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    Ran Out of Fuel - Gas Gauge at 1/4 Tank

    On my way to work this morning, I plugged in my Cobb AP and checked for codes. Code P2A22 (reservoir fill status, correlation) was present. I looked up that code and found little to no information on it. I cleared those and it didn't come back.


    On my drive home from work, the car stuttered and shut down conveniently across the street from a Shell station. I checked the code and codes P29DC (Cylinder Injection Shutdown) and P2AAF (Fuel Pump Plausibility) were present.


    My first thought was an injector issue and second was fuel pump. I cleared the code hoping the car would restart and no dice. I had run out of fuel once before after installing my Walbro inline pump so I remembered it acting the exact same way when I would try to start the car. I looked at the fuel gauge and it was just below 1/4 tank.


    I had the AAA card out and decided that I should buy a gas can and put a gallon and a half in the car to see if it would fire up and it did immediately. I drove across the street and put another 15.5 gallons in so I now realize that the tank had to have been bone dry.


    For those who are wondering, the tank will hold 17 gallons when bone dry. My question is, what could have caused the gauge to read 1/4 tank when in reality I was out of gas? I look forward to hearing your thoughts.
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    PTF Tuned Cobb Stage 2+ | H&R / Koni Sport | BBS LM

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    I'm sure my guy @SteveAZ will have some valuable input.
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    Do you have a walbro inline? I ran into a similar situation when I had my brand new lpfp with a walbro inline on my previous 135i but haven't had it in my current 335i with the walbro inline.

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    I do. I had it happen the day that I installed it but just chalked it up to the new pump and the float possibly getting stuck during install. I had a new LPFP and Walbro inline installed at the same time.
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    My car fuel gauge did the same couple of weeks ago with brand new bone stock LPFP. Ironically, just after I saw the similar thread here Click here to enlarge

    On my case everything was fine after installation and then after 2 months, gauge was dropping only to 1/2 tank. I thought that I didn't do proper installation and something has moved to blocking the float movement. I tried JB4 1-5 menu to reset the gauges but nothing changed.

    Then one day, the temp gauge was set to show under/overboost and I was about to set the fuel gauge to show boost - both gauges freeze. When exiting the dash menu, fuel gauge was showing the fuel level & oil temp was showing the oil temp even the menus had set otherwise. So, parked my car and did the 1-5 (reset gauges) everything went back to normal. Since then the fuel gauge has been showing correct level.

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    I responded on the other board so I'll copy and paste...Click here to enlarge

    With all due respect, I think we're talking about two different things here.

    The OP is talking about physically running out of fuel and the DME reporting incorrect fuel levels.

    As for the the float sensors...in Jstang's case since his issue only appeared recently...it seems as though his calibration may have walked it's way out? There are a few others that have had issues with their fuel gauge reading incorrectly but it's usually immediately after they've been in the tank. They fill up and the gauge only goes to 3/4 and then doesn't go below 1/4 tank.

    At this point, I'm honestly not sure what's causing it. I personally have had multiple pump configurations, float sensors, top hats....in my car and never had this issue despite regularly running my car near empty for pump changes and testing.

    A couple people that have had the issue have changed float sensors and the issue still persisted. So it doesn't seem to be a float sensor issue.

    A couple thoughts....the float sensor is just a resistor....when the tank is full IIRC it reads approx. 1000 ohms.....when it's empty, it reads approx. 50 ohms. There are two of them, one on the drivers side and one on the passenger side. If that resistance changes for some reason, your gauge will read differently. In some cases it almost seems as though the DME has been reset in that regard because even when those that have experienced it put their old float sensor back in...they still had the issue.

    Possible causes (brain storming here)

    1. Float sensor itself (either one)
    2. Float sensor wires
    3. Pinched wires
    4. Connectors at top hat (both sides)
    5. Stuck float (either one)

    I'll try and play with some sensors tomorrow and see if/how I can influence their readings.

    My car is currently getting aligned...hoping to have it back tomorrow. If so, I'll play with INPA a bit as well.


    What it comes down to is that I haven't experienced this nor have any of my local customers as far as I know. I didn't really want to purposely mess up my fuel gauge just so I could try and fix it....but it looks like that's what I'm going to have to do. Click here to enlarge
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    BTW...your P2A22 error is a good observation. I'll look that up in the book tomorrow and see what it says (I don't trust an internet search) and if I can reproduce it.

    Did you happen to notice any change after you cleared the code? ie. gas gauge reading changed?
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    Click here to enlarge Originally Posted by SteveAZ Click here to enlarge
    BTW...your P2A22 error is a good observation. I'll look that up in the book tomorrow and see what it says (I don't trust an internet search) and if I can reproduce it.

    Did you happen to notice any change after you cleared the code? ie. gas gauge reading changed?
    Thanks for your help Steve. Always appreciated! I didn't really pay attention to the gauge reading after clearing the code. Just an FYI, the car sat for around 3.5 days this weekend as I was out of town. I'm hoping this was just a fluke occurrence.
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    Click here to enlarge Originally Posted by JStang Click here to enlarge
    Thanks for your help Steve. Always appreciated! I didn't really pay attention to the gauge reading after clearing the code. Just an FYI, the car sat for around 3.5 days this weekend as I was out of town. I'm hoping this was just a fluke occurrence.
    Try taking the buckets out and testing the floats w/ a multimeter? See if they match Steve's ohm readings?

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    Sorry if I'm hijacking but with similar issue.The fuel gauge & miles left in dash,Is there one more accurate then the other?My fuel gauge used to read at 1/4 tank 100 miles left,1/2 tank 200 miles left etc and full tank was over 400 miles.now it's about 20-30 miles off.example 1/4 tank left would say about 80 miles left etc.this all started about over a year ago when I used to use the fuel gauge for boost reading through jb4.then when I stopped using that hijack method it started to do this.i tried to reset same thing.Unless you have to reset it a certain way?

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    Click here to enlarge Originally Posted by SpanKy Click here to enlarge
    Sorry if I'm hijacking but with similar issue.The fuel gauge & miles left in dash,Is there one more accurate then the other?My fuel gauge used to read at 1/4 tank 100 miles left,1/2 tank 200 miles left etc and full tank was over 400 miles.now it's about 20-30 miles off.example 1/4 tank left would say about 80 miles left etc.this all started about over a year ago when I used to use the fuel gauge for boost reading through jb4.then when I stopped using that hijack method it started to do this.i tried to reset same thing.Unless you have to reset it a certain way?
    Sorry about hijacking too. First reset was done with car running, second time reset was done before starting. I still doubt it's tune related because OP has COBB and still have this kind of issue. Well there could be many different reasons. My $.02 is one of those what @SteveAZ mentioned or bad CAN/earth connection. Bad float connection could rise the resistance and the gauge is not showing correctly. Maybe we should ask from @Terry@BMS if he has some kind of idea about gauges acting weird... even this is not N54Tech support section. Click here to enlarge
    Last edited by -335i-; 09-04-2014 at 06:09 AM.

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    I just ran across this thread and wanted to chime in... I had a similar issue where I had installed the 255 LPFP in my car and had just arrived at Ocean city the night before with the fuel gauge indicating 1/4 tank left. Well the next morning I went to start the car and it started up and then cut out...It repeated this behavior about 3 more times in the parking garage. It seemed as though the car was not getting gas because it would start and then die out a few seconds later. It would run really rough too. Lucky for me Ocean City does not have any E85 pumps around and I just Click here to enlarge Happened to have a 5 gallon jug of E85 in the trunk. As soon as I added those 5 gallons of E85 the car started right up the very first time. I had that same thing happen once since then but 80% of the time the fuel gauge reads accurately. Very odd. I think something must be interfering with the float level sensor. Thank you Steve for all your hard work and contributions!

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    Click here to enlarge Originally Posted by Vertigo44 Click here to enlarge
    I just ran across this thread and wanted to chime in... I had a similar issue where I had installed the 255 LPFP in my car and had just arrived at Ocean city the night before with the fuel gauge indicating 1/4 tank left. Well the next morning I went to start the car and it started up and then cut out...It repeated this behavior about 3 more times in the parking garage. It seemed as though the car was not getting gas because it would start and then die out a few seconds later. It would run really rough too. Lucky for me Ocean City does not have any E85 pumps around and I just Click here to enlarge Happened to have a 5 gallon jug of E85 in the trunk. As soon as I added those 5 gallons of E85 the car started right up the very first time. I had that same thing happen once since then but 80% of the time the fuel gauge reads accurately. Very odd. I think something must be interfering with the float level sensor. Thank you Steve for all your hard work and contributions!
    Is your Walbro pump attached to the OEM LPFP or floating in the tank?
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    Click here to enlarge Originally Posted by JStang Click here to enlarge
    Is your Walbro pump attached to the OEM LPFP or floating in the tank?
    The 255 is attached to the bottom outside of the OEM bucket (zip tie'd)

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    Update: 8 days later I need to fill the tank up again. I have kept an eye on the fuel gauge and the low fuel light came on this morning so it seems like I am back to normal on this tank. I hope this was just a fluke accident or maybe the inline pump just happened to get stuck under the float.


    I will update this thread if it happens again.
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    Happened to me as well.. Checking pump now, probably loose line from oem pump
    07 335i AT - MOTIV 750 - MHD BMS E85 - BMS PI - JB4G5 - Okada Coils - NGK 5992 Plugs - Helix IC - Stett CP - Custom midpipes with 100 HJS Cats - Bastuck Quad - PSS10 - QUAIFE LSD - BMS OCC - Forge DVs - AR OC - ALCON BBK - M3 Chassi - Dinan CP - Velocity M rear Toe arms - Advan RZ-DF - LUX H8 - Level 10 AT upgrade
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    Just thought I'd add a link to my thread with similar issues. I replied over on e90post as well.
    http://www.bimmerboost.com/showthrea...ird+fuel+gauge

    The P2A22 is a reservoir fill status, correlation error as seen in post #22 in my thread. This was read by the BT tool. It was cleared and has not returned but unfortunately it did not fix the problem Click here to enlarge
    E92 335is DCT

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    Happened again when I set JB4 to show boost on fuel. Now the fuel gauge won't go under 1/2 tank... Quite annoying.

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    So it is a fluke or is there some kind of fuel gauge reset necessary?

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    So it is a fluke or is there some kind of fuel gauge reset necessary?
    This time I haven't been able to fix the fuel gauge reading. I've tried different variations of JB menus 2 and 7 + made gauge reset couple of times... Last time the JB gauge hijack went suddenly crazy and after that fuel level was shown correctly. When I have time, I'm going to remove the JB4 and check does that change anything.

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    Doesn't seem to be isolated to one specific tune. I am running Cobb and others running JB4.
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    Running strict COBB with the OEM/Walbro 450mod. I've have had similar issues with the fuel gauge being "iffy" at 1/4 of a tank, and also got strander once. It's not a huge deal since I'm now aware of it now, just try to be mindful once it gets to 1/4 of a tank and either get gas or avoid getting on it and remembering I've got ~75 miles until I'm on fumes.

    Obviously this creates an unnecessary headaches since I'm tuned for 100% and now have no idea how much gas is left in the tank. As far as codes go, I've only seen the "normal" P2AAF/Fuel Pump Plausibility code.
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    Click here to enlarge Originally Posted by JStang Click here to enlarge
    Doesn't seem to be isolated to one specific tune. I am running Cobb and others running JB4.
    I was thinking that too and still do, but I had these symptoms right after playing with JB gauge menus, so I decided to eliminate the JB possibility. There could be different reasons. The only thing common with the problematic cars is the fuel pump change.... Maybe bad/corroded connection on lpfp?

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    2 out of 2 members liked this post. Yes Reputation No
    So I've been reading a lot of threads about this between E90post and here, I even experienced the problem my self after installing the inline 255. For me the problem was that I got fuel into the vent system which then caused the tank to not properly vent and pull a vacuum when pulling fuel out of it and it wouldnt fill all the way due to too high a pressure. The problem was solved when I blew the system out and put a hose clamp on the offending tube that was leaking.

    That aside, as I dont think its what most people are experiencing here, the system seems to use some equation on the resistance reported between the two floats (as the passenger side of the tank holds more gas than the driver side) to get the fuel reading.

    Based on the values that people who have taken measurements are reporting from the floats, the floats appear to be fine them selves, however when they are in tank something is amiss. Given that the electrical connections for the floats are exposed to the fuel, I'm wondering if there isnt some parallel resistance that is reducing the seen resistance by the DME, this would seem the most likely to me given my EE background.

    I suspect that something in the steveAZ kit may be reducing the resistance of the fuel its self for a short period until it is "flushed" out by running enough fuel through the system, like say the heat shrink has some chemical that comes off of it in the ethanol that reduces the resistance of the fuel (some ion or the like) until that chemical is run though the system and no more added as its been stripped off by the ethanol and flushed away with enough tanks of gas. Or maybe us screwing around in the gas tank and getting moisture into the ethanol off our skin (sense its so hygroscopic) does the same, or even perhaps some ethanol its self simply has a lower resistance....

    Anyways, the point is that to know this for sure we need someone to measure the resistance of the fuel per unit length (so fix 2 volt meter probes 1 inch apart) and measure the resistance of the fuel in the tank at the time of failure vs at a time of no failure (make sure its near the floats POT (where the wires attach to the float). If they are the same, well then we've at least eliminated the idea, if its not then given that measurement we can come to a ball park idea of what the parallel reported resistance of the float would be and it might explain things.

    Only a theory, needs data to back it up, but I see it as plausible. The only issue I see with the theory is that it explains the 3/4 report, but the 1/4 report at empty means that one or both of the floats is reporting a higher than expected resistance, which this would only explain if the car has a calibration that it re-set to report empty at a different expected resistance than simply both the floats at about 50 ohms.

    I know that there is a "fuel scavenger" port on the driver side that is also supposed to help the pump pick up fuel, and from screwing with all those tubes recently it looks like that fuel scavenger is supposed to allow the fuel on the driver side (which is higher than the passenger side) to siphon into the passenger side of the tank so the fuel pump can pick it up. Perhaps there is something going wrong with that such that the driver side reports it has fuel but the passenger side reports empty and thus you get a 1/4 tank but go empty. That however doesnt line up with with the reports that the tank then took a true 17 gallons (true empty).

    The other 2 possibilities that I can come up with are: 1. The new pump puts out a lot of EMI which then induces a current on the passenger side sense lines and causes a miss read of the resistance for that float (if this was the case you'd think it would be more consistent, not just a passing thing that some people see) and 2. the circuit that reads the resistance of the floats draws its reference voltage from the same source that supplies the current to the pumps, thus by increasing the fuel pump current the reference voltage drops which then messes up the reading until it re-calibrates its self (assuming it does so), but we'd really need to see the circuit diagram of this whole part of the system to know that.

    Those are my thoughts... really muddy water here, need data to make things more clear.

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    A few points..

    -The heat shrink is PTFE, commonly used for it's chemical resistance and in applications where high purity is required. IMO, even if there were a film on any of the components (that doesn't appear to be the case), that would be sooooo minimal I can't see it accounting for any real discrepancy and certainly not long term.

    -When your tank is anything other than full...your float wires at the top hat on both sides are no longer submerged but are only getting potentially splashed with fuel. I can't tell you for sure if the float body is sealed...I'd need to investigate that.

    -In my bench testing, I was curious if people may have been wrapping their float wires around the pumps power wires. I literally took the float wires while running a stage 2 assembly at 100% duty cycle (13.5V and pulling 21amps) and wrapped them around the power wires, fuel fitting, and pump. There was no change in the resistance the float was reporting.

    -I thought I remembered Musc putting a stock pump back in and still having the issue with his fuel gauge? In addition didn't 335i say theirs was on a bone stock LPFP? There doesn't seem to be any strong correlation.

    Thus far I have been unable to reproduce this and I have probably had more pump assemblies and different configurations in and out of that tank than anybody as well as multiple float assemblies on both sides of the tank. However I usually run without a stock regulator (more on that later). In addition as far as EMI from the pump goes...not only was I running one 450 pump....I've run two in a stock bucket for Stage 3 testing with an otherwise stock tank and LPFP plumbing. Second with the inline setup the stock pump remains in the bucket and the 255 pump should be on the opposite side of the float assembly.

    Has anyone unplugged either float assembly (especially the drivers side) and filled their tank or driven around like that? I'd be curious to know its affect. I currently have parts of my car disassembled for development...but will put it back together Wednesday and perform this test.

    Another thought as I'm running through the entire tank assembly in my head...as I said on my car I usually run without the drivers side regulator but I put a stock one back in for Stage 3 testing. The stock float assembly on the driver's side connects to that regulator. I haven't noticed a difference with it in place or removed but I'm sure that wire is to ground the metal component of that regulator to dissipate any charge that may build up from fuel flowing through it. There is no such grounding that takes place on the driver's side of the E series. HOWEVER, if you look at the F-series pumps...the ground wire on the pump motor has 2 additional leads on it. One that connects to the regulator and one that connects to the filter as they are both contained in the same assembly but are separate unlike the E series.

    I need to check something and report back, but I'm wondering if the body of the 255 pump is grounded. I've read about a charge build up in fuel and if that pump body isn't grounded with all that fuel flowing through it...what the affect is when it reaches the regulator that is attached to the float assembly????

    Just brainstorming at this point. Anybody have an o-scope to put on their float sensor. Click here to enlarge
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