Have a 1992 240 Wagon that is getting terrible gas mileage, roughly 15mpg commuting at 40-55mph with little stopping or traffic. Bought the car a while back and have just been living with it since we don't drive it a ton, but looking through the extensive maintenance history from the previous owner, looks like they noticed the problem as well (unsuccessful diagnostic noted for a loss of mpgs from 28avg to 20). This is my second 1992 240 with an auto, my first would very reliably get 25-28mpg all day long.

I have tried a couple of things and have some ideas, but some guidance on where to start could be great!

Replaced 02 Sensor (helped slightly for highway driving, but the car is still drinking gas like you wouldn't believe. Seems to be back to it's old ways.)
Checked plugs, wires etc (plugs are a nice tan color, as they should be NOT fouled or black)
Verified injectors are working using the test module near the strut tower
Pressure regulator not leaking
Throttle body and MAF hot wires are clean (used proper cleaner for MAF wires)

Generally a bizarre issue it seems--I would have expected if it was drinking so much gas that the plugs would have shown signs of running rich, but this was not the case. There are no cold start problems, but am thinking perhaps a new coolant temp sensor may be worth replacing just in case it's faulty and sending a bad signal to the ecu (again, wouldn't the plugs be fouled?). The MAF is new within the past 5 years (mechanic replaced when previous owner noted poor mileage), but is it possible that they replaced it with the wrong one, as it's not the oem Bosch part? Clean throttle body regularly, but it is rarely very dirty. Car doesn't overheat, but temp gauge tends to sit slightly above center (which is abnormal in my experience), but thinking this a caused by the replacement thermostat I installed a few months back which may run a few degrees warmer.

In addition to poor gas mileage, the car has always had a tendency to "bog down" under hard acceleration. You cannot break the rear wheel (open diff) loose even on a dirt road, which is definitely contradictory to my experience with my last car. Once in a while you actually cannot accelerate faster than just above idle (car just bogs down and shudders if you give it hardly anything), but this eventually goes away after maybe 10 miles or so and happens rarely. Generally the car does not seem to rev as freely as I feel it should, and certainly less freely than my friends '89 (which is a bucket duct-taped together with half its parts missing and vaccum hoses disconnected and clamped, no o2 sensor and yet still gets 28mpg). Could the catalytic converter be plugged? I do know for a fact that there is a slight leak just in front of the cat, could this be giving false info to the o2 sensor? Clogged flame trap? Bad coolant temp sensor? Stuck cold start injector? Wrong/Bad MAF?

Last I checked there were no codes after the o2 sensor was replaced.

There just seem to be so many possibilities it's driving me nuts! Please help if you can!

 

Yes, the CAT could be a problem, also I'd check TIMING and make sure you don't have some type of BRAKE DRAGGING issue.

 

Will be checking out the cat and repairing the leak, but didn't think that timing was adjustable in late model 240's? Since it's a 1992 I assume it has the LH2.4 system. Possible that the timing belt (I believe was replaced within the past 5 years) could be off a tooth? Wouldn't this result in an obvious rough running? No dragging brakes that I'm aware of.

Just went out to confirm that there are no codes--ignition or fuel system.

Is it possible that the MAF could be the wrong part for this year 240? How can I find out (wouldn't it throw a code)?

I've been reading into the whole idea that an exhaust leak can fool the o2 sensor into thinking there's a lean condition, and making adjustments (ie adding more fuel). Anyone have any experience with this? Surely I couldn't account for more than 10MPG worth. If it did, I'd imagine that the plugs would be fouled for sure?

What about the intake heater system? Could this be stuck open, causing the intake air to be too hot and resulting in poor performance?

It is unusual that this bad of gas mileage wouldn't trigger a fault code one way or another?

Thanks for your help!

 

OK, but you said you REPLACED the O2, no?

And by TIMING I do mean exactly that, tooth off, a bad belt, pulley slipping, not adjusting the timing.

Easy to check on the heater system, just disconnect the thing.

 

bad cat converter
crankshaft pulley shot.....there is a rubber ring that gets cracked and old...jacks up your timing..
extensive maintenance but at what intervals? last tune up?
fuel filter changed?
trans fluid changed?
running on one pump?

 

Ordered a bunch of parts last night, including a new catalytic converter mid section. Transmission flush, plugs, wires, distributor etc are all new within the past 30,000 miles. Have a fuel filter but haven't installed it yet.

Can the timing be checked with a light? Can the condition of the crankshaft pulley be assessed without removing?

Also, forgot to mention that gas mileage appears to drop quite a bit as tank gets below half tank (gauge shows this anyways), but hard to calculate what it is exactly to know for sure. How do I know if it's only running on one pump? With the ignition on I can for sure hear a fuel pump running.

Thanks again for all your help!

 

You can check the timing with a timing light but that will only confirm whether the pulley has slipped due to worn out rubber on the harmonic balancer as analogies has mentioned. Keep in mind though, even if the pulley is worn out and slipped, it will not affect the ignition nor valve timing. I would check it just to make sure that the timing mark on the pulley is still accurate. If it lines up with the mark on the timing belt cover, then your pulley is ok.

Also, check for exhaust leaks upstream of the O2 sensor as these can lead the computer to think the engine is running lean and cause it to enrich the mixture. Another item to check is the engine coolant temp sensor.

Of course, check the CAT as the others have mentioned. Given the condition of your plugs, this is a prime suspect.

 

What brand tune up parts are you using? When I had my 740, I once installed some NON OEM plugs and my mpg dropped 30%. I pulled them out a week later.

 

All parts (except the MAF, strangely) replaced during maintenance were genuine Volvo parts. Plug wires are some french made Volvo branded wires. Previous owner had all maintenance done at the dealership, and followed the service schedule to the t, every page of the service schedule is signed at dated by the local Volvo dealer. I think maybe in the last year of ownership they stopped going to the dealer.

Thanks again for all your help, everyone.

Any ideas on worse gas mileage after half a tank?

 

Check compression.

 

Thanks, worth a try. Have dealership maintenance document showing a compression test done 20,000 miles ago with excellent compression (don't have the numbers), same values across all cylinders if I remember correctly. No overheats or lack of regular maintenance since then.

Again, any ideas on worse mileage below half tank? I know there can be hard start issues after half tank if one of the pumps is not functioning, but haven't heard much about worse gas mileage.

 

air leaks in the intake plumbing between the MAF and throttle body. vacuum leaks.

if you pull the vacuum hose from the back of the fuel pressure regulator is it wet with fuel? sign of blown FPR, which usually means too much fuel is getting dumped into the engine.

since you have LH2.4, you have "OBD-I", onboard diagnostics that do NOT require any special reader, just the blinky-box on the left side suspension strut... see Engine and OBD Diagnostic Codes for the procedure to read these (the meanings of the codes are down below). not all codes will light the "Check Engine" light. codes are often just symptoms of other problems, so don't just automatically replace what the code initially suggests without a bit of testing first.

ECT (Engine Coolant Temp) sensor is easily tested. pull the footwell liner off the passenger side footwell, the ECU is on the side against the fender. with the engine already hot, (car off!) unplug the ECU, and measure the resistance from pin 13 (ECT) to pin 5 (ground) of the socket (digital multimeter in ohms mode). if the engine is HOT (say, 200F), that should read in the low 100s of ohms. wait a few hours for the engine to cool down, it should be several 1000 ohms. if you read anything close to these, then your ECT and associated wiring is probably fine. if its way off, then you know what to look for. fyi, the ECT itself has two sensors in it, the other one is wired to the ICU pin 2; ICU pin 14 is ground. To be thorough, check both.

• 32F (0C)-- about 6000 ohms within a range of +/- 10%
• 68F(20C) -- about 2300 ohms
• 104F(40C) -- about 1300 ohms
• 140F(60C) -- about 600 ohms
• 176F(80C) -- about 300 ohms
• 212F -- about 190 ohms

 

Sounds to me as if the engine is running just fine. LH2.4 will learn around many flaws if the O2 is good; the plugs seem to bear that out. Your mileage isn't that far off base for an auto car with the ubiquitous 3.73 rear axle ratio. Brakes dragging, clogged cat/exhaust, poor compression possibly. Is your overdrive working? No offense but I still haven't seen a 240 that would pull 28 mpg in stock form unless it was running extremely lean. Maybe a 5 speed w/ a 3.31 rear end could do it but not your average 240. Google Volvo 240 mpg and you'll see what typical mileage is. Oh...the AMM is most likely correct. Should be Bosch 016. The 012 from a 960 will work also, but it is a larger diameter and rather noticeable.

 

our 87 240, totally stock, in reasonable condition, does about 25MPG running around the county, and has gotten almost 30 on long road trips when driven with a light foot and smoothly.

my turbo 740 wagon, OTOH, hah. I'm lucky to see 22mpg on that, and usually get 17-19 leadfooting it around the county. one of my few complaints on that car is the small size of the gas tank relative to the fuel consumption (this was specific to wagons prior to 93 or 94 when they enlarged the tank by a couple gallons).

 

I'm not saying that sort of mileage isn't possible; only that I haven't seen it. The 240 wasn't built as an economy car...anything above 20 is a blessing from Oden. I too would have liked that late model gas tank...until I saw that the drive shaft bisected it and had to be pulled to pull the tank.

 

Averaged 25mpg in my last sedan over a 2000 mile roadtrip with two people, at least 300lbs in the trunk and and a 40lb DH bike on the back. Seriously overloaded.

Anyways, just wondering if anyone would be willing to explain exactly how this crank pulley has anything at all to do with timing, even in the older cars. Isn't it basically just a rubber donut connected to the end of the crankshaft that drives accessories? How on earth does this have anything to do with timing? As far as I can tell, none of the accessories mind if how the pulley is oriented (I'm sure the belts slip on their own over time anyhow) and it's not as though the pulley interfaces with anything timing related, right? Please set me straight.

 

First of all, it isn't technically a crank pulley; it's a harmonic balancer. Two concentric steel rings bonded with rubber. After years of heat, vibration and oil mist, the rubber deteriorates and the outer ring with the timing mark no longer remains constant...it slips relative to the inner circle. Doesn't mean anything at all on your car as you have LH2.4 fuel injection and timing is set by computer. For 88 and earlier cars with LH2.2, it means there is no way to get an accurate timing reading.

 

What about your overdrive. If it is not working then you have a 3 speed trans and that kills MPG's like no other. I was missing 4th gear in mine and when I checked the relay it was bad but did not turn the light on(indicating a issue). Once I changed it out with a junk yard one the OD came back

 

thats a good point about the OD.

the system is a little wonky. the light is ON when the OD solenoid in the transmission is NOT powered, and the light is OFF when the solenoid IS powered. powering the solenoid enables automatic OD operation, depowering it disables the operation.

failure modes include...

1) pushbutton on shifter and/or wiring goes bad. very hard to access to repair.
2) OD control relay goes bad. trivial to swap, but not a cheap relay, best to verify its bad before replacing.
3) solenoid is bad.

if its the button or wiring, many people opt to disable the solenoid, this can be done with a kit from IPD, or by dremelling a slot in the end of the solenoid plunger. ditto this can be done if the solenoid itself is bad. in either of these cases, removing the OD relay will disable the OD light from whatever madness its doing. after this 'fix', your car will be an automatic 4 speed, but you won't be able to disable the OD for 3rd gear engine braking, towing, mountain driving.

 

Really appreciate all of you guys' help, thanks so much.

OD works just fine, drops a gear when engaged and when enabled makes it to 4th gear no problem. I'll report back this weekend when I replace the worn out exhaust/cat, coolant temp sensor and a bunch of other various parts I suspect may be contributing to this problem.

Also note, while there isn't any gas in the vacuum line going to the FPR, I did notice a bit of a gas smell from the line when checking it yesterday. Not sure if this means anything, I assume if the diaphragm is leaking fuel will end up in the line and just a gas smell is likely normal? is there a test I can perform without taking the fuel rail apart and putting a pressure gauge in? i'll be checking both pumps today.

I know it's not really relevant to my problem, but just for the sake of understanding--isn't the harmonic balancer/crank pulley just a piggyback off of the crank to balance moving internal mass? Unless it drives something related to ignition or valves etc, what bearing did it have on timing in the older cars? I must be missing something here. I understand it's purpose to reduce vibration and compensate for the various differing weights of moving internals, and that you can check to see if it has slipped by comparing its rotation relative to TDC, but how did this ever have any effect on timing?


Thanks again!