Am I in over my head? - Page 1
Forum section: electronics / projects

author: eurokid
author_rank: Newbie
timestamp: March 09, 2011, 02:21:56 pm
content: I've had a idea kicking around in my head for some time now. I would like to design a smaller more capable, or more powerful if you will, frequency valve controller for a project car that I've been working on. In my opinion this is a pretty simple device, it uses very little input from a few sensors to control what is basically a single fuel injector via duty cycle. What I wana do is basically build a more modern version with the addition of a map sensor and a pot to dial in the correct duty cycle under boost. Because this car will be turbo charged I need a better way of making adjustments to the fuel system so the thing won't blow up. This is the main motivation behind this project. Here is a photo of the original FV controller module.It's a single sided board, the small 14 pin IC is a LM2902N low power OP AMP, and the rest of the components are all through hole resistors, a few diodes, capacitors, and a voltage regulator. The longer black device is some kind of proprietary Bosch IC which I haven't been able to find squat on. In a nut shell this controller uses the voltage signal from the O2 sensor (0-1V) and translates that into the duty cycle that drives the frequency valve. This is a closed loop system when the engine reaches operating temp. the O2 sensor voltage and FV duty cycle are constantly changing to keep the AFR in check. That's all this controller does. It has a WOT switch for full throttle enrichment wich switches the system to a fixed duty cycle of about 70%. I have actually seen a unit similar to the one I wana build, it was for converting european market VW's (water cooled) to meet US emissions standards. Heres the linkhttp://www.dc-johnson.com/default.htm. I'm wondering if I could just integrate a arduino or some other programmable IC into my design to handle the minimal processing that will be needed to make this work? I'm confident I can do this, I just need to start prototyping to see what is going to work or not work. I know there are a lot of smart people on this forum who could probably do this in they're sleep. That being said, any advice would be greatly appreciated!

author: DJPhil
author_rank: Frequent Contributor
timestamp: March 09, 2011, 03:09:12 pm
content: I remember there being a few diy engine control projects out there back when I was tinkering heavy with cars. They're for the most part straightforward, but things can get complicated with a turbo. If something goes wrong you might not have time to swear before blowing a hole in a piston with a lean mix. Aside from the usual safety and legal concerns when tinkering with a car, turbo instant death syndrome would be my biggest worry. The use of pretty much any microcontroller capable of keeping up with the math should be fine. Don't forget to take the harsh environment in a car into account in your design.

author: eurokid
author_rank: Newbie
timestamp: March 09, 2011, 03:37:15 pm
content: So something in like the 8bit range? I don't even think the IC in this controller is more than a few bits? it's hard to say. I plan on running a wideband so I'm not too concerned with going lean. My main concern at this point is getting this project up and running. You have any micro controller suggestions? I've also considered doing like a secondary stand alone system with a second FV and controller that uses a GM 3 bar map sensor for a boost reference. Basically I need to integrate a GM map sensor, stock VW frequency valve, and some way of adjusting the duty cycle for tuning purposes to make this work. Duty cycle needs to increase as boost increases on like a 5:1 level, and be adjustable of course.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 10, 2011, 06:14:09 am
content: Phil, can you point me to a good diy engine controller site? i also have similar thought as OP. this thread can be a good reference for me. for now the safety i can think of is start with very little fuel injection and move bit by bit higher if stable, if something wrong, failed mcu etc, then cut the fuel out coz, its the fuel that blown things apart. and start with smaller engine first, generally, as the other forum suggested to me. and dont forget a dyno, i think its a prequisite for a "proper" engine performance tuning, my 2cnts.

author: eurokid
author_rank: Newbie
timestamp: March 10, 2011, 08:12:40 am
content: Yes a dyno is good for checking HP and torque but for safety and tuning purposes a wideband AFR gauge is all you need. That way you can see if your going lean and take the appropriate actions.

author: DJPhil
author_rank: Frequent Contributor
timestamp: March 11, 2011, 04:48:06 pm
content: When I was looking into diy ECU stuff the big name was Megasquirt. It's been about seven years since I last looked into them but they're still around. They're very free with there info, though I'm not sure it's totally open source. It looks like they used an 8bit Motorola micro. The oldlink to their online manualstill works, and there's lots of old and new forum info to dive into.The only other think I remember relating to turbo control was that there were some folks using hacked GM ECUs as opposed to shelling out for expensive aftermarket electronics. A quick google and it seems it's still a common technique.Hopefully it'll help get you started. I wish I could tell you guys more, but I never wound up diving into this very deeply myself.