I struggle to maintain 8mpg on my '95 940 turbo wagon. I've been driving as economically as I possibly can for the past few months and nothing has changed, so I'm assuming this has to be a mechanical problem. Any thoughts on what might need to be checked out?

 

Hello,i am not too familiar with your model but i can suggest maybe checking the obvious like the air filter, vacuum leaks,stopped up catalytic converter,is your check engine light on?if so do you have access to a code scanner to pull codes and see if possibly the oxygen sensors or other sensors have failed?Remember that codes do not guarantee a particular failure but can help to diagnose.Also check the EGR valve for proper operation if is a vacuum operated type(not sure about the electronic operated type), sometimes they stick closed or open,in addition stuck open thermostats can cause fuel economy issues not allowing engine to warm up, does your engine come up to normal operating temp? Like i said i am not a Volvo expert but i hope these suggestions help.

 

Do you see black smoke from rich running out the tail pipe? Have you checked a plug for rich running? Just pull a plug and look to see if it looks black. Do you smell gas when outside the vehicle? That could be a fuel leak and a big safety concern. Oh yeah, have you checked for codes?

 

No check engine light, spark plugs are brand new, throttle body has just been cleaned, no black smoke, no smell of gas, clean air filter, engine warms up just fine even in this cold weather we're having.

I'm thinking about purchasing a code scanner to help me out with this and any future maintenance.

 

What kind of plugs are installed? When I was pushing my '87 740 GLE, I installed some champ plugs once and my mileage dropped from 24 mpg to about 17 mpg over night. I pulled those plugs and tossed them.

Also, make sure they are gapped correctly. I'm with Quick Dent all the way. A plugged catty would cause performance problems.

Does your car have a OBD-II port? Does it have the OBD-I test box under the hood?

 

Not sure what kind of plugs. Can I check them myself or should I call my mechanic and ask?

I have OBD-I, but now that I think about it, if there were any codes, the check engine light would be on, correct? So I don't think I'm going to purchase a scanner just yet.

I'm going to check out my catty myself when it gets a bit warmer out, I'm tired of dealing with mechanics at this point. I'm going to start self-maintenance for the first time.

 

Quote:

Originally Posted by Jakeness

I'm thinking about purchasing a code scanner to help me out with this and any future maintenance.

You don't need to buy a scanner to read the codes, you have onboard diagnostic capability. See the following: Engine and OBD Diagnostic Codes

The knock sensor doesn't always light the check engine light when it has a problem, although it may set a code 143 on the ignition side (#6 hole, not #2) If it's not working, the computer retards the spark timing 10 degrees, which plays hell with your mileage/performance. Worth checking.

 

Running higher octane gas will sometimes help with a knock sensor issue. I'm pretty sure that car is supppose to have 87 octane. Shouldn't need 91 but you can try that.

You can check to see what type of plugs you have by pulling one of the plugs out ans seeing what writing is on it. Most standard ratchet sets have a spark plug socket. Pull 1 wire off and unscrew a plug to see what type they are and maybe check the gap if you have a spark plug gap tool.

 

has the fuel filter been replaced?

rspi, the turbos are recommended to run high test, but for some reason, my 92 seems to run stronger on mid-grade...

 

Thanks! I was totally unaware of this. Definitely going to check this out. I'll post the results here.

Thanks, gonna check that too. I doubt I have a spark plug gap tool, but at least I can check the writing.

Not that I'm aware of. I'll see what I can do in that area as well.

Also, how odd. My car can barely function with mid grade. It's always been run on premium except for the one time my mom put mid-grade in accidentally.

 

Man ...seems like a robbery going on..are u sure no one is taking gas outa ure tank..?
9% unemplt can do strange things like $5/g gas price did...

Otherwise..serious fall in mpg got to relate with either out right loss of fuel before it reaches the injectors ..OR
Some serious screwed up combustion ...either by improper firing or valve timing.
OR
some cylinders maynot be firing properly, or say missing.

The missing of firing is obvious at exhaust and poor idle, but confirmation is easy by checking indiv sparks strength at the plugs.
I am not sure spark plug brand change can throw the mpg from 18 to 8...[gapped same] boy thats a serious invasion on the engine.Neither the Octane change from 93 to 89 can do such a robbery.

I don't know the model and its timing belt/chain situation...and the means to confirm the ignition timing..but worth checking both.
How old is the car/engine [miles..?]
Were the SP wires ever changed, and how is the spark distribution ..is it mech dist and rotor...? If so check the rotor, but again it has tobe real bad[like metal missing/consumed] to justify this loss of mpg.
The worn out rings and real poor compression can do some loss of mpg too..and that should show up as blow by into the Cr Case.

The newer cars are designed [ig timing and exh cam lob/valve-opening] specifically for high octane which has a slower/smooth combustion...so the spark can be timed early.
The low octane has quick ignition[ the time between actual spark, and start of ignition],so the same spark timing[as for the H Octne], causes ignition so quick that the compression is not even complete...so the knock occurs.
Then there is an issue as to how the combustion [flame front] progresses till the entire mixture is burned.If it burns very slow ..the combustion may still be in progress when the exhaust valve opens...and dumps the pressure out w/o giving the the mech work or power to the C Shft.
But higher compression ratio obviously means quicker ignition[like diesel] of highly compressed mixture, so H Oct use[slow combustion] almost becomes necessary.
Using gasoline in diesel eng will ignite the mixture way before the 18:1 compression is complete, [and that too w/o the spark near 10:1/ 11:1]...and the north going piston heads south...before reaching tdc. Now that is a real KNOCK w/o a spark....and even a very slow burning dieselfuel creates a rattle. Wonder what the Octane of diesel is..140 something.!.don't know !!

High C. Ratio [called gamma] has a square effect on the efficiency...which is what all car makers are after. And more efficiently the fuel burns less are the pollutants to help meet EPA standards.

Diesel with less fuel value than gas burns well in a very effcnt engine, but 18:1 CR is far cry from 9:1, and net effect is still far more mpg..and the exhaust is full of solid carbon, can almost make black paint ..if collected well by the truck drivers..lol

[didnot mean to bore ya folks..just refreshed my memories of 40 yrs back... wonder where everything else has changed...this Old F gasoline IC engine still farts the same way..as it did about a century ago..just a resonator added]

 

Sorry, forgot to post here. I averaged 12mpg on my last fill up

My OBD came up totally clean, no codes. Kind of disappointing, I was hoping something was broken so I could fix it and end the problem.

My fuel filter was changed less than 20,000 miles ago.

I haven't checked my plugs, I don't have the tools and I was getting the same poor mpg before they were changed anyway.

I'm considering Seafoaming my vehicle, as many people report an increase in mileage after usage. Anybody know anything about that?

 

If you are down to 12 mpg, seafoaming will not fix it. There is something not working properly here. Several things that can affect the mileage:

1) Temp coolant sensor - a faulty temp coolant sensor will make the ECU thing that the engine is cold and enrich the mixture. If the sensor is not totally failing, it may not throw a code.

2) Faulty Oxygen sensor - The oxygen sensor measures how much oxygen is in the exhaust and the ECU uses this signal to enrich or lean out the fuel mixture. If the sensor is faulty, the ECU may think the mixture is too lean and thus enrich it. However, generally this will throw a code.

3) Exhaust leaks - If you have an exhaust leak upstream of the oxygen sensor, air will enter the exhaust causing the Oxygen sensor to read high. The ECU will detect this as a lean condition and enrich the fuel mixture. I have had this occur and it did not throw any codes.

4) Clogged cat - I don't believe this will throw any codes but you should see your performance drop.

Pulling a spark plug and inspecting them should give you a good indication whether it is running rich or not (black sooty deposits mean rich). You should have the tools to remove the spark plug since the lug wrench that came with your car has a spark plug wrench on the other end. Use that to pull the plugs and inspect.

 

Either you rarely drive or have more money than you need. It's been 45 days and you still have not checked your plugs? Go get a gap tool ($3) and pull a plug. If they are not Volvo, replace them with Volvo plugs or have someone do it for you.

 

First I'd make sure that you accurately measure the gas consumption; not to be condescending but many times that in itself is a problem. Then, given that the car seems to be in decent shape and not throwing codes, may be the type of driving you do is the culprit if you indeed get 12mpg. This time of year (cold), making many short trips (as opposed to long trips), and aggressive driving style can very well get you 12mpg...

 

the best way to measure consumption is to fill the tank till the spill. Then drive on hway at least for 60, or better 100 miles[not unpurposely], and go back and monitor the excat fuel amnt needed to fill again to spill. Then obviously divide the miles by the gallons[shown in 1/100 of a gallon on the pump].
Now the mileage drop has been seen by me while using gas fron no brand stations like XTRA, CLARK, FUEL NOW and the like, compared to Shell, BP Exxons...which will protect their brand...so from their big tanks, they haul upper 90% of fuel to 'their' stations and rest auction to NO BRANDS...why?, cause its the bottom which collects water and other ****.

But with 12 mpg the reasons seem tobe more than one, and bad fuel may be just one of three OR maynot be.
Smell the exhaust to see if the unburned fuel is going out, suggesting bad fuel/air ratio by the system ECU or whatever.

The sp lug gauge is fr a $ at Autozone and others, but a gap hastobe really bad, that s why gaps re given/suggested in tolerance like .032 +/- .004

Bad fuel/air ratio combined with bad timing[related to gas octane]...is enuff to give you 50% loss easly. All other factors like bad wires, filter etc etc are of less significance.
Now a bad , totally choked air filter, by vitue of choking air flow CAN mess up or ENRICH the ratio, but it will also need air flow metering system to malfunction or go out of range its designed.Clean the MAF and ensure no leaks from rot of rubber or bad clamps. Good luck
I would be very curious when u find the reason...which should be easier than electing a president..

 

Sorry but it is simply not possible to drive these cars so bad that they get 12 mpg. If you drove like a mad man you'd get 16 mpg. Now you could have a dragging brake caliper causing a drag problem.

 

Thanks act, I'll check all of those as soon as I can.

rspi, to be honest, I was a bit hesitant about messing with the spark plugs as I don't really know what I'm doing. I'm just gonna go for it now, time to get some experience.

lev, I measure mileage by filling up the tank and dividing the miles on my trip by how much gas I put in. I doubt the problem is how I drive, as I make use of as many hypermiling techniques as I possibly can. However, I do make many frequent short trips.

ETA: how would I test for a dragging brake caliper?

 

To check for a sticking brake caliper just jack the car and try to turn the wheels.

You will need a long extension on your socket to reach into the spark plug hole to get the out. Turn them counter clock wise to get them out.

 

Many short trips, especially if the car gets to cool down in between, will give you bad mileage. As far as dragging caliper, you'd need to lift the car and spin the wheels individually, and if one spins less freely or you can feel drag, you'll know. The sensation while driving will be as if the parking brake is partially engaged. Don't fear the plugs, as long as you don't break one you'll be OK... The Turbos get extra heat so sometimes the plugs are kinda tight, so careful unscrewing them. Gapping them is easy, that round gauge is pretty logical, and if you haven't looked at the plugs in the last 10-15k miles, I would take them out and regap them at the least.