I may need to design a “remote start” capability into a product. This device currently has an ignition override, so that the engine can’t be turned off in certain circumstances (the RUN and ACC lines are connected to 12v by a relay under computer control). It may be a requirement for this device to start the car. It’s pretty obvious that all I need to to do is to connect the starter circuit to 12v to do this. The hitch is - how do I know if the car is actually running? I don’t want to try to start it if it’s already running (GRIND!), and I want to make sure that the engine actually “caught” if once I give it a 5-second crank signal. So, is there any easy (and universally available) signal to tell if the engine is running? I’m sure I could pick a signal off of the tachometer, but that seems like a hack…
No answer, but some thoughts… could you install a sensor on some moving part that would indicate the car was running? Maybe there’s something in the OBD that you could tie into w/o needing to install your own sensor…
No real trick.
The device in the car should have a simple switch - if there is voltage coming from the alternator then the car is running. If it’s running, don’t follow through with any start commands.
Some automatic starters have a ‘hard start’ option whereby it monitors (somehow, no idea how) the tachometer. It’s designed to keep the starter engaged until the tach gets above a certain number, but it would probably be the most surefire way to tell whether or not the car is running.
I like the alternator idea. I’m trying to avoid any under-hood mods - I would like to be able to have all the wires necessary to install the device available under the dash, although if I need to have a wire run to the alternator, I will.
Go to the Bulldog Security website, pull up the installation manuals for some of the starters and search the PDF’s for “tach” and you should be able to find instructions on locating the correct wire for that. IIRC they even have vehicle specific wiring diagrams, you might just be able to pull that up for your vehicle and see which wire you need.
That’s a good resource, thanks.
Monitoring a tach signal is how the car manufacturers do it. I wouldn’t call it a hack.
There will be voltage in the alternator output wire whether the engine is running or not – it’s connected to the battery. The voltage will be higher when it’s running, but I would expect that trying to distinguish between rest voltage (~12.6) and charging voltage (~14.5), each of which could vary by about a volt depending on conditions, is both more difficult and less certain than reading the tach signal.
Professional mobile-electronics installer, specializing in remote start, checking in here.
In short: Gary T (as usual!) is correct.
It’s not clear from your post exactly what you’re doing. Is this a product that will be manufactured, and needs to be able to installed in various cars? Or a one-shot deal for your own car? Any reason you can’t just purchase and install an ordinary aftermarket remote starter? (If you’re developing a for-sale product and don’t want to answer these questions on a public forum, I’ll understand.)
Anyway, your options are going to be to monitor a tachometer signal, monitor for a voltage increase, or choose to simply blindly start the car and hope that it starts successfully.
For a better explanation, follow this link and go to the fourth post down…and oldie of mine from 2002:
http://www.the12volt.com/installbay/forum_posts.asp?TID=5821
Another option, depending on the type of car and your level of budget/sophistication, would be to monitor the car’s databus system to pick up the tachometer signal. There are many immobilizer-bypass modules intended to help in the installation of remote starters, and if the car carries the tach info on its databus, the module will often have a tach output.
By the way, when we say “tachometer,” it doesn’t have to be the actual tachometer on the car’s dashboard. There are various devices attached to the car’s engine that will make pulses when the engine is running…fuel injectors, coil packs, crankshaft position sensors, camshaft position sensors, and so forth.
Also, you’ll notice that in the car’s instrument cluster, nearly all of the various warning lamps will be illuminated if the ignition is on, but the engine is off (oil pressure, battery, and so forth). Once you start the engine, and assuming the engine is in good running order, all these lamps go out. You might be able to use the status of the oil pressure lamp as a running/not running indicator to your system.
Other resources:
Great message board for novice installers, with many professionals there to answer questions:
www.the12volt.com/installbay
Message board for industry professionals, with lots of talent there. To join, you need to show that you are somehow employed in the mobile electronics industry.
www.12vinsider.com
Audiovox wiring information database. You need to sign up to get a password, but they don’t check if you’re a dealer or not.
techservices.audiovox.com
P.S. Whether this is something you’re doing as a business venture (maybe you’re hiring?), or simply something to install in your own car, and you need a hand or have a question, just let me know. christopher.luongo@gmail.com
Thanks for the input.
This is for a commercial product. Version 1 is already shipping, V2 may need the start option. There are quite a few different makes of vehicles that this system might get installed in, and we are going to need to have explicit instructions for each vehicle, which is why I’m trying to keep it simple. I’m actually thinking of just using a clamp-on pickup coil around one of the spark plugs, which might make installation easier (there wouldn’t need to be a zillion different wiring diagrams).
BTW, I can’t be more specific about the product, because there are patent and disclosure issues.
There are many vehicles where this would be problematic, if not impossible. The trend has been to “coil-on-plug” designs, where each spark plug has its own little coil mounted directly upon it. Getting access to the ignition secondary could be extremely difficult on some of them. Even on engines with spark plug wires, a faulty ignition module, coil, wire, or plug could result in no signal through the chosen wire even if the engine will still run.
Typical coil-on-plug coils with spark plug boots. The boots attach directly to the plugs.
What you can see on some designs. Other designs have more stuff in the way.
I’m currently working on a vehicle that requires removal of part of the intake manifold to get to the module/coils assembly. As you might see in this picture, no part of the coils is exposed until the assembly is removed.
Fully understood there. I’m guessing that your product might be somewhat similar to Secure Idle? But I won’t ask any more than that.
I know the Straight Dope isn’t a job-search forum, and I hope the moderators won’t be upset with me, but I’m good at writing manuals, beta-testing products and providing good feedback, and I’m always interested in new products. Whether you need help with your install guides, or even simply someone to sell/install your products in the northeast, please keep me in mind.
Back to the technical part:
To keep an already-running car running, as you surely know, is simply a matter of maintaining power to the appropriate ignition and accessory circuit(s).
However, to get the car to start, you’ll have to deal with more than just the tachometer issue.
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Turn off factory anti-content-theft alarm: Depending on the car, if it has an alarm system, it may sound when started.
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Disable anti-theft immobilizer system: Most late-model cars have a transponder inside the key head. Depending on the car, there might be a module available to temporarily bypass the immobilizer via data, or if not, one of the car’s existing keys would be placed permanently into a small bypass box and installed under the dash.
Another option might be for your product to simply have an output that makes a momentary negative 12 volt pulse…this would allow anyone to install any aftermarket remote starter separately.
Don’t worry, Michael. Your secret is safe with me.
Drat! Foiled again by the Teaming Masses™
