Ok, I love my dually. Right now it has a '92 454 TBI/turbo 400. I know it needs a map sensor but at the moment it's getting about 6-7 mpg. Also where are the O2 sensors located? I don't know if when the engine was swapped(the truck is a '89) they put a different exhaust but I can't find anything on the exhaust!

Since I don't tow that much I was thinking of putting in a 350. What do you think my mileage would be? Better? Worse? I really love this truck but the mileage is killing me. And yes I know it won't get 20 mpg but I'd be thrilled with 10-12. It's a 2wd.

Did I mention I love this truck?

not sure what milage you'll get but i'm planning on doing the same thing, taking the 350 out of my daily driver burb to put in the dually

your o2 should be on the driverside exhaust manifold and if its gone along with your map you computer is like a drunk fighting to keep it between the lines

When I drove my truck all the time, it got around 13 with the 350tbi and a set of 4:11 gears.

13??????????? I would kill for that! Would the Map and O2 kill the mileage that much?

i have a 2000 with a vortec 454 in it, and running empty at 75 on interstate i am getting 14 towing my dime it drops to 11

I had a 95 crew cab dually with a tbi 454, the worst milage it got was 9 and a best of 15, most of the time it would do 12-13.

My best guess would be the 350 will do 3-4 mpg better then my 454 did with no load, and 3-4 less then the 454 loaded.

Does your truck have the th400 or the 4L80? If you don't have overdrive it will kill your milage.

Turbo 400. Yeah, OD would be nice.

Before I spent the time and money on the engine swap, I would look into installing an overdrive behinde the th400 (gear venders) or an OD trans. just my 2c.

^x2

and get all the sensors installed and working right.

i have over drive in mine..

Well I hooked up the O2 sensor and then the Map sensor(which we thought wasn't working) and now it runs quite a bit better. It can't hurt the mileage. Now just some exhuast work and we should be doing much better.

Oh and I was trying to sell it. I couldn't. I love this truck too much. I guess it's a sickness.

FWIW I have a 88 Crew Cab Square with a 92 TBI 454 in it also. Still running a TH400 but looking into doing a Gear Vendor OD unit as well. Right now without the OD I am getting 11 mpg empty. I put a load on it the other day and with truck and trailer I weighed a total of 16,740 lbs. I made 200 mile round trip and averaged 9-10 on the highway.

When I drove mine from ohio to texas I got about 8 with a turbo 400 I am saving for a od
A 350 won't get any better milage because it has to work harder to move the truck
So you have to step on the pedal more