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View Full Version : So you think you know how much gas is in the tank, do ya?



MattRobertson
02-22-2010, 04:46 PM
On track, the biggest rookie move of the century is the run-out-of-gas move. You are bombing down the track and having so much fun you forget to look at your gas gauge. Then the car suddenly dies. For awhile - while you are sitting on the side of the track, waiting for the tow truck and looking like a total a$$hole to all the other guys in the hot pits waiting for your sorry butt to get dragged off-course for no good reason - you wonder how much damage you have done to your engine by beating the holy crap out of it like you just did. You start thinking about things like macaroni and cheese, and how warm newspapers can be if you cover yourself with them while sleeping on a park bench. Cuz thats what you'll be doing soon after you pay a tow truck for a 300-mile tow ... and buy a new engine.

But then, in the paddock, you find no problems. You put gas in it and it fires right up.

Hopefully no one nearby has an empty coke bottle, crescent wrench or rock in hand because if they see you start the car with a gas can next to it, chances are good you are going to get beaned.

the first recipient of the King Idiot award was Cam, who ran out of gas on Willow Springs ages ago. We (I) have made fun of him as much as possible for that ever since.

Since then, I have run out of gas myself. Twice. The first time was on Thunder Hill. I put it down to a 1/4 tank of fuel and an unusually long 25-minute session, coupled to a dose of stupid... but I couldn't shake the feeling that it hadn't been that bad and I had seen fuel in the tank. But it was heat of the moment and I wasn't sure of what I had seen through the proverbial red mist. The next time I was on Laguna. This time I was dumbfounded. I was *sure* I had gas in the tank. The little orange gas thingie wasn't even lit up. I think. It wasn't, was it? Damn I did it again. I think.

So... On Saturday at Willow Springs (Big track) during a 25-minute session I started out with 26% fuel in the tank (DashHawk reading). This is the last session of the day and we (Hemi Family and I) have been getting fantastic fuel consumption numbers thanks to the high gears you can use on this track. HF is about where I am on gas in the tank.

So off I go and I'm bombing around, happy as a clam until I come sailing around Turn Five and... the motor dies in a suspiciously familiar way. I look down and confirm I am not even in the red on the gauge. Not even close in fact. I pull off track and hurriedly check the DashHawk (with the key still on, you can cycle thru the menus and get data even though the engine has died). It reads 12% fuel. OK so the good news is I didn't run out of gas again. The bad news is the motor is dead for a more serious reason. But the DH also shows no codes.

After a wait that takes forever I get towed in, and I find out why it took so long.

Hemi Family ran out of gas too. Right before I did. The two jerk-offs in the matching black station wagons both don't know how to read a gas gauge. My my we must have been popular.

Here's the deal: Our gas gauges suck donkey you-know-whats when the car is getting thrown around. Thats not exactly a news flash, except the problem is worse than anyone ever figured. The lesson to be learned is Do Not go out on track with much less than half a tank of gas. If you do... watch out for flying rocks and wrenches.

p.s. as I was 'going in' I got more and more readings out of the fuel gauge that showed 10% fuel, then 9%, down to 3% and finally zero... This was over a period of minutes and not the seconds it would take for fuel to quit sloshing from the side of the tank to the bottom... and even then, such sloshing would increase the available fuel... not lessen it.

Paywithdeath
02-22-2010, 04:52 PM
I run out of gas all the time. Ask the fl crew and hemi31.

aslcharger08
02-22-2010, 05:00 PM
I usually put in just a little over a 1/4 tank for the drag track for both 1/8 mile and 1/4 mile......knock on wood haven't ran out of gas yet but I did come close at Famoso back in November.....the gas light was on and it wouldnt even go into autostick it just cruised in 3rd gear wouldnt go any higher so I had to mantain a low speed for about 3mi to the gas station.

The light came on right after I turned around to go pick up my timeslip. Ever since then I always make sure to have a little over a 1/4 tank.

Maybe you should get a 2-3 gallon fuel can so next time you run out just throw that in there and head to the gas station.

budoboy
02-22-2010, 05:05 PM
I've taken 2 quarter mile runs after the gas gauge light comes on. You can probably push it a lot farther though.

Charger4Life
02-22-2010, 05:05 PM
Hemi 31 must be getting used to it Paywithdeath.

I ran out of gas on the last run of the day at Rockingham last Saturday.

Luckily I had a gas can and my new buddy Alcharger helped me out. Which I forgot I never you for that gas Kent!!!

Charger4Life
02-22-2010, 05:07 PM
I've taken 2 quarter mile runs after the gas gauge light comes on. You can probably push it a lot farther though.

I took about 15 runs since the light was on when I got to the track.... I should have skipped that last run.

Mr. iNCREDIBLE
02-22-2010, 05:19 PM
too bad you don't have EVIC Matt, because the fuel readings in the hidden menu would give you a more accurate readout of what's going on, esp was the fuel is sloshing between the tanks (e.g. 2 sides of the tank).

the Daskhawk is "ok" but even as a daily driver I find it to be inconsistent with it's percentages readings.. sometimes my low fuel light comes on when it reads 13% other times when it reads 9% and it never goes past 96% on a tank fill and it's been at 0% for 10 miles and when I filled the car it only took 17 gallons..

the EVIC reading however does a good job letting you know if either tank has run dry..

Hemi Family
02-22-2010, 05:19 PM
To add to the drama, this was the first time ever running out of gas for me. I like Matt checked the gauge before heading out and was reading 5/16 of a tank, right between 1/4 and 3/8 on the gauge. I figured for sure I broke something, she shut down right as I hit the apex on 9 under full throttle. I tried to restart but only got a few burbles and she died again. I tried over and over but nothing, surely something was broke, the gas gauge still said 1/8 of a tank.

I get towed to the pits and figure I'll wait for my savior Matt Robertson to come in for my ride home. When I arrived the gentlemen pitting next to us said what happened to you two? I said I think I broke something...what do you mean two? He said the other Magnum is off track in turn 6...oh s**t now what? So here comes Matt being towed and pulls along side my car, he's thinking, why are you parked so funny? Then he comes to the realization that the guy he was counting on for a ride was broke too. When I descibed my condition to Matt he said "sounds like fuel", so I borrow a can from Matt and fill the car...vroooom, she fires right up...sweet, now let's fill Matt's. Fortunately both cars were fine but, two Magnums in the same lap WTF? We were on totally different fueling schedules, never really compared notes and both on the SAME LAP??? Go figure...

SRT8_in_CT
02-22-2010, 05:29 PM
Could have been worse. You could have been flying an airplane :)

MattRobertson
02-22-2010, 05:53 PM
Maybe you should get a 2-3 gallon fuel can so next time you run out just throw that in there and head to the gas station.Hah. I have four 5-gallon fuel jugs in the paddock. Three were full. Based on fuel consumption up to that point (80% fuel at start of day, ran four sessions and 26% remained) I didn't think I needed it. Do the math on fuel consumption and I should have been easily in the clear. The gauge isn't linear. Again thats not a big shock but again... its worse than people have though up to this point.


too bad you don't have EVIC Matt, because the fuel readings in the hidden menu would give you a more accurate readout of what's going on, esp was the fuel is sloshing between the tanks (e.g. 2 sides of the tank).

See, thats the especially weird part: Both of us were getting decreasing fuel readings that took MINUTES to stabilize. Not moments like you'd expect for sloshing fuel, and if its sloshing fuel, then as I said the available fuel will go UP and not down. Sloshing fuel will give you the opposite effect of what we saw when you make one critical assumption that I think we can take away from this (see below)..


the Daskhawk is "ok" but even as a daily driver I find it to be inconsistent with it's percentages readings.. sometimes my low fuel light comes on when it reads 13% other times when it reads 9% and it never goes past 96% on a tank fill and it's been at 0% for 10 miles and when I filled the car it only took 17 gallons.
Hmmm. My experience has been the opposite. The DH reads the same signal as the EVIC gets and its always been dead-on accurate for me. I can absolutely count on the fact that, the instant that fuel reading goes from 10% to 9%, the fuel light will go on and I'll hear a ding. It never varies. And I've been surprised in the past that its percentage readings match the analog gauge's positions precisely. None of us believes the fuel gauge is measuring accurately. i.e. its common perception that the gauge is loaded to the top half of the arc and from 1/2 a tank down it moves quicker. My DH readings have contradicted that, showing a 1:1 constant relationship, tested over many long-distance commute trips (edit: this contradicts my first conclusion voiced to aslcharger08 above and I have no explanation for that).


So here comes Matt being towed and pulls along side my car, he's thinking, why are you parked so funny? Then he comes to the realization that the guy he was counting on for a ride was broke too. Which took a minute for me to wrap my head around.

"No I said I was out of gas. Why is your hood up? What do you mean you just got towed in? That was me. You got towed in!? As in You and Me both? Just to confirm, you are telling me you got towed in when I got towed in? So we're in the Mojave desert and we're walking home. OK got it."


The only thing that makes sense to me here - and which jibes with some other things I have seen but never really put together - is that our gas gauges react, but not as fast as we think they do. They don't react in real time. So... when we are draining them at a high rate of speed, they don't read empty when we go empty. There's a lag. Why else would you have an empty tank that reads 12% at stall, then 1 minute later reads 9%. Then one minute later reads 6% and so on until it takes lets say three minutes to go empty?

I'll hypothesize that the gauge has a limiter installed in it that keeps the thing from jumping around wildly as we slosh the car around. Probably something that takes an average of readings every few seconds and posts the average to the gauge every minute. Thats the only theory that, so far, seems to fit the observed facts (dead engine, slowly declining fuel gauge as minutes go by). We throw the gauge off by racing the car and draining the tank so fast the gauge software - which wasn't designed for that application - can't keep up.


Could have been worse. You could have been flying an airplane :)True dat.

ylwnana
02-22-2010, 06:13 PM
LOL! same story. went out with 1/4 tank indicated and was on the side of the road watching like 3 laps in.

MattRobertson
02-22-2010, 06:20 PM
You got pulled in that day too or it was a different one? I don't remember you getting hauled in.

ylwnana
02-22-2010, 06:46 PM
i started with a full tank and only did maybe 25 or so laps. but i did have less that a 1/4 tank and had to fill up when i left! i ran out @ buttonwillow raceway while doing the "university of v.a.r.a." driving school a year or so ago.

MattRobertson
02-22-2010, 07:14 PM
ok... I thought for a minute there we'd managed a threepeet.

http://www.infoaddict.com/wp-content/uploads/HLIC/dailybail.com/storage/three_stooges.jpg

BobCrespo
02-22-2010, 07:59 PM
:doh:

MattRobertson
02-22-2010, 08:02 PM
:doh:
Hey Bob I didn't crash it again!

... no, wait thats not true. I did a Dukes of Hazzard at the entrance to Turn 9.

...

Hey Bob I didn't wreck it again!



much. Video and new thread to come maybe Wednesday.

Hemi Family
02-22-2010, 08:13 PM
Hey Bob I didn't crash it again!

... no, wait thats not true. I did a Dukes of Hazzard at the entrance to Turn 9.

...

Hey Bob I didn't wreck it again!



much. Video and new thread to come maybe Wednesday.

Yeah, I got to witness the whole thing...as I was applying brake for turn 9 I noticed Matt wasn't. I was thinking man those Hoosiers must be awesome, then he seemed to be running the "high" line, then higher, then higher, then poof dust everywhere. Being the bleeding heart I am I considered lifting for a split second just so I could view the carnage, instead I just took a glance in the rearview mirror while shifting to forth. :racing:
I could see him making his way back on track...:thumbs_u:

BobCrespo
02-22-2010, 08:18 PM
Maybe it's time for a fuel pressure gauge/idiot light?
Perhaps flashing lights and bouncing gauge needles would help.

I wonder how many times it went lean before quitting?

Good thing you bought the extended warranty on that motor:bahdumcha:

MattRobertson
02-22-2010, 08:56 PM
Yeah I and if it turns out I don't like the warranty coverage I can always file a grievance!

http://www.giftadditions.com/images/Complaint%20Dept01.jpg

hemiwagn
02-22-2010, 11:15 PM
Okay okay, my 'road course' is kinda straight and short, but it happened ONCE at the 1,000 ft mark, resulting in this.....

http://i41.photobucket.com/albums/e287/hemiwagn/Miscellaneous/IMG_0569Medium.jpg

and my fav video on the subject...

http://i41.photobucket.com/albums/e287/hemiwagn/Miscellaneous/th_lonelygallon.jpg (http://s41.photobucket.com/albums/e287/hemiwagn/Miscellaneous/?action=view&current=lonelygallon.flv)

okay it did happen one more time - in the burnout box...... Yep, I got each end of the track covered....

bigjim
02-22-2010, 11:34 PM
Its good to be able to laugh at yourself...

After having the pump assy and sending unit in hand, I wouldn't believe them at a road course if you paid me. The g forces we do will send the float to about half full in a corner, confusing HAL to the MOON! I FILL after each run and havd been getting about 3.5mpg on track. Course now that Erik has been under the hood maybe 2.8?

Eric Bryant
02-23-2010, 02:22 PM
See, thats the especially weird part: Both of us were getting decreasing fuel readings that took MINUTES to stabilize. Not moments like you'd expect for sloshing fuel, and if its sloshing fuel, then as I said the available fuel will go UP and not down.

Sensor inputs are typically low-pass filtered in software, and the equivalent time constant of that filter will be selected according to the expected slew rate (rate of change) of the sensor data. For something like the fuel level sensor(s), the slew rate is very low - typically on the order of a gallon per several minutes. The software will take this into account to make sure that "noise" (sloshing, electrical noise, etc.) is properly filtered such that the gauge isn't moving unnecessarily (that sort of thing tends to upset the average customer). I would not be surprised if this filtering changes with level, the idea being that sloshing is more likely with a low fuel level (I don't know for sure if that is the case with the LX, though - this is just speculation).

At the track, you are perhaps using fuel much faster than anticipated, and that's probably why you observed what you did with the gauge and scan tool.

There is typically some logic that allows the gauge to react quickly when filling the tank - it's usually a combination of seeing a quick but steady change in one direction (towards full, obviously), as well as watching for a cycle of the ignition key.

The EVIC allows a near-realtime reading of the left and right sensors, from what I've observed.

Hemi Family
02-24-2010, 01:04 AM
I guess I should have consulted the EVIC...next time!


http://www.lxforums.com/images/How_To/diag/kb_minLminR.jpg
19g = 19 gallon gas tank.
Since the gas tank is split into a left and right section that straddles the driveshaft, there are fuel quantity sensors on the left and right side.
LT: fuel quantity sensed in the left tank
RT: fuel quantity sensed in the right tank
AVG: an average of the total fuel quantity. This number is necessary for displaying proper fuel quantity on the gas gauge. See MinL & MinR discussion.
MINL and MINR: So far, the only sensible theory focuses around this excerpt from the service manual, pages 8J59 to 8J60:

MattRobertson
02-24-2010, 01:16 AM
At the track, you are perhaps using fuel much faster than anticipated, and that's probably why you observed what you did with the gauge and scan tool.Thats exactly what I was thinking.

The EVIC allows a near-realtime reading of the left and right sensors, from what I've observed.
I wonder if the DH has identified the right and left fuel PIDs. I don't think they have. Dammit. I don't have an EVIC. And that explains what Marc was talking about then.

crapcrapcrap. Oh well. I just run with more gasoline. Thats all.

BobCrespo
02-24-2010, 02:01 AM
Look at the bright side Matt fuel weight is very low in the chassis.
Just eat light on raceday.

Eric Bryant
02-24-2010, 11:12 AM
Oh well. I just run with more gasoline. Thats all.

Due to the crappy stock fuel tank in my Impala - it's basically a flat box with baffling that seems cleverly designed to keep fuel away from the pick-up - I've gotten very used to running with a nearly-full tank at the track. The car weighs 4348lbs with me in it and a half-tank, so another 60 lbs ain't gonna slow me down much.

hawkxp
02-24-2010, 12:41 PM
See, thats the especially weird part: Both of us were getting decreasing fuel readings that took MINUTES to stabilize. Not moments like you'd expect for sloshing fuel, and if its sloshing fuel, then as I said the available fuel will go UP and not down. Sloshing fuel will give you the opposite effect of what we saw when you make one critical assumption that I think we can take away from this (see below)..

Matt

Its possible the sensor is loose in the car. I was working on a car that had a similar complaint years (18+) ago, would be at 1/4 tank while driving "she swore" and run out of gas.

We dropped the tank and it turned out the mount for the sensors had cracked so when low, the reading was way way off...

Eric Bryant
02-24-2010, 05:17 PM
Its possible the sensor is loose in the car. I was working on a car that had a similar complaint years (18+) ago, would be at 1/4 tank while driving "she swore" and run out of gas.

We dropped the tank and it turned out the mount for the sensors had cracked so when low, the reading was way way off...

Fuel contamination can also result in "optimistic" gauges - at least in GM vehicles.

But considering Matt's description of the problem, where the indicated level slowly dropped to the actual level, I am not inclined to believe that a mechanical or electrical fault is to blame.

MattRobertson
02-28-2010, 04:49 PM
Its possible the sensor is loose in the car.
I'm with Eric on this given the behavior and that we can confirm this behavior on three cars on the same track (I'm counting Cam). However loose stuff is always a potential factor in road racing so I will check this angle out.

JOKERCANTSMOKE-EM
02-28-2010, 05:19 PM
when my RT says 0 MILES TO EMPTY I have still gone prob. close to 4 or 5 miles