# ECO m6 tank size mod, has anyone done it the right way yet?



## blackonblack (Feb 22, 2013)

I also am very interested in the answer to this question - I have read that both fuel pump and sending unit are different.


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## firehawk618 (Feb 24, 2013)

blackonblack said:


> I also am very interested in the answer to this question - I have read that both fuel pump and sending unit are different.



Welp, we're going to soon find out if it's just the fuel pump module or not.

I looked high and low and cannot find a single person who's posted their success in getting the capacity with factory parts.

I saw a post somewhere that a person drilled holes and modded the vent, basically ruining their evap system. No thanks.

I bit the bullet and ordered a fuel pump module out of a 2012 Eco Auto trans that has only 1k miles then was totaled. 

I did lots of looking at pictures and part numbers. The tanks are listed as different, sending unit is different and the fuel pump module is different.

From the pictures of the fuel pump module I can clearly see a difference in the vent at the top of it. No question those are different.

I'm just hoping the tanks aren't different enough to matter.

Does anyone know how to / where the access is for the fuel pump on our cars is?

PLEASE tell me there's an access and I won't have to pull the tank out!

I will post updates with pictures when I get the part here.


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## firehawk618 (Feb 24, 2013)

Here's the pictures I'm talking about.

13 Gal on top, 16 Gal on bottom. Notice the vent thingeymcboober on top.

Notice on the 13 Gal one that thing goes quite a bit farther down into the tank. Totally matches up with what others have said about the vent being blocked sooner by fuel on the smaller capacity tank.


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## H3LLON3ARTH (Dec 16, 2011)

How much is that part 
And do you have part number

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## firehawk618 (Feb 24, 2013)

I found one used with 1k miles for 50 bucks, complete assembly.
I don't want to quote part numbers. My reason is if I do that then someone orders the wrong one they'd be justified in blaming me for it.

I only saw 3 different modules. 1.8L cruze, 1.4L WITH 13 gal tank, and 1.4L without 13 gal tank.

I purchased the one from a 1.4L Eco with auto trans, 16Gal tank.



H3LLON3ARTH said:


> How much is that part
> And do you have part number
> 
> Sent from my Droid using AutoGuide.Com Free App


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## firehawk618 (Feb 24, 2013)

What makes me nervous is the fact that they list 2 seperate part numbers for the fuel tank. 13Gal and not 13 gal. I know i've read a few threads that claimed the part numbers were the same but I can say with 100% confidence that I have found 2 different listings for tanks.

We will see.


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## obermd (Mar 3, 2012)

We have confirmed that the Fleet models have a smaller tank. I know that my ECO MT has the 15.6 gallon tank by having put 16 gallons into it.


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## XtremeRevolution (Jan 19, 2012)

Mike is right. The reason for the two gas tank part numbers is that one is used for fleet models and the other is used for consumer models. 

While I have not personally verified this, I am fairly certain that all consumer Cruzes use the same gas tank. 

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## H3LLON3ARTH (Dec 16, 2011)

Well whem I get back to wotk ill oreder a ltz. Pump

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## Erastimus (Feb 9, 2012)

Wow - DIY taken to the extreme. All I know is that I trust my DTE reading and system because it was designed by really smart engineers (like me) and software written by really smart computer programmers and when I fill up, it says I have about 470 miles to empty. That's a long way between fill ups!! I'm getting 39 mpg overall, so that tells me my tank is about 13 gallons. I'm not going to risk soaking myself in gasoline with a static spark causing me to immolate like a monk in an orange robe by messing around under the car at the fuel pump port on the tank. Be careful all you DIY extremers.


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## Maxzillian (Sep 16, 2012)

Pretty sure that this is less about trusting the DTE calculations and more about being able to toss another 2-3 gallons in the car. I don't know about you, but I personally don't enjoy pumping gas in my car. The less often I have to do it, the better.


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## H3LLON3ARTH (Dec 16, 2011)

Maxzillian said:


> Pretty sure that this is less about trusting the DTE calculations and more about being able to toss another 2-3 gallons in the car. I don't know about you, but I personally don't enjoy pumping gas in my car. The less often I have to do it, the better.


I don't likr having to sit at tge pummp for 15 min to get 500 miles out of my tank on trips


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## obermd (Mar 3, 2012)

I usually fill up once a week after driving 300-450 miles so the quick cut off doesn't bother me. However, I can understand the desire to get the other three gallons in, especially if you're someone who drives the extra 100+ miles each week. Artificially restricting the size of the tank was a stupid marketing move that actually costs GM money because now they have to stock a second fuel pump assembly.


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## firehawk618 (Feb 24, 2013)

Erastimus said:


> Wow - DIY taken to the extreme. All I know is that I trust my DTE reading and system because it was designed by really smart engineers (like me) and software written by really smart computer programmers and when I fill up, it says I have about 470 miles to empty. That's a long way between fill ups!! I'm getting 39 mpg overall, so that tells me my tank is about 13 gallons. I'm not going to risk soaking myself in gasoline with a static spark causing me to immolate like a monk in an orange robe by messing around under the car at the fuel pump port on the tank. Be careful all you DIY extremers.



I can appreciate what you're saying but to be honest, those SMART engineers should have gotten the bcm/ecm calibrated correctly with the Eco M6 cars. Me as well as thousands of others fill up and the gauge sits at 7/8 of a tank. Simple software remapping would solve this completely. I say bcm/ecm because I haven't been able to find a schematic for this car yet to study which commands readings on the gauge.

Worst thing that will happen with this mod is the gauge sits on full a long time before starting to come down. That's assuming the mapping in the ecm/bcm is actually different for a M6 ECO vs the rest of the Cruzes.

That being said, if the calibration is in fact different then the DTE will sit at whatever number it calculates for a full tank and just stay around there for a 100+miles until the sending unit drops enough to where the module starts to "see" the fuel level dropping. No big deal to me. DTE only matters when dropping below 1/2 a tank for most people.....right?

Replacing the fuel pump module IF there's an access port should be very easy. Just discharge any static buildup on a good ground AWAY from fuel vapors. Not much to it really.


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## DMC (Oct 22, 2012)

obermd said:


> I usually fill up once a week after driving 300-450 miles so the quick cut off doesn't bother me. However, I can understand the desire to get the other three gallons in, especially if you're someone who drives the extra 100+ miles each week. Artificially restricting the size of the tank was a stupid marketing move that actually costs GM money because now they have to stock a second fuel pump assembly.


I fall into this category. I drive to our office in Chicago a couple of times a week, 220 mile round trip from my house, or to clients in IL. I prefer to fill up at the gas station near my house, not to mention that gas is significantly cheaper in WI. As it is, I don't quite have enough range to make two full round trips. If I had a couple of extra gallons, I could fill up once a week and be done.


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## sciphi (Aug 26, 2011)

I must have broken my fuel sender's top range restriction. When I fill up with 10 gallons with ~2.5 gallons left in the tank, my fuel gauge will peg above the full mark and stay there for 10-15 miles. I also keep the pump on a slower speed. Otherwise it clicks off at 8 gallons or so, and the fuel gauge is well below the full mark. 

Sounds intriguing, and let us know if the fuel pump can come out through the back seat, or if the tank needs to be dropped. Pictures would be great!


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## firehawk618 (Feb 24, 2013)

I don't think there's any restriction. It's all mapping / coding in the bcm or ecm.
When I overfilled my car last night, the sloooooowwwww fill it pegged full.

I discovered that my car definitely knows it's only supposed to hold 12.6 gallons.

See the image below and do the math. 12.6

So, when I do the modification I am sure that my DTE will show whatever amount my mpg x 12.6 is for many many miles then start dropping. I"m perfectly fine with that.


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## CruzeTech (Mar 23, 2012)

I definitely hate my Eco gauge only going to 7/8 of a tank. I remember when I bought my 94 civic brand new. 124 miles before the gauge even moved off of full on a highway trip. Still got about 400 miles to the tank. 


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## obermd (Mar 3, 2012)

My ECO MT's guage also only went to 7/8 at the first click off. After I filled the entire tank, including the final three gallons, a couple of times it now reads "full" at 12.6 gallons.


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## CruzeTech (Mar 23, 2012)

I've never put the 15 gallons in it. Just don't have the patience. Although, I have had the DIC tell me I had 483 miles left when I filled 11.3 gallons. 


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## firehawk618 (Feb 24, 2013)

Last time I filled the car I sat there and made it take a full tank. 100+miles gauge hasn't moved from full. That's what i'm after. 
As stated earlier i'll post a few pics when I install the new fuel pump module.
I'm shocked no-one has done / tried it and posted their success / failure.


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## firehawk618 (Feb 24, 2013)

Those bastards at GM!
I found the online manual for the european cruze. To remove the fuel pump module you have to remove the tank from the car.

Why, WHY NOT PUT AN ACCESS!

Bright side: Brand new car, all will be clean and rust free for tank removal.


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## firehawk618 (Feb 24, 2013)

Here's a link I found to a downloadable manual for European Cruze's. 
It's better than nothing.

http://www.cruzetalk.com/forum/57-h...load-here-better-than-nothing.html#post174292


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## XtremeRevolution (Jan 19, 2012)

I said this before, and I'll say it again; as soon as someone figures out how to do this without a hack mod of some kind, I will be one of the first to follow. Please keep us posted on your progress.


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## firehawk618 (Feb 24, 2013)

Definitely will do. I am all for it using only factory parts. If it works then awesome. If I fail then bummer. Either way I'll keep this thread updated.


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## H3LLON3ARTH (Dec 16, 2011)

I could not find an aftermarket pump I really don't wanna wait for a week from rock auto

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## firehawk618 (Feb 24, 2013)

H3LLON3ARTH said:


> I could not find an aftermarket pump I really don't wanna wait for a week from rock auto
> 
> Sent from AutoGuide.com Free App


Aftermarket pump? Why not just get the oem one? Ones with <1k miles can be had for cheap.


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## rpcraft (Jan 12, 2013)

This may have been discussed before but has anyone really stated what the purpose of putting a smaller tank in a high mpg rated car is? Is there some weird legislation that says car can only go xxx amount of miles if it gets over a certain MPG ratiing?? It' seems stupid as **** if you ask me......


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## Mick (Dec 31, 2011)

More gas = more weight = less mileage. Same reason spares aren't included.


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## spaycace (Feb 9, 2012)

firehawk618 said:


> I found one used with 1k miles for 50 bucks, complete assembly.
> I don't want to quote part numbers. My reason is if I do that then someone orders the wrong one they'd be justified in blaming me for it.
> 
> I only saw 3 different modules. 1.8L cruze, 1.4L WITH 13 gal tank, and 1.4L without 13 gal tank.
> ...


So ... you're trying to tell me (and everyone else reading this thread) that the Eco w/automatic transmission has the "16 gallon tank" fuel pump assembly, but the Eco w/manual transmission magically has the "13 gallon tank" fuel pump? I'm curious as to where you discovered this difference? Because by trickle filling my Eco w/manny tranny, I can get more than 13 gallons in the tank. I will be waiting to see if any of this works. If not, I'm thinking about heading to a junkyard to get the fuel tank/pump/filler neck from a wrecked LT w/1.4L and just swapping the whole **** thing!


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## spaycace (Feb 9, 2012)

Mick said:


> More gas = more weight = less mileage. Same reason spares aren't included.


I would agree with this on the spare tire note ... but fuel? REALLY GM!? I'm no genius, but I'm 99.999999% positive that as I drive, the weight of the fuel in my tank goes down to the tune of ~8 pounds every 38-48 miles driven; therefore, my MPG will not be affected like it would be carrying around an extra 20-25 pounds (i.e. spare tire) ALL the time. That extra 3 gallons of fuel would let a person who gets 42 mpg go 126 miles further on a tank, & that's one day's round trip to work and back for me! and when I go on real road trips, and get 47+ mpg, that's an extra 141 miles! The range on my Eco would go from 571 miles to 697 miles (at 42mpg) on a single tank of gas.

I completely understand the desire to increase mpg by decreasing "unnecessary" weight, but I don't think manipulating the fuel tank's capacity with a mechanical part inside was the brightest way to go.


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## sciphi (Aug 26, 2011)

GM dickered with the fuel tank capacity for city fuel economy and city CAFE ratings. Having to repeatedly accelerate an extra 30 lbs of gas for most of a tank until the tank's mostly empty does burn more fuel. Multiply that by 40-50k cars, and that's quite a bit of extra fuel burned to haul around extra fuel. Also, GM's been taking lumps ever since the Eco trim line was released about how it "makes no sense economically" to get one. We know that argument is hogwash. Having the same city rating on the Eco MT as the non-Eco Cruzes would have given some teeth to that argument. City fuel economy is all about weight, highway fuel economy is about aerodynamics and rolling resistance. 

It's long been established that the Eco MT has the same 15.6 gallon fuel tank as every other consumer-sold Cruze out there. We're now establishing just what changed so it only will hold 12.6 gallons before clicking off and not allowing more fuel in without a battle, and how to make the Eco MT use all that tank capacity if desired.


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## obermd (Mar 3, 2012)

Well said sciphi. :sigh:


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## cronyjabrony (Aug 10, 2012)

Well I would welcome the extra capacity, as wouldn't that extend my range?


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## OnlyTaurus (Mar 20, 2012)

Yeah it would, but you're also adding weight to your load. Not much, but it'd be there.

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## cronyjabrony (Aug 10, 2012)

no different than carrying passengers?


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## obermd (Mar 3, 2012)

Frankly, adding the weight of a spare tire to my ECO MT hasn't impacted my overall fuel economy at all. Winter driving has dropped me from 42.3 to 42.1. I have actually seen less of an impact with my ECO MT than I would have expected. The real issue is how the EPA tests for fuel economy and then adjusts for the weight of the car. Because of this GM had to lighten the ECO MT to keep the all important combined average as high as possible, even though it appears most people who have purchased this car predominately drive it on the highway where the highway MPG is far more important to the overall fuel economy.


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## spacedout (Dec 7, 2010)

cronyjabrony said:


> Well I would welcome the extra capacity, as wouldn't that extend my range?


Yes it will increase your range. A 1LT that has the 15.6gallon tank & gets 38highway, low fuel warning comes on at 2.5gallons. Filling it 13.1 gallons thats 497.8miles. If the eco has the same 2.5gallon reserve its the low fuel warning would come on at 10.1 used. 10.1gallons X 42mpg is 424.2 miles. 

In short even though the eco manual gets 42mpg highway(4mpg higher) becuase if less fuel capacity it has 73.6miles less range.


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## tecollins1 (Nov 6, 2011)

With all the cld tiles i have (35-40) and the tank like subwoofer box 2 amps and IDMAX 
That I have I'm still seeing 30mpg city (mph rating is 23mph avg per tank)

3 xtra gal isn't going to matter 

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## obermd (Mar 3, 2012)

spacedout said:


> Yes it will increase your range. A 1LT that has the 15.6gallon tank & gets 38highway, low fuel warning comes on at 2.5gallons. Filling it 13.1 gallons thats 497.8miles. If the eco has the same 2.5gallon reserve its the low fuel warning would come on at 10.1 used. 10.1gallons X 42mpg is 424.2 miles.
> 
> In short even though the eco manual gets 42mpg highway(4mpg higher) becuase if less fuel capacity it has 73.6miles less range.


Based on the EPA estimates, you are correct. Based on what I've seen on the road, the ECO MT has the longest range of any Cruze trims. This is because the ECO MT gets significantly better MPG than the EPA estimates until you get above 75 MPH. At that point, the other Cruze trims higher coefficient of drag has had a larger impact on MPGs than it has on the ECO MT.


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## sciphi (Aug 26, 2011)

You folks who are insisting that GM is silly for doing what they did on the Eco MT are ignoring CAFE and the EPA fuel economy tests. They don't actually measure fuel economy directly. They infer it via tailpipe emissions, and then run those numbers through a formula to come up with unadjusted EPA fuel economy numbers. Those numbers are then adjusted downward to reflect a "more realistic" estimate of how the car "ought" to do for an "average" driver. What GM did was figure out a way to make the car do better on the city part of the formula. 

In the real world, we know the Eco MT will routinely whip its fuel economy numbers silly, even when being driven quickly. GM probably figured this out during their road testing, and decided that the target market for the car wouldn't care about 3 extra gallons of gas when the car can realistically achieve well over 42 mpg. The car has a long enough range as it is. Besides, if it's really necessary filling the tank completely can be done. 

I'm still interested in seeing the results of this, so owners can modify their car to suit their wants/needs.


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## firehawk618 (Feb 24, 2013)

sciphi, I was in the group of WTF GM WHY???? But with your explanations it now makes sense why they did this. I had no idea that how it's done.

Ya know, if they'd calibrated the fuel sending unit to gauge properly it wouldn't be as big a deal to me "my wife" All she sees is I fill this car and it's ALREADY below full! All I see is spending 15 extra minutes at the pump so she's happy AND I'm all for an extra 100+ miles per tank.

Updates to come. Down to <3/4 of a tank, access to a lift lined up and part in ups's hands.


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## firehawk618 (Feb 24, 2013)

Fuel module is scheduled to be here tomorrow. If I don't end up working late tomorrow night I will be dropping the tank......


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## sciphi (Aug 26, 2011)

Glad I could help, and awaiting the outcome of your venture!


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## firehawk618 (Feb 24, 2013)

I have the replacement module in hand. It looks exactly like the one in the 2nd picture which is for the larger capacity. Heading to the shop to put her up on a lift and drop the tank now. Pics and results to come.


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## blackonblack (Feb 22, 2013)

Take lots of pics - many will be interested. Thanks for being the pioneer - I'll tackle about anything, but dropping the tank intimidates me.


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## firehawk618 (Feb 24, 2013)

Welp it's done. Worked perfectly. I want to punch the engineer who decided NOT to put an access portal in the car to get to the module but other than the pain of dropping the tank it went pretty easy.

This is how much fuel I had used since my last trickle fill, so the tank should have about 3 gallons left in it....










This is before work is started: 










Car up on the rack, some pics of the underside:





































Removing the tank itself isn't that hard after you remove all the underbody plastic stuffs. Those come off easy, lots of 10mm plastic fasteners. Unhook a few quick disconnect tubes, couple electrical connectors and the fuel filler tube. I disconnected the rear section of the exhaust because the pipe is going to interfere with lowering the tank. Disconnected both tank straps and bent them out of the way. They bend easy and bend back easy.

Here's the tank out of the car:




























Here's the ECO M6 sending unit next to the ECO A6 sending unit. Very obvious what's different here. Just like the ac delco pictures I linked many posts ago.





















Put it all back together and here's my fuel gauge with the new fuel pump module, as you can see the gauge reads exactly the same:












Straight to the gas station, this is pump full throttle after it shut off by itself:











After I took that pic I pulled the nozzle again, immediately cut off:











Here's the gauge after this fill up. Before this mod my gauge was below full after a fill up:


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## firehawk618 (Feb 24, 2013)

It sure looked like that vent piece would be replaceable IF gm sold it by itself.


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## obermd (Mar 3, 2012)

Closing this thread. Please refer to http://www.cruzetalk.com/forum/57-how-library/12035-how-15-6-gallons-into-eco-mt-tank.html.

Firehawk - thanks for doing this and settling the 12.6 gallon retail ECO MT tank size issue.


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