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.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.
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!
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