I replaced a number of parts on my 240 and while the old girl with 300K now purrs like a kitten, I'm only getting about 17 MPG. I'm more used to 25-27 MPG using regular unleaded.

Here's what I've done: New 02 sensor, IAC, NKG plugs,wires,cap,rotor,hall pic-up sensor, Head Gasket with cylinder head re-surface and pressure test, new main pump and filter, new tank pump and filter, new FPR. New engine and ignition wiring, new pump relays. Timing belt is correct and injectors are clicking away with no gasket leaks and no other hose vacuum leaks, Timing is good, compression is good,idle is great. TPS seems OK and Throttle body was cleaned. New air filter and airbox thermostat. Car does not hesitate and pulls strong through the gears. Just poor fuel economy. AMM passes the simple disconnect test. Any ideas ??

Check fuel pressure with a gauge to make sure it is within specs.My 83 had the same problem and I changed every part you changed with the addition of a fuel pressure regulater.Fuel pressure was too high and it ran OK but had poor mileage.Once it was in spec the car ran 100 percent better.

You must be disappointed with 17MPG after all that work.

Sounds like you've covered most things, but is the ECT sensor properly connected to the harness, and does it show the proper temperature/resistance characteristics? When it goes bad, or wiring is pinched/grounded the ECU sees a "Cold Engine" signal and richens the mixture.

I'm guessing you put in NGK BP6ES plugs...what do they look like after a good run?
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and a few old motorcycles)

Seeing how the car didn't run very well at the time, I needed to replace all those components as they all were mostly shot. Now it runs well but bad gas mileage. I'm not sure what the ECT sensor is ? Is it the Temp sensor in the head ? If so, mine is original. The knock sensor is also. I tried to replace the temp sensor with one cross referenced from an auto parts store but it gave really erratic readings so I went back to the original one. I replaced the harness and the connection is good - maybe the sensor ? I'll look at the plugs again- Last I looked they are black and dry on the edges and clean at the spark gap, no black oily residue on them.

I should have been more clear: Yes it's the Engine Coolant Temp sensor as Pageda said. There are two temp sensors in the head close to each other. The one that drives the temp gauge in the cluster is closer to the front of the engine and has a single wire going to it with usually a spade connector. The ECT sensor has a proper clip-on connector with two wires in there (Blue and Black).

..and you can test the ECT as he said by pulling the ECU connector off and measuring resistance on the ECT terminal to ground. On my Haynes (can't find my Volvo books tonight) this is shown as Pin No.2 for 1983/86 models with LH-2.0 and 2.2 . The 1982 LH-jet (1.0?), 1987-91 LH-2.4 and 1989-93 LH-3.1 has it going to Pin #13. In those later years the wire colour is Blue-Red. (thanks for being consistent, Volvo...)

If there's any soot on the plugs after a good run, that's a sure sign of rich mixture.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and a few old motorcycles)

Thanks Bob and Dan for clearing this up. I'll test the ECT this weekend and replace if neccessary. Guess I was getting it confused with the one that drives the temp guage.

It is the engine coolant temperature sensor for the ECU (computer) if it isn't working it will tell the ECU the engine is cold and feed extra fuel all the time. I believe it is in the head of the 83, buried under the #3 intake manifold runner. Test your old one and if you need to replace it get a Bosch from FCP Groton $20. Good luck! Dan

Thanks, guess I just knew it as the temp sensor. Is there an easy way to test it ? Yep, it's really a pain to get to it w/o removing the manifold.

The Bentley manual says to check the ohms hot and cold which means remove the sensor. You could test it cool, 68 degress is 2280- 2720 ohms and hot 176 degrees is 290 - 364 ohms at the ECU connector pin 13 and ground with the ignition off. If the readings are outside this range replace it. Dan

Seems like you have everything covered. I assume your tire pressure is within specs. What about alignment, suspension, is that all in order? Have you ever had your injectors professionnally cleaned?

I get 20-21 MPG in suburban driving and about 26-28 highway.
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'89 244DL M47 166K miles