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Is there a list somewhere on the BB of all possible causes of poor gas mileage? If not, maybe we could create one here. :)
My mileage went from the mid to upper 20s in mixed driving to the lower 20s. I have a B23F with LH 2.0 and M46 tranny). I have a few theories specific to my case but don't want to rule anything out.
My theories are dragging brakes (one of the rear rotors is warped but the car free-wheels just fine and doesn't pull to one side) and a bad coolant sensor. My air filter may be dirty as it hasn't been changed in a few years. My O2 sensor is new - I had hoped that it was the cause but it doesn't appear to be. Plug and wires are about mid-life; it idles and starts fine. AMM is old; I'll do the Bentley tests when it gets warmer to see if it needs to be replaced.
I thought it may be the winter-grade gasoline but usually my mileage in the winter is mid-20s. I use premium fuel due to knocking issues.
Thanks in advance!
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Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15
1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40
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Hi Lord Volvo,
In the begining, I was getting around 15 mpg. I found out that the air filter box was filled with nut shells, cleaned out and put new air box thermostat/air filter. I also cleaned the AMM, it was clogged with white animal furs. After that, gas mileage improved to average 27 mpg (32 mpg once from NJ to MD with tail wind).
A year later, the rear passenger caliper was sticking, my gas mileage drop to 22-23 mpg. I replaced the old caliper with new one and went back to 27 mpg but I did lost "Porche" like braking performance.
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I would start with the basics before throwing any parts at it. Change the air filter first - cheap...:)
How old are the cap and rotor? Any air/vacuum leaks? Take a good look at all the hoses. Particularly the air hose to the throttle body (I"m assuming here that the b23f engine has the same air hose as the b230f engine).
While you're testing the AMM, remove the connector and clean it with electrical spray. Check for bent or broken pins. Carefully straighten any bent ones and make sure the connector is reseated securely.
--
95 855 GLT Sportwagon 218k, 90 244 DL 300k - after 11 years has a new home
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I'm working on a few theories such as an AMM running too richly based on the resistance tests outlined by the Bentley manual, and a defective LH coolant temp sensor. I have a spare AMM and just received a new temp sensor. I've never replaced that temp sensor before and it seems buried underneath the intake manifold. That will be a fun task to do in the cold.
The air filter was a bit dirty but not clogged by any stretch. I replaced it anyway since I had a new one sitting around. The air intake hoses seem to be fine, although once in a while the engine will rev by itself while idling, which in my experience points to a vacuum leak somewhere.
The cap and rotor are a few years old. I took the cap off and it seems to be okay - no cracks or charring.
If I think of it, I'll yank out the plugs to see what they look like.
I also need to check the fuel pressure reg. It's a newer one but aftermarket.
My cat is old. Maybe it's clogged up. Any easy way to test that besides opening up the test port on the downpipe?
--
Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15
1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40
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Just a thought... You may want to check the belts to the alternator.
My belts had been coming loose and I noticed that my MPG was really dropping, like I couldn't get above 20 MPG even with winter gas.
I didn't know that this was happening until I was coming home one night, late of course, and the whole dash went dead while the car lost power. I nursed it almost all the way home by turning off the lights. Not something I recommend doing, but I needed to get home.
Without checking anything I ordered a new alternator as I believe I still have the original one in there. It wasn't till I started looking at taking it out that I noticed that the belts were loose, thus the inability for the alternator to charge the battery. I tightened them up and all is now well.
I found this little tidbit on the FAQ page for the alternator, that when it dies your gas mileage will suffer. If the gas mileage continues to suffer since I've fixed this then I will start looking into other things like the temperature sensor.
Good luck,
Matt
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Actually, the alternator belts in my car were a bit loose a little while ago but have since been tightened. My MPG is still poor, though. I do keep an eye on my voltmeter for any electrical issues especially since the death of my last alternator a few years ago.
--
Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15
1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40
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Failed coolant temperature sensor and/or harness connector?
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Harold Thompson '84 245 Virgos
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You can check the Engine Coolant Temp sensor by FULLY warming up the engine (thermostat OK?..should be the 87C or 92C), then turn off, key out, and pull the ECU connector. Check the resistance between ground (terminal 11 or 25) and the No.2 terminal (ECT) in the connector (they are numbered - check Art Benstein's "cleanflametrap.com" site for a descriptive photo), and you should get approx. 200 ohms. If so, ECT sensor and its wiring are OK.
--
Bob: Son's XC70, daughter's 940, my 81 and 83 240's, 89 745 (V8) and S90. Also '77 MGB and some old motorcycles
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Thanks for the tips. I did replace the ECT sensor but haven't fired it up next due to pending repairs and cold weather. Once it's back together I'll run the test on the ECU connector as you suggested.
I'm not sure if the thermostat is good; it's been a while since it's been replaced. The engine seems to warm up normally and operate at nominal temps according to the temp gauge in the dash. I guess it couldn't hurt to replace it with a new one.
--
Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15
1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40
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I wonder about the temp sensor and teh system being too rich at low temperatures.
Greg
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I already have a new sensor waiting to be installed; hopefully it's as simple as that. I'll check the wiring while I'm down there...if it ever warms up around here.
--
Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15
1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40
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Low tire pressure is an easy one.
My car loses about 3-4 mpg with winter gas.
Greg
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on teh B230F engine .. Fuel Pressure regulator is always my first suspicion. when the diaghragm starts to leak, the raw gas flows into the Intake Manifold
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/
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Good point. Mine went bad a few years ago and was replaced after a loss of power upon acceleration. I'll check it again in case it went bad.
--
Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15
1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40
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