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'99 3cyl transplant in tractor - need wiring info
Topic Started: Sep 9 2013, 09:47 AM (3,084 Views)
kthelen
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There are two kinds of '91's. Manual and automatic transmission. The manual transmission models have a Throttle Switch (TS) rather than the Throttle Position Sensor (TPS) that's on the automatic versions.


Yup, read the '91 schematic and saw that. The donor would be a manual car, so it has the idle/WOT switch rather than a TPS.

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To make a complete installation to '91 standards, so to speak, you'll need the intake manifold, the throttle body, the ECM and wiring harness.


I'm hoping I can reuse my existing intake manifold - haven't gotten to compare them yet, so I don't know if it can be done. Otherwise, my shopping list looks pretty similar to yours (with the addition of the MAP sensor and CTS, since I don't yet know if they're electrically compatible from old to new).

Either way, I should be able to get out of there for $50 or less.

My original hope was to remake the body harness for my application, and leave the engine harness alone so it'd be 100% factory compatible. But at this point, I no longer care about making it factory correct - I just need to mow the lawn :lol
Edited by kthelen, Sep 14 2013, 05:05 PM.
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There is absolutely no way to use the existing intake manifold. Way different.

No crankshaft position sensor on the '89 - '95 engines, so no worries. You can use the crankshaft gear and oil pump that are currently installed on your engine.

You might want to rig a throttle stop to keep you off the WOT switch, or a light or something so that you'll know where you're at on power.
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kthelen
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There is absolutely no way to use the existing intake manifold. Way different.


No biggie, just another $14 at the local u-pull junkyard.

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You might want to rig a throttle stop to keep you off the WOT switch, or a light or something so that you'll know where you're at on power.


I understand how the switch works, electrically - but programmatically I have no idea how it's treated. What does the ECM do when it sees the switch go to WOT?
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kthelen
Sep 14 2013, 06:59 PM
I understand how the switch works, electrically - but programmatically I have no idea how it's treated. What does the ECM do when it sees the switch go to WOT?
It's a switch that enrichens the fuel mixture. I don't know exactly how much. When I get the throttle open on my '90, it's like the four barrel :hmm two barrel kicks in :hmm . . . squirrel got a hit with a cattle prod. :D

The WOT switch will close before WOT.
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kthelen
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Given that I don't need to merge or pass on a lawnmower, I can see where that might not be a desirable feature for my application :D
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clarkdw


You never know. You might just want to challenge this guy. :D

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kthelen
Sep 14 2013, 08:04 PM
Given that I don't need to merge or pass on a lawnmower, I can see where that might not be a desirable feature for my application :D
Sure. Disconnect the WOT switch wire.

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Flash
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53 mpg last trip

Just wondering ( and I love a challenge as much as the next guy ), but would it be easier to adapt a one or 2 barrel carburetor and use an aftermarket ignition system?
But then, how many guys can brag that they have fuel injection on their lawn mower? :)
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kthelen
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Probably not, if things go smoothly.

I actually pursued this a bit this afternoon. Since the ignition system is now standalone (nothing but the distributor and coil are needed to make spark with the older setup I installed), I was strongly considering going that way. But the selection of downdraft 1bbl carbs I could find locally was pretty limited. The cost of the carb, the rebuild, and the time/expense of making a plate - plus the inevitable headaches of getting a mismatched carb to work right, and the fact that I'd probably be looking at using a vacuum-powered snowmobile fuel pump or some such - drove me from that option.

If all goes well, I'll be able to snag the parts I need tomorrow for much less than the carb project would have cost. And, hopefully, it won't be a project all its own to get going - just bolt on, wire up, and use. (I hope.)

Not quite as nice as having completed the swap with all the OBDII goodies intact, but if it works, who cares? Not like I'm going to mass-produce this setup or anything.
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Flash
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53 mpg last trip

:popcorn
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Flash
Sep 14 2013, 08:57 PM
Just . . .
:lol You said "just". ;)

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Flash
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53 mpg last trip

no comprendo :hmm

Just wondering, is "just" an inside joke on GMF, is it 'just' for me to ask that?
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Flash
Sep 14 2013, 09:36 PM
no comprendo :hmm

Just wondering, is "just" an inside joke on GMF, is it 'just' for me to ask that?
Something like that.

Kinda goes along with, "It's simply a matter of . . . ", and "All you have to do is just . . . ".

When I see "just", it means there's a little bit more to the story. Just like this guy putting a G10 engine in his lawn tractor. ;)

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kthelen
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A little like saying, "I'm gonna be rich! I just have to start a wildly successful business, and I'm home free!" :D

For testing purposes, does anyone know what the *minimum* amount of sensors, etc. are required for the fuel injection to work on a '91? Not to run properly, or run well, just to work at all?

High school auto shop was a long time ago, but looking at the wiring diagram, it would seem that everything pretty much relies on the MAP, since there's no MAF or TPS. The CTS would then be used to make adjustments and to determine open/closed loop, and the O2 sensor also to adjust the mixture; neither being absolutely required to fire the injector... right?

I don't plan to actually run it that way, but it is useful to understand the system before I try and troubleshoot it (and I guarantee I WILL have to troubleshoot it!).
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3cyltom
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nice write up. sounds like your in for all sorts of fun. i was gonna suggest going for the much simpler 94-90 injection set up, but looks like you are headed that way. retro fitting other vehicle carbs could be a nightmare. i tried to go from a quadra junk 4bbl on an old 86 truck i had years ago to a 2bbl pop can carby and use an adapter plate. what a fiasco. with all the time\money i had tied up in it i could have bought a rebuilt quadra junk and saved time. ended scaring the crap outta the wife though. she came out of the trailer hollering. the stupid 2bbl backfired thru a hole in the adapter plate and shot a huge fireball out. lol you shoulda seen the look she had. the poor truck never ran right again even with a 2bbl intake mani. you might find an old carby sprint and rob the carb\intake?
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