22r terrible mpg

[Eugene13]

Hey guys, have noticed. recent dramatic drop in fuel economy over the past couple months. I used to get around 16-18 city/highway and around 15 when loaded down with gear. Now I average around 12.5 and have to fill up every 150 miles! Haven't made any changes to the truck that I thought would decrease it this dramatically. No added weight, nothing down to the carburetor, no bigger tires, nothin! Any thoughts on what might be causing this? Engine has 208k and just recently did a timing chain on it.

 

[toyotarunner1]

Hey guys, have noticed. recent dramatic drop in fuel economy over the past couple months. I used to get around 16-18 city/highway and around 15 when loaded down with gear. Now I average around 12.5 and have to fill up every 150 miles! Haven't made any changes to the truck that I thought would decrease it this dramatically. No added weight, nothing down to the carburetor, no bigger tires, nothin! Any thoughts on what might be causing this? Engine has 208k and just recently did a timing chain on it.

Any check engine lights?

 

[Eugene13]

nope, and nothing else is out of the ordinary either, it runs perfect. Idles a little high, but I don't think that would affect on throttle fuel delivery.

 

[sweetbeats]

Does it feel like it’s down on power?

Are you getting your fuel from the same place you usually purchase fuel?

 

[Eugene13]

Does it feel like it’s down on power?

Are you getting your fuel from the same place you usually purchase fuel?

No not that I can tell, its just always been this slow:rofl: I get my gas from either Arco or Costco, always 87. Would different octanes burn at different rates, like would I get better fuel economy with 91?

 

[sweetbeats]

Well arguably yes, but whether or not that would pan out financially you would have to see.

All refined automotive fuel is not created equal. I assume the fuel where you are is 10% ethanol, yes? Ethanol is a terrible thing and in order for it to be not as terrible there are additives in the fuel. The quality and effectiveness of those additives, and the quality of the fuel itself is what you pay for. And the fuel quality varies seasonally. I remember we used to get 20-25 mpg in my ex wife’s Honda minivan, then we couldn’t get over 17mpg to save our lives. It was a nearly new vehicle. We were told by the service center it was the fuel quality.

I always use Chevron. Maybe I’m a chump. But my motorcycle runs better on it, a VW bus I used to have ran way better on it (both of these compared to ARCO)...when is the last time you changed your fuel and air filters? And may it is worth picking up a couple cans of Seafoam and running a couple tanks with that?

I realize it’s an unfair comparison to a carbureted gas engine, but I was getting 13mpg in my Ford F-350 diesel and the top end was non-existent, changed the fuel filter and it was a different truck...16-18mpg now.

What about ignition system? Plugs? Coil? Weak spark can have a significant impact.

Anyway, some ideas. Hopefully I’m not leading you astray from some other issue...

 

[Eugene13]

I did general maintenance about 10k ago, plugs, wires, filters, fluids. I'm not sure of the intervals to change this but it'll be something I definitely look into. Thanks for all the ideas! [MENTION=275380]sweetbeats[/MENTION]

 

[sweetbeats]

You’re welcome [MENTION=206802]Eugene13[/MENTION]. You didn’t list the ignition coil in your list of general maintenance goodies...it might not hurt to check your spark quality, and if it’s weak test the coil and also check the connections to/from the coil. And another thing...when’s the last time you checked your tire pressure? If you go wheeling regularly this is probably not an issue, but if you haven’t checked it in awhile it’s worth it. Tire pressure, in my experience, that’s down 5-10psi from where it should be can impact your mileage 2-3mpg or even more depending on your setup. Good luck. Post back what you find.

 

[Eugene13]

You’re welcome [MENTION=206802]Eugene13[/MENTION]. You didn’t list the ignition coil in your list of general maintenance goodies...it might not hurt to check your spark quality, and if it’s weak test the coil and also check the connections to/from the coil. And another thing...when’s the last time you checked your tire pressure? If you go wheeling regularly this is probably not an issue, but if you haven’t checked it in awhile it’s worth it. Tire pressure, in my experience, that’s down 5-10psi from where it should be can impact your mileage 2-3mpg or even more depending on your setup. Good luck. Post back what you find.

True, I haven't checked my coil and honestly don't know how to check it. And my tire pressure should be around 35~ last time I checked. Ill do a look over of all these things within the next few days and get back to you!

 

[sweetbeats]

The best thing to do, DIY-wise would be to look in a service manual regarding checking the coil. Alternatively, you may be able to take the coil to a local auto parts store that offers diagnostic services and they may be able to test it (but this won’t tell you if there are issues in between the coil and the plugs), -OR- to get down to brass tax and see if you’ve got good spark remove spark plug #1 (or any other plug), leave the plug wire attached to it, pull plug wires 2, 3 & 4 (or whatever plug wires are not associated with the plug you removed) and tuck them out of the way, and then hold the spark plug ground electrode to a bare metal spot on the cylinder head or cylinder block *using an insulated tool and for good measure insulated gloves*, and have a buddy crank the motor over.

I’m not a professional, and I’m not liable for any damage or personal injury that may result from doing this. Proceed at your own risk. Milliamperes can kill.

What you are looking for is a nice bright white or blue-ish spark. If it’s orange or difficult to see then you want to work backwards in the ignition system to discover what is the weak link, which may be the coil, the distributor or any of the low voltage wiring or grounding associated with the ignition system. I say low voltage wiring because you indicated you replaced the plug wires (and I’m assuming the coil wire too...?), so it’s safe to rule those out, but if you discover you have weak spark and you are running up against a wall all components should be considered a causative suspect until you can narrow down the cause.

 

[toyotarunner1]

Seems like a long shot...but could this mileage be linked to the top of the 4runner? I dont know if you keep it off or have recently removed it. Might change the areo dynamic drag on the vehicle? Just a thought.

And just for follow up...Octane is added to fuel to prevent 'early combustion' from taking place. The pressure and heat in the cylinder can combust the air/fuel mixture before the actual 'spark' so you get early combustion (knock). So octane helps the fuel resist pre-combustion. I think it mis-advertised as a power adder, but thats not it's purpose.

If your vehicle has a compression ratio of greater than or equal to 10:1 I think its typically recommended. The more cylinder volume, the more pressure and risk of pre-combustion. For example my honda 07 civic runs 87, but my brothers 08 civic si ran premium. Larger compression ratio.

Maybe consider anything that could add rolling resistance to the truck...wheel bearings, or any bearings in the mechanical driveline really.

Also, you need 14.7 parts of air for every 1 part of fuel. So you could be wasting fuel by not having enough air to burn it (running rich). Any possibility air is being restricted? Vacuum lines etc?? Clogged air filter?

Good luck!

 

[Eugene13]

Seems like a long shot...but could this mileage be linked to the top of the 4runner? I dont know if you keep it off or have recently removed it. Might change the areo dynamic drag on the vehicle? Just a thought.

And just for follow up...Octane is added to fuel to prevent 'early combustion' from taking place. The pressure and heat in the cylinder can combust the air/fuel mixture before the actual 'spark' so you get early combustion (knock). So octane helps the fuel resist pre-combustion. I think it mis-advertised as a power adder, but thats not it's purpose.

If your vehicle has a compression ratio of greater than or equal to 10:1 I think its typically recommended. The more cylinder volume, the more pressure and risk of pre-combustion. For example my honda 07 civic runs 87, but my brothers 08 civic si ran premium. Larger compression ratio.

Maybe consider anything that could add rolling resistance to the truck...wheel bearings, or any bearings in the mechanical driveline really.

Also, you need 14.7 parts of air for every 1 part of fuel. So you could be wasting fuel by not having enough air to burn it (running rich). Any possibility air is being restricted? Vacuum lines etc?? Clogged air filter?

Good luck!

Thanks! I have a lot of things to check on my rig now, most likely Ill get to it this weekend. Ill update!

 

[Eugene13]

Checked over some things on my truck. Here's was the spark plugs look like.

Not sure what this means, and this is what all 4 look like. I also checked my fuel filter, looks good. Checked all my spark plug wires and wire from the igniter and all spark is good. Checked air filter and that also looks good to me. Still not sure what it could be and it seems like I'm getting even worse fuel mileage now. :yell:Im going to take it to a mechanic soon so someone with more knowledge than me can look over this.

 

[ddonovan48]

anyone have any advice on how big you can go tire-size-wise to get better MPG before it starts getting too big to reasonably/comfortably travel long distances (cross country drive soon)

 

[ev13wt]

anyone have any advice on how big you can go tire-size-wise to get better MPG before it starts getting too big to reasonably/comfortably travel long distances (cross country drive soon)

The smaller and thinner the tires, the better the MPG.

That would be 225/75R15, AKA 28" tires.


The undercarriage and tires make up 45% of your drag. Lower the truck, skinny original (or 29" if you must) and win 2-3 MPG.

 

[Eugene13]

Follow up. Since I got my new gears, I'm up about 5 MPG. Used to get 12.5 which is 150 miles for 12 gallons. Now I just got 184 miles out of 10.5 gallons which is 17.5 MPG. Didn't know gears could make that big of a difference.

 

[maco33]

What size tires and gears do you have now?

 

[Eugene13]

[MENTION=67916]maco33[/MENTION] 33x12.50 and currently 4.88 gears. Had the stock 4.10s and even the slightest hill would need to drop a gear or 2

 

[barongan]

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