What is "Bad" MPG for a '94 5.7L ?

[RawbDidIt]

Couldn't really tell from the video, but if the play in the pulley is along the axis of the shaft (front to back in relation to the truck), your bearing is shot. PlayingWithTBI is right (about the WD40 too, I usually relubricate anything sprayed with WD40 with some 3 in 1 or grease after, but you could just skip the WD40 part and the results would be the same), you could run it till it dies, but I've had some instances where a shot bearing can cause undue stress on other pulleys in the system. If it were me, I'd replace it, but I can't stand pulley or bearing noise. I doubt it'll make a noticeable difference in mileage, but it could prevent future problems, plus nice and quiet air conditioning

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[PlayingWithTBI]

Some folks swear by cold air intake, headers, full flow cat and open mufflers. The ultimate TBI mods will help but, you'll need to get your PCM tuned which is also a good idea anyway, it'll help with or without mods. GM was quite conservative with their tunes. You can go with Hyway Lean Cruise too which will raise your AFR (from 14.7:1 to 16.5:1+ and timing up to around 36*+ when cruising above 40 or 45MPH, lots of good stuff to play with...

 

[L31MaxExpress]

My old 83 G20 with a TBI 350, 4L60E and 3.08s would routinely pull down 19 mpg running 75 mph. It had the 1-ton low compression HD TBI 350. Stock heads and stock cam at the time with 1.6:1 full roller rockers. Edelbrock performer RPM intake with the 4 center bolt holes elongated and tapered washers to seal properly. Marine TBI-Square bore carb adapter. 2" bore late 454 style Marine TBI with the 30 psi regulator and high pressure 46 lb/hr injectors. Hypertech powerbowl with the air cleaner base cut out to match. Doug thorley tri-Ys into a dual 2.5" exhaust with a X pipe under the drivers seat and dual 4" case magnaflow magnapack race mufflers. Had the 93+ TBI PCM that was dialed in and tuned by me. Crank rated at 180 hp and 300 tq. It made 200 rwhp and 300 rwtq. About 260 hp at the crank.

A signifigant part of the puzzle is a good tune on the ECM/PCM. VE tables, Spark timing tables, getting the AE correct and the DE correct. Also shift points and lockup mph can aignifigantly improve the MPG. Enabling 2nd gear lockup with the 4L60E helped ALOT around town.

Running the carb intake, swapping the injector control wires helps the fuel have time to vaporize at part throttle longer before it hits the intake valve. Edelbrock swapped the injector/cylinder pairing on the 3704 intake for the same effect. The GM Vortec TBI intake is also swapped.

 

[df2x4]

What intake and exhaust system would you recommend ?

Just going to throw in a quick thought on this. IMO the factory intakes are fine for most trucks, but if you really want an aftermarket intake the only one worth buying is a Volant. They're the only ones who sell a kit that uses a sealed air box which draws outside air from the hole in the fender. Everything else on the market is an open box design that will raise your intake air temperatures pretty significantly.

 

[Redneckgeriatric]

my 1990 k1500 came from factory with a "cold air intake". best MOD you can do for MPG that will cost you nothing? drive slower! 50-55mpg will yield better, but you are getting good milage for your driving habits.

 

[LVJJJ]

Compared to my 94 GMC K1500 those are great numbers. Have never got over 12.6 with it. Bought it to tow a travel trailer and had 126,000 miles on it. Is a crème puff, one owner, always garaged, but engine was gutless. It had original plugs, wires, etc. First thing you need to do is get rid of the very restrictive air box at the intake, throw it away and run a 4" dryer duct directly from the fender to the air cleaner. Apparently that air box was designed to cut down on the air intake noise, it reduces the intake size from 4" to 3". I went further and installed dual exhaust without cats. When that still didn't wake up the low compression engine, had a 383 stroker installed, now I can tow anything. Also added a second 4" air intake from the other fender to a new hole I cut in the side of the air cleaner. Can never have enuff cold air. Now I can tow our 5,000 lb trailer in 4th and get 9.5 mpg towing, old engine would get all of 7-8 mpg and sstruggled up hills in 2nd. Still get 12.6 mpg running solo. Before I bought the burb from a car lot in Everett I had them replace most of air conditioning system. But, getting 17 on the highway is amazing. As a long time RV'er, I quit worrying about gas mileage cause that takes all the fun out of traveling. If the truck drives nice and is comfortable, I wouldn't worry about gas mileage and enjoy the ride.

 

[Supercharged111]

You can pull that restrictor out of the airbox with your bare hands.

 

[RawbDidIt]

You can pull that restrictor out of the airbox with your bare hands.

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[Clay Smith]

Never understood people that buy these trucks and worry about gas mileage. If that’s a concern for you than daily driving 20 year old American truck is just not a good idea. There’s thousands of cars And trucks made to get good mileage, obs chevys were never ever one of those.

 

[PlayingWithTBI]

They were in 88-98, now a days, not so much, LOL.