Fuel Level problem

[nolmt50]

I've had this problem for a while now, but it seems to be getting worse lately. I know the 03 m45's had the problem with the fuel gauge, but I was wondering if anyone else with 06 and up have had any problems? For me when I turn on my car the fuel gauge is usually off or shows a diff amount of fuel by about 2-3 ticks. An example is I turn my car on and I'm on empty, park come back and when I turn it on it's at a 1/4 tank. Not parked on any hills, so I know it's not that. Also the last few times I've filled up from at or right below E mark, my car only takes 15 1/2-16 gallons of gas, when I start it will go to 3/4 then slowly go to full after about 20-30 min of driving. Anyone else have this problem or know what I need to do to fix it?

[Larz]

That first part hasn't happened to me, but i have that same situation after filling the tank. I usually don't buy fuel until I'm at 1/4 tank or a little lower - then I do a fill up - only until the pump handle stops - I never top it off.
This is where it happens to me as well. As I'm leaving the station, my gauge jumps to about half way between FULL and 3/4. After driving for a considerable distance (maybe 10 miles), the needle jumps to FULL and from that point on, it seems to show an accurate level. This same story happens at every fill-up. I can't work out why it happens, but it does it to me as well. My dealer checked the gauge (dunno exactly what they did) but they claimed they determined how many gallons remained at the time and said the gauge was showing the appropriate level and they saw no reason why this fill-up discrepancy would happen. They appeared as if they either didn't believe it happened, or never heard of it happening.
They didn't charge me as it was in the shop for tire rotation at the time, which was nice although I'd rather they had an answer for the fill-up situation.

[The00Dustin]

I think we have saddlebag style gas tanks, and it sounds like both of you are consuming more gas from the driver side. However, that is based on what you are saying about fill-up. Otherwise it could theoretically be the passenger side, because I don't know which side the fuel sending unit is on. I don't know if this would imply a weak/bad fuel pump on the opposite side, but since the fuel will level out between the sides, it probably isn't an urgent maintenance issue even if it does imply that. However, when your needle goes up to full, it probably doesn't go past, and you probably don't have near 20 gallons in your tank. My needle normally stays above full for quite a while (I haven't paid close attention in a long time, but I'm thinking maybe 50 miles, probably somewhere between 2-3 gallons is above the full mark, same below, when it gets down to E, I think I have about 3 gallons left). If you've got all sorts of time to kill, you could shut the car off at the gas station and wait long enough for it to level out, then go fill up. This would help confirm my suspicion if your needle went higher immediately after filling up when you did that. Presumably you'd need to sit in a parking space while waiting and then move the car so as not to block a pump for that long (I would probably put it in neutral and push it instead of starting it, but I'm goofy, starting it for that short period of time obviously wouldn't conusme enough fuel to get the levels way off again).

[nolmt50]

I was reading more last night online, and it looks like it's happened a lot with G35's also. And it looks like a fix would be replacing the two fuel level units in the tank, anybody know how difficult that would be? Or anyone who has ever done it?

[The00Dustin]

Having a fuel sending unit on each half of tank would make sense, however, when I had fuel level problems several years ago, the service advisor (not that they are really qualified to talk about service) told me the techs took out the fuel sending unit (singular) and verified it was sending a good signal at all levels, so they re-installed it (and then my problem went away). If you can find instructions for replacing the fuel sending unit(s), I would recommend removing it/them for cleaning/testing first (I believe they tested with an ohmmeter). You should be able to find the field service manual (FSM) on this forum, and I should imagine it would have instructions for the removal and replacement of the fuel sending unit. Also, as an update to my previous post, while I thought I got ~50 miles above full, it closer to ~25 (I got ~100 on my previous vehicle). So there is only ~1 gallon above full (and while I still haven't run my car dry, I am pretty certain there are 3 gallons below E), however, the amount of fuel moving the needle above F or below E could be different on every vehicle.

[FH212]

Glad I read this post. I had a 06 M35 a couple years ago that did this and it drove me nuts!! I could never fill the car. It was one of the many reasons I got rid of it. (the car was a boarderline lemon.) I am picking up my latest M today. Hopefully it does not have this problem!

[nolmt50]

I did some more research and found this is an FX forum, seems like the same problem I have and this is a fix for some, and a temp fix for others. Seems easy enough so I will try my luck doing this and if it doesn't work, replace both level units.

http://www.infinitiscene.com/forum/thre ... +gauge+fix

[Larz]

Thanks NolMt50!
Great research on your part - Right now I don't mind the slight delay in gauge reading FULL, but if this leads to the trouble you're having or worse, I have a sticky on my desktop for that DIY just in case it isn't covered under my warranty.
Cheers !

[nolmt50]

Just did this yesterday, and so far it has worked. Cleaned up the fuel sending unit contacts because they were pretty dirty and my gauge is so far accurate. As soon as I did it I went from below empty to about quarter tank. So if anybody else is having this problem or if it comes up, try this first!!

[Larz]

Here is another idea you may want to try before rermoving the rear seat, etc. When I bought my M, the gauge read just slightly over the F mark at fill-ups. I never 'manually' top off, just let the pump handle stop after it fills, and I buy my fuel at the same station and the same grade (93).
For a few months now, at fill-ups the gauge stopped reading that high - stopping just at the upper end of 3/4 - slightly under the F mark. Out of curiosity, I once even topped off by hand (please forgive me, tech people) and still the gauge remained under the F mark.
I recently began using Seafoam after reading lots of testimonials from other members here. Last week I filled up, added one full can (1 oz per gal) of Seafoam - first time I ever used a fuel additive. The gauge still read slightly under the F mark as it had been. However, at the next fill-up, the gauge is back to reading just above the F mark and seems it's reading more accurately along the entire range. It's either an extremely rare conicidence that the sender units 'fixed' themselves, or its due to the cleaning done by fuel mixed with Seafoam.
I suggest adding Seafoam to your next fill-up and see if your gauge shows improvenents with subsequent fill-ups. The can doesn't say how often to add, or how many tank-fulls to wait between adding Seafoam, but I should think adding at every oil change should do nicely (not based on any science - just a poke at the wind). I suppose it depends on just how dirty the sending units are - it may take more cans over a longer period to clean them effectively, but I think it's definitely worth a try.

[svard75]

This is awesome. Thanks nolmt50!