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 Post subject: Re: A locost EFI
PostPosted: April 17, 2015, 10:36 am 
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Those can routinely break 34400°C under moderate load.
That's pretty hot! I think the copper melts long before that!

Just kidding :cheers:

I've never seen Teflon wire under the hood of factory cars except possibly for O2 sensors, usually irradiated PVC or even irradiated polyolefin.

Another plus IMO for using a modified factory harness in these buggies.

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 Post subject: Re: A locost EFI
PostPosted: April 17, 2015, 10:40 am 
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:oops:
300°C

fixed it

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 Post subject: Re: A locost EFI
PostPosted: April 17, 2015, 12:20 pm 
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selective bundling and routing play a big part in this heat thing, if you can break the bundles down and use multiple plugs instead of one really convenient big plug, also select what goes into each bundle, then i think this could be managed.

current engine harness design tends to route bundles on the engine and usually on the top of the engine, sometimes even under the intake manifold where heat would "accumolate" due to lower air circulation.

the rats love the silicon insulation, they like the pvc but they love the silicon.

its damage from rats that has had me opening up harnesses to repair the damage only to find heat damage is also present.

i don't suffer from the rats at home as i have cats but many locals do and wiring chewed or completely gone is very common here, i guess they like the night time warmth in the engine bay with a free complimentary breakfast thrown in, (rat ramada).

i have a personal interest in under hood temps as i have been fighting vapor locking on fuel injected engines here, it would appear that some manufacturers are also fighting this as fuel pressures are on the rise from the normal injection pressure of 40 - 45 psi to 60- 65 psi on both return and returnless systems and also the design of returnless systems has changed slightly to be a completely one pipe system as opposed to a two line to and from the filter then one line to the fuel rail.

i have probably written about this before, my locost had a system directly from the ranger where the pump applies fuel to the filter where some goes to the fuel rail and some returns to the tank where it is regulated on the intank module at 65 psi.

the real fault here is that the fuel returning to the tank is unfiltered so wear occurs in the pump and regulator if there is any sand present in the tank,(i live in a desert), this causes the system pressur to be compromised down to as low as 40 psi at which point you will experience vapor locking when the fuel gets hot enough and the pressure is down, in fact it seems to be worse when you cruise at about 70 mph for an hour or two and then stop, the engine will missfire.

i have since modified my system to have the return in the tank on the supply line and ued a regulator with an integral filter, this simplifies the system to the filter and fuel rail, so far no vapor locking but it is only 85 degrees here at the moment, we will see when it gets to 110.

i also have an astro van with a spider system where the injectors are inside the manifold on top of the engine, this has a system pressure of 45 psi, the regulator is inside the manifold so is not easy to access.

this system, in spite of two fuel pump replacements and several pressure checks which are within specification, vapor locks to the extreme because when the fuel turns to vapor, the pressure is maintained but is gasious, the regulator orifice is too small to displace this vapor as quickly as it forms and can be heard disipating in the gas tank for several minutes after the engine quits as new vapor is formed until the engine cools down.(45psi is not enough pressure to stop the fuel boiling in the fuel rail).

i have measured fuel tank temps and it is normal to see temps in the region of 150 - 160 degrees.

this may be the reason that manufacturers are choosing to use adjustable fuel pumps and constantly measure the fuel pressure at the fuel rail.

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Last edited by john hennessy on April 17, 2015, 12:59 pm, edited 1 time in total.

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 Post subject: Re: A locost EFI
PostPosted: April 17, 2015, 12:39 pm 
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Location: Louisville KY
I realize that it's frustrating talking with a noob on these things, but let me suggest that I'd love to get my '95 GM 3.4 running with all of its EFI glory before too long.

I have a modified factory ECM, and all of the factory harness, and as far as I know all of the doo-dads on the engine (I replaced the obviously suspect ones, like the broken O2 sensors).

Before I broke it down to move it, the fuel tank was in place (but plumping was to be run), and the motor at least cranked, and the oem speedo unit showed some lights.

Beyond that, I'm just looking for a good way to start and run the thing. After I get it running, then I will try for some braver stuff. But at least I need to know that I can get it running.

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 Post subject: Re: A locost EFI
PostPosted: April 17, 2015, 1:13 pm 
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Geek, i think this needs to move over to your build log as this is Marcus's efi system post.

if we go there, then i can help you with the specifics of your particulat system.

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 Post subject: Re: A locost EFI
PostPosted: April 17, 2015, 1:35 pm 
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Thank you, I've replied to your post over there.

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 Post subject: Re: A locost EFI
PostPosted: April 18, 2015, 2:31 am 
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TooBusy, I didn't get what you meant when I first read it. Your suggesting the larger wire size to reduce heating of the wire from current I think. Makes sense. The coil wires carry a lot of current.

I'm not in a rush to make wiring harnesses, but it probably comes up for a bunch of us working with older motors.

So I'm going thru my design now from the beginning more slowly and checking things as I go. I thought it would be good to try and get a few traces just from my own cars. I still live in the dark ages. I guess they don't always have cigarette lighters anymore. I hooked up my little scope and couldn't get a signal until I turned on the car. Then got a shock when I looked at the trace from starting the engine. I think I'll have to get a trace directly from the battery tomorrow.

I went for this trace because I'm trying to decide how much and long of a droop to handle when starting the car so as not to reset the processor. This is a lot worse than I expected, especially considering it wasn't even really cold out. It was just the first start of the day in the late afternoon. I think this power outlet that used to be a cigarette lighter has it's own electronics or voltage regulator behind it. Something that causes it's own droop.

Here it is:


Attachments:
Honda_Start1.jpg
Honda_Start1.jpg [ 225.35 KiB | Viewed 2545 times ]

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 Post subject: Re: A locost EFI
PostPosted: April 18, 2015, 11:35 am 
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Location: meadview arizona
and you wonder why they need you to depress the clutch, disengage the a.c. drop all the accessories and kill the headlights while cranking and why the fuel pump primes the system before you start cranking.

believe me if your system voltage drops below 9 volts it won't start, the starter probably won't turn the motor.

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 Post subject: Re: A locost EFI
PostPosted: April 20, 2015, 1:25 am 
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I got another trace for starting the car, this one from the battery terminals. It looks completely different, so that power socket on the dash has something that runs it. That's sort of too bad, it would have been easy to collect data just plugging a cord into that outlet.

It's not as clean a trace, I had my daughter start the car, but she doesn't have a license yet so she didn't stop using the starter motor until a couple seconds after the motor was running. I think that's why it doesn't jump to 14 volts so fast.

So we get a dip to 8+ volts and then a gentle rise. They have specs for these things and the ISO standard calls for a dip to 5 volts to get the motor to start turning and then a longer pause at 6 volts for cranking until it fires. That's supposed to be a sort of unhealthy battery in the winter.

I'd like to look for some spikes next from turning on and off loads like the headlights. But without a convenient way to do it, I'm thinking I'll skip it. The standards say to allow for over 100V spikes for almost 1/2 second.

These spikes are mostly handled now by modern alternators, but I think these ECU's will get fitted to older pieces of equipment at least some of the time, so I decided it will be worth putting in a big protection diode for these events. It costs something like $3 and will need to be soldered in by hand, but I figure that's why I have children... :)

The part I'm looking at is a TVS diode (LittleFuse SLD16u-017), a special diode for transient protection. It's a monster, rated for 5000 watts peak, but just 8 watts continuous. It's the smallest unit I found that said it was rated for an "alternator load dump".

I'm not sure this makes sense. I need to figure out how wire is rated for short pulses. The actual ECU I think would always draw less than 1 Amp. The injectors and coil drivers can carry a few amps, maybe even 15 for the coils. They will need their own grounds and probably shouldn't need protection from these events. The ECU does though. I suppose this means the 1 Amp ECU gets a 16 gauge or maybe bigger wire... And a slow blow fuse or PTC...


Attachments:
Honda_start2.jpg
Honda_start2.jpg [ 242.06 KiB | Viewed 2507 times ]

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 Post subject: Re: A locost EFI
PostPosted: April 20, 2015, 9:38 pm 
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that is a much better trace.

are you intending to feed the injectors with 12 volts and switch the grounds or give them grounds and switch the power?

as far as wire size goes, if you could get a wiring diagram with the pin outs of a factory ecu, then go to a wrecking yard and physically look at the wires in the ecu connector, this would give you a starting point on sizes.

also play special attention to the wires on the altenator and where they physically go in the factory system, not just the electrical circuit they connect to, this may help with managing spikes.

if you can control all the other wiring in the vehicle such as headlights, by means of relayed circuits with the main power taken and grounding directly to the battery and only low amp circuits to relays local to the emgine management system this may also limit spikes.

i feel that the only cure for voltage drop in a cold climate is a bigger battery.

keep at it Marcus, this is going to work.

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 Post subject: Re: A locost EFI
PostPosted: April 20, 2015, 10:06 pm 
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Taking power directly from the battery for the ECU is the best IMO. Not from the starter lead or alternator. The voltage drop on the starter wire does not affect the voltage to the ECU. The battery chemistry and size determines the voltage drop at the battery. Further, the battery itself will help to control spikes. Taking power from anywhere else (for the ECU) will have less than stellar effects.

Wire size for short pulses is chosen based on the allowable voltage drop mostly. Certainly it has to be rated for the average current, which causes heat. The maximum temp under worse case conditions must be lower than the insulation temp rating.

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Visit my ongoing MGB Rustoration log: over HERE

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 Post subject: Re: A locost EFI
PostPosted: April 20, 2015, 10:11 pm 
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john hennessy wrote:
are you intending to feed the injectors with 12 volts and switch the grounds or give them grounds and switch the power?

Is this really an open question? I believe the choices for low-side, automotive grade protected drivers is so much wider, while switching power there are barely any options?

I know it's all about the process, but I am wondering if re-using at least some of the to-some-extent tested components would get you to a running ECU faster? But that's if the goal is to get a running ECU :)

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 Post subject: Re: A locost EFI
PostPosted: April 21, 2015, 12:34 am 
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The plan is low side switches for the fuel injectors, that means switching the ground. They used to do high side switching and made special parts for that but that was some time ago and now the auto industry has settled on low side switches. All questions are welcome here though.

Russian2, for me this is not about the process, I am focused on the result - to produce some ECU boards. I think the best way to do that is to produce and use your work as soon as possible. I am trying for some re-use, so I am not sure what you mean by "re-using at least some of the to-some-extent tested components"? I am likely unaware of many things. So at one end my project is using a Freescale evaluation board for software and some initial testing and at the other end I am drawing schematics and doing board layout. I would show this stuff more, but I don't know how to get the schematics into a PDF since the tools are running on Windows and I am almost completely ignorant about that.

I am currently planning on using the Freescale MC33810 chip to drive the injectors and coils. These chips can drive 4 channels of each and I will likely put 3 on the board.

Here is a description of the issue with the voltage spikes. I think it is an issue of old cars vs. new cars and also cars designed as a unit by a factory compared to cars built in garages. Also possibly I over design things :rofl:.

Cars have powerful alternators. They store a lot of energy while they are running. If you have questionable wiring to the battery, if it ever becomes disconnected, if you ever turned off a master or battery disconnect switch on a race car that's running, and perhaps a few other things - you can get something called a "load dump". The standards for this are like 100V for a half second, potentially lots of amps too. Modern cars handle this in the alternator of voltage regulator. A vintage car not so much...

So at the moment I am thinking I will not depend on some other piece of equipment in the car to do this for me. Someone could easily buy this unit and put it into a car that used to have a carb. and get into trouble. I looked at a reference design for these chips and it had a device to help with this but it would have depended on a larger unit somewhere else in the car to prevent a crater from forming where that device used to be :rofl:

The unit I am thinking of putting on is rated to handle these load dumps. It's a couple of dollars and it will also take probably a larger wire size. These are rare events though and they don't last long. I only need about 1 Amp to run the ECU, but the wire needs to handle a big burst for a bit less than a half second.

Another thing is that I think the ECU needs separate ground wires for the electronics and injectors and coils. People have been telling me you can't put the drivers for the coils in the ECU box, but I would like to try and get that to work. If nothing else it may look like one box on the outside and more boxes inside. At least covers inside over different parts of the board to keep things electrically separate.

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 Post subject: Re: A locost EFI
PostPosted: April 21, 2015, 6:18 am 
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Marcus, a few things that may be of interest to you.

The guy who designed my initial ECU was adamant that the unit be wired from the battery totally independent of the rest of the cars electrical system. That included grounds. He also "required" very heavy wiring (8 ga minimum, I think) from the battery to the ECU. His thought was the battery was biggest electrical spike sink available.

Also, in the Megasquirt world, DIY Autotune mounts coil drivers inside the Megasquirt case, using the case as the heat sink and claim no issues.

Bill


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 Post subject: Re: A locost EFI
PostPosted: April 21, 2015, 7:59 am 
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horizenjob wrote:
I am trying for some re-use

Before you have a full board designed, is there an option to start with a bunch of small and ugly, but existing boards with a mesh of wires between them? This way you get a running concept sooner.

Injector options:
http://rusefi.com/forum/viewtopic.php?t=249
http://rusefi.com/forum/viewtopic.php?t=435
http://rusefi.com/forum/viewtopic.php?f=4&t=577

Ignition options:
http://rusefi.com/forum/viewtopic.php?f=4&t=450 (external igniter)
http://rusefi.com/forum/viewtopic.php?f=4&t=286 (DDPAK IGBT)

Obviously this would not be a piece of art with all the wires between the boards, but as a first step?

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