Thread: Loss of mileage

IIRC there was some kind of recall/warranty thing w/ the stock cats..well that was with my car at least..('98 b14)

you can normally tell pretty easily if you cat is clogged. normally they will glow orange if they are clogged. you can also see if you have consistant flow through the rear tailpipe or muffler.

I would check this stuff (click low gas mileage)
http://se-r.net/car_info/problems/index.html

Im suspecting O2 also. Better make the car run less rich, you might melt the cat internally, and that can give all sorts of headaches with annual inspection.

Did you take a look at your plugs?

x2
by simply using a DMM you can check and see if that's the problem or not.

or do it this way.

From SE-R.net
"Replace O2 sensor, probably every 60,000 miles. O2 sensor function can be checked via the ECU’s self-diagnostic mode, which is a neat test. The ECU is in the center console, below the stereo/HVAC and in front of the shifter. Remove the front-most inside kickpanel on the passenger side. Behind that is a sturdy, rectangular metal box. That's the ECU. In my G20, on the passenger side, there's a cutout covered by a little sheet of plastic. Just behind the cutout, toward the back of the car, is a screw that sets the diagnostic mode. Turn the ignition to ON (do not start the engine). (This screw seems to be located elsewhere in other cars - activate brain at this point to find it.)
Turn the small screw fully CLOCKWISE for at least two seconds, then turn it fully COUNTERCLOCKWISE. (You have to redo this every time you turn off the power to get the diagnostic mode. Make sure not to drive around with the screw set CLOCKWISE, always set it back counterclockwise!) Start the engine, and warm up the O2 sensor by idling at 2000 RPM for about 2 minutes. The CHECK ENGINE light will now flash with the O2 sensor condition: ON = lean, OFF = rich in closed loop, if it stays one or the other it’s in open loop.

At 2000 RPM idle, Nissan claims it should switch on and off more that 5 times every 10 seconds. I think that is WAY conservative – it ought to be switching a LOT more than that. Drive around with the diagnostic on to get a feel for when it’s in open and closed loop, and to make sure it gets really hot. I think if it only goes 5 times in 10 seconds, your sensor is HOSED and probably has been for a while. Since this sensor is kind of the kingpin of the whole mixture control system, I tend be on the liberal side with replacement. There seems to be sentiment that anti-seize compound can ruin O2 sensors, so keep that in mind.

Another note on O2 sensors: the sensor is designed to be grounded through the exhaust header – there’s a ground strap to the body just before the catalytic converter. If you have an aftermarket ceramic-coated header, there may be a poor electrical connection through it. Check the voltage on the sensor body at hot idle (careful of burns). So far, there is no data on what is acceptable. You may wish to add a ground loop regardless. I used a big cable clip from a surplus store – if you can find an enormous ring terminal to fit around the sensor that would be great too. Run it to the ECU ground on the intake manifold, behind the throttle body. Use gold-plated connectors if you’re hardcore (audio guys have them lying around, ask your friends). I don’t know for sure what effect this may have, still collecting data."

DMM = Digital Multi Meter?

I meant plug colour, my car had bad O2 and MAF, it was running rich I could smell that from the fumes of the exhaust even with warmed engine but my plugs kept showing signs of lean while my MPG was way lower than most people reported on this forum.

yeah dmm is digital mutli meter. You could always have a exhaust leak and have it smell like it's rich so just having that smell doesn't mean it's exactly both of those

I've never had that anymore after replacing MAF and O2, while my flex pipe was torn pretty bad. However, you might have. I still don't get it how I can get real bad mpg and lean plugs.

Btw, the text you posted from SE-R.net is good read. I would like to add to that that the blinking doesn't say it all about quality of the lambda, mine did just that, and it was totally worn.

dmm can't keep up with the speed the O2 should switch in, way more then 5 times in 10 sec, rather 10 times in 5 sec and faster.

I can show you some Datascan pics if you like, this will show that measuring 0.5 Volt can both mean O2 really dead, 0.5Volt DC or really fast, new, 0.5V AC so to say.

SE-R.net to the rescue.



The stock cat is not very restrictive at all. MK wrote 1-2psi when he measured it for the B14 SE-R project in SCC iirc. It can get clogged and foul out though for sure.

X2... I remember reading that a few months back