tune-up questions

essentially, I get 15 mpg (16 mpg if I cruise at 65 mph for the whole tank) in my 2000 w/33's, 62,000 miles. This sucks because I got 18 all the time, and better highway, until about 4 months ago.

symptoms aside from horrible mileage:
-Black soot on tail pipe (and creeps back about 5 mm onto outside)
-Black soot on cat/muffler interface
-check engine light once every couple months due to a misfire
-ran with a dirty air filter for quite a while
-engine has to crank a bit on extra-cold starts (but instantly starts when warm)

so, I want to tune it up. On the menu are spark plugs, wires, insulation for the intake manifold, air filter, a fuel additive for cleaning...

but what about all those sensors? Does the soot mean my 02 sensors are bad, or can the sensors just be cleaned up and re-installed? I would take it to the dealership but I think I'd invariably be given a bill for new sensors.

(I have the CA emissions with the 02 sensors before and aft of the mini-cats. Also, the switch from no-name octane 85 to no-name 87 conincides with the loss of mpg, as 85 isn't available out here). Any help is appreciated.

I would try the MAP, O2 sensor/s, or coolant temp sensor. Looks like your running rich. The black soot on the tailpipe is a giveaway.

Have you pulled any diagnostic codes?



K

the check engine has only come on twice in the last year, but I when it did it was a misfire in a single cylinder.

How do I know which sensor(s) to replace. I've got 4 and just a quick search shows $112 for each sensor on autozone.com

I think this came up recently on an 01. If I remember right, there was a technical service bulletin for a lean misfire on the #3 cylinder and it being related to a heat shield issue and a reflashing of the CPU. I think some even had to change to a 180 degree thermostat to help with it. Do the search for it on this forum....it may or may not apply to your 2000.

Dave

kubtastic said:

insulation for the intake manifold

Click to expand...

check
Would that make it run with black soot?
Wouldn't a bad 02 sensor trip the computer?