87 TBI swap

[HuggerCST]

I just bought a 85 GMC with no engine, and I have a 87 Chevy parts truck with a 350 TBI that I want to put into the 85, using the 87 harness, computer, etc. Since this was the first year for TBI in the trucks, are there any problems with the 87 that I should address while the engine is out? I plan to rebuild it before putting it in the 85.

[beaterC10]

I have an 86 GMC that looks like your 85 that I have considered doing the same swap too. The biggest issue I see is installing the harness from the 87 into my 86. It looks like I will have to remove most of the dash to get the new harness installed. It looks like most of the required mechanical features are in place on the older cab to allow the harness install to be a remove and replace after I remove all the dash mounted stuff.

I did notice the tbi trucks attach the heater hose to the rear of the intake instead of the front, which requires a factory hose.

I have also heard the computers are prone to failure from a few different sources, but I have not been able to confirm this.

[72C203503ONTHETREE]

Why not go with a TPI, its a lot better than basically a two barrel carb and still gives you lots of bottom end power, more than a TBI would. Of course that would be a bit more and you have the TBI set up allready. You could swap out to a 454 TBI throttle body(I think from looking at them before but make sure the bolt patterns are the same) since they flow more. I was never a fan of TBI having owned a TBI truck and carbed trucks/cars. The carbed trucks had a lot more power than the TBI. The only real difference is that the TBI could get a little better mileage. I never had any trouble with carbs as far as running well even in -30 degree winters in Iowa. If you off road and get on steep inclines TBI is the way to go.

[HuggerCST]

I've always wanted a loaded short wide 87 because of the fuel injection, mileage, and reliability. I found this truck for sale for $4k a couple of weeks ago, with a new crate 350 in it, and the original owner claimed that he got 16mpg. I wanted it, but before I bought it, it got stolen and stripped of the engine, wheels/tires, and radio. He had no insurance, so when he found it, he called and asked if I still wanted it for $1000. I did, so I bought it. It actually made the deal better for me, because now I'll build the fuel injected truck that I always wanted. It will take some time, but less money. It will be an everyday driver, so I'm looking for mileage and reliability over power. I hadn't heard that about the computers, but I guess there's not much that I can do about that, other than carry a spare. Did 87s come with a 700, or a 350 trans? I haven't checked my parts truck yet.

[edman87]

You are in north LA, no wonder it was stolen. It is pretty common for a real noce 81-87 to get ripped off here in the south. I know of several that were stolen around me and many are then burned! sux!
Any way, unless you are trying to build a race truck, tbi is THE way to go!
Very simple, reliable and decent mileage. I have read that there were inprovements after 87, but I would assume that none were major. I had all of the reciepts for my 87 k5 from the PO since it was new and the only recurring problem seemed to be the ignition module going out. I am not aware of the computers being faulty, but remember it is almost 20 years old. I have known of more computers in 96 up vortec going out than tbi, and they are way more $$$.
I say build your dream 87 and keep it in stock configuration under the hood for reliability.
OH, 87 was 700r4 and they do not hold up well to a 4x4. If you want to use 1 of them, I would stay away from the stockers and go with one from an aftermarket builder.

[edman87]

BTW that looks to be a clean truck and if the interior is decent, it was stolen twice- once by theives and then by you for $1000.

[HuggerCST]

Originally Posted by edman87

BTW that looks to be a clean truck and if the interior is decent, it was stolen twice- once by theives and then by you for $1000.

Yeah, it's pretty clean inside. I just have to figure out how to keep it from getting stolen a 3rd time. Thanks for the info. I was kinda hoping that 87s had 700s, that means my parts truck should have everything I need for a TBI/OD. I have a 700 out of a '90 van, but it may not be much better. I guess I should have one rebuilt before I go back together with it.

[kevinr1970]

This past spring I put a TBI 305 in place of a TBI 4.3 in an '87 SWB.
I could be wrong, but I believe the harness for the computer/throttle body stands alone - meaning the harness that is your alternator and starter is seperate from the harness that goes to your ECM(PCM?) that is mounted under your dash. There must be some way to get it power?
But I don't think it requires taking your dash apart and rewiring it. I think all it would require is to drill a 1" - 1-1/2" hole in the firewall for the ECM harness. I removed the ECM from my donor truck by removing the glove box. It was in plain view after that was gone and this was an A/C truck will all the ducting under the dash. It mounts to the bottom side of the top of the dash.
Not sure how the ECM mounted but I do remember it involved a few screws. You might have to fab up a way to mount it.
As for the heater hose, mine did go to the back of the manifold. It had a formed/fitted hose much like a power steering hose but larger. On mine it had a fitting spliced in for a flush kit. Other than that it ran to the same place on the firewall. This wouldn't be an issue at all.

In '87 it could have been either a 700 or a 350. Depends on how it was optioned and what the previous owners have done to it? I remember someone on here talking about a 4.3 with a 400 tranny from the factory so I guess you'll never know until you look.

72C203503ONTHETREE - I only drove my '87 donor on the freeway once and around my house a few times but it seemed to have at least as much power as my 4wd '86 carbed truck. It seemed to have plenty of low-end power.
Are you comparing a carbed engine with some mods to it (like removed emmissions) vs. a stock TBI?
Not an argument just trying to learn as much as I can.

[EricS76]

from 87-95 the computer harness is stand alone. It just runs the throttle body and connects to all the sensors. Alt, starter, ect. don't concern the computer. You can still run the origional gauges . The only problem may be the VSS sensor in the trans unless you're using the trans from the '87. A good book to check out is "Chevrolet TPI & TBI swapping" by Mike Knell. There shouldn't be very much work done in the dash. Just mounting the computer, the ALDL connector and check engine light. I'm about to swap a '91 350 TBI into my jeep CJ, so i've been researching this for a while.

[Russell]

Should be pretty easy to pull off -- Just unbolt everything connected to the 87, and swap it straight over to the 85. Take the entire wiring harness, shouldn't need to cut any wires at all in the process.

[HuggerCST]

OK, I looked at the 87 parts truck, and the indicator showed PRN(OD)D21, but it did have a th-350. Maybe that's normal? Or, most likely, has been swapped.
I helped swap an 85 cab onto a 87 a few years back, and from what I remember, the ECM harness was for the most part a "stand alone" harness, but I think it did have a few wires tied into the main harness. Just enough to justify changing the whole thing. I guess I'll know soon enough.

[72C203503ONTHETREE]

72C203503ONTHETREE - I only drove my '87 donor on the freeway once and around my house a few times but it seemed to have at least as much power as my 4wd '86 carbed truck. It seemed to have plenty of low-end power.
Are you comparing a carbed engine with some mods to it (like removed emmissions) vs. a stock TBI?
Not an argument just trying to learn as much as I can.


I had a heavy duty 76 3/4 ton 4WD with the SM465 and 305 transfer case, it had no emissions crap stock since it was in the higher GVW rating. I had a 90 c1500 with the TBI 350 and 700 trans, it was slower. A Furd 302 beat it. TBI is good for low end torque and mileage, and better starting in cold weather. A properly set up Q Jet would beat it for power and a lightly modified engine would be even better. If youre wanting a daily driver that runs good and not into power the TBI is good.