98 Blazer, low mileage

My grey 1998 s-10 Blazer was lost to a wreck. The new one, green, also 4.3 engine, but fewer features. Last one ran about 18 MPG and this one about 15 MPG. I put in some
Berryman's B-12, which hasn't done much.
What are some of the common things? Spark plugs comes to mind. Truck has about 175,000 miles.
Today I had to put refrigerant in the AC system, there was zero psig in there. Blows cold, but we'll see for how long.
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Christopher A. Young
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Stormin Mormon wrote:

Plugs, cap, rotor, vacuum leak, leaking fuel lines, leak inside the intake plenum (fuel lines and regulator) leaky injectors, partly plugged cat, over-sized tires, crappy NY gas...
The common ones are plugs/wires/cap/rotor, leaking fuel lines and fuel leaks inside the intake.
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I'll check some of those. I've not heard of fuel leaks into the intake. Wouldn't that just rich up the mixture?
My guess at the moment is very old spark plugs.
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Stormin Mormon wrote:

Hope you have the proper socket to get the one behind the steering shaft.
The leaks are fairly common. The regulator assembly sits out in the open under the plenum and gets the vacuum signal directly from inside. The problem is that unlike an outboard mounted one you can't just pull the vacuum line to see if it's leaking.
It causes a VERY rich mix and will actually burn out a cat/con if left alone. Most times the leak is enough that it is just raw fuel that gets dumped through the system. Some times a clue will show up with gas smell in the oil.
Plugs, cap, rotor, wires (pay VERY close attention to the routing and use a good wire set) Plug wise I recommend Delco platinum plugs. I have seen other brands that just don't seem to work well in GM vehicles. Weird but true.
The 97 I have will give me 20+ on the highway and about 17-18 around home. Of course I screw that up real bad by letting it set and idle while in FD calls. Should be able to stop that soon, won't need heat...
Oh one thing I forgot to ask, what temperature is your engine running at? A stuck fan clutch could be cooling the engine and causing the ECM to richen the mix. Normal should be 195-210
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On Wed, 13 Apr 2011 02:36:13 -0400, Steve W. wrote:

I had a sticky thermostat on an 03 TB I6 LL8 Vortec causing the sevice engine light to stay on. Blocked half the radiator with Plexiglas for a few months until I was ready to replace the thermostat. If that engine doesn't run at 210 the service light comes on and gas mileage drops from 14 in the city to 10. A stuck fan clutch would be very noticable at higher rpm. Had an old Lincoln MKV 400 CUI that had one and it sounded like a jet engine at 4000 RPM.
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A. Baum wrote:

The SEL won't come on if the engine runs cold. BTDT with a 96 and a 97. One had a bad fan clutch and the other a bad thermostat. In both cases the mileage went down but nothing else (other than the temp gauge reading low)
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On Wed, 13 Apr 2011 16:53:12 -0400, Steve W. wrote:

Most people wouldn't know if there coolant temp was lower than normal. Enough to increase fuel consumption. With an aluminum block the LL8 comes to operating temperature in 5 minutes or less depending on the outside temp. Around 1 mile when it's 32> F. That's what puzzled me about the thermostat. I'm used to them sticking open. The LL8 wouldn't warm that fast with one that was stuck open. Or would it. When I removed it it was closed of course. Never did try to heat the capsule up to see how far it opened. It would have to have opened completely for the coolant temp to be below normal in the summer. I do recall a heat wave we had of temperatures in the 90's for a week or so. The SEL went out during then as the coolant temp reached 210. Anything below say 85 and the temp never reached 210. Evidently the thermostat was jumping from closed to wide open.
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