Trunk Mounted ECM - Length of Wiring Harness?

[piratebaseball]

Hey guys,
'67 Camaro with vintage air under the dash. I have no room whatsoever to mount the ecm under the dash and I do not want to mount it in the engine bay (prefer to keep it clean looking). I know you are supposed to keep the ecm away from the radio which is what I'm mounting in the center console. Which brings me to mounting it in the trunk. I know quite a few people have mounted theirs there, but when doing the search, nobody said how long the wiring harness had to be in order to get it from the trunk to the engine bay. So, for those that did, how long was your wiring harness? I know most companies come with a 4 foot harness, just checking to see how much longer you had yours made?
Thanks!

[cjsgarage]

In running lights to the trunk, there's usually 12-15 feet of wire before you get to any turns or kinks. So 12-15 feet along the rocker.

Not to shoot your idea down, but what about under a seat or in the kick panel? I have done both and much prefer it to such a remote distance. There's 56 wires on a t56, drive by cable car. That's a kind of a large bundle to be running the length of the car.


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[kevin_l]

I am certainly no electrical expert, but I was told lengthening the ecm wires that much could cause resistance issues.

[68EFIvert]

I plan on running my ECM and transmission controller behind my rear seat. I had my harness made 9' longer than stock. I have only started the car to verify I did not have any problems so I can't say if there is a resistance issue but it seemed to run just fine while in my garage. I could have had a 10' extra length harness and it would have given me more mounting options.

[Ketzer]

I am certainly no electrical expert, but I was told lengthening the ecm wires that much could cause resistance issues.

Only on FAST systems..... :stirthepot:

[out2kayak]

If you want a deeper discussion of what happens with CANBUS and wire length, see:

http://www.eetimes.com/document.asp?doc_id=1274178

The CAN standard specifies cable with 5ns per meter propagation delay, and a maximum cable length of 40 meters for signaling at 1Mbps.

If a cable stub (unterminated cable) or T-connector is used to tap into the bus line, then the stub distance should not exceed 0.3m at 1Mbit/s rate per DS 102 Version 2.0.

If you want more information on CANBus, see:

http://www.ti.com/lit/an/slla270/slla270.pdf

Realize that GMLAN is developed with CAN technology. GMLAN includes two CAN buses that connect to each other via a “gateway” node. One bus is a high-speed dual-wire CAN, and the other is a lower-speed single wire CAN.

The high-speed dual-wire CAN bus uses a differential signal for noise immunity at relatively high speeds. The bus has a maximum length (from the node at the head of the bus to the node at the tail of the bus) of 30 meters, and the bus can accommodate a maximum of 16 nodes. The bus operates at 500 KBS rather than the maximum CAN specification of one megabit per second since the lower speed allows a longer bus length, reduces radiated emissions, and is sufficient for the high-speed vehicle nodes.

As the lower speed allows longer bus wires, I'm going to assume the above is sufficient.

http://www.public.asu.edu/~pheanis/documents/VBI_CAN.pdf

So, the question that you have not answered is: what form of ECU bus are you running and how fast is the vendor using the bus? I covered two most likely options.

Thoughts?

:cheers:

[cwylie]

Put it under the passenger seat. Thats what I did.

[67RSRAG]

I am certainly no electrical expert, but I was told lengthening the ecm wires that much could cause resistance issues.

I have my ecm /tcm in the trunk no issues. They have been in there for 7 years.