Hello!

I have 1993 940 fd stw with automatic trans.


I have owned car near 6 months now. At beginning i drove many full tanks with 23.5 and + mpg (under 10l 100km).


Now ive been fighting too high consumption for 3-4months. I drive 80-90% highway and i get +-18 mpg (13l 100km).


Even pure highway driving mpg is about 23.5 (10l 100km). This is my fourth volvo with this technig and other has been not that thirsty.



What ive done:
New intake gasket and vacuum hoses, tested with vacuum gauge no leaks and good vacuum

New o2 sensor bosch oe, twice ( it reads 0.4-0.8 volts and wont jump 0.1-0.9 volts, if i do vacuum leak then it goes o 0.1-0.2volts. What causes o2 sensor to lean my fuel ratio?


Tried with two oe maf's

New ignition parts, rotor, cap, plugs, wires

New engine temp sensor


Exhaust wont leak + new gaskets manifold + pipe


Compression test very good

Pretty new timing belt and timing is okay


Injectors checked and ultrasonic cleaned, fuel pressure regulator tested, new fuel filter


No fault codes


Starts, idles and works whole rpm range with no problems or hesitation no matter temperature or rpm.



Brakes wont grind or jerk, serviced all brakes.


Automatic works fine, wont slip and turbine lock works. Rpm at 55mph is about 2200.



I wonder why o2 sensor acts like that? That was reason to buy another but i dont believe that two oe bosch o2 sensors are both bad.


I have video. And my multimeter works, tested with another cars and they read like should.


here is video and you see lazyness and that high reading




Help me please

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What are you expecting? It's a Volvo, they get 18 MPG.

But one possibility is - in my part of the country they have a cold weather gasoline formulation and a hot weather formulation (At least I was told that by Chevron when I owned a gas station). Perhaps the cold weather formulation has something to do with your MPG. Or in the winter the engine takes a slight bit longer to heat up - and the mixture will be richer for longer. What temp thermostat do you have in the engine?

 

Well, I think you are rightly puzzled by mileage decreasing over time.
Good question, reading the post from 23 mpg to 18.5 is a significant decrease. And for a NA car 18.5 MPG mainly on hwy driving is a bit low. My '94 945 gets 22mpg mainly city driving. Turbos are worse. I don't know for sure but something that was done to improve the car must have caused this, what else?

 

I have heard this psalm before. I have owned six different volvos, 240, 740 carburettors and 760 v6, 960 r6 and two 940's. I know what they took when working nice.



I know that city, automatic and volvo is a thirsty combination but at highway and mixed driving they consumpt same that same class/size/engine cars.



And i had higher mpg for months when it became worser. So its not like should.

 

My experience with 240s with LH2.4 fuel injection systems is that they should get around 23 mpg mixed city/highway driving so 18mpg is a bit low. I had this trouble with our '90 240 and found it was due to exhaust leaks upstream of the catalytic convertor. I use a plastic hose as a stethoscope to look for leaks while the engine is idling. Check each runner where the exhaust manifold bolts to the head. Also check where the downpipe connects to the exhaust manifold. On the downpipe, check the whole thing for leaks as well as the joint where it bolts to the cat. Check the Y-junction of the downpipe as cracks can develop there.

 

our 1987 240 automatic would get 28-29 MPH straight highway driving, like going 300+ miles non-stop on a single tank without any traffic and maintaining 65 MPH on cruise the whole way.

 

Yeah i agree. My sedan 940 with same 230fd+automatic went 30mpg highway and i had results for 20k miles for it.


At city only it took couple times low 15mpg