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Engine swap in my '85 Blazer

ColoradoSlim

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I have an 85 K5 Blazer with a 305 4bbl Q-jet and a 700r4 k case 4x4, all mechanical hookups. I picked up a 350 tbi with most parts to make it work off a 95 Blazer, however a lot of the research I have done makes it seem I wont be able to use the ECM with the 700r4? Is there an adapter I can use to make the tbi work with the transmission? New to engine swapping, can take apart and rebuild easy enough, but knowing what adapts to make new things work with old things is a bit beyond my knowledge so far.
 

Blue85

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The ECM will take care of load and speed conditions, so you won't need the vacuum switch anymore, but I think the brake pedal switch is the same. Your transmsision should be similar to below. The TBI-year 700/4L60 were simpler. The ECM signal will need to go to the A terminal, but I think that's still through the brake switch. You can find links to the year-specific wiring diagrams and verify this. C is never used. You should be able to leave B and D unattached.

TH700R4InternalWiringDiagram01.jpg
 

dyeager535

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Given that 4L60E's started in trucks in 1993 (according to wiki), this is going to cause a host of problems I assume.

I'm not thinking this through very well, but perhaps it's possible to get either a PROM (if still separate that vintage) or ECM to replace the PCM, from a manual truck. It wouldn't be a perfect fix, as the tunes were different manual vs. automatic, but generally the difference in tune doesn't seem to be a big issue when a non-electronic automatic is coupled to an engine controlled via a manual trans PROM/ECM.

I'm guessing the wiring is significantly different from for the 1987-1991 R/V trucks to the 1988+ C/K's, but perhaps it would be possible to swap in an older TBI ECM. I don't know if the terminals on the ECM and PCM's changed from 1987-1995 however. I'd bet the plugs themselves did at least. This would be a fairly complex idea even if the terminals interchanged from the old vs new plugs.

To simplify, I think your problem is because of the year of the PCM/wiring, not the 700R4.

Another option, perhaps, would be to find a 4L60E?
 
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Blue85

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Oops, I missed the part about a '95 donor. Yeah, the ECM would have to be reprogrammed for the "missing" trans and only control lockup. You also need a correct T/V bracket mounted on the intake. A trans swap makes even more sense if your donor harness already has the trans connector(s). Nice thing about a 4L60-E is there is no T/V cable to screw up and shifting characteristics can be tweaked.

If you keep the 700 with newer ECM, you need a way to generate a vehicle speed signal for the ECM. If you use a 4L60-E that signal is there already, but you'll need something to make your speedometer work. An ECM, harness and other parts from an '87-91 donor could be a pretty straightforward way to keep your trans, as there were factory parts to solve VSS with square body speedos. I'm not sure which sensors and connectors are the same/different between the two systems. Worst-case would be having to use the early TBI intake manifold and throttle body instead of the '95. This might require the special vortec/TBI manifold, so maybe the rest of the stuff could mount on the '95 intake instead.
 

dyeager535

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I don't *think* the '95 stuff got real crazy compared to earlier TBI in terms of wiring or sensors. At worst they probably added things like inlet air temp sensor. Do I read the first post right that you got the complete '95 motor? Throttle body, all the sensors that were attached/bolted to the engine, no wiring cut up, fuse panel, interior wiring, etc?

Realistically, the best idea here is probably to just get an '87-91 R/ harness and TBI setup. The EFI stuff is all wired through the fuse panel, and I can't imagine the '95 will swap straight across for the '85 fuse panel. You are talking a lot of cobbling due to the trans and year diference. I say best based on my perception of cost and ease. A brand new wiring harness from someone like Painless could probably be made to work, but I suspect if that was in the cards, it would have been the solution in the first place.

I want to say all the TBI 350's installed in trucks were the same 1987-1995 were the same internally and the throttle body, so I imagine taking a 1987-1991 setup (wiring, brackets, ECM, sensors) and putting it on a 1995 motor is possible.
 

ColoradoSlim

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@dyeager535
@Blue85
I got I'd say 85% of everything from under the hood. I dont have the fuse box, dont have all the sensors, but I have a majority of them. I got this engine cheap off CL, just saw it and decided to pick it up, I'm talking around 200 bucks. Getting new wiring is possible, I'd like to remain inexpensive but I'm not against spending money to get it to work the best way we can. The problem with getting a new trans is that trying to find a 4x4 4l60e makes it more expensive than I'd like. I'm betting I can scrounge around my local pickaparts and get used ecm or pcm or wiring or whatever, I just need to know what to look for.
 

dyeager535

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So '95 is pre-vortec heads?

Vortec V8 (classic SBC architecture) was 1996-2002.

If you didn't get everything, I'd just start looking for a donor 1987-1989 (so you don't have to mess with the speedometer that changed for '90-91). Wiring, sensors, throttle body just in case, and all brackets for coil, TV cable, etc.

The TBI harness is integral with the truck wiring harness, there is no easy way to work around that. IMO it's just better to get the right fuse panel/interior wiring harness, and underhood wiring harness.
 
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