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Billy
Billy, Trainer/Master tech.
Category: Nissan
Satisfied Customers: 3498
Experience:  Trainer 8+ years - master tech. 10+ years, SAE member
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Quest SL: I purchased my Nissan Quest 4 years ago. It had plenty

Customer Question

I purchased my Nissan Quest 4 years ago. It had plenty of acceleration and also I got 24mpg on the highway and about 19-20 mpg in the city. That lasted about 2 years before it occasionally started making a droning sound from 500k rpm to 2000k rpm. Accompanied by the droning sound was a loss of acceleration. It occasionally happened more and more often until it now always does it and it is the new norm. My mpg went down to 17 in the city and then 16 and then 15 and now I am hovering over 13 -14mpg in the city. I haven't moved and my driving habits have not changed. I need help please. There are no check engine lights.
Submitted: 2 years ago.
Category: Nissan
Expert:  Billy replied 2 years ago.
Hello and Welcome! I'm Billy and i will assist you with your inquiry. Feel free to ask if any further info is needed.
Was the exhaust checked for any leaks?
why did you change only the bank 2 sensors, and not the bank 1?
do you have access to a scan tool, to get me the fuel trim numbers?
Customer: replied 2 years ago.
exhaust was not checked for leaks. I do have a infrared thermometer that I could get some temp readings before and after the cats (three of them) for you. I also do have a scan tool. I will get the fuel trim numbers for you. Any specific instructions for getting the fuel trim numbers? i.e. rpms at 2k or anything?A couple of months ago I had a check engine light on that indicated I needed to replace the bank 2 sensor 2. I did that and then I got a different code indicating the bank 2 sensor 1 so I replaced it also.
Expert:  Billy replied 2 years ago.
Hello,
so when the o2 sensors were replaced, you got no fault codes anymore?
and it would be great if you would be able to get the temp readings right before and after the cats.
As for the fuel trims:
the short term and long term trims at idle, and at 2000 rpm.
I will be waiting for the results...
Regards,
Billy
Customer: replied 2 years ago.
Long Term Fuel Trim at Idle - 9.4% steady
Short Term Fuel Trim at Idle - 0% to 15% changing up and down about every 2 secondsLong Term Fuel Trim at 2k- 0% steady
short Term Fuel Trim at 2k- -.08% to 14.1% changing up and down about every 2 secondsIt would not stay at 2k rpm very easily. It would try and go up or down but didn't want to stay at 2k.Bank 2 cat before 280 degrees Fahrenheit at idle (at operating temperature)
Bank 2 cat after 240 degrees Fahrenheit at idle (at operating temperature)
Bank 1 cat before 375 degrees Fahrenheit at idle (at operating temperature)
Bank 1 cat after 375 degrees Fahrenheit at idle (at operating temperature)
Final Cat before 280 degrees Fahrenheit at idle (at operating temperature)
Final Cat after 240 degrees Fahrenheit at idle (at operating temperature)It was very difficult to reach the top of the two cats on the banks, I think this temp is accurate though.
Customer: replied 2 years ago.
The check engine light turned off about a week after I replaced the O2 sensor.
Expert:  Billy replied 2 years ago.
Hello,
The numbers indicate a problem:
the fuel trim (short term) playing within 15% is too much.
The long term at idle is high.
Those, along with the erratic temperature readings, i would start as following:
- check for a vacuum leak within the intake manifold
- check for any leak at the exhaust pipes, and mostly before the cats
- try another temp reading at front cats (before and after.. i know this is hard, but we need to confirm), engine at operating temperature and at around 2000 rpm. Right at the begining and the end of cats.
PS: do you have any stored fault codes?
Regards,
Billy
Customer: replied 2 years ago.
I checked all over for vacuum leaks and found nothing. I am usually good at hearing them as well.I found a small leak in the exhaust pipe right after the muffler. It was about 1 inch long and very small but I can feel the exhaust blowing slightly on my hand. I am not able to get close to Bank 1 just before the cat to feel for exhaust leaks and Bank 2 has the fan blowing hard on it so it is also near impossible for me to feel any leaks.I could not find any stored engine codes. I went to auto zone and had them double check with their scan tool and they didn't find any either.I found two spots on the exhaust pipe where it is collapsed a bit. Although it looks like it was on purpose from some kind of tool (I assume that is not the issue but I have pictures in case you want to see them).I jacked up the vehicle to get better readings on the cats.
Bank 2 cat before 285 degrees F
Bank 2 cat after 340 degrees FBank 1 cat before 400 degrees F
Bank 1 cat after over 500 degrees F (my tool wont go higher than 500 so I can't tell you the exact temp).I didn't have a second person to rev the engine to 2k rpm for the cat temps. If needed I will try and get someone on Monday to help.FYI
I still get decent fuel economy on the highway (around 21-24 mpg). Power seems to be much better after 2k rpm. I tried driving around the city for a day keeping it above 2k as much as I could and the mpg actually got better (around 16 instead of 13 - 14 mpg).There is often a strong fuel smell in the exhaust. The O2 sensor readings seem a little weird to me as well. If you think that would help, I can get those on Monday as well.
Expert:  Billy replied 2 years ago.
Hello,
The first impression and given the symptoms the bank 1 cat seems clogged.
But the city consumption as well as the fuel trims do indicate some kind of leak and clog.
The fuel smell is normal, given the extra 10 to 20 percent you are putting on the system.
Before the O2 sensor readings (although those might help), i would double check for leaks (at least exhaust as you seem to be sure on the intake), but mostly, i would double check the temps at the cats, as the bank 1 does seem like clogged, and it would cause this.
Regards,
Billy
Customer: replied 2 years ago.
If I got an emissions test would that help diagnosis whether or not it is the cat? How should I go about checking for exhaust leaks before the cat? Bank 1 is tucked way into the firewall area under the dash (any easy way to do this)?what should the cat temps be when working normal?Thanks,
Jess
Expert:  Billy replied 2 years ago.
An emissions test would always help, but it's not needed, as we need only specific info now. If you hold a plastic cup near leak, it would vibrate and you would feel it much more than the place without a leak. Here's a trick i thought i'd never disclose...
The cat temps should be around the bank 2 measurements you got.. a bit higher, but bank 2 seems good... bank one however, is way to high...
Customer: replied 2 years ago.
I still can't find exhaust leaks before the cat. The bank 1 cat is up against the firewall and I can not get anything let alone a cup or my hand up there to feel. I check again with a mechanic friend for intake leaks and couldn't find anything. He thought that the cat would surely give a cel if there was any clog in it. Is that your experience? Short term fuel trim on bank 1 is now from 14 on the low side to 24 on the high side. Bank 2 fuel trim is around 9 - 16%. Any other ideas?
Customer: replied 2 years ago.
My Friend also thought that the hotter the cat the better as long as it is cooler going in and hotter going out. Is that your experience?
Expert:  Billy replied 2 years ago.
Hello,
Most of the times with a clogged catalytic converter, we don't get any fault codes.
Having this high positive fuel trim, means (if the o2 sensors are good), that you have little fuel, or too much air. The system is trying to compensate, and as the numbers increase with rpm, it's either a fuel shortage, or MAF sensor (again, given that o2 sensors are good).
Would you be able to check the O2 sensors signal (banks 1 and 2, sensors 1 only, upstream of cat), and maybe swap the MAF, or reset the adaptation parameters using the scan tool?
Customer: replied 2 years ago.
b1s1 shows .3 steady at idle. When driving around it will go from .33 to .2. Only dropping to .2 when I let off the accelerator. B2s1 stays steady at .6 at idle. When driving around it will go from .62 to .2. The fuel trims looked good this morning when I drove around. bank 1 and 2 at about -.3 to 3. By the end of my driving, they are now ranging between 2 - 7.5.Bank2 s1 is brand new. B1 sensor 1 has not been replaced.
Customer: replied 2 years ago.
I have it idling outside will I do things in the garage. I just went back and checked and now bank 1 is oscillating between 11 and 22 and bank 2 is from 11 to 15.
Customer: replied 2 years ago.
on the fuel trim short term
Expert:  Billy replied 2 years ago.
Hello,
The reading on b2s1 is good.
b1s1 is not good. it is showing a lean mixture, hence the high fuel trims.
the highest fuel trims you are getting at idle do indicate an air leak problem, if the sensors are good. but i believe that b1s1 needs replacement, as the fuel trims were oscillating, while the sensor was stuck at .2 volts.
the b1s1 as per your observations has very slow response, it is still working within limits, but needs replacements (this is why no fault codes are set).
Regards,
Billy
Customer: replied 2 years ago.
So your sure I should replace that o2 sensor, bank 1 sensor 1? If so, I will go ahead and replace it.
Expert:  Billy replied 2 years ago.
Hello,
If no air leaks are present, then the b1s1 sensor should read like the b2s1, even if the scan tool has slow response, it should at least jump between .2 to .6 as b2s1. Since it is not, this means, it has slow response and need replacing.
I'm not sure that this is the only issue, and the problems will be fixed, but i'm sure that this one needs replacement as it is stuck at lean (and causing high fuel trims accordingly). High fuel trim, means high fuel consumption.
Regards,
Billy
Customer: replied 2 years ago.
Billy,I have been on vacation and havn't had time to change the o2 sensor yet. Just yesterday I got a check engine light coming on P0422. I checked the gas cap and it doesn't seem to be the issue. Maybe this is also one of the problems going on. What do you think?
Expert:  Billy replied 2 years ago.
Hello again,
The P0422 might be caused by the sensors, but first we need to replace the O2 sensor, and then we'll proceed as necessary.
Regards,
Billy
Customer: replied 2 years ago.
I am having trouble getting access to the bank 1 sensor 1 o2 sensor. Do you know if I have to remove the cat to get enough access to it? or do I have to take off the intake manifold to reach it? Or some other way?Thanks,Jess
Expert:  Billy replied 2 years ago.
Hello Jess,
This diagram should clear things up:
https://drive.google.com/file/d/0B6Zgf4dbmODzQjlaSmdsUUFkRms/view?usp=sharing
Regards,
Billy
Customer: replied 2 years ago.
I finally got the bank 1 sensor 1 changed about 2 days ago. The Short term fuel trims have not seen the high spikes as before. Now the range seems to be -4 to 10 with an occasional spike around 12. Long term fuel trim at idle still is at 9.4%. I have not driven a lot since I changed it, but it seems like I get better gas mileage when I am driving but it all drains when I am stopped. I am getting low 15 mpg on average these last two days instead of mid 13. Any thoughts on the long term fuel trim?
Expert:  Billy replied 2 years ago.
Hello,
The long and short fuel trims need time to re adjust. Or you can use the scan tool to "reset adaptation parameters", and take the vehicle for a test drive and then test the trims.
Customer: replied 2 years ago.
My scan tool doesn't have that option on it. Is there another way to do this? Does disconnecting the negative on the battery for 30 minutes do the same thing?
Expert:  Billy replied 2 years ago.
Hello,
Disconnecting the negative cable for some time should erase the live memory and reset the fuel trims. You'll be able to confirm by connecting the scan tool upon restart.
And you can use the vehicle for a couple of cycles and the trims should adjust as needed.
Thank you for your trust! Get back to me if you need more assistance...Thank you in advance for the positive rating...
Regards,
Billy
Customer: replied 2 years ago.
I got it reset. The Long term is showing 0 I drove around for about 20 minutes. While driving the bank 1 and bank2 range from -9 to 12 but at idle, both show 14 to 23 could this indicate there is still a problem? That seems kind of high for idle.
Expert:  Billy replied 2 years ago.
Hello,
Indeed, at idle having a positive 14 to 23, would indicate a problem.
If at high rpm you have good trim numbers, then this would definitely be caused by an air leak.
And intake manifold leak, or an exhaust leak (pre cat).
Regards,
Billy
Customer: replied 2 years ago.
Billy, Sorry to keep contacting you, but I have pressure tested the intake system. It has no vacuum leaks. I put a shop rag in the tail pipe to create some pressure and then I sprayed soapy water everywhere before the cats. There were no leaks. I did find two leaks after the final cat and in the muffler, but I don't think that would cause my problem. To make it weirder, the A/F ratios were going from 19 to -25 on both banks while in park but at 2500 rpm. At idle, I still get 7 to 19 on both banks. Any other ideas?
Expert:  Billy replied 2 years ago.
Hello,
The leaks in the muffler should not cause any mixture problems...
are you able to swap the MAF for testing?
can you check the pressure at the exhaust (clogged possibility0?