Poor MPG

So this is interesting: I replaced both my cat and my exhaust from the cat back. Runs way better now, my idling issues on startup and issues trying to crank over (idle would surge on start up or I had to crank it over for a long time sometimes before it would finally catch) are gone.

BUT now my mpg has radically dropped. Yes the temps have been horrible lately, barely making it into the lower 30's and Im letting it idle and warm up every day for about 15-20 mins before leaving. But Im somehow getting 12-13mpg consistently. Yes winter fuel is bad and less mpg, I have used 4wd alot (several fill ups didnt no snow), but it stays consistently low. No CEL light, no performance issues, driving same way I always do.

Im thinking maybe I should replaced the O2's. Rear O2 I replaced, the front poses a problem. Front sensor wire somehow came undue and got to close to the cat. The plug is melted enough I cant seem to get it apart of salvage it really. Im leery of those direct connect sensors since I have zero clue which wire would go where (maybe they have directions?). So I was thinking I need to find me a 89-95 toyota truck and yank the sensor/wiring off of it just to get the plug and then I can use a normal sensor.

Truck had a fulltune up last year, t-belt about 7k ago, and was consistently getting about 15mpg (mostly city/some hwy) for eons. I do wonder if the new cat and exhaust is contributing to it-but if the old cat was clogged (and it was kinda) I would think I would have had to make the truck work harder and used more gas.

IDK..

I bet the replacement of the sensors would help.

My cold starts and short drive in the mornings yields about 13 mpg where as I can get 20 mpg on the highway. I've thought about blocking my radiator in an effort to keep things toasty but it's probably not worth the trouble. Currently our lows are a balmy 40*F. I'm still at high idle when I get to my park and ride 3 miles from my house.

For replacing the front O2, cut as close to the connector on the truck side, then remove the sensor. See what color wires go where on the sensor side of the connector. Buy a plug in connector (one meant for your specific vehicle), then cut the connector and solder it up, this way you can match wire color and get it right the first time.

I think Im gonna hafta track down the wiring or just stick a cut to wire sensor on from denso/ngk. My drive consists of going to school: 10 miles roughly local and 10 hwy and work is 20 local but at speeds approx 45-60mph. Like I said tho, Im letting the truck warm up and idle before I leave in the morning about 15 mins too.

I just fixed my temp issue a month ago. Blew out heater core and changed the little flapper switch for the controls (wasnt even opening all the way I found out).

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Originally Posted by Seanz0rz

For replacing the front O2, cut as close to the connector on the truck side, then remove the sensor. See what color wires go where on the sensor side of the connector. Buy a plug in connector (one meant for your specific vehicle), then cut the connector and solder it up, this way you can match wire color and get it right the first time.

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Thats what I really would like to do vs a direct wire. Just sorta hard finding the plug and what to nab it off of. The wires are two blacks a blue and a white I recall. I wonder which way the two blacks go is whats gonna stink trying to figure out.

Quote:

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Originally Posted by CJM

Like I said tho, Im letting the truck warm up and idle before I leave in the morning about 15 mins too.

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As you know, ethanol in the fuel, cold temperatures and short drives all destroy fuel economy. Letting your truck idle for 15 minutes is excessive, you are burning a ton of fuel there. My 3.4L has some sort of sensor that triggers a rich condition on startup when temps outside are below about 45 degrees. I can see it on my wideband and it is done to heat up the cat converter(s) as quickly as possible. It takes about 1.5 miles of driving (in temperate California, mind you) before the air fuel ratio even gets to normal. Double that for cold climates. It takes quite a while to warm up if the truck is just idling.

Also, ethanol in our fuels are killing O2 sensors at 4X the rate, so it needs to be replaced much more often. I just did mine and noticed an increase in mileage. ($57 shipped on amazon.)

Even a hybrid car gets dismal mileage in cold weather and short drives. A Prius fires up the gas engine and it won't shut down until the engine reaches a certain temperature. Many of the Priuses [driven short distances] that pull into my park and ride are still idling. I asked some of the owners and they indicated it takes a couple of miles before they'll shut off, so you don't gain anything with a hybrid.

Even my 2.3L Volvo got 14.5 MPG on my short 2 mile drive to park and ride. (The 4Runner actually got 0.5 MPG better.)

Anyways, all of those factors are hell for mileage.

Oh believe me Paddlen, it takes quite a while to warm up here. Were talking about 15 mins of idling and then about 2-3 mile down the road its warmed up enough to be toasty (im actually quite cold all the time..even in summer so I like a toasty warm cab). It was 15F outside today as well. Im thinking the local gas station I like to use has more than 10% ethanol in it as well maybe, or maybe its just all the idling and local driving. I always track my mpg and until I replaced everything was still getting about 14mpg.

Im thinking A) need the new o2 and B) Probably letting it idle to long. Hell, today I know my mpg took a nice dip, I wasin 4wd for a good 2-3 hours the roads were so bad. I also wonder if it will take some time for the cat to truly break in, only been on there for about 1000 miles-also doesnt help I replaced it with a bosal b/c the factory one was INSANE new. Walker didnt make one for my truck either.

I would start by cutting your idle time down to under 2 minutes and see how it affects your mileage. If your O2 sensor hasn't been replaced in a while, it might be time.

Im sure its time, last replaced about 120k ago afaik.