I wanted to swap my '91 4.9L L6 for a '91 5.8L v8, so I just recently bought a '91 5.8L v8 with a dual exhaust setup, and the 5.8 ECU.

What are all of my obstacles and what is absolutely necessary to get the truck running and what is advised? Will the old wiring harness work? Do I only need to buy one motor mount?

I have an E4OD transmission.

 

P.S. I have a 1991 f150 custom

 

Did you buy a donor truck or just the engine?

You will need V8 frame towers and engine mounts and the I6 versions have to come off, you need a complete 5.8EFI motor from oilpan to throttlebody and including accessory brackets, a complete V8 engine harness, a 5.8/E4OD PCM, a 5.8 specific flexplate(28oz imbalance), and a V8 rad and hoses.

 

On the engine frame towers, the I6 ones will unbolt from the cross member. The V8's have 2 or 3 rivets on the driver's side you will have to remove and replace with grade 8 bolts and nuts.

Also to make live much easier with a swap, try to get the entire engine bay harness too. Best to get the same year as your truck, then it will be plug and play with the firewall bulkhead electrical connector.

I done the opposite of what you are going to do. I replaced a blown 302 with a fresh rebuilt I6. Trying to use a 92 engine harness with a 89 electrical system, took me a week to repin/resplice to get it running!

 

I have a 1991 f-150 custom with a 4.9 L6 (original motor), and I bought a 351/5.8L to swap it with the 300. The engine I bought is a complete assembly valve cover to exhaust manifold.

I currently have in possesion: 5.8 ECU, Summit Dual catback exhaust for 91 f150, Magnaflow Direct Fit Cat for 5.8, 5.8 engine assembly

I wasn't sure on the mounts, harness, rad/hoses, flexplate, old accessories, etc.

Sorry for the lack of information given, but I just want to make sure I have everything I need before I start this job.

 

I just bought a radiator, rad hoses, a/c and p/s brackets, flexplate, and mounts.

So for the swap, I have:
- 1991 EFI 5.8L V8 Engine Assembly
- 5.8 ECU
- Summit Dual Exhaust Catback System
- Direct Fit Magnaflow Cat
- 2 core aluminum radiator for 5.8 V8
- rad hoses (upper and lower)
- 5.8 Engine Mounts
- 5.8 flexplate
- 5.8 power steering and a/c brackets

Hopefully I will be able to make everything else work, but with the mounts and flexplate I should at least be able to make it driveable (not that being the goal, I will immediately purchase anything that needs to be purchased to make it right).

Have an e4od that I plan on keeping, maybe just change the fluid and filter on it. Going to do the same with my rear diff.

Any pointers are highly appreciated.

 

As stated before, you will need the wiring harness. Your six harness will not work correctly with the V8 setup.

 

Will a 5.0 harness work?

 

I've never had a 5.0 engine. Just the 5.8. Is the harness available for your 5.8 engine from the truck you got it from?

I think a difference would be the different fuel injection systems that the 2 different engines use... location of sensors, connections to the intake, etc, etc, etc....

 

Yes a 5.0 harness will work as long as it is from the same year truck as you have now, the 5.0 and 5.8 are almost identical in terms of sensor layout and connections.

 

Thanks for that. I never knew until now that they are the same.

 

So the engine I have is a piece of ****.

If I buy a 351 windsor crate motor, will it fit the same? (Do all the 351w have same bell housing/ would the swap be the same)

p.s. I'm going carbureted now

 

A "crate" 5.8L will have the same bellhousing pattern as a donor/production engine.

If you go carb. how do you plan to control the E4OD transmission already in the truck? It's 100% electronic controlled by the PCM (computer).

 

Haven't gotten that far any advice would be helpful. I'm guessing a 5.8 PCM is programmed for a stock 91 5.8 and it won't work with a 5.8 crate motor.

How would someone make it work?

 

If you buy a stock crate engine it'll work just fine, but if you're gonna do that why not just rebuild the one you have?