daytraitors

I've been getting 14MPG over the past few weeks, and before that, I was averaging about 20. I noticed it going down a bit week by week, but my measurements weren't scientific.

I'm driving a mostly stock 2000 4Runner Ltd (Fed emissions). I have NGK IX plugs a standard aftermarket oil filter, and a Fram performance air filter, all fairly new. Other than that, everything else is Toyota. I have 146k mi and the only hardware I've replaced would be the u-joints underneath.

I have some performance upgrades I want to install, but before I go there, I'd like to get the 4Runner back to factory spec to isolate this problem I'm having.

I did a few things to see if I could get better mileage, but none of these seemed to do the trick.
1. new spark plugs, NGK IX
2. Seafoam in the tank (2.5 bottles so far) and the crank case (half bottle).
3. Tried 35psi and 30 psi in the tires.

Here are some of my observations:
1. Exhaust tailpipe is black on the inside. (result of seafoam?)
2. Exhaust fumes smell like . . . chemicals . . . maybe turpentine
3. There is no visible smoke coming out of the tailpipe.
4. An audible squeal comes from the front. When parked, there is no squeal. However, when driving, there is the squeal. If I drive slowly, I can hear it chirp every ten feet or so. Should I get an exact measurement of distance?

I'm wondering if the problem is my timing belt. Is that causing the chirp? It is a pulley attached to the belt?
Or is the problem with my O2 sensor? I figure since I can smell the fumes I must be running a rich mixture. I ordered the NGK AFX meter with wideband. Will that work as a replacement for my before-cat O2 sensor? I figure I could test if my mixture is rich if I hold a lighter next to the tailpipe, but that sounds too risky.

If I get the timing belt replaced, should I also have the water pump and thermostat replaced? How do I know if it needs to be replaced? Can I get away with just swapping out the gasket for the (expensive) water pump?

Thanks for any help.

David

BC_4runner

sounds like the o2 sensor just went sour

how many km's?
and CEL?

daytraitors

BC, how do I know the O2 sensor is bad? What's a good test for this?

Also, what about the chirping sound? It happens only when I'm moving. When I move slowly, it chirps every five to ten feet or so (didn't really measure), as if there were a bad spot on a pulley or something.

Any ideas on the noise?

I'm not exactly sure how many km's, but it's got 146k miles, which is what, 243 km's?

There's not CEL blinking, but I did order an Auterra scan tool setup on eBay. Maybe that will help somewhere. It's supposed to have a pseudo-dyno built in.

-d

RunnerUp

if the exhaust pipe is black then your running lean and it could be either your MAF needs to be cleaned, your A/F sensor needs to be replaced, or your cat could need to be replaced. it should throw a code fairly soon if your truck is running poorly.

rimpainter.com

Did you mean to say "rich?" Black "soot" in the exhaust pipe is a sign of a too rich condition, which would explain the bad mpg.

RunnerUp

perhaps i did, ive never been able to remember which is which all i know is that when i got the code pulled and it was a p0420 it said bank 1 system 1 system too lean and my exhaust pipe was very sooty

daytraitors

I'll wait 'til my Auterra comes. Should be less than a week away. But, there is no CEL. Will the scan tool tell me anything?

-d

rimpainter.com

It might. It just depends if the system has anything stored or not.

daytraitors

Hmm. . . do you mean that I shouldn't have pulled the EFI fuse last night in a desperate attempt at maybe getting better mileage?

Will resetting the ECU erase any of these stored messages?

-- I was reading another post about someone's crappy 3.slow. He said his calipers were out of alignment and killing his mileage. Could this be the cause of my noise and mileage problems?

-d

rimpainter.com

If your calipers were rubbing your brakes would be red hot and you'd smell it. I guess anything is possible though.

As for pulling the fuse - I am not sure. I don't think that resets stored codes; you have to pull the NEG on the battery to do that I believe.

It sounds like you track your mpg. Did you change anything on the vehicle about when you saw a step-function down in your mpg?

Beartracker

No, You did not erase any codes and if by chance you did they will come right back if you have a problem and it sounds like you do. When my pipe turned black, mileage went way down it wasn't long before the light came on and after checking it the code was for the A/F sensor on the manifold. It cost me $130.00 and about 20 min. to replace it. Problem solved ! It took about 50 miles before it started running great again and the mileage was greatly improved. It's also a good time to clean the amf and the throttle body.
Don't use anymore Sea Foam for now. It sounds like you have run plenty through that system. Next time just add a bottle of Tectron to the gas and it will run like a scared rabbit and clean everything at once.
The cost of the sensor depends on what year your vehicle is and if it's a 4x4 or not. They are not cheap but the book says they should be replaced every 75,000 miles.
Hard to say what the chearp is , may be a belt or pulley. If you have never replaced the timing belt then you are over due for that too. Mike

daytraitors

I'm going to try changing the front pads and rotors to see if that solves the squeal. I think it's the problem.

As for the mileage, after I pulled the EFI fuse, I drove 31 miles on 1.57 gallons, so over this very small sample size, my mileage went back up. I wonder if it's because the ECU hasn't had enough time to recalibrate itself to the bad (?) O2 sensor.

As far as any major changes since mileage suffered, everything is mostly stock, as described above.

-d