Bad Fuel Economy - Continued...

**** PLEASE USE SUBTOPICS BELOW FOR NEW TOPICS ****

Moderator: volvite

User avatar
disallow
Site Admin
Posts: 2820
Joined: Wed Aug 13, 2008 9:02 am
Location: Winnipeg, Canada

Postby disallow » Mon Feb 28, 2011 9:47 am

NVSteve wrote:What it could be is one of a gazillion different things-the proverbial needle in a haystack. If that 12mpg you are mentioning is highway, or overall mpg per tank, AND I couldn't find the cause (or have a Nissan mechanic find the cause), I'd be looking for a a new vehicle.

Keep us updated & good luck.
I will be taking to an experienced technician over the next week or so. The puzzling thing about this is that there are no driveability issues, it runs great, no hesitations. Also, no engine codes to point at culprit parts. Very frustrating.

A couple of factors to keep in mind though. This truck sees mostly short trips during the week. My wife drops my daughter at preschool, about 8kms from my house. She takes my son with and the truck idles about 30 minutes overall. This happens twice a week. She also takes my daughter to dance class once a week, and same thing, about 30-45 minutes of idling. I know all this idling is a major MPG killer, as the vehicle is not moving anywhere. If I factor this in, then my average MPG is probably closer to 14 USMPG.

Weekends are different. We usually go to the city at least once, about 40km one way. Many times, I will fill up at the edge of the city and drive home. Usually I am about 1/2 way though the first 1/4 tank by the time I get home. That would be 100% highway. And usually I can't get more than 75-100km on the first 1/4 tank, either.

I can get my Average L/100km to about 12.5L/100km if I am cruising at 100KPH, as reported on the speedo. As soon as we slow down, or do any city driving at all, the average creeps up to about 19L/100km quite quickly.

I recently posted regarding a change in the way my oil pressure gauge is showing the oil pressure. At idle, sometimes the oil light even comes on. I have a new oil pressure switch I will try to put in today, but if the oil pressure is actually low, then maybe I have bigger engine problems. Yech... I am fairly certain this is not the case though, the engine isn't making any knocking or bad noises, and the performance seems fine.

So, if I start shotgunning parts at this thing, I figured I better come up with a priority list. I already did the tires (to no avail) and that cost me $350 (but I did get new tires out of the deal). Here goes:

1. Tires - changed from LT265/75/16 REV02s (48lbs each) to P265/70/16 REV02s (40lbs each). $350.

2. Intake leak? - will replace gaskets on collector and intake manifolds to eliminate any potential leaks. My thoughts here are that a leak here would bypass the MAF and cause the engine to think its running lean, and therefore compensate by dumping more fuel. Also not good as the air being leaked in would be unfiltered! Should cost about $30-60.

3. MAF - Did some reading this weekend, there is a procedure one can do to clean the MAF. I will attempt this, but I did find this part on Rockauto for $170. If cleaning doesn't work, I will try a new MAF.

4. O2 sensors - Rockauto sells Denso O2 sensors for $93 for the uppers, and about $140 each for the lowers. Figured I would start with the uppers, if no improvement, then do the lowers. Does everyone think the Denso ones are the way to go? I noticed Bosch is cheaper, but I have never heard anything good about Bosch O2 sensors. Total cost of this would be about $350.

5. Coil Packs - Rockauto has the coil packs listed at about $60 each. Not sure if I would get all 6, but I haven't found a procedure to test them either. Total cost would be about $360.

6. ECM - I am wondering if my original stock tune was 'fouled' by my superchips tuner. I am thinking of getting the ECM reflashed to stock, or getting a new one. I've seen prices from anywhere from $200-500.

7. Transmission binding - Though I am positive this would manifest in a driveability issue, I could take the trans in for inspection to see if there is a problem. Diagnostic fee proabably under $100. To me, this seems highly unlikely though.

8. Bad Cats - Could take to an exhaust shop to have the Cats inspected. If the lowers are no good, I've heard you can just have them removed. Once again though, this should probably manifest in poor performance. My truck has no acceleration issues at all. So this is unlikely.

9. Compression test - I haven't done a compression test yet. Need to get the adapter so I can get to the bottom of the sparkplug tube. I don't think this is a problem though.

Any other items I may have missed? Anyone disagree with my priority of things I can try?

I don't want to get rid of this truck. I can do all of the items above myself, so I won't be paying ridiculous shop rates, and this thing is mostly paid for. I am certain its got to be one of the above. At 170000kms, its not new anymore, and some of these components could be worn out.

Any thoughts are appreciated!
t


User avatar
taz
Posts: 22
Joined: Mon May 24, 2010 11:34 am
Location: BC, Canada

Postby taz » Mon Feb 28, 2011 11:25 am

disallow wrote:
1. Tires - changed from LT265/75/16 REV02s (48lbs each) to P265/70/16 REV02s (40lbs each). $350.

Shouldn't change a thing except make the car feel slightly more peppy due to less rotational mass

2. Intake leak? - will replace gaskets on collector and intake manifolds to eliminate any potential leaks. My thoughts here are that a leak here would bypass the MAF and cause the engine to think its running lean, and therefore compensate by dumping more fuel. Also not good as the air being leaked in would be unfiltered! Should cost about $30-60.

Faster and easier way to diagnose a manifold leak is too use carb cleaner. spray it around the rim of the manifold once while engine is running cold, and again while the engine is warm. If the engine boggs down at any time then there is a leak present

3. MAF - Did some reading this weekend, there is a procedure one can do to clean the MAF. I will attempt this, but I did find this part on Rockauto for $170. If cleaning doesn't work, I will try a new MAF.

The MAF is pretty easy to clean, just make sure to be gentle and to not have the power on when you unplug or plug it back in :)

4. O2 sensors - Rockauto sells Denso O2 sensors for $93 for the uppers, and about $140 each for the lowers. Figured I would start with the uppers, if no improvement, then do the lowers. Does everyone think the Denso ones are the way to go? I noticed Bosch is cheaper, but I have never heard anything good about Bosch O2 sensors. Total cost of this would be about $350.

We work with the Altima/Maxima VQ's fairly often and it is quite common for the upper 02 sensors to become lazy. When they do they seen lean conditions and dump fuel that the sensor can't read well anymore

5. Coil Packs - Rockauto has the coil packs listed at about $60 each. Not sure if I would get all 6, but I haven't found a procedure to test them either. Total cost would be about $360.

don't waste your time on this one right now

6. ECM - I am wondering if my original stock tune was 'fouled' by my superchips tuner. I am thinking of getting the ECM reflashed to stock, or getting a new one. I've seen prices from anywhere from $200-500.

7. Transmission binding - Though I am positive this would manifest in a driveability issue, I could take the trans in for inspection to see if there is a problem. Diagnostic fee proabably under $100. To me, this seems highly unlikely though.

Again skip for now unless something really draws your attention to the transmission

8. Bad Cats - Could take to an exhaust shop to have the Cats inspected. If the lowers are no good, I've heard you can just have them removed. Once again though, this should probably manifest in poor performance. My truck has no acceleration issues at all. So this is unlikely.

If you have bad cats it is likely the precats up in the manifold, not the 2 you see under the car. Again with our experience with the Altima/Maxima VQ the lower removable cars are pretty much always fine and we remove LOTS of them, it's the uppers in the manifolds that are more likely to grenade. They see much higher heat and are the first to see unburnt fuel and oil which raises their temp even more and eats them alive. We're toying with making high flow variants for the path/frontier like we do with the FWD VQ's but haven't yet started the project. Will likely start in April on my own Pathfinder for testing


9. Compression test - I haven't done a compression test yet. Need to get the adapter so I can get to the bottom of the sparkplug tube. I don't think this is a problem though.

If the cats have done any damage the compression test will for sure let you know

Any other items I may have missed? Anyone disagree with my priority of things I can try?

I don't want to get rid of this truck. I can do all of the items above myself, so I won't be paying ridiculous shop rates, and this thing is mostly paid for. I am certain its got to be one of the above. At 170000kms, its not new anymore, and some of these components could be worn out.

The front main "precats" are very common the fail on the FWD VQ's, when they do go they sometimes start to break apart and send small fragments back in to the motor where they score the cylinder walls and cause oil burning issues. Have you noticed any oil consumption?
Beyond all the items in bold I would clean and chase down intake and tune up related causes, change gas stations and then look into the upper wideband o2's

User avatar
disallow
Site Admin
Posts: 2820
Joined: Wed Aug 13, 2008 9:02 am
Location: Winnipeg, Canada

Postby disallow » Mon Feb 28, 2011 12:10 pm

Thanks for the reply Taz.

I have to remove the collector anyways to do my last 2 spark plugs. I guess I didn't put those on my list, I did 4 of 6 earlier this winter when I first started trying to diagnose the bad fuel economy. But I will give the carb cleaner a go before I screw with the collector. One of the things I discovered (and mentioned in another thread) was that I found oil in my back curb side plug tube. I have a new rocker cover ready to go on, but its been too cold and I haven't had time to mess with it. Would oil in the tubes possibly interfere with the spark transmission and cause a weak spark at the electrode?

Also, re: compression, I have no oil consumption at all, which makes me discount low compression. However, I have a compression gauge, so I will give it a try if it ever warms up out here.

Re: upper o2 sensors, any preference on brand? What have you had the best luck with?

Any thoughts on my (hopefully) unrelated issue of low oil pressure showing on the dash gauge?

t

User avatar
pathology
Posts: 55
Joined: Tue Nov 09, 2010 7:33 am
Location: Front Range, Colorado

Postby pathology » Mon Feb 28, 2011 1:14 pm

If I let my (ex) Camry Hybrid idle for 10 minutes every morning to warm up, my gas mileage goes from 34 to 22. I'd look at the idling as a major factor.

Luck!
Al.

serturbo
Posts: 74
Joined: Thu Sep 18, 2008 12:36 am
Location: Kauai, Hawaii

Postby serturbo » Mon Feb 28, 2011 2:36 pm

Have you tried or thought about looking at OBD2 data first? Check AFR as well as short/long term fuel trim numbers. Parts stores often rent OBD2 scanners.

User avatar
disallow
Site Admin
Posts: 2820
Joined: Wed Aug 13, 2008 9:02 am
Location: Winnipeg, Canada

Postby disallow » Mon Feb 28, 2011 5:27 pm

serturbo wrote:Have you tried or thought about looking at OBD2 data first? Check AFR as well as short/long term fuel trim numbers. Parts stores often rent OBD2 scanners.
I can pull data like this from my superchips tuner. However, without knowing what the normal values are, I have no idea what they should be.

serturbo
Posts: 74
Joined: Thu Sep 18, 2008 12:36 am
Location: Kauai, Hawaii

Postby serturbo » Mon Feb 28, 2011 10:59 pm

AFR should try to hover near stoichiometric (14.7) during low load or cruise conditions. It'll go on the richer side during WOT. How rich will depend on your mods. If your trim values are extreme (like 20%), then something is wrong. Normally, trim values are between -5% and 5%.

Since your fuel consumption is really bad, I'm expecting your AFR to be super rich. Like 12s or worse during cruise conditions.

User avatar
HillbillyJake
Posts: 352
Joined: Fri Dec 12, 2008 8:55 pm
Location: Pitcairn Pa.

Postby HillbillyJake » Tue Mar 01, 2011 1:17 pm

I have always wondered how much fuel these trucks use idling. when it is cold out I let it warm up anywhere from 5 to 15 min. also I have noticed that until the transmission fluid comes to temp it likes to hold a higher RPM, even in overdrive. all of this has my fuel mileage averaging around 13-14mpg. have you ever tried to reset your mileage before certain errands. it seems that is the closest to real time readings that we can get. maybe doing this you can pinpoint better where you get the worst economy and the best.

serturbo
Posts: 74
Joined: Thu Sep 18, 2008 12:36 am
Location: Kauai, Hawaii

Postby serturbo » Tue Mar 01, 2011 2:45 pm

Wow, you guys get terrible MPG numbers. I live on a tiny island, so my highway driving wouldn't be considered highway compared to the mainland. Even so, I normally get 15-16 mpg. If I go on a long drive, I can get over 17 mpg and I have a V8. But I don't think we get winter blend gas.

User avatar
HillbillyJake
Posts: 352
Joined: Fri Dec 12, 2008 8:55 pm
Location: Pitcairn Pa.

Postby HillbillyJake » Wed Mar 02, 2011 9:41 am

I checked last night and am averaging 14

silver x0ne
Posts: 31
Joined: Thu Apr 01, 2010 10:45 pm
Location: DFW, TX

Postby silver x0ne » Wed Mar 02, 2011 6:18 pm

Speaking of "winter" gas, I don't know how Canada is but the wonderful people in charge in the U.S. are increasing the amount of ethanol in gas resulting in lower mileage. I see a remarkable difference of 3 MPG when I go from regular (no ethanol) gas to the 10% ethanol. When you add up that potential with your idling/short drive it makes a lot of sense why your mileage would be that way. I think we get 15-16 MPG including a lot of highway (50+/day) on 87, 18-19 on 93. -- 2008 v6 4x4 SE.

User avatar
taz
Posts: 22
Joined: Mon May 24, 2010 11:34 am
Location: BC, Canada

Postby taz » Thu Mar 03, 2011 1:11 pm

disallow wrote:Thanks for the reply Taz.

I have to remove the collector anyways to do my last 2 spark plugs. I guess I didn't put those on my list, I did 4 of 6 earlier this winter when I first started trying to diagnose the bad fuel economy. But I will give the carb cleaner a go before I screw with the collector. One of the things I discovered (and mentioned in another thread) was that I found oil in my back curb side plug tube. I have a new rocker cover ready to go on, but its been too cold and I haven't had time to mess with it. Would oil in the tubes possibly interfere with the spark transmission and cause a weak spark at the electrode?

Also, re: compression, I have no oil consumption at all, which makes me discount low compression. However, I have a compression gauge, so I will give it a try if it ever warms up out here.

Re: upper o2 sensors, any preference on brand? What have you had the best luck with?

Any thoughts on my (hopefully) unrelated issue of low oil pressure showing on the dash gauge?

t
excessive oil in the spark plug chamber could cause a misfire or poor detonation but you'd probably throw a misfire code if it got that bad.

The oem fit NGK's are nice but a touch more than the bosch units, both work well though.

oil pressure could be alot of things some easy ( sending unit) some bad ( pump), so it's really hard to guess. first step would be to find and check the connection on the sending unit. Not sure where it is on the pathfinder as I've never had to look for it yet

User avatar
disallow
Site Admin
Posts: 2820
Joined: Wed Aug 13, 2008 9:02 am
Location: Winnipeg, Canada

Postby disallow » Sat Mar 05, 2011 3:50 pm

What is the normal voltage for the O2 sensors? My superchips tuner reads this over OBDII. All of them read at 0.6V except bank 1 sensor 1 which read at 0.3V. Also does anyone know what the normal values for the O2 trim is supposed to be?

I will post a video of the readings later tonight.

User avatar
disallow
Site Admin
Posts: 2820
Joined: Wed Aug 13, 2008 9:02 am
Location: Winnipeg, Canada

Postby disallow » Sat Mar 05, 2011 7:59 pm


CPLTECH
Posts: 222
Joined: Wed Sep 08, 2010 9:30 am
Location: SW Ohio

Postby CPLTECH » Sat Mar 05, 2011 8:20 pm

http://www.aa1car.com/library/o2sensor.htm
Rich equals higher voltage readings
Lean equals lower voltage readings

Questions I do not have an answer for:
1-Does towing affect life of the sensors?
2-At what age do the sensors start to get “lazy” reaction times in the PF?
3-Do we replace with OEM or is there another preferred aftermarket brand?


Return to “2005-2012 Pathfinder (R51)”