8.1 motor swap into a 1994

As i have posted in an other section I bought a 1994 ext cab dually pretty cheep. The motor is JUNK and so is most of the wiring in the truck. The wiring has been hacked up rigged up and totally FUBARED. I have gotten the radio, AC(blows cold but wont blow hot), PWR windows, PWR door locks, Cruise Control,turn signals, brake lights, headlights and fog lights to work,

So I have been looking on line and I have found I can buy a complete 8.1 Vortec motor fairly cheep with the wiring harness, all the accosories and PCM. My question is has anyone done this yet? What do you do about connecting the wiring harness from the motor to the turck. I plan to reuse my 4L80E so I want to PCM out of the 8.1 to shift/control the Trans. I know I will need to get the anti theft removed from the PCM and the second O2 (i think).. Am I missing something seems fairly easy.

I read a wright up about installing one in a square body chevy and it looked like a major pain in the ass, the 94 might be easier.

I would but evetthing has been hacked up and butched up.

I would but evetthing has been hacked up and butched up.

Having the PCM and harness gets you ahead of the game a little bit, but trying to mate that PCM/harness to your '94 4L80E is going to be a challenge. Not only is the connector different IIRC, I know for sure the internals are different. Since '96 the 4L80E has a bunch of PWM stuff in it and your '94 has none. The two transmissions are not swappable for each other. Honestly I see this as your biggest challenge.

Next challenge is mating the wiring up with the '94 wiring. I'll tell you this, I did a similar swap recently. Put a '96 7.4 into a '94 that had a 6.5. I didn't use ANY of the truck's original wiring. I brought the entire donor truck harness over and used it as an excuse to justify the hassle of doing the interior upgrade. So I'm running the '96 dash, cluster, A/C controls, everything. You can bore yourself with the details in my 3500HD project thread in the Projects section.

Otherwise you have a lot of splicing and figuring to do. The wiring in your '94 and whatever truck you're getting that 8.1 from couldn't be more different.

Another thing to take care of will be the fuel supply. You didn't mention what engine is in the '94. Hopefully it's already a gas motor, not diesel. The '94 small block TBI has a 14psi pump, not nearly enough for that 8.1. The '94 big block has a pump that is somewhere around 35psi ('94-'95 big blocks have redesigned injectors, higher pressure pump, compared to earlier ones which have the same low pressure pump as the small blocks), still not enough. Double-check the pressure spec on the 8.1, it's probably the same or very close to a Vortec 7.4, in the 50-60psi range. If so you can use a '96-'97 pump and sender, this is still the old style sender that will fit the '94 tank. Late '97 and newer have that integrated plastic POS with a redesigned tank mouth. The rubber lines that lead to the hard lines are probably not up to the job of the higher pressure so you may want to hit a boneyard and get the lines from a '96-'97.

You got some work ahead of you...all of it can be overcome, sure, except for that transmission will probably be the thing that gets you. Get the newer transmission if you can as it would solve a lot of problems.

Richard

Thanks for the advice.
my truck has a 454 in it now its a 1994.

I didnt know about the tranny. I guess now i am looking to get motor aand tranny.....

I was thinking about getting the fuel tank out of the donar truck too fixes the fuel PSI issue and return line issue.

I found a guy that cliams for 500 he can modify the harness off the 8.1 to mate up to the 1994 truck all I will need to do is find a few 12 circuits (no big deal there). Here is the email from Jims Performance "all gauges can work....I can rework the 8.1 system to become a stand alone system.The harness work is $300 and programming is $200...you will need 8.1 main harness, pcm, tac module, pedal and pedal harness..now....the tbi old truck part...You can do it or we can do it..you will need to delete some of the old tbi harness as needed and find some old circuits and re-use then like water temp and oil pressure which are seperate signals anyway and you will plant your old oil sender and old coolant temp sender into the 8.1"

I am seriously considering this figure 2000 for the motor and trans (maybe fuel tank too) 500 for the harness mod. anothe 500 for BS stuff 3000-4000 not a bad deal there.

wonder what I could sell them 454 tbi and trans for????

What truck is this 8.1 coming out of? I wouldn't depend on the tank fitting your truck.

Richard

hmmm any updates on this? im kind of intrrigued by this swap but into my 98 gmc that has a 454

Why so? Are you just unhappy with the mileage? Or performance? Or just want a newer engine?

I have been tossing around a couple of ideas with mine since I already have a lot of big block parts, but my heads will not work with the factory intake (factory is oval port, and heads are rectangle).

I am underwhelmed with not only the mileage, but also the power ... I dont mind 8 mpg as long as the truck has some nads to go along with it.

wel lthe motor is a 0 miles replacement i have in there now... hasn't even been fired up yet.... jsut replaced the tired 454 that was oem and i got it for free so i couldn't pass it up, pretty complete just needed a few small things transferred over...
reason i was thinking 8.1 or something was to be a lil different and to possible lose a lil weight like by goign to a 6.0 aluminum and maybe a vortech or somethign i dunno... figured i went crazy or wil lbe goign crazy everywhere else y not try a different motor.....