Fuel Economy woes (oh no again?)

[Life2]

So I've been spending several days trying to figure out what is causing me to get 17.5mpg on my 96 1MZFE. This is 50% city 50% highway. Mostly I've been searching on the forums to figure out what could be causing this poor fuel economy and what is NOT causing it.

My car has just under 130k on it and oil changes have been very consistent at 3000 miles because I know about the potential engine sludge issues with the 1MZ. The air filter was replaced last year so that couldn't be involved in the cause.

I understand that typical suggestions are spark plugs, wires, cap/rotor, and tire pressure. I know I need to work on all of these except for tire pressure (it's at roughly an average of 33, probably wouldn't be bad to top off some air). However I have a hard time believing I can be hurting from just this stuff.

Could it be bad O2 sensors or a clogged cat? I mean these things usually throw codes and I haven't gotten any.

Any ideas would be well appreciated, also I'd REALLY like to hear suggestions from you guys on what specific spark plugs/wires and cap/rotor set I should pick up. Links would be awesome.

[ShawnTRD]

At 130k if you haven't replaced your O2 sensors I would. They don't have to throw a code to be feeding your computer bad information. Same goes for the ECT (Engine Coolant Temperature) Sensor.

[projektvertx]

As far as spark plugs go, I would buy something like NGK Laser Platinums or Iridium IX's. I'm not sure what you put in there? The 1MZ is distributorless ignition Does the car idle rough? When was the last time you did a timing belt on the car? WHERE are you filling up? It might be a "half water" station as my dad calls them

[Life2]

If I could just say a big "d'oh!!" to the distributor part....

I'll note that O2 sensor tip and try to get that done today or tomorrow. My car idles beautifully I'd say. Timing belt was last changed at 65k so it does need that but I'm just waiting to get the go ahead from my dad before I do that. Otherwise though at idle it's at a nice 700-750rpm's (once warmed up) and doesn't hesitate or anything. It literally sounds like a new car at idle.

[96v6wagon]

Same issue here - lousy fuel economy on 96 v6 (nearly 160k miles). It used to be 20 in city, and nearly 30 on a long trip.

So, ECT sensor and O2 sensors could be going bad, and not throw a code? I suspected those, but couldn't convince my mechanic, because of no codes. I thought I'd just change them myself, but can't get the ECT sensor wiring loose - I have to put a mirror down in back of it to see how the connector works, but can't seem to find the tabs you're supposed to push to losen it.
Any suggestions?

Also - in CA - do more than one O2 sensors need to be replaced? If so, which ones cause these issues?

Mine idles a little high, maybe about 850, and last smog test, was higher on HC than previously.

My mechanic (who I usually trust) says the only thing he can suggest is to clean the injectors with one of the closed cleaning systems.

Would appreciate any thoughts and suggestions.

[ShawnTRD]

First have you done a tuneup lately? If you have a Advance Auto Parts near you I would order up some plugs and wires. I priced the Denso Ignition Wire Set, and 6 Denso Iridium Power Spark Plug for a total of $55.43 after discount code BIG35 ($35 off $85+ (41%) with code BIG35)

Then after that I would do the O2's if you still see bad MPG. Again if you use code BIG35 you can get the OE fit ones for $65 each. You'll have to do two separate orders. I use paypal and "pickup in store" and it works great. If the store doesn't have stuff in stock see if you can get someone there to order them and add then to there inventory. They shouldn't have a problem.

I don't know about what O2 to try first or ECT sensor wire. Sorry

Originally Posted by 96v6wagon

Same issue here - lousy fuel economy on 96 v6 (nearly 160k miles). It used to be 20 in city, and nearly 30 on a long trip.

So, ECT sensor and O2 sensors could be going bad, and not throw a code? I suspected those, but couldn't convince my mechanic, because of no codes. I thought I'd just change them myself, but can't get the ECT sensor wiring loose - I have to put a mirror down in back of it to see how the connector works, but can't seem to find the tabs you're supposed to push to losen it.
Any suggestions?

Also - in CA - do more than one O2 sensors need to be replaced? If so, which ones cause these issues?

Mine idles a little high, maybe about 850, and last smog test, was higher on HC than previously.

My mechanic (who I usually trust) says the only thing he can suggest is to clean the injectors with one of the closed cleaning systems.

Would appreciate any thoughts and suggestions.

[fenixus]

if there is no hesitation while driving and idle is perfectly fine then most likely it's none of minor tune up items (plugs, wires, filters).
still could be o2/AFR sensors.

but have you checked stuff that allows your car to actually roll freely? brakes could be dragging, wheel bearings could be going bad, parking brake might be set too tight, too low pressure in tires will have some effect on MPG too, same as carrying all toolboxes, jack and stands in trunk