Reading tech mags some even recommend changing them as scheduled maintenance around the 100K mark.

And most people recommend replacing the O2 sensor with the OEM part, which in this case would be a Mopar#56029052AA (Denso Part #2344410)

Fully agree about the lambda sensor, a bad one could easily foul up the mixture ratios, and it's working in a hostile environment too -- defo. a candidate. An exhaust gas analyser would show it up of course as unburnt hydrocarbons, but I'd hazard a guess you don't keep such an analyser in your garage. If of course you have a friendly tame mechanic with access to one, e.g. MOT testing....

Leedsman.
n.b. An afterthought -- have someone in back watch out for the slightest sign of black smoke as you floor the accelerator pedal on a quiet road. Another way is to wait until someone at night is following with headlights on, then floor the pedal. This really does show up any smoke. Nowadays there shouldn't be any smoke whatsoever from a petrol engine under any circumstances -- provided the micro is controlling the injection period properly as appropriate to data from the sensor, so there is slight free oxygen in the exhaust gas at normal running. The mixture is of course rich at idle, under acceleration and at full power. Unless all this control is working as it should, fuel will be wasted.

Before we sympathise too much with low mpg figures on U.S. vehicles, those of us on this side of the pond should remember that a US gallon is only 0.83267 of a UK gallon. :D

Hi steveatpa. There is a common issue which can cause this very problem and one I've come across before. The advise I was given before changing anything is to have a vacuum test performed and a compression test. If the compression is good then you should see 17 to 19 inches of vacuum, if its lower then you could be looking at an intake valley gasket failure. I've change it now on 3 Chrysler mini vans and all have seen an improvement however these are the before and after figures. MPG taken from the fuel/trip computer.


First time was with a friends 3.3 2001 GV, 128,000 miles, good compression. Before 14 to 16 mpg ave, 14 inches of vacuum. After intake valley 18 inches of vacuum 19 to 24 mpg

Then again with a 3.8 T&C (I think 2004 ) 187,000 miles , good compression. Before 12 to 14 mpg ave, 15 inches of vacuum. After intake valley almost 19 inches of vacuum, 17 to 22 mpg

And back here in the UK on my 98 3.3 GV 152,000 miles , good compression. Before 12 to 16 mpg ave 12 inches of vacuum, after intake valley almost 18 inches of vacuum, 19 to 22 mpg

On all 3 occasions gas mileage has returned however, something I should point out when comparing mileage between the US and UK and that is my UK spec GV fuel computer is calibrated to US gallons. I discovered this while doing mileage check and found that the figures I was seeing with a full tank to full tank didn't match the trip computer until and adjusted them for US gallons

I use the Felpro kit available from Autozone for around $20

I found these videos below very helpful

Handy rule of thumb:--
One US gallon = 3.8 litres.
One UK gallon = 4.55 litres.

Leedsman

Good info everyone..... :D I'll check the vacuum first since its easy and free.

Question though about the O2 sensor..... if the sensor(s) are faulty, can I unplug them and see how the engine/mileage reacts? I realize this will throw a code but my concerns would merely be to see if there's a large negative reaction which may point to a working O2 sensor? Throwing $100 at new sensors just to see if that does anything isnt always pleasing to the wallet.

Second question too..... After reading through the thread I realized that I failed to mention that over the past few months the engine has also developed a starting issue whereby it will crank at least twice as long before wanting to start. It used to fire right up with the touch of the key. Sometimes now I'll crank it for a half second.....let off the key.....and crank another half second so it fires up easier. Not a huge cranking and cranking issue either but just longer than normal. This is what led me to feel that the fuel pump was faulty in the beginning of the thread. Could the O2 sensors or low vacuum attribute to extended cranking? And also, it generally cranks longer with the engine hot or cold but will a little more when cold. :confused:

Replaced both O2 sensors. The CEL came on immediately regarding code p0135 and cylinder bank 1 running lean. I presume this is because the new O2 sensor is bad or incompatible.

Waiting for another sensor to replace it with. Also, the fuel mileage hasnt changed. So my next move it to check the fuel pressure.

Did you disconnect the battery when you replaces the sensor? If not try disconnecting it for a few minutes.

When I installed a new sensor upstream sensor on my '09 and the CEL returned almost immediately (within minutes) with the same code I had been getting, even though the code was a two trip code and I had disconnected the battery.

I did some research and found that while the negative battery cable is dis-connected you need to touch it to the positive cable to clear the "stored" data, in the PCM, from the old sensor. I tried it (I left the cables connected for several minutes) and the light has stayed off ever since.

It might not work for your '04, but it's free to try.

Hmmm..... I'll give it a try but I also have a scan tool which allows me to erase any codes. When the P0135 code immediately popped up after installing them, I deleted it and took the car down the street. The CEL didnt show up again until the next day when I went to town. About a mile down the road the CEL came back.

I did a little research on this and there seems to be a known issue with Bosch O2 sensors on these engines. I'm going to try another one and if that doesnt work then I'll try Denso.