4.3 TBI Harness on a 2.8L - S-10 Forum
 
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post #1 of 15 Old 09-24-2015, 06:02 PM Thread Starter
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4.3 TBI Harness on a 2.8L

I'm working on swapping my 85 S10 2.8L over to a stock TBI setup and am having a hard time finding a 2.8L S10 in any of the local pick a parts w/ the wiring harness. But there are a lot of 4.3L TBIs in the yards.

So my question is can I used one of the 4.3L wiring harnesses? If so, is there a specific year or range of years to look for?

I have the intake, tbi unit, distributor, ECU and sensors for a 2.8L. Still need the harness and a VSS. Along w/ a few misc items.

Thanks and sorry if the question was already answered on here. I did a search and couldn't find the answer.

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post #2 of 15 Old 09-25-2015, 04:59 PM
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Re: 4.3 TBI Harness on a 2.8L

They are pretty similar. Should be able to use it. There may be a plug or two you have to swap over, but if you look at the wiring diagram, the terminations are the same for the most part. You can add or remove whatever you need. Whatever year 2.8 EFI system you have, you should try to get as close to that same year which will be at least 88.5. I have a sticky where I did this myself you should check out. Also look at deathpheonix99 's wiring diagram. You will see they are very close. Whatever pigtails you need should be findable on other similar cars If you need one. Are you going to just modify it to a standalone harness independent of the rest of the existing wiring? The easiest route is to do a standalone for sure. You will clip a lot work that way. I set mine up with its own fuse box to control the ECM.

You won't regret doing this by the way.



1984 xcab s-10 3.4L GM crate engine 91 S10 TBI swap w bored intake, Edelbrock headers. 2" Rough Country Lift. Custom exhaust, shift kit, e-fan.


EFI swap https://www.s10forum.com/forum/f106/...e-help-513616/

My build thread (3.4L)https://www.s10forum.com/forum/f106/...stions-427168/
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post #3 of 15 Old 09-25-2015, 11:19 PM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

Thanks for the response. I'm going to try one more yard this weekend for a 2.8L harness if I can't find one I am going to try and mod a 4.3L harness to work.

I saw your "2.8V6 Carburetor to TBI Swap, Tips and Tricks" from another post which was the way I intended to handle the conversion.

Still it seems like one of those "once I have my hands on it" projects that I will understand it better. I read your tips and tricks a few times now but I haven't removed a harness yet so parts of it are hard to picture. So, I am sure I may have another question or 2 once I get started.

I have the intake and TBI swapped over. The distributor is in. The knock sensor is in. The fuel tank and pump has been swapped. So, I am at the point where the harness is needed to really move forward.
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post #4 of 15 Old 09-26-2015, 08:56 PM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

Found a few 2.8L 5 speeds in the yard. No autos. Can I use the harness and the computer, which are 062s, for the swap into an 85 Auto? I suspect I would have to forgo using the computer connection at the trans. But will everything else work?
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post #5 of 15 Old 09-27-2015, 08:10 AM
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Re: 4.3 TBI Harness on a 2.8L

I've done this conversion also, which jimmy always seems to forget.

The computer connection for the tranny you will be concerned with will for the TCC lock up.

Also, I believe that the 1227747 ECM uses the same pinout for the ECM harness as the 8062.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #6 of 15 Old 09-27-2015, 10:18 AM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

So then the 5 speed harness and computer won't work in an auto?

I was hoping that if I could retain the factory TCC wiring setup from '85 if I used the 5 speed harness. Understanding that the newer computer system may be better and provide an increase in MPG. But this is a truck I drive about 2,000-3,000 miles a year if that and I can't seem to find a 2.8L Auto harness right now. So, t this point I need to get it up and running for winter.
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post #7 of 15 Old 09-27-2015, 10:55 AM
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Re: 4.3 TBI Harness on a 2.8L

The TCC lockup from the computer simply locks the TCC when certain conditions are met. You could use the vacuum lockup, but it essentially does the same thing. I opted on my 85 to let the computer do it.

I've looked at the programming in a lot of BIN files and each BIN is different. I don't recall that there is a difference in the harnesses between the auto and standard transmission vehicles.

Also, if you have an '85, and, it has cruise control, then you already have a VSS. It is a little box up under the dash that has a set of wires going up to and attaching to the rear of the speedo.

*BIN file = programming in eeprom that tells the computer how the engine should be running at any given operational parameters set for that specific setup.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #8 of 15 Old 09-27-2015, 11:23 AM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

Ah. Ok. That makes sense. I figured the auto harness had a connector on it from the 700R4 than the manual harness would not. I have never done a carb to TBI conversion. I have done several 4.3L TBI to 5.7L TBI and frankly I found them less confusing that the 2.8L carb to TBI.

No cruise control on this 85. So I am going to have to get the VSS and wire it up from what I have been reading on here. But that doesn't sound too hard.

Thanks to everyone for the help so far. Please post up with any other advice or tips as I am sure I could use them!
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post #9 of 15 Old 09-27-2015, 03:19 PM
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4.3 TBI Harness on a 2.8L

One important thing to note is that the VSS sensor you should be able to source it from a later truck. It will fit the older speedometer head so don't kill yourself looking for one from an older truck. It's super simple to wire up too. There's already a place for the check engine light too which is easy to add the wire.

Damanx knows more about this than I do for sure. I'd probably not attempted it without his help on the phone since we did them at pretty much the same time. That was invaluable.

I have yet to tune my truck due to things I have going in my life that keep me from it so we can help you get it installed but Damanx is the man for the tuning. It's challenging because GM never had this combo available.


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1984 xcab s-10 3.4L GM crate engine 91 S10 TBI swap w bored intake, Edelbrock headers. 2" Rough Country Lift. Custom exhaust, shift kit, e-fan.


EFI swap https://www.s10forum.com/forum/f106/...e-help-513616/

My build thread (3.4L)https://www.s10forum.com/forum/f106/...stions-427168/
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I had to cut my nut in half .
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post #10 of 15 Old 09-27-2015, 05:50 PM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

Good to know on the VSS interchange. Thanks. Shouldn't be too hard to find that part then.

I am down to the VSS, the harness, and the fuel lines including the filter bracket under the hood to source. The last two being rather frustrating to find.
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post #11 of 15 Old 09-29-2015, 02:09 AM
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Re: 4.3 TBI Harness on a 2.8L

It's low pressure so if worst case scenario just make some out of npt fittings and rubber hose. Mine are cut. Have not had any problem.



1984 xcab s-10 3.4L GM crate engine 91 S10 TBI swap w bored intake, Edelbrock headers. 2" Rough Country Lift. Custom exhaust, shift kit, e-fan.


EFI swap https://www.s10forum.com/forum/f106/...e-help-513616/

My build thread (3.4L)https://www.s10forum.com/forum/f106/...stions-427168/
Quote:
Originally Posted by Racer_X View Post
I had to cut my nut in half .
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post #12 of 15 Old 10-08-2015, 08:39 AM
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Re: 4.3 TBI Harness on a 2.8L

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Originally Posted by wpd View Post
Good to know on the VSS interchange. Thanks. Shouldn't be too hard to find that part then.

I am down to the VSS, the harness, and the fuel lines including the filter bracket under the hood to source. The last two being rather frustrating to find.
The harness can be found rather easily. Use this page to cross reference all the vehicles you can get the harness from. Look at those covered by the 1227747 and the 1228062 ECM's.

http://www.exatorq.com/ludis_obd1/c3xref.html

Fuel lines, just cut the lines from the fittings on the donor vehicle about 3" or so. You want those fittings. Then, when you get ready to run the lines, use 3/8's fuel line on the supply, and I think 1/4" on the return. This will be fine as stock pressure is typically around 9 psi. While you are at the scrap yard, take a look at any of the late 80's to early 90's Caddy's with the 4.something engines with TBI. Some of those have the regulator that you can adjust because you will eventually figure out that the fuel pressure being about 12-13 psi will be much better, especially when you get on it.

What "filter bracket" are you referring to?

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #13 of 15 Old 10-08-2015, 06:02 PM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

Thanks for the link. I am going back to the yard tomorrow since the rain has finally stopped here in PA and I have a day off.

Unfortunately so far I have not found any w/ the lines still there or the lines have been mutilated for some reason. One truck still had both lines but someone destroyed the ends that go onto the TBI unit. I have no idea why as the TBI until was still present.

My understanding is that the 2.8 TBI had a fuel filter w/ bracket that bolted onto the bolt in the area of where the stock mechanical pump would have went on a carb application. I could be wrong though.
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post #14 of 15 Old 10-09-2015, 09:22 AM Thread Starter
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Re: 4.3 TBI Harness on a 2.8L

In the event that I cannot locate a used harness today can I use this:

http://www.ebay.com/itm/141793600925...S:1123&vxp=mtr

It's a new aftermarket harness for a V8 that uses the 747 computer.

More $ that I want to spend but I need to get the truck running.
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post #15 of 15 Old 10-13-2015, 04:12 PM
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Re: 4.3 TBI Harness on a 2.8L

I'd hack one up first if I could. Those harness are pretty expensive...but then again, it's not a point of failure to worry about as much. I think Damanx is right on with the fuel lines. I can't honestly remember. Maybe you could piece some fittings together to make it work without the old lines? I can't see why you couldn't run rubber all the way from the frame rail.



1984 xcab s-10 3.4L GM crate engine 91 S10 TBI swap w bored intake, Edelbrock headers. 2" Rough Country Lift. Custom exhaust, shift kit, e-fan.


EFI swap https://www.s10forum.com/forum/f106/...e-help-513616/

My build thread (3.4L)https://www.s10forum.com/forum/f106/...stions-427168/
Quote:
Originally Posted by Racer_X View Post
I had to cut my nut in half .
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