Volvo 240 Terrible Gas Mileage!

dowst · Post by **dowst** » 25 Mar 2013, 06:08

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!

Post by **billofdurham** » 25 Mar 2013, 13:02

You have given a number of things you think may be causing the problem.

If the hole in the exhaust is in front of the O2 sensor it will, in all probability, be getting wrong information. I would certainly be trying to close the hole with either an exhaust bandage, exhaust paste or a new pipe. Three options but I would start with the bandage to see if it does cure the problem.

Before spending money on a new coolant temp sensor you can check the old one with an ohmmeter. Instructions are attached. Ignore the year of the car as yours is the same.

240 Coolant Temperature Sensor check.pdf: (102.59 KiB) Downloaded 545 times

Bill.

dowst · Post by **dowst** » 26 Mar 2013, 05:38

Thanks Bill,

I have a bunch of parts on order now--front header pipe, cat pipe, coolant temp sensor and flame trap. Well see what happens!

Some mentions on another forum that this could be caused by poor ignition timing by a bad crankshaft pulley as well as a possibly running on on fuel pump or a bad fuel filter? Any insight on this?

Gas mileage certainly appears worse when past half tank. How can I check to see if only one pump is running, as I certainly can hear one when the ignition is on.

Thanks again

Post by **billofdurham** » 26 Mar 2013, 13:40

The crankshaft pulley is an oscillation damper - basically two metal plates with a rubber insert between them. Over the years the bond between the metal and the rubber will deteriorate giving three separate pieces. However, it is my understanding that this does not affect the timing which is computer controlled. A bad fuel filter - usually restricts the flow rather than allowing too much through.

If you can hear one pump running at ignition switch on it is most likely the main pump as it is louder and nearer to the driving compartment. The in-tank pump can also be heard at ignition switch on if you remove the filler cap and listen at the filler neck whilst someone switches the ignition on.

One other quick check is on the fuel pressure regulator (FPR). Pull off the small vacuum line and sniff for petrol. It is possible that the diaphragm has a pinhole and is bypassing fuel directly into the intake manifold. But even if there is no fuel smell, the regulator could have increased the fuel pressure creating an always-rich condition. This is not uncommon.

Bill.

RustyH · Post by **RustyH** » 16 Apr 2013, 11:31

Hi Dowst, This is an interesting topic. If you solved the problem, please reply. Being a novice, I throw parts in which of course is expensive and not terribly smart. You might look for a used known-working MAF and give it a try. There is a national network www.car-parts.com
I have a spare used MAF which I would be happy to send you, but I believe mine is different from yours. I have a 1990 240 (LH 2.4).