I have a 1986 240. Bought it about 2 years ago from a shop that specializes in Volvos. Ever since I have had it the gas mileage has been poor, approx 13/14 miles a gallon. About 3 months after having the car, I let another Volvo repair shop talk me into replacing the air mass meter ($600) that they said would dramatically help increase the gas mileage and fix the no power going up hills problem I was having. It solved the no power going up hills problem but did nothing to fix the poor mileage. Just after the new year it stalled once while driving, I restarted it & got home. Next day I tried to start it (from cold) it turned over but would not start. Now it has been sitting in the garage for 3 weeks. (It's my daughter's car she's at College). I finally got a mobile mechanic to look at it to see what was wrong. He said it has compression, a spark, no exhaust blockage and fuel pressure however he says that no fuel seems to be coming out of the injectors. He consulted a volvo repair shop and they reccommended replacing 'the computer' with a used one ($125).

My questions are:

1) Is it really 'the computer' that's crapped out or is it something else causing the car not to start?
2) Why the bad gas mileage and any suggestions to make it better?
2) Would replacing the O2 sensor help the poor mileage situation?

Thanks

1) Is it really 'the computer' that's crapped out or is it something else causing the car not to start?
I would guess that your visiting mechanic checked the fuel pump fuses. One's located on the panel (I forget what number, but you could check and turn them all) and there's another located under the hood over the drivers side wheel. It's one of those horse shoe shaped "modern" ones. I think it should be a 30 amp. They (and their holders) are known to go bad and keep a person guessing about what the problem is.
My car had the same symptom, and although it could be the ECU, my guess would be the ignition computer. They go for about the price you mentioned. I got an ECU from a junk yard for a lot cheaper - $25.


2) Why the bad gas mileage and any suggestions to make it better?
I think that mileage is about average for around town. You could clean the thottle body and check the flame trap.


2) Would replacing the O2 sensor help the poor mileage situation?
I don't think replacing the O2 sensor would help with the mileage, but I could be wrong about that. I replaced one to fix an emission problem.

Probably the fuel pump relay or the 25 amp fuse, very cheap items to fix. As for fuel consumption, I would pull the front hose off the fuel pressure regulator to check for gas (should not be a trace). Computers in '86 240s have extremely low rates of failure and you can get a replacement for $25-50. The AMM should have been $50-75.

Once you get it going again and if you aren't getting the mileage and power you expect check the timing. Mine came back after some engine work and I had to set the timing up because of same symptoms you're experiencing.
JR