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

[name]

Hi guys,

I have a new to me 1994 GMC K1500 Suburban with 110k miles, It is all stock with new air filter,plugs, wires, cap and rotor. This vehicle has no mods and is not throwing any codes, everything works fine except the rear A/C ( front still blows cold but the R4 is extremely noisy )

I get 13.5 MPG with about 80% of my driving being done on the highway with the cruise set at 60 MPH

The best MPG I have ever gotten is 17 MPG on an interstate trip ( 100% highway miles ) with the A/C compressor disconnected and cruise set at 65-70 MPH

My questions are :

1) Is this normal for this truck, or is this considered "Bad" gas millage ?

2) If this is bad gas millage for this unit, what should I be doing to get the truck back to where it needs to be ?

Many Thanks,

 

[Supercharged111]

Those are normal numbers.

 

[RawbDidIt]

Hi guys,

I have a new to me 1994 GMC K1500 Suburban with 110k miles, It is all stock with new air filter,plugs, wires, cap and rotor. This vehicle has no mods and is not throwing any codes, everything works fine except the rear A/C ( front still blows cold but the R4 is extremely noisy )

I get 13.5 MPG with about 80% of my driving being done on the highway with the cruise set at 60 MPH

The best MPG I have ever gotten is 17 MPG on an interstate trip ( 100% highway miles ) with the A/C compressor disconnected and cruise set at 65-70 MPH

My questions are :

1) Is this normal for this truck, or is this considered "Bad" gas millage ?

2) If this is bad gas millage for this unit, what should I be doing to get the truck back to where it needs to be ?

Many Thanks,

That's more or less consistent with what I've heard from others, depending on the differential gearing and how gleefully you use the happy pedal. If you want to run a few checks to make sure she's tip top, I recommend checking vacuum, fuel pressure, and compression.
The part that makes me curious is what you said about the AC being loud. What kind of noise are you hearing from it?

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[name]

The part that makes me curious is what you said about the AC being loud. What kind of noise are you hearing from it?

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It sounds like a coffee can of bolts being swirled around when the Clutch kicks in ( the clutch was replaced but the noise still exists )

 

[RawbDidIt]

It sounds like a coffee can of bolts being swirled around when the Clutch kicks in ( the clutch was replaced but the noise still exists )

Turn the AC on and wait for the clutch to engage. When the noise starts, spray the pulley with WD 40. If it goes away, it's the bearing, you'll want to replace the compressor.

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[name]

Well, I guess I am glad that these are normal numbers, Is there any Mods I can do to get these numbers up ?

My gear ratio is 3:73 and the truck is used primarily as a people mover, ( no heavy towing or hauling )

 

[RawbDidIt]

Well, I guess I am glad that these are normal numbers, Is there any Mods I can do to get these numbers up ?

My gear ratio is 3:73 and the truck is used primarily as a people mover, ( no heavy towing or hauling )

I've heard of people having luck with increasing the compression ratio. Even then it's only by a couple of miles per gallon, what's your goal here?

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[PlayingWithTBI]

When the noise starts, spray the pulley with WD 40

Please don't spray WD40 on anything but tar on your fenders or a wet distributor (WD40 = Water Displacement formula #40), once dried it'll actually make things stickier. These R4s are known to be loud sometimes, it's a rotary piston pump and may have sloppy bearings and/or pistons internally. Run it until it dies and get a quality rebuilt, check your air gap on the clutch (s/b 0.020" - 0.030" pressed fit, the nut doesn't do anything to adjust it), flush the system, change the orifice tube, accumulator and/or condenser, but that's a different story, ha ha.

 

[PlayingWithTBI]

If this is bad gas millage for this unit, what should I be doing to get the truck back to where it needs to be ?

Pretty much normal but, you can install a better flowing intake and exhaust system.

 

[name]

Turn the AC on and wait for the clutch to engage. When the noise starts, spray the pulley with WD 40. If it goes away, it's the bearing, you'll want to replace the compressor.

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WD-40 has little effect on the noise, however there is some play in the clutch bearing but I did not think is was excessive, Here is a link of a video I made when I replaced the clutch.

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I did think of replacing the A/C compressor with a newer Sandco ? unit, but wasn't sure if the time and trouble was worth the potential MPG gains.

 

[name]

Pretty much normal but, you can install a better flowing intake and exhaust system.

What intake and exhaust system would you recommend ? would doing the TBI mods listed on this forum do me any significant good without going with a new intake ?