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I searched the forums, found some helpful info, but still no answer, so I post this in hopes for some more info.
So, here's the deal.
89 Volvo 740 turbo wagon. 146k Summer mileage (in a hilly, poor road condition state) in town 20-21. Highway 24-26.5 (and has been getting better steadily) Winter mileage (same conditions, no snow until today) in town 12-16. Highway no more than 20.
Work done/mods:
Plugs, wires, cap, rotor button, vaccumed cleaned all four injectors, cleaned throttle body, adjusted TPS correctly, cleaned IAC, engine temp sensor and guage sensor, fuel system check valve, fuel filter, checked both fuel pumps for operation, fuel pressure regulator brand new, k and n drop in filter, synthetic engine oil, brakes-none dragging, four studded snows on steel rims (this may be part of the problem as the stock alloy rims/tires were about 7 pounds lighter each), adjusted ignition timing to 13 BTDC (book says 12, did this mod to try and resolve poor fuel economy) as it was at 10 BTDC, camshaft seal, timing belt/tensioner, thermostat, new flame trap (called something else on a 740) complete assembly and cleaned all hoses, fittings, etc, checked turbo for wear (no axial play at all), battery, camshaft cover gasket, new headliner, cleaned MAF and connector, probably more I can't remember right now.
Reduced the curb weight by about 100# by removing- frame "vibration dampeners", A/C all components, interior floor mats (under carpet mats), stock radio amp, all extra brackets under the hood, and a few other things I can't remember. Air box is intact, thermostat is fully functional.
No codes, or at least no codes that produce a light. Cannot find a module inside the engine bay to check for codes. All books/stuff on the net says it's on the drivers fender well and show photos of theirs; mine is absent.
Outside temp above 50, great fuel economy for a heavy car. In fact, with a 2500# trailer behind it on the highway I still saw 18mpg. Our weather has been intermitent as of late. I check fuel economy everytime I fill up. One week it will be warm and I get great economy. The next week it's cold and I get terrible economy.
I figured winter gas formula, sure. 1-2mpg. But it doesn't fit because I'm using the same gas station, and one week to the next then back again I'm getting good, bad, good, etc. No snow to speak of so no tire spin, or extra drag, etc. No extra ballast in the boot until today.
I was thinking tires/wheels but that would be bad all the time after putting them on. No beans there either, although they probably aren't helping.
Running out of ideas. Never changed the 02 sensor. Who knows how old it is. Car does use some oil, say a quart in 5k miles at most. Still, I would assume this to be bad fuel economy no matter what the temp is outside.
Thinking of picking up an air/fuel guage. Not sure how to install it, but probably worth a shot.
At my wits end, any suggestions?
B
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