Mileage sucks

[DJStillman]

Ok, I have a 91 Nissan Stanza, and I get as of my last tankful with no significant driving changes 16.6 MPG. The car is rated to get 21MPG City, and my last tank was a good mix of city and highway, and this mileage sucks.

I have just reduced octane from 89 to 87, same brand, Shell.

I would love to test my oxygen sensor, but it only has one wire. How do I test it?

Also, I have heard from the Allpar.com site that Mopar cars fare very badly with Bosch O2 sensors. What brands are good, and what ones should I avoid? I had been looking at a NTK O2 sensor, which is the NGK brand.

I would really like to get better mileage out of this car, as gas is so expensive right now. I have just done an intake manifold cleaning with Seafoam, and have recently used Lucas UCL and cleaned the Throttle body, replaced plugs, rotor, cap, wires, oil, filter, fuel filter, vacuum hoses.

I do have leaky injectors. Could this be the problem, and not the O2 sensor? Would changing the O2 sensor help? I am figuring that it is the original with 100,000 miles on it.

Thanks

David

 

[Dave H]

Leaky injectors should be checked, but I'm not sure if this would be your problem. Some Maxima.org members have had very good luck at cleaning their O2 sensors. All you do is remove it, and if carboned up, spray it down with carb cleaner or brake cleaner. Then reinstall. I wouldn't sand or buff it just because I don't know enough if abrasives could screw up the coating or whatnot. This would be worth a shot, as it may improve your situation. Worse case scenario would be you need to replace something that was faulty anyways.

Dave

 

[Eiron]

My first guess would also be the 02 sensor. (Mine's a 3-wire sensor.) Can you get access to a manual for the diagnostic?

Have you also tried an injector cleaner? (I didn't recognize one in the list of things you've done.) I've had good luck with BG-44K. If the leaks are caused by a build-up of crud in the injector (

), then this may help.

 

[Steve S]

how about the coolant temp sensor? To do it your self a service manual is a really good idea .One with trouble shooting charts ,makes the job easier.

[ September 03, 2003, 11:26 AM: Message edited by: Steve S ]

 

[DJStillman]

quote:

---

Originally posted by Tim H.:
also, look real hard for a vacuum leak, these will cause/fool engine 'puter into thinking it is lean and dumping more gas in. check those hoses!!!!

---

Thank you, I have already replaced all of my vacuum hoses.

 

[DJStillman]

quote:

---

Originally posted by Eiron:
My first guess would also be the 02 sensor. (Mine's a 3-wire sensor.) Can you get access to a manual for the diagnostic?

Have you also tried an injector cleaner? (I didn't recognize one in the list of things you've done.) I've had good luck with BG-44K. If the leaks are caused by a build-up of crud in the injector (

), then this may help.

---

Unfortunately, I have not been able to find a manual for this year of car. Checked pretty much everywhere.

Yes, I have used Lucas UCL (FI cleaner and UCL) several times in the car, along with changing the fuel filter 2 times in the past few months.

 

[DJStillman]

quote:

---

Originally posted by Dave H:
Leaky injectors should be checked, but I'm not sure if this would be your problem. Some Maxima.org members have had very good luck at cleaning their O2 sensors. All you do is remove it, and if carboned up, spray it down with carb cleaner or brake cleaner. Then reinstall. I wouldn't sand or buff it just because I don't know enough if abrasives could screw up the coating or whatnot. This would be worth a shot, as it may improve your situation. Worse case scenario would be you need to replace something that was faulty anyways.

Dave

---

Dave:

Sounds like a plan. I think I will go get some cleaner...

 

[Dan4510]

DJ,

Be sure to clean the 02 sensor when its dead cold. If its hot and you put cleaner on it, it could shatter from the heat shock. 02 sensors are very hard, but very brittle.

If you havent checked the coolent temp sensor, you need to do that to. when it goes bad, the engine thinks its cold all the time, stays in open loop and drinks gas.

good luck and let us know what happens.

Dan

 

[RussellA]

I have a 90 240sx. Put a bosch o2 sensor in it a while back and it seems fine. Don't really know if it helped mileage since I don't drive that car that much. I can say that my 98 Altima factory original front o2 sensor is Bosch. Had it out just a few days ago to clean it. Though I didn't run the diags on the old sensor on the 240sx since it had 159K on it and was time to replace, an o2 sensor test in the onboard computer does exist. Your 91 Stanza may be similar. don't know where your computer is, the 240 is under the plastic passenger side kick panel (where the passengers right foot would hit.). Altima (came from Stanza line) manual shows it's somewhere in the driver side kick panel area, but not sure exactly where since I use an OBD II scanner on that car.

I have the service manual for the 240sx (actually for all my cars), I'll try to make this as short as possible

You need to have the ECU (computer) in mode 1. turn the ignition on. Turn the ECU mode selector (flat head screw looking pot) fully clockwise and wait until the led flashes a 1 (one flash and pause). It will cycle thru the modes 1 - 5. After it flashes mode 1 turn back counter clockwise.

With engine stopped green led is on, red is on. With engine running , green led on solid in open loop condition, blinks in close loop condition (when warm and o2 sensor used).

After engine is warmed up, inspect number of blinks with engine reved at 2000 rpms. Lamp should flash more than 5 times in 10 seconds.

Turning off the ignition and turning it back on will automatically return the diagnostic to mode 1.

Oh, sounds like you skip step 1 since it starts in mode 1. Do step 1 if it you need to confirm you are in mode 1.


It appears each flash is a reading change from the o2 sensor. More flashes , the more reactive and sensitive the o2 sensor is. I can tell you that AFTER I replaced my o2 sensor I did check this and it was very fast like well over 20 times in 10 seconds.

Sorry for the long post, but not sure if the aftermarket manuals have this stuff. Hope this helps you.

[ September 03, 2003, 10:17 PM: Message edited by: RussellA ]

 

[Propflux01]

also, look real hard for a vacuum leak, these will cause/fool engine 'puter into thinking it is lean and dumping more gas in. check those hoses!!!!

 

[DJStillman]

Well, I cleaned the sensor yesterday and put it back in. Started the car up, let it get to a fully warm position, and I went from 1000rpm idle to 900 rpm idle. Shut it off, started it back up, and it went to 800rpm, smooth idle.

Start it up this morning, warm it up, and it gets to 900rpm with a bit of a rough idle. Shut it off and start it again, and now it is idling at around 1100rpm.

Since after trying to clean the sensor (did nothing else whatsoever) I now have an odd rough idle, does this sound like my problem?

What is the verdict with the NGK/NTK Oxygen sensor? Anyone use one before? Results and opinions, please?

 

[badnews]

could someone post a picture of a O2 sensor ?

 

[mph]

BTW, I just ordered an NTK oxygen sensor, but haven't received it yet. My exhaust manifold is cracked so I'm replacing it, and at 140,000 miles on the original sensor, I figure this is a good time to replace it as well.

I'm guessing that NGK/NTK is the OEM for Honda, but I don't know that for sure. They are the OEM spark plug manufacturer, and the consensus is that their plugs are the best choice, so I'm hoping that's true for O2 sensors as well.