Digital ECU Project

What's in the tube providing air data? Hot wire or grid or something else?
The sensor on top of the tube is definitely a air temp sensor...looks like a GM type. But the other item, on the side of the tube is a bit puzzling. Most set-ups use a MAP (air pressure) sensor to provide input, as Steve H said. However I've never known it to be mounted next to the air filter and they don't usually look like that one (but I'm sure there are all types). Usually they measure the vacuum/pressure in the intake manifold/plenum; typically
a small vacuum hose attaches to a nipple on the manifold and goes to the MAP sensor remotely mounted. From there a wired connection inputs data to the ECU. If that is the MAP sensor for this one, mounted on the tube by the air filter, it would seem to give a incorrect input.


The current version of the MS system is very good and given its capability, support and cost
When I looked into the current offerings from MegaSquirt, I wasn't impressed. I'm no expert so perhaps I'm missing something. But they tend to offer fewer features, with older technology, for more money than several other products on the market. I won't go into long detail here (I don't want to hijack this thread, we can start another thread on if desired). But I think it is no longer the "bargain" it once was. The market has seen MANY new offerings at excellent prices.
 
because the SOHC engine doesn't have any of the fancy stuff like variable valve timing, you could use a Micro Squirt system instead of the Mega Squirt system
Not true. MicroSquirt will not support low impedance injectors like the SOHC uses. There might be some sort of mod that can be patched in to make them work, but it seems to me such hacks shouldn't be needed on a item like this.
The only current MS model that will work with our injectors (without mods) is the top of the line "3 Pro" (I think its called) for something around the $1300 price level. There are several other systems on the market for less money that offer more features, like knock control, boost control, wide band control, etc...all built into the ECU.

I'm not disagreeing with you Steve, I'm fully with you on everything else you've said about the virtues of a aftermarket ECU. I just did not see the supposed 'value' of MS compared to the competition. I think the name has grown and the prices are no longer a "deal". Unfortunately the technology is a little behind the market also.

Edit: perhaps I have missed something regarding the virtues of MS, I know at one time they were a real bargain. I'm just not convinced they still are.
 
A MAP (Manifold Absolute Pressure Sensor - 1 bar), mounted in the intake plenum down stream from the throttle plate. It cannot be mounted in the intake feed upstream from the throttle plate because it couldn't read vacuum with the plate closed.
Agreed, and that's what's bugging me about the pictures above. It appears to have the MAP sensor mounted way before the butterfly, next to the air filter. However it might not be a MAP. Could it be a mass air flow sensor (as in 'hot wire')? The ECU can be programmed that way as well. But from what I've read that is not the preferred method of doing it these days.
 
OK here goes nothing.
I did a bit of research re available units and from what I could see they were out of my budget range. It shouldn't be that difficult and I expect to learn a bunch along the way. I have no intention of making this a commercial venture - just an experiment at this point.
Progress so far:
I have characterized all the inputs and outputs and the interfaces are not at all complex.
I have breadboarded everything I need to bench test an existing analog ECU which I am going to use to
develop the algorithms/mapping.This will be the most difficult bit and I plan to start on that this weekend.
I have preliminary designs for the hardware bits. I am basing it around the Arduino UNO which, if you don't know,
is a really cool device. It consists of a microprocessor with a few ancillaries like a clock and a USB interface. It has 6
analog inputs, 14 programmable digital I/O ports, PWM capability, 2 interrupt inputs, serial comms via the USB port (which also powers it
and is used for the upload). A clone is available from Amazon for $12 USD. That is just ridiculous.
The best part of the Arduino story is the IDE (integrated development environment) which is fully open-source, easily downloaded from the Internet and
runs on WIndows, MAC or LINUX. It provides a 'smart' text editor, compiler, uploader and serial comms capability. The language is based on C and is really easy to learn.
I have prototype software up and running. There were only a few issues and I have resolved them all (there will be more I'm sure but I'm confident that there are no show-stoppers).Now I need the detail of the calculations of the injector pulse width. The prototype stores all of the various bugger factors in an array so that I can easily program alternatives and switch them on the fly with a simple rotary switch. I've done timing tests and I don't see any issues there.
That's it for now. My goal is to be able to do running tests by the end of July.
If anyone has a dead or unwanted bosch analog ECU I could really use the 35 pin connector (or if someone knows how to obtain one that woulkd be good too. I just haven't had the time to search as yet.



Thanks for any and all suggestions and comments. And check out www.arduino.cc. Be careful; it's addictive.
 
Wally, if you haven't already "Speeduino" has been out for a little bit now and is open source.

https://speeduino.com/wiki/index.php/Overview

Lots of good info there.

Something like the Microsquirt I could get behind, but not if it won't work with our low impedance injectors. Thank you Steve for taking the time to explain things a little better for me. I have a Plenum with a true TPS already installed, if I ever decide to get into this it will definitely come in handy.

Edit: After some quick research regarding the low-impedance injectors and Microsquirt, I did find this;


"Injector Resistors

Your MicroSquirt® EFI controller will limit the injector current to ~5 Amps per driver. This may be too much for the injectors, especially if you only have one or two low-impedance injectors per driver. High-impedance injectors (i.e. injectors that have a DC resistance of more than 10 Ohms) will not flow more than ~1 Amp at any time, so they do not need any additional current limiting. Low-impedance injectors (< 3 Ohms) can flow up to 15 Amps if not limited, and this will burn them up. To do this, use a 5 to 8 ohm resistor (with a 20 to 25 watt rating) in series with each injector.

You connect the ballast resistors in series with the injectors. You should use one resistor (20-25 Watts) in series with each injector, otherwise the injectors may not all draw the same current, and the failure modes become complicated and difficult to diagnose."
http://www.useasydocs.com/details/inject.htm
 
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What you’re seeing is just a connector that John used to enable the use of the stock harness. The MAP sensor is on the board in the ECU and connects to the plenum via an 1/8” hose.

Agreed, and that's what's bugging me about the pictures above. It appears to have the MAP sensor mounted way before the butterfly, next to the air filter. However it might not be a MAP. Could it be a mass air flow sensor (as in 'hot wire')? The ECU can be programmed that way as well. But from what I've read that is not the preferred method of doing it these days.
 
Edit: After some quick research regarding the low-impedance injectors and Microsquirt, I did find this;
Waterburry, that's the hack I was referring to earlier. The other products on the market will run low impedance injectors, and therefore do not require adding resistors, etc...something I don't think should be required on a $1300 ECU.


What you’re seeing is just a connector that John used to enable the use of the stock harness. The MAP sensor is on the board in the ECU and connects to the plenum via an 1/8” hose.
Ahhh, that makes much more sense. I can see it now, thanks.
 
John Allen’s plug n play system utilized a set of Volvo heat sinked injector resistors located inside the ECU to address the low impedance issues of frying the flyback diodes. It’s a well thought out package.

Waterburry, that's the hack I was referring to earlier. The other products on the market will run low impedance injectors, and therefore do not require adding resistors, etc...something I don't think should be required on a $1300 ECU.
 
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I wouldn’t be too hung up about using our existing injectors. They are old and outmoded. There are modern alternatives with more choices for capacity which could be used in making a more powerful engine.

The microsquirt still seems like a bargain to me, it’s on my list of future jobs for one of my X’s. The biggest values to me is the opportunity to use a more aggressive cam, knock sensor and so on.
 
John Allen’s plug n play system utilized a set of Volvo heat sinked injector resistors located inside the ECU to address the low impedance issues of frying the flyback diodes. It’s a well thought out package.
Thanks Mark. I was commenting on the MS ECU's in general and not on the kit John built. I made several remarks that addressed the original topic of this thread (building a new ECU) and how the MS products compare. Those comments were not meant to be a reflection of the system you discussed. The discussion gets a bit confusing when we are addressing multiple things at the same time.
 
I wouldn’t be too hung up about using our existing injectors.
The problem (as far as I could find) is there aren't a lot of choices in high impedance injectors that fit the stock fuel rail and harness, and within the general capacity range needed for this engine. This type of injector tends to be low impedance (in the target range). I'm sure there must be something out there but after a lot of researching I found no references to such an item.

The microsquirt still seems like a bargain to me
Before you decide that, it might be worth a look at some of the options on the market. By the time you add a couple needed features (not included with the MicroSquirt) the cost is the same or higher than others that include them. To put it into money context, the other ECU's I'm referring to are around $800-900 with a harness, wideband O2 closed loop, knock control, boost control, Bluetooth, basic sensors required, and other additional features (depending on brand). I'd rather not have to add external modules and connections and set them to cooperate with everything else when they can be had within the main structure of the ECU. However this will depend on your intended application; for a completely stock 1500 SOHC in standard trim some of those extra features are not needed. In which case the choice would be different.
 
The problem (as far as I could find) is there aren't a lot of choices in high impedance injectors that fit the stock fuel rail and harness, and within the general capacity range needed for this engine. This type of injector tends to be low impedance (in the target range). I'm sure there must be something out there but after a lot of researching I found no references to such an item.

Check out Bosch 0280150254. 16.15 ohms, 23 lbs / hour (increased from stock at 18 lbs / hour I think). To use mine I had to lightly machine the fuel hose input, and put a slight shim above the rubber spacer that holds it in place.

Paul Davock
 
Not true. MicroSquirt will not support low impedance injectors like the SOHC uses.

True, but there are simple work-a-rounds, including swapping injectors. I bought a complete set of good used injectors for another project for $100.

I know there have been a bunch of new, low cost, systems hit the market in the last few years. I don't have much experience with them. Most of my experience in the last 15 years has been with the higher end systems (Motec, Cosworth, Bosch MS, etc...). I used the MS systems not because they are cheaper but because of their capability and support. My tuner is one of the best MS guys around. Using what he can make the most of makes the MS system a better value for me. Given that the MS system is widely used and supported it makes good sense.
 
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I doubt anyone would mind more of the install pics :)

Here are the rest.

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There we can see the vacuum line from the ECU to the Plenum for the MAP sensor as previously mentioned. It's coming off a T next to the fuel pressure regulator.
 
I had to lightly machine the fuel hose input, and put a slight shim above the rubber spacer that holds it in place.
Thanks Paul D, I'll look into these. Ideally I would prefer not having to do modifications in order to mount the injectors. Wonder which is the better option; build in resisters with heat sinks for each injector circuit, or modify the injector to fit? Certainly neither is desired in my opinion, as with some of the newer ECU options available. But as Steve says....


Using what he can make the most of makes the MS system a better value for me. Given that the MS system is widely used and supported it makes good sense.
Agreed, and that was why I looked there first.

I know there have been a bunch of new, low cost, systems hit the market in the last few years.
This is what I've been referring to. I guess it might take a little time/experiences of others to find out just how well these do. But they offer so much more technology for the money. To get all the features they offer, like I noted above (in one of my earlier posts in this thread), plus sequential fuel/spark, better processor, longer warranty, etc. you would need to start with the top of the line MS (3 Pro I believe its called) and still add quite a bit of other modules/accessories to it. By the time that's been done you are almost twice the cost of these newer products. However one BIG question I have not looked into yet is getting them programmed. They have authorized dealers/installers/tuners listed on their sites. So it is available, I just need to make contact to learn more about the available maps, etc. As Paul D said,that is a benefit to the MS stuff.

True, but there are simple work-a-rounds, including swapping injectors. I bought a complete set of good used injectors for another project for $100.
Do you recall what model injectors they are/what specs they offer? And did you find it necessary to do any modifications to make them fit?
 
Check out Bosch 0280150254.
Interesting, they seem to be unavailable everywhere I looked. Wonder if they are a very rare/low demand item not worth stocking, or very desirable/hi demand one that can't be kept in stock? I'll keep looking. But this is reminiscent of what I found when searching for a injector of this description before (a high impedance one of this design). That's why I eventually gave up on finding something that is a direct fit on the X's fuel rail with the needed capacity, to use with a MS ECU.
Maybe Steve H has another part number to try?
Thanks.
 
Interesting, they seem to be unavailable everywhere I looked. Wonder if they are a very rare/low demand item not worth stocking, or very desirable/hi demand one that can't be kept in stock? I'll keep looking. But this is reminiscent of what I found when searching for a injector of this description before (a high impedance one of this design). That's why I eventually gave up on finding something that is a direct fit on the X's fuel rail with the needed capacity, to use with a MS ECU.
Maybe Steve H has another part number to try?
Thanks.
Am following to this thread, but haven’t read all latest carefully. Jeff, don’t You better go same way as I am- use newer type of injectors with adapter?
 

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Have you looked at Nissan 280zx turbo and 300zx injectors? I don’t have the specs in front of me but have sets of both because of their higher flow rates and hose end connectors making them a direct drop in.

Interesting, they seem to be unavailable everywhere I looked. Wonder if they are a very rare/low demand item not worth stocking, or very desirable/hi demand one that can't be kept in stock? I'll keep looking. But this is reminiscent of what I found when searching for a injector of this description before (a high impedance one of this design). That's why I eventually gave up on finding something that is a direct fit on the X's fuel rail with the needed capacity, to use with a MS ECU.
Maybe Steve H has another part number to try?
Thanks.
 
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