just like the speedometer). in my project, i'm not trying to read anything being sent to the gauges, i'm just trying to read the output of sensors that are going to the ECU and the output of the ECU going to the injectors. that seemed to be the easiest way to do it. | |||||||||||||
|
Posted by BobG on May 23, 2005, 5:21 pm
Please log in for more thread options
The alternator has 3 humps per alternator rev (its 3 phase), and if you measure the diam of the alternator pulleys, you can get the crank rps from the pd of the alternator pulses (cap couple and use a schmidt trigger) | |||||||||||||
|
Posted by on May 23, 2005, 9:40 pm
Please log in for more thread options
Bob, that's quite a clever way of determining the RPM! That would be great on an older vehicle with no dedicated CPS output. In my case however, I plan to use the sensor already in place. Mike, I do indeed have a FSM, and it has certainly been an invaluable purchasse. The engine in my Nissan is also multiport fuel injected. In my Nissan the engine will fire sequentially normally, but will fall back to simultaneous when in 'safe' mode or starting. You brought up a good point that I had not considered: the tachometer gauge signal is probably analog. I would rather read the signal going to the ECU, as you have planned. Good call there. What frequency range have you observed in your Toyota? Thanks to both of you for your responses. -Jamie | |||||||||||||
|
Posted by Mike Deskevich on May 24, 2005, 12:39 pm
Please log in for more thread options
klijam64@email.pct.edu wrote: there are three signals i can choose from to read the rpm on the toyota. there's the ignition signal that comes from the distributor and that fires for each spark (2 times per revolution - 4 cylinders on a 720 degree cycle). i have that hooked up to a cheap aftermarket tach (my gauge cluster doesn't have a tach). then there are two AC signals that go to the ecu. one of them has a period of 180 degrees on the crank and the other has a period of 30 degrees. i have looked at both of these, but haven't used them yet, i'll probably just put a low pass filter one one of them and read the voltage with an A/D. i'm doing my project in two steps. the first step is just to make some cool gauges that i can use to monitor as i trim fuel delivery, the second stage will be to hook up a PIC or something similar and do actual data collection. since engines are relatively slow compared to electronics (rpm signal is only 10-100Hz), i can get away with cheap electronics. my first project is to read the signal from the ecu to the injectors. i put a low pass filter which gives me an analog signal that is proportional to how long the injectors are open. hooking that up to a voltmeter gives me a gauge of how much fuel i'm burning per unit time. if i had a speed sensor in my car, i could divide the signal by speed and get an analog instantaneous gas milage gauge. i also need to hook up a gauge to my o2 sensor (1-2Hz frequency) so that i can watch how rich/lean i'm running. after i do that, i'm going to add a trim pot between the air flow meter and the ecu so that i can tell the engine that it's getting more air than it really is. this way the ecu will lean out the mixture a little more. i can then use the o2 sensor gauge to make sure i don't lean it out too much and melt my pistons. the reason i'm doing this, is that in the primitive efi in the toyota, any time i run more than 1/3 throttle, the ecu goes into open loop mode and ignores the o2 sensor. the default programming is to run rich at WOT. i'd rather save a little fuel and go a little lean at WOT. especially since with my little 100HP motor i'm running WOT anytime i'm on the highway. after i get the fun gauge project done, it'll be easy to hook up a couple of A/Ds and send data to my laptop. haven't decided exactly what i'm going to do with the data yet. but it sure would be fun to have. mike | |||||||||||||
> gauge signal is probably analog. I would rather read the signal going
> to the ECU, as you have planned. Good call there.
>
> What frequency range have you observed in your Toyota?