At what point does your fuel slosh to the back of the tank during hard acceleration?

It seems as though when I reach four bars it gets iffy, at three bars forget it, might as well hit the gas station because I'll get embarrassed on the street running out of fuel during a hard first gear run.

The first time this happened I thought something went wrong with the car, then realized it never did it on a full tank. So it has to be fuel slosh.

 

From what I understand -- just about everyone has this problem. And I know my guage isn't great either (same with everyone else too). When I have a half tank it shows full on the gauge and drops like a rock from there.... But for me I can have as many as 5 bars showing and have WOT problems...

 

I get worried anywhere near a 1/4 tank

 

And its no better in an extended high speed turn. It falls flat on its face halfway through the turn and you can forget accelerating out.

I'm like AGENT, at 1/4 tank, I'm done with the fun.

 

Happened to me the other day with 1 bar under half a tank. Left hand hard accel seems to be the worst for me.

 

Mine only did this once and it was on the reserve level! But it is always recommended to not let any fuel injected vehicle to get below a 1/4 tank of gas so it wont suck off the bottom and perhaps get some by products past the filter system!

Thanks,Matt

 

If you get that low on fuel this wont help you, but at least you will know where you are before you get there.

Tired of not having the gas gauge drop as you use gas. The inaccuracy was to much for me to stand so I investigated the problem. According to specs the float unit has a range of 0 to 90 ohms. I measured 20 to 110 ohms on my float unit. The 20 ohms representing the empty end and the 110 representing the full side (most other cars the low represented full but in the digital world they can do what the want).

The basic problem is the resistance doesn't not drop fast enough as gas is removed from the tank. I had to move the float arm to the 65 ohm point before it would indicate a one bar drop on the gas gauge. 75 to 110 ohms read full. It was not before I got down to about 37 ohms that I got a half tank indication on gauge. In reality the float resistance range is not properly matched to the electronics in the CCM. How to fix properly, you can’t unless you rewind the float wires (I don’t think so). So the best you can do (rather than redesign CCM) is to compensate for the problem. Make the resistance read lower faster as gas is burned. I added a 180 ohm resistor (yours might me slightly different) across the float unit, this will accomplish this. To little resistance and you will not get a full reading, to much and you are giving away accuracy which you a targeting in on. If I really really fill my tank I can get a full indication, if I let it click once or twice I might get a one bar down. I’m on the edge and I can live with that. But I do get more accurate readings right down to ¼ tank. Its not perfect, but I’m within 2 gallons or less when I get gas.

All you need to do is to add the resistor across the tank wiring. You do not need to take out the tank unit. Just remove the gas door and the rubber boot. Come back 6 inches or so from the tank unit and skin back the black and purple wires. I did not cut the wires, just removed about ¼ inch of insulation, wound the resistor ends around each wire and tape it up. I don’t think I soldered mine because I was not sure of the resistor I wanted to use and how the whole thing was going to work out so wanted the option of removing it easy. So temporary became permanent 2 years ago. Hope this can be of use to some of you.

P.S. - There are 3 wires. Black is ground and gray is power for the pump and the purple wire is the float unit.

 

I read somewhere that the ZR-1 tank has better baffling, can anyone confirm? Could I just swap in a ZR-1 tank w/o any problems? Otherwise, I've talked to a couple guys about cutting my tank open and adding some baffles. I'm not sticking foam or anything in there though.

 

I'm surprised your car loses pickup at 4 bars. With my car I try to get to the drag strip with 4 bars showing for less weight, and I never am starved during a run. Even launching with drag radials I'm OK at 4 bars.

OTOH, one event only, just one trip to Capitol and only in the left lane, I had the car bogging in 1st gear after it hooked. Maybe that was fuel pickup.

 

In my track experience, if I do a run with four or fewer bars showing, I risk having the power cut out upon acceleration. Five or more bars: RACE ON!

 

I think each C4 is going to be a little different, and having a flimsy 'old tech' float and sending unit doesn't help establish any kind of consistency from car to car.
Of course, aftermarket fuel pumps or even just a replacement pump will affect sensitivity to actual fuel levels. My big Bosch pump doesn't use a 'sock' and is not installed the same way the stock type pump mounts, so around 1/4 tank I have to "play nice", or add 5+ gallons to the tank. Also, a higher VOLUME pump will suck more fuel, quicker, possibly starving itself before the excess/returning fuel can reach the suction point on the pump when the fuel level is getting low (or getting sloshed around).

 

Must be one of the fortunate ones, the guage on my 87 is very close to accurate.

 

I had this problem rounding corners with 4 bars or less before I changed the fuel pump. Wanting to never run lean spraying nitrous I replaced the stock pump with a Walbro 255lph pump and lo and behold, I can damn near run the tank dry and never feel any hesitation in corners or upon acceleration.

My stock pumps sock was black and kind of crinkled up. Maybe the new sock did more than the new pump....I dunno.

 

I have the same pump, did nothing for the problem in my case.

 

While we are on the subject of fuel pumps and gage readings...here is my problem. When I fill the tank or take a hard turn and get a 'full' reading, it sticks there. I have found that if I take the fuel door off and the boot out then remove the flange bolts and lift the pump/float assembly and shake it it will give me an accurate reading...until I fill the tank again. If I don't completely fill the tank I don't have any problems.

Thanks for any help anyone can give me.

John

 

allt4, i think i sent you a pm, check it.......i have a fix that may work for you. i have done it and works like a champ.....