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Crew cab guys

85 Jimmy

85 Jimmy

Sheepdog
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My buddy is looking at a 91 4x4 crewcab with a 350/4l80/???
The guy that has the truck now swaped it from TBI to a carb and if my buddy gets it he wants to swap it back over to TBI. What kind of mileage should he expect to get out of it?

Also, I'm trying to convince him to do a 12valve cummins swap. If he did that what kind of real world mpg numbers should he expect? I know cummins guys exagerate their MPG's so I figured someone here could give me an honest estimation.

One issue that the owner says the truck is having is that the transmission won't shift out of 2nd gear. Is that a common issue with the early 4l80? Could that be a result of having a carb swapped over the TBI stuff?

Right now it has a 6" lift and 32" tires, but he plans to lower it back down to close to stock and run close to stock sized tires.

His goal with the truck is to have something he can reliably drive everyday, haul his 3 kids around, and pull a camper around.
 
Honestly, if I was him I would find another one. I mean possibly burned up tranny, which that 4L80E is real deal expensive, and its lifted, which he doesnt want. And I wouldnt expect more than 12ish, tops.
 
I had a 91 crew cab for about 4 years (350, 4l80e, 205), with 4.56's & 35's it got around 10~12 mpg in town.

When I had the trans rebuilt it set me back $1800.

FYI, originally that truck would have had a 205 tcase.
 
Well, if the trans just needs a rebuild it would only really cost me the rebuild kit. We rebuild them at work, and the guy that rebuilds them owes me a few favors anyway.

We may go take a look at it, if it's not what he want's he won't get it. He's pretty good at jewing people down anyway, so he may be able to get it for alot less than the $2500 the guy's asking for it.
 
2nd gear is limp home in the 4l80. I wonder if he ever got it working right after the carb swap. All the early 4l80 computers I have dealt with would freak out with almost any input missing/incorrect.
 
For the transmission that's my main question. Could the second gear issue be a direct result of swapping to a carb?
 
85 Jimmy said:
For the transmission that's my main question. Could the second gear issue be a direct result of swapping to a carb?
Click to expand...

That tranny is the 4L80E for electronic, so if homey botched up the wiring or the ECU in his "conversion" to carb, then, yeah, the tranny computer is all confused. Me, I'd run, not walk, away ... gonna be some serious fun un-doing whatever homey did to put it back to stock. Fixing electrical is hard enough when the pieces are there, but if they're missing/fiddled with ... ugh.

-- A
 
I get about 18 mpg hwy and about 14-15 in town with my cummins swap with 37" tires. I would assume running smaller tires could easily make the truck get over 20 mpg
 
Same setup as ^, I get about 16 highway running 75-80 which is out of the motor's efficiency range. I can't drive 55.
 
Kinda off topic, but my 90 V3500 is a 6.5, banks turboed,TH400,4.10's with 35" tires I get a honest 20mpg avg but I drive like a grandpa
 
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