Re: Engine swap computer & wiring question

[steve ravet <sravet@arm.com>]

Tim, I'm not familiar with those models, but I have been through an
engine swap (replace 2.8L w/ 5.7L in my Blazer).  What is the concern
with the dash?  Is it electronic, and wants to talk to the ECM to get
MPG info or something?  If not then I don't think it matters too much.

I'll talk about my swap some, it's probably similar to what you'll
find.  There are two places where wires cross from the engine
compartment to the inside of the vehicle.  One is the ECM harness, which
runs from the engine thru a hole in the firewall to the ECM behind the
dash.  This bit of wiring is almost completely isolated from dash/body
wiring.  Exceptions that I can recall are ALDL signals like data, TCC,
etc. that have to run over to the ALDL connector.  VSS also comes from
the dash in my app, not sure about yours.  Anyway, as long as you use
the ECM that comes with the engine there is no problem here, just splice
in the handful of wires for ALDL/whatever and the rest plugs right up.

The other connector is the bulkhead connector.  The car side is anchored
to the firewall, the engine side comes from the engine bay.  When you
get your new engine it'll have it's own bulkhead connector, and there is
basically no chance that it will plug directly into the existing car
half of the plug.  Wires and signals here can be different even on the
same year model cars, depending on options etc.  Fortunately there is
little/no engine wiring through here.  Typical things here are wiper
controls, A/C controls, power to and from fuse box, engine sensors that
go to dash gauges (but NOT ECM sensors, they are in the ECM harness),
etc.

What you'll have to do is go to the junkyard and buy an engine side
bulkhead connector that is physically the same as yours (from the same
model car), and all the wires attached to it as long as possible. 
You'll cut off the bulkhead connector from the new engine, and connect
the wires to the appropriate places on the junkyard bulkhead connector. 
Use crimps, and then solder them, like the service manual shows.  The
junkyard connector may have blank places in it where yours has wires, in
that case you'll have to add pins and wires.  You could re-use your
current bulkhead connector but I wanted to leave the old engine as
intact as possible so I could sell it.

You'll need a service manual/schematics for both the donor engine and
your car to properly match these up.  I spent probably 20 hours or more
sitting in front of the computer, going over the schematics, typing in
what went where, and double/triple checking all of it.  Then I printed
it out and started cutting and twisting wires together.  I wrapped all
the twists with bright green electrical tape.  Lots of time but I had no
wiring errors to track down later.  Once it's working, take off all that
green tape, crimp and solder the wires properly, put them back in the
loom, tape it up nice, and off you go.

All bets are off if the dash wants to talk to the ECM via ALDL, though,
like the digital dash vettes did.  hope yours isn't like that.

You'll make the swap easier if you get the new engine intact with all
it's wiring, accessories, sensors, etc.

write back if you have more questions.

--steve

Tim De Coster wrote:
> 
> Hello,
> 
> I'm new to this list, and have to admit that much of what goes on here is a
> little over my head.  I do however, have some advice to ask for.
> 
> I have an '88 Sunbird GT with a 2.0 OHC non-turbo engine and am eventually
> going to install one of the '96+ 3400 OHV v6's.  My question is:  what is
> the best way to handle the wiring and computer change-over?
> 
> Ways I have thought of:
> 
> Getting the complete dash wiring and engine wiring from an '87 or '88
> Cadillac Cimarron (it had the same style dash and a 2.8 mpfi v6 engine).
> This way I would have the v6 wiring that I need, though the computer will be
> programmed for the 2.8.  I think it would work, but I'm not sure in
> real-life what sacrifices would have to be mad going this route.  I'm sure
> that I would have to run the engine in MPFI mode like the 2.8 is, unlike the
> SFI mode that the 3400 was built for.
> 
> Another idea was to use the existing dash wiring and computer that is
> currently in my Sunbird and getting the wiring out of a '91+ Chevy Z24 that
> had the 3.1 v6.  I would then have to change the EPROM, but I'm not sure if
> the engine wiring will plug right into the existing harness and computer.  I
> think the computer itself is the same, but this isn't confirmed.
> 
> Getting a computer for the '96+ GM minivans or other GM vehicles the 3400
> came with is probably out of question because they use the OBDII computers
> which I understand are a pain as far as engine swaps are concerned.
> 
> Any comments or suggestions on this would be VERY appreciated!
> If you're interested, check out my website listed below.
> 
> Thanks in advance,
> Tim De Coster
> '89 Z24 Conv.
> '88 Sunbird GT Conv.
> '98 Intrepid
> www.sunbirdconvertible.com
> www.z24convertible.com
> 
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-- 
Steve Ravet
steve.ravet@arm.com
ARM,Inc.
www.arm.com
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