Got this strange thing going on after I installed my AAM fuel system and had the car tuned the following day. Well it might not be that strange, I thought it was strange that I got a hole in my P/S line, but apparently that is quite common.

Anyway, it seems that my car reads the gas quasi-normally when I am driving normal, but then when I drive hard (i.e. acceleration and corners) the needle goes up like 1/4 of a tank or so. Then over the next few miles of normal driving or few minutes of idling stopped, it will go back to close to where it should be. I have only been driving it for about 2 weeks with the new fuel system and I went back inside the fuel tank and the floater moves freely. I just can't figure out what this could be. Any ideas?

 

The floater might have not gone back right or gotten damaged during the reinstall of the pump assembly.

 

With the driveshaft tunnel in these cars it means that the tank has a dividing hump in the middle of the tank. There are 2 sensors in the tank....one on each side of the hump. The ecu takes readings from each side, averages the fuel levels, and relays this to the gauge. The pump assembly has a siphon feature which draws fuel from the passenger side of the tank...over the hump...and into the passenger side so both sides remain essentially equal. Under hard cornering and acceleration you may have some sloshing from one side to the other which is throwing off the readings from one of the sensors. As ths siphon returns the balance to normal the gauge will come back to normal.

 

Thanks for the explanation. I just thought it was weird that it never did this before the fuel system install and now it does. I guess I shouldn't be worried then.

 

Well the return system alters the siphon system slightly by plugging the stock regulator.....so the dynamics of the system have been changed somewhat.

 

Yea, I guess the main reason for my concern was that it said I had 1/4 tank of gas one day driving to work and the car started to die on the interstate and I pulled into a gas station and it died as i reached the pump. Put a little in and it was fine. This is my first tank of gas after rechecking the fuel pump assembly since then so I guess we will see what happens. I'm watching my miles and know about what I should get.

 

Is this an old AAM kit or newer, I thought there was an issue that if something was not done withthe syphoning portion the AAM would run out of gas as it would not pump from the other side of the tank and that why phunk came out with his correction kit.

 

Yes, Charles did a great post explaining this with pictures and all - but I can't find it yet

 

It should be newer. AAM mailed it to me about 3 weeks ago. If I got the old syphon part of the kit, that will be sehr gay.

 

You have the newer kit. You might want to double check the seating of the FPR plug, and make sure the spacer and o-ring are secure. If the siphon action is deminshed, they your tank will run dry at 1/4 level. AAM address that issues several months ago, back when Charle's first surfaced it.

I recently had the unfortunate experience...of running my tank complete dry the other day...and it was well below the final hash mark, so I can confirm that the siphon does work. Funny how fast the fuel is consumed when you drive like an animal. I got just 11mpg on that last tank....wooho! Freeway cruising, I get about 22mpg.

 

Looks like the fuel pump assembly is coming out again then to check that the plug is seated properly. Probably wait a bit for that though, so much work over the past 3 weeks its been rediculous.

 

This is not a knock on AAM or any other product but

You always read about how people are gushing about an aftermarket mod but there are always minor "annoyances" that go wrong and what not or stuff we have to live with by being on the cutting edge.. These things people hardly mention in posts

It's something the newbie never really reads about when they want to know if it's worth it to "turbo" your car..

Some observations from my return fuel system w/injectors:

1. The stock trip computer is no longer useful for estimating mileage or gas consumption .. i filled it a half tank the other day and it said my effective range was 444 miles and my current MPG is around 23 haha i wish... but who cares.. i can live with that..

2. My gas gauge seems never reach the Full line anymore.. it's always a hair off.. and sometimes when it reaches 1/4 tank left it stays there for an ungodly amount of time and then drops like a rock to "E" ...but only sometimes LOL.. oh well, the gauge gives me a close enough estimate..

3. When I fill it more than 3/4 tank, the car smells like gas.. changed the gasket in rear 2x.. epoxy the lines on top... still smells like gas.. no matter.. easy workaround: drive it below 3/4 tank or don't fill all the way up and I'm fine.. the car is faster with less gas anyways

4. SES light for gas vapor problem comes on sometimes.. BAH.. just reset with Digimoto and I'm good for another 2 weeks actually is hasn't popped up in about a month now so it fixed itself haha

--mike

 

^^^mostly ture^^^ When we start modding cars aggresively, its unreasonable to think they will run and behave like they are bone stock. You can get them close, but there are always little things that you just have to deal with, as the car is making double or even triple it's intended power.

The mileage computer is inaccurate now, becuase of the larger injectors, and your scaling, and really has nothing to do with the fuel system.

The fuel gauge should operate normally, as long as the float wasnt bent even slightly, upon re-insertion. You also want to make sure its not binding on anything.

The fuel vapor...this is a tricky one. The vapor is coming from the return fitting hole. If the hole is drilled too big, some vapor will seep through. You can try putting a couple of o-rings, and larger flat washer on the inside of the assembly, and that will likely give it the stability it needs to be vapor free at all times. The ones that CP Racing and me install do not leak..or smell vapor at all.

 

As far as the gas mileage on the computer is concerned, can't we just simply multiply the number on that computer by how much bigger the new injectors are? So 280-440 would be 63.6% larger so you take your mpg, take mine on the highway for instance ~38 and multiply it by .636 and you get 24.2mpg, which is about what I get on the highway. I think this should work at least.

For fast conversions I usually just cut the number in half and add 10 percent or so, so 38 would compute to about 23 (close just not exact).

 

There is a ton of epoxy on top of the return fuel line.. so I don't think that's leaking... plus it only smells like gas vapor when my tank is nearly full.. so I have a feeling it's the o-ring gasket on the pump housing.. it's just not fitting right some how, some gas is sloshing around and getting out..... BTW, when i went to nissan to get a new gasket, they told me there were two diffeent versions if the gasket.. one for 2003 and one for 2004+.. They said one was round and the other was sorta flatter.. I opted for the 2004+ (because I have an 04).. but maybe I should have opted for an 03 because I have an EARLY 04.. which was still mostly 03-ish LOL.

--mike

 

When done completely correct, there should be no sacrafices at all in the OEMness perception from the drivers seat.

**except** a tad bit of inconsistency in the fuel gauge is common if you watch it like a hawk. This is because once you install a walbro 255 pump and have a CJM, AAM (later version with correction kit) or APS fuel system in the car, the siphon jet is hardcore over run by an intense increase of return fuel thru the assembly. This will cause the drivers side saddle of the tank to run dry while the passenger side has yet go down.

I believe this is what causes a little action by the fuel gauge because it probably was not calibrated for such extreme level differences from one side to the other, because stock it would TYPICALLY stay pretty level between the 2 sides... depending on your habits of filling the tank (running almost empty and then not put in more than a few gallons for example would only end up filling one side of the tank.

its quite interesting the dynamics that are going on in our damn fuel tanks, and its really a huge pain in the *** when it comes to trying to get proper function of everything while increasing the flow.

The good news is that even if the gauge tends to move a little here or there, you still HAVE a gauge and the car will not completely run out of gas before the gauge starts getting very near the bottom... once again assuming you are properly routing return fuel thru the assembly via CJM, AAM, or APS fuel systems. I dont know if anyone else makes any and if they do if they are making it right... but what most of us have is all good.

Oh I forgot about the mileage meter thing... I am the last person to care about gas mileage in my own car... but IIRC some of my customers have told me that the mileage meter is completely out of wack after fuel system installs... I am not sure if thats the case or not.

If your getting vapor smell... you have a leak. The first place I would check is the top of the gas pump assembly where your return line goes on. Fill your tank ALL THE WAY and check there. Most installations will require a little epoxy such as JB weld around the top of the bulkhead to seal. Getting the bulkhead to seal on the plastic pump assembly is hard... and I think more cases then not it doesnt. Personally I dont even give it a chance, I epoxy it the moment I install the return line bulkhead when doing these installs. JB weld WILL hold up to gasoline, as I tested it myself when R&Ding the kit by putting a large bit of it inside the tank on the drivers side. I pulled it out a year later to find it had BARELY become soft at all, and this was completely submerged..