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Installation & Wiring Tips 
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This is what I came up with in about 45 minutes of dumping everything I've ever learned about wiring up FreeEMS systems out of my brain, into a keyboard. I'm sure there is more than this, or some errors, or both, but it's a solid start. I'll add more to it as people suggest things, either through retelling their own experience, or by making mistakes in a public way :-)

Cable selection:

  • Use coaxial cable for all analogue sensors (IAT, CHT, TPS, etc)
  • Use coaxial cable for all RPM/Position sensors (CAS, crank wheel, distributor, etc)
  • Use two core + shield for all individual VR sensors (not Toyota CAS)
  • Prefer coaxial cable with braid and foil which gives better shielding
  • Make sure all cable used is capable of handling high temperature
  • Make sure all cable used is capable of handling solvents and chemicals
  • Make sure all cable used is multi strand "flex" for vibration resistance (coaxial included)
  • Use ground wire that is at least twice as "thick" as the power supply and reference wires
  • Using multiple wires of "normal" size to achieve that is acceptable
  • Even if current is low, do not use very thin wires, they do not handle vibration well (ignitor drives, ext P&H boards, etc)

Connections:

  • Always connect all of your grounds to the head or block
  • Never ground anything to the body of the car behind the dash
  • Solder or crimp all grounds into one large lug under one bolt/nut&stud
  • Make sure that that bolt/nut&stud can not come loose (lock nuts, nordlock washers, nylock,etc)
  • Always run separate grounds for CPU/ADC reference, injector drive and accessory drives
  • Size your grounds for the heaviest load, and make the other two the same
  • Use multiple "normal" ground wires to gain the capacity that you need
  • Be sure not to use the key switched power that is disabled while cranking
  • Key switched power is only acceptable for switching relays or key-on signal
  • Constant power supply should come directly from the battery
  • Switched power supply should come directly from the battery, through a relay
  • Reference power supply should come directly from the battery
  • Fuse all power supply wires close to the source (ie, close to the battery)
  • Rate fuses to the size of the wire used, not to the device draw
  • Never install a fuse of a higher capacity than the wire that it is "protecting"
  • Ground the screen/shield of coaxial cable at one end only
  • Never ground the screen/shield of coaxial cable at both ends
  • Never leave the screen/shield of coaxial cable completely disconnected

Routing/placement:

  • Keep all high current runs as short as possible
  • Keep all high current runs away from signal wires
  • Keep all signal wires as short as possible
  • Keep all signal wires away from high current runs
  • Keep all signal wires away from high current devices
  • Always mount your FreeEMS as close as possible to the bulkhead hole(s)
  • Never mount your FreeEMS in the engine bay
  • Never mount coils close to your CAS, crank wheel or distributor
  • Never run signal cables and high current cables in parallel
  • Use two different bulkhead holes to achieve this if possible
  • Ground ignitors, smart coils and injector driver boxes directly to the head or block
  • Never put ignitors and injector driver boxes inside the cabin or near the ECU
  • It is MUCH better to run ignitors in the engine bay than drive the coils directly
  • Avoid driving the coils directly, run ignitors in the engine bay instead (just like the OEMs)
  • All injectors, coils, ignitors, injector drivers, idle solenoids, boost solenoids, etc are high current devices
  • All high current devicse have high current runs to and from them, both power and ground

For true DIYers:

  • Use good connectors or...
  • Solder directly to the board(s)
  • Use a closed metal case
  • Mount the board to the case properly
  • Mount the case to the car properly
  • Make sure all components are physically well supported
  • Make sure all to220 devices are heatsinked
  • Make sure the heatsink is well supported
  • Make sure that board to board connections are by stand-off and screws
  • Do not rely on the stiffness of the board to board connectors to support cards

Read this article for some overview level material of high level wiring: http://www.rbracing-rsr.com/wiring_ecu.html

If you're experiencing noise issues and your setup doesn't match with the above, we're going to ask you to fix some of the issues. It's better to do things right the first time than to have to rework wiring looms later when you discover problems. If you have done some things wrong, and have troubles, post a thread about your issues and details of your setup with respect to this thread, before making changes so we can suggest what to try fixing first.

Also, feel free to add your tips, but not questions, to this thread. Put your questions here instead:

viewtopic.php?f=54&t=1350

Fred.

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Fri Oct 07, 2011 9:52 am
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whilst coaxial cable is exceptionally good, I also have to say that there are some good multi-stranded screened/shielded multicore cables out there that are very suitable for VR sensor and other signal use. I have used individually screened cables on ecu installs before with very good success.

A key point to mention for those not so wiring-savvy is to make sure the screens are only grounded at ONE end of the cable run!

DO NOT ground the screen at both ends of the cable and DO NOT disregard the screen altogether and leave it disconnected!


Fri Oct 07, 2011 11:05 am
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Thank you Dan! I meant to put the note about screen/shield connections in there, but forgot. Added now.

To clarify about the screened/shielded terminology, Dan is talking about cable with two cores, each with a shield of its own, and another shield around both of those. That is nice too :-)

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DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Fri Oct 07, 2011 11:45 am
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Somone else asked why OEMs don't use screened/shielded cable for analogue sensors, only on knock sensors and RPM inputs such as CAS and crank wheel, and the answer is, filtering, you can filter analogue stuff, both in software and hardware, and get good results, but you can NOT filter RPM stuff much in hardware or easily in software (or in some cases at all) due to the nature of the signal requirements and use.

However, if you do less filtering of the analogue signals, you get a faster effective response from them, which although no use for CHT, is very useful for IAT if you are boosted and TPS always.

Software filtering also has a tendency to mask wiring issues that can be causing issues else where. For the time being FreeEMS has no analogue filtering code and I'm not planning to add it for a while as wiring issues should be solved first, and when they are, there is actually no need for it. When we do add it, it will be strongly discouraged.

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DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Fri Oct 07, 2011 11:50 am
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Fred wrote:
For the time being FreeEMS has no analogue filtering code and I'm not planning to add it for a while as wiring issues should be solved first, and when they are, there is actually no need for it.
I read this as "We won't be supporting PnP applications or adapted factory wiring harnesses. You have to make your own. :(

Might I suggest adding a warning about connecting or disconnecting the ECU plug(s) with the battery plugged in. This should be done with the battery disconnected to prevent a situation where many power pins are connected and possibly only one small ground pin is connected (or the other way around) which can cause problems. This might not be an issue for the FreeEMS ECU plugs? For Nissan plugs it is a huge problem due to their long and awkward design.

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Sat Oct 08, 2011 3:21 pm
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BenFenner wrote:
Fred wrote:
For the time being FreeEMS has no analogue filtering code and I'm not planning to add it for a while as wiring issues should be solved first, and when they are, there is actually no need for it.
I read this as "We won't be supporting PnP applications or adapted factory wiring harnesses. You have to make your own. :(

False. OEM wiring harnesses are, usually, very well designed. You can't connect pile-of-shit systems up to OEM harnesses, though, because they are incompatible. Perhaps that is where your confusion lies. In any case, this isn't the thread for it. This thread is here to be purely informational for those less experienced when installing stuff for the first time. I'm not sure that the other suggestion is in the right thread either, but it can stay here for the time being. I guess you interpret "installation" in that way, which I don't, but that's cool.

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DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Sat Oct 08, 2011 6:03 pm
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