sudden mpg loss

[Eagle 16]

1996 q45 - great car approx 145k miles; about 3 months ago, noticed that mileage dropped from 21-22 to 12+. No sensor lite or warning. After several cans of fuel and injector cleaner and new air filter went bac k up to about 16-17 where it has stayed. What gives? How common? About year earlier had replaced "Knock" sensors which markedly improved acceleration. Shop not sure replacing front oxygen sensors will help. Any ideas? HELP

[Q45tech]

145k on O2 sensors is a problem they tend to get sluggish between 80-100k. What does the O2 waveform and switch rate per minute test show?Are you using BH 44k prior to each 90 day oil change? Plugs were replaced at 60k and 120k?

[maxnix]

What Q45tech said. A little maintenance history please

[Eagle 16]

This replies to Q45 tech and to MaxnixRegarding maintenance history: diligent, everything done on time and by shop that does only infiniti and lexus. They do use BH44K at each 15k but not at each oil change. Plugs were replaced at 60k and 120k and they serviced it at 135k

They did the 02 waveform test when they changed the oil at 144k. I have attached it to this message. Not sure I know what readings should be.

Is it your view that the front sensors would ordinarily be replaced by now? Could replacing them still not improve the mpg?

[Eagle 16]

Second reply to Q45 Tech and Maxnix

In case you cant read the original download of the sensor readout, I am attaching it in another format.

[AZhitman]

Can someone give Eagle a hand with these Consult results?

Thanks all!

[Q45tech]

Switching rate appears slow and assymetrical.........but not seeing every parameter of test, all I can say is, I change mine at least every 100k and always see impovement.

My 305K ATL mileage last weekend on an all interstate 235 mile trip was 22 mpg as it has always been for last 16 years.

O2 really only come into play at steady highway speeds.

[elwesso]

I agre, you have other problems if you dropped so low..... Maye a MAF or soemthing, but NOT o2 sensors, o2 sensors can only change things by 10-20%.

[Q45tech]

I was asked at T3 to run a fuel cost simulation of O2 replacement vs doing nothing. We had a discussion concerning your [?] or another similar car.

The real problem is they [O2] are almost never dead just impared to varying degrees, so you cannot use the 20% theoretical and I always split the difference at 10%.

Assumming 15,000 miles of constant highway cruising and 22 possible and 20 actual the 68 gallons saved [at $3.10 ATL] =$210 however that is roughly the price of one factory oem 96 sensor installed.

Therefore this takes up to 2 years to pay for itself if you are not a heavy highway user. It could take only a year for both IF your car improves more than average 10% >20% on highway.

T3 has many salesman types who drive 30,000 miles plus on the interstates obviously O2 are very cost effective for them.

When gasoline goes to $4 it becomes more cost effective.

Takes a lot of mental diagnosis to find MPG defects when no codes are shown because systems are all staying inside the 20% window from ideal== thus no codes. However multiple defects can be cummlative.

The way I test the system is to go on a road trip annually filling up until it runs out the filler neck..........then get on I75 and drive a hundred miles no AC constant speed and turn around retracing route and fill up at the same station again until running out...........= highway MPG. [No side street traffic just open road no traffic jams or redlights].

Once one has the truish highway MPG you evaluate from there.

[maxnix]

RR looks slow, I think, Difficult to read sideways.

Best get a screen capture or photograph from scope for each.
Modified by maxnix at 5:39 PM 4/27/2006

[Q45tech]

I usually spend 4-8 hours testing and diagnosing these esoteric problems.Few want to pay $300-$750 just for the CORRECT answer sometimes you need to spend another $100 and another hour or 2 getting to an accurate reliable dyno. to avoid pulling plugs and doing compression and leak down test which can take another few hours.

[elwesso]

My fuel mileage on the highway is roughly normal... WHen i went down to ATL last summer we averaged 75MPH (as calculated on a G35 I tailed) and i got about 20-21MPG... I think thats reasonable.

However you mix even a little bit of city (20/80) and MPG drops down to around 17, at least on my Q. Could have to do with the high stall converter wanting higher RPMs.

[DenverQ]

best thing i ever did for mpg was replacing the O2 sensors, bosch makes a nice univeral unit that you use your existing connector, this worked great on the "other" car.

But I still have a lingering Question maybe Q45tech, what if any is the difference between

Universal Type; 4 Wire; Planar; and 4 Wire; Wideband;

[Q45tech]

Bosch USA in the discount automotive parts stores is not a Premium Brand.These stores buy on price and accept very low standards and get very low standard based on the prices they pay.

There are so many ways to make a cheap O2 SENSOR that will function for 1 year 12,000 miles and maybe even double that just like after market PERFORMANCE CATS.

Google is your friend for O2 background.

[DenverQ]

Planar: This sensor was introduced by Bosch in 1997 and also uses the zirconia ceramic sensing technology, but placed in a more compact thin flat shape (hence the name) instead of a thimble or conical shape. This allows the sensor to be smaller and lighter. They also require less electrical power as the heater is integrated into the smaller sensing element. By model year 2004, planar oxygen sensors are expected to account for over 30% of all new oxygen sensor applications and by 2007 for over 50% of new oxygen sensors. These sensors also have only four wires. Click here for a diagram of a planar oxygen sensor.

Wideband: This is the newest design of oxygen sensor and it offers the increased accuracy needed to meet the latest emissions requirements. Unlike all the other types of oxygen sensors, the wide-band sensor can actually measure the air/fuel ratio from 11:1 (excess fuel condition) all the way to straight air (no fuel)! (The ideal air/fuel ratio is 14.7/1.) This improved measurement allows the engine control system to measure the actual air/fuel ratio and eliminates the switching between lean and rich associated with a traditional type of oxygen sensor. These sensors use a planar zirconia ceramic element, so that they heat up much faster than other types of sensors- reducing cold start emissions. These sensors can be identified with having five or more wires. In addition, these sensors are used with the newly developed gasoline direct injection engines. Direct injection engines can use stratified charges, which produce a very lean mixture in the combustion chamber, and these sensors must be used because of their ability to measure from very lean to very rich accurately. Click here for a diagram of a wideband oxygen sensor.

Ok nevermind glad I didnt do this on a Q and just a Toyota 3.0L

Denso is it then from now on, its just hard to spend 236$ x2 on O2 sensors, but glad I dont care as much.

[Q45tech]

I know it's awful that dealers are able to double the prices of the good they sell to public and Nissan has to pay for shipping, warehouses, employees in US and make a profit.

Not to say these inexpensive sensor won't switch as well as oem just the time they will last and maintain sensitivity.

If you change them yourself and don't count your time obviously a half priced unit might be cost effective.........even swapping out every 30k instead of once every 100k.

[DenverQ]

Do the dealers/manufactuars get special sensors made?

I looked on the denso site and the denso "super" class a/f sensor is only 146, the only difference I can find between that and the universal one is that the "super" one has the OE connector.

The bosch premium are not premium? So only go OE is what im getting from this? I just want to make sure I do the new Q right thanks!

[Q45tech]

Everything supplied to a car manufacturer has at least a 10 page written specification..........obviously excess production volumes and non spec parts have to be sold somewhere..............you don't scrap non conforming but functioning parts you sell them in the after market with reduced specs at reduced prices............the really bad ones get shipped to 3rd world countries where price is really important.

Are you not aware that even Nissan has 3 tier parts pricing:Japan, USA- Canada- Europe, and third world.

I found this out while having two Nissans in Puerto Rico [3rd world pricing]. I shopped the exact same parts on my bimonth trips to ATL and always got them cheaper in PR

• .
  
  Can you imagine the prices of an O2 sensor or other maintenance part in Mexico or Venezula or Panama and how that would have to be adjusted for the local income level!!!!!!!!!!!!!!
  
  Just like Pharmacuticals...........duh you charge what the market will tolerate.
  
  WE [1st world] are RICH relatively we should pay more, without the collective us, there would be no lux cars.

[DenverQ]

Ok, got it thanks for the info, makes me wish when I was in ATL last year (for work) I would have found T3 just so I could absorb and take pix.

Thanks Dennis, glad I can test this stuff out on the lexus before I get the Q (again)

BTW 150k and no sludge in the 3.0L

[maxnix]

Denso is it then from now on, its just hard to spend 236$ x2 on O2 sensors, but glad I dont care as much.

TDK (NGK brand for O2 sensors) from Sparkplugs.com is about $55 for the VH41DE and VH45DE.

Don't believe that the specifications shown on their website are the correct ones. Call first f to order the correct ones.

[silver2k2]

Has anyone else used sparkplugs.com that can report on the quality of thier 02 sensors

[lino]

Has anyone else used sparkplugs.com that can report on the quality of thier 02 sensors

Mike has...you can see it near the bottom of the following thread:

zerothread/231461

[maxnix]

Has anyone else used sparkplugs.com that can report on the quality of thier 02 sensors

NTK seem to be OEM quality, but I haven't run it the fill 100K cycle. At about 40K, but I haven't scoped it.