I just have to ask about the recommendations of using the BGK44 gas treatment. I have a J30 97.5, with about 51,000 miles on it that I just purchased. I had averaged about 31 mpg on the drive home (1200 miles) after purchasing the car, but only about 16 mpg around the city (less than 40 mph). Then after following a few people's advice on this board, I just used a can of the BGK44 during my last fill-up, and now I'm looking at about 10mpg half-way through my tank of gas. I can also smelled a little gas in the exhaust, which was there before I added the BGK44 treatment. My car runs great, though. I don't have any power-related problems. Just wondering if the low miles-per-gallon is normal with the usage of this gas treatment product, and if you have any thoughts about the gas smell in the exhaust.

I'm located here in Iowa City, and it just recently gotten really cold this past week. On Monday when I took the car out in the morning, where it was 23 degrees, I swear I heard a hissing sound coming from the gas tank area, behind the back seats everytime I hit the gas peddle. I went underneat the car, as best I could without jacking it up, with a flashlight and every hose coming from the gas lid area to the tank that I could see where fine, showing no evidence of a gas leak. Any advice would be appreciated. Take care all.

Alex,

BG44k is a well established product even used by many dealers it will not worsen your milage (often increases it a bit).

gas smell in the exhaust is often a product of poor MAF connection (or MAF itself).An increase in gas consumption is also a problem with a faulty MAF or MAF connector.You should notice a drop in power as well though.Is the exhaust sooty at all?

At your low milage MAF failueres are almost unheard of in our community.The only exception is if it (or most likely teh connector) got damaged during a serviceThis happens more ofetn than many realize.For example on a Q the most common cause of damage to teh MAF connector is oil change providers changing the oil filter from the top for convinence and disconnecting the MAF in the process.

I am unsure what kind of services may lead providers to inadvertently damage the MAF on a J30.But perhaps this is connected to your recent service?

But in order to have a bad MAF you should see sooty exhaust, as well as drop in power in addition to loss of MPG.Put a white sheet of paper in front of your exhasut with the car running warmed up to catch any soot.

Since you dont have unusually strong vibrations we can exclude the psossibity of injectors in your case ( your car is way to young for injector failure anyway)

Fred...

Thank you so much, Palmerwmd. I was really concerned that it could have been the injectors that I have been reading about on this forum. But yes, you are correct on all accounts: I don't have ANY vibration at all, there are no power loss (the car runs strong and responds quickly off the line), there are no drop in rpm during All operations, and I don't see any soot on the exhaust, but I will perform the white-paper test as you have suggested. And I have not gotten the car serviced since I purchased it a few months ago, because there were no problems with it. If it's the MAF that's the culprit, can you point out where it is, so that I can check the connections? One more thing. Everyone suggested that I should replace the filter when using the BGK44 product, which I agree completely. But do I replace the filter at the same time that I add the BGK44 product or should I wait until the treated tank is out before replacing the filter? It would make sense to wait until after the treatment, wouldn't it? Thanks for your help.

Wait until the treated tank is out.

Actually the service, where it iscritical to change the fuel filter, is a BG44k injector rail flush, which is what most refer to, when suggesting to change the filter.

A fuel treatment into teh tank to protect injectors is done often enough by many to make the fuel filter change unpractical.

Actially if u only do the "additive to the tank" BG44k you dont really need to change the filter, but since you just bought your car and are probably unsure when it was last changed go a head and change it.

Also be sure toi use Nissan OEM fuel filter.Nissan OEM parts are very very good and superior than most aftermarket at only slightly higher cost.But with much better performance (PS: I dont work for Nissan just saying how it is..;0)

Consider a new air filter as well.And since we are on the subject of filters some good oil filters are:Bosch, Nissan OEM, MOBIL1 and the better STP's.

Fred...

PS: Keep checking your milage though, we wanna track this down.

Thank you so much for your help with this. I'll wait until the treated tank is finished and let you know how the next tank will fair in terms of gas milage. I will change the air-filter tomorrow, and do the soot-paper test then.

I know that you stated that it could be the MAH if there is a drop in power, soot in the pipes and low gas milage. Well, I definitely have low gas milage, not sure about the soot or the loss of power. Since the day I purchased the car, I didn't notice any drop in power. This is not to say that there isn't. But I drove from New Jersey past the mountains and back to Iowa City averaging over 80 mph, sometimes 90 with no problem. And we also own a v6 Toyota Solara, and the J30 is comparable to it in terms of power.

Any way, can you or anyone here tell me where about the MAH connections are located under/above the car's engine, so that I can check it myself? Take care, palmerwmd.

I know nothing about Js and little about Qs, but I do wonder if your O2 sensor (only 1 on a J?) is kaput?

are you judjing the MPG by the fuel gage on the dash? If so, do not. I have read and experienced a variation in the readout due to oxidation on the contacts. As far as I know the level is read by resistence and with oxidation that can vary.

I gave up using the gage and now only go by fillup measurements. Much more accurate. I get 21 MPG around town (semi-urban)

alex, my mpg actually went up when running the bg44k. at least compared to what i ran after it was out. i was in the low 20's then afterwards i was about 18-19 mpg. It could have been just driving habits, but who knows. I should continue to get random measurements to get a good average for the year.

juiceman, that's how i measure it. Just set the trip meter and divide the accumulated miles by howmany gallons you put in yournext fillup.

Yeah! That's how I always measured it. I take the amount of milage divide by how many gallons it take to fill up the car. Usually, I have been getting about 233 miles per 14 gallons (16mpg). This always gives me about 50 miles per gauge bar (my gauge on the J30 is divided into 4 sections/bars). And I don't drive hard at all. I'm conscious about the milage problem. I have been averaging 16 mpg around the city (hardly ever going past 40 mph, mostly 25-35 mph). But right after I added the bgk44 last week, I have been getting about 25 miles per bar. At this rate, I will be getting around 133 mph for the whole tank. Something is definitely wrong here. I'm just trying to get a sense of what's going wrong before I take my car to a mechanic. I'm new in town, and there's no Infinity dealerships here. And when I tried to take the car to a local shop a few weeks back for diagnosis, I saw how their eyes lid up when they saw me drove up, and three different mechanics came out and started looking under the hood. I just got this feeling that they didn't know much about my car.

I know that a good mechanic is hard to find, and that there are quite a few good ones here on the board, which is why I'm here.

I also ran the soot test this morning by holding a white piece of typing paper over the pipes for about 2-3 minutes, and there were no blacks on the paper at all.

If you guys think it's the oxygen sensors, can you please tell me how I can check on my own or do I have to take it in for a mechanic to correctly diagnose it? And is this a common problem on a 97.5 J30 (with around 51,000 miles on it)? And roughly about how much I can anticipate on paying for this to get fixed? Thanks for all your help, guys. Take care. Enjoy the week.

juiceman wrote:are you judjing the MPG by the fuel gage on the dash? If so, do not. I have read and experienced a variation in the readout due to oxidation on the contacts. As far as I know the level is read by resistence and with oxidation that can vary.

I gave up using the gage and now only go by fillup measurements. Much more accurate. I get 21 MPG around town (semi-urban)

I have also noticed the gauge irregularities. Gas pumps also appear to have different sensitivities as to when they do the automatic shut off. I follow the clean air recommendations about not topping off the tank and, depending how the nozzle is set up, there can be almost a two gallon difference from pump to pump.

I too get ~21 mpg on average (20% city, 80% freeway) using the odometer divided by the gallons purchased. The highway EPA number is 23mpg but who drives 55 mph? More like 70-80 and at those speeds your car is pushing a whole lot more air compared to 55.

Likely gas mileage drags are: Dirty air filter, low tire pressure, MAF sensor, O2 sensors and a heavy right foot.

Is there anyway for me to diagnose whether it's the MAF sensor or O2 sensors on my own, just by examing them? Thanks for the advice.

VimyJ wrote:I have also noticed the gauge irregularities. Gas pumps also appear to have different sensitivities as to when they do the automatic shut off.

i noticed that to. that's why i use the same pump # at the same station whenever I can now. It's nice finally having a chevron right next door.

alexhho wrote:Is there anyway for me to diagnose whether it's the MAF sensor or O2 sensors on my own, just by examing them? Thanks for the advice.

I know in my J manual they list resistance reading to check the MAF and I think O2 sensors.

Do you have the manual? If not get one I have found it very useful in finding the source of problems

Thanks, Juiceman. Yes. I do have one. Read it last night and it doesn't seem like I have the necessary equipments for the job.

Mayhem_J30. I concur with your thoughts on using the same gas station and pump. I can also tell you that my car seems like it runs even better now half-way through the treated tank with the BGK44 treatment. Thanks for all the help you guys have given me. Have a nice weekend everyone.

I agree there as well - I always use Chevron in my Q and one day on my way to work I stopped @ Texaco and filled up - the same day 2 injectors went bad on me with no prior warning at all.

This may have been a coincident - but you never know.

alexhho wrote:Thanks, Juiceman. Yes. I do have one. Read it last night and it doesn't seem like I have the necessary equipments for the job.

i think Fluke is who manufactured my multi-meter. comes in handy when it comes to narrowing down which electronic device has failed or is about to. Saves $$ by not having to go to the dealer.

Mayhem_J30. I was wondering if most of the J30 owners here follow the manufacturer's recommendations on the tire pressures. Mine suggested that I should inflate my tires to 29 psi. Isn't that a little low? Someone here mentioned that my poor gas milage may have been too much pressures in the tire. I have always had about 32-33 psi on my tires. There's only me and my wife in this car at all times. At 33 psi, the tires already look underinflated. Just wondering if I should drop another 4 psi to 29 psi as suggested.

I use 31 to 32 psi. I am looking at tread wear using a caliper every on to two thousand miles. Take measurements at certin points across tread.

I have always used a few psi over recommendend and never had a problem on any of the cars I have owned. No abnormal tire wear either.