MIKER

Short Version:
Ran car WAY too low on fuel.
Filled car at unfamiliar station with gas containing 10% ethanol. My regular station does not have a “10% ethanol” notification sticker on the pumps. I know that the ethanol is probably not an issue but may be worth mentioning since it is known to be somewhat corrosive.
Fuel gauge tripped off line within 30 miles.
Suspected corrosion on the fuel level sending units.
Poured a can of Sea Foam into tank and reset gauge (No Techron on shelf in my shop so I used what I had available…Sea Foam).
Gauge tripped a couple of more times while consuming this tank prior to running out of gas.
The drivers side fuel tank ran out of fuel. I was stranded in traffic. :o Passenger side tank still had fuel.
Filled up with gas knowing that my range is now limited to the capacity of drivers side tank.

ATTEMPTED DIAGNOSIS:
Obviously a problem with the fuel transfer system between tanks. If the fuel level sending unit within the drivers side tank registers a fuel level lower than the sending unit within the passengers side tank a code is set and the gauge is tripped off. By design, fuel in the passenger tank should be consumed first.

After researching the service manual and searching the Corvette Forum archives I suspected that either the small orifice located in the “Y” diverter for jet pump fuel supply was clogged with debris or that the jet pump itself was clogged with debris.

ATTEMPTED SOLUTION:
Disconnected the jet pump supply and return fuel lines from passenger tank.
Used compressed air to purge both lines and jet pump. (Gasoline running down to arm pits burns!!! )

So far everything seems to be functioning perfectly. Not having the fuel gauge trip off line within the first ~75 miles is promising. However, I have not consumed enough of fuel to be absolutely sure that the fuel from the passenger side tank is being transferred to the drivers side tank at a normal rate.
Hopefully the problem was just debris and I was able to remove it with compressed air. Time will tell.

Corvette Don

Maybe I did not see it but how does one side of the tank run out of gas while the ohter still is full? They are supposed to feed each other and be at the same level at all times...but I could be wrong

alini

The Electric fuel pump located in the left hand tank supplies the engine and the jet siphon pump in the right tank. The Jet siphon pump sucks fuel out of the right tank and puts in in the left...theoretically both tanks are supposed to stay even with each other.
Your theory of debris has merit, but the only way to know for sure is flushing the pump.

If you drove more then 75 miles already it should be good, the fuel gauge shuts down if there is a disparity between tanks, I think I remember reading 1 gallon difference, so in the first 2 gallons of gas you would have it shut down

MIKER

alini you summed it up nicely.

I'm not sure about this part though...
I'm under the impression that the left tank is continually topped off by the jet pump from the right tank. I do not understand how the tanks could remain balanced other than when the the fuel level is above the cross-over fill tube such as when you have just topped off the tanks at the gas station.
The right tank is continually being pumped to the left while the engine is running.

Please elaborate.


I had no idea how the fuel system on 2003 and older Corvettes worked prior to becoming stranded the other day.
After studying the service manual and reading on the forum I have a basic idea of how it works on my 2002 Vette. I hope that someone will correct me if my description is wrong. I'm certainly not solid on this but I believe it to work like this:

-Two tanks.
-Electric fuel pump in left tank.
-Non-mechanical "Jet Pump" in the right tank.

While the engine is running there is a continuous flow of fuel from the electric pump > to fuel rail > back to left tank. A small portion of fuel from this circuit is diverted through a "Y", that has a ~.050" orifice in it, to the Jet Pump located in tank on the right side.
The Jet Pump, which has no actual moving parts, uses this small portion of diverted fuel flow to move fuel back to the left tank using the venturi effect.

If this diverted flow of fuel used to "power" the "jet pump" becomes restricted by debris, fuel will no longer be transferred out of the right side tank.
When this happens your fuel capacity is basically cut in half.

The side effect of this problem is that your fuel gauge will become erratic or shut off (pegged EMPTY).
The computer expects to see the fuel level drop in the right hand tank before the left hand tank. Otherwise it will trip the gauge off and throw a code.
I can't help but suspect that problems with the fuel gauge have at times been mis-diagnosed as being corroded sending units thus needing the "Techron treatment" when in reality the fuel transfer from right to left is too slow or non-existent due to debris reducing or completely blocking flow to the jet pump.

The fuel system was revised for the 2003.5+ Corvettes. The previous discussion does not apply.

Any and all comments/corrections are welcomed. I would like a better understanding of my fuel system.

vettenuts

Any photo's? This may be good for an archive "just in case"

R Devil

My 98 has the same issue. I've delayed tearing into the fuel system for fear of a wild goose chase. My dealer offered to "look into it" for $1,400.
Not!

Please keep us informed on your progress.

Bill Curlee

MIKER

Your right on the money! Thats exactly how it works. My thoughts are, if there was crap in the siphon jet, its still in the tank and will sooner or later cause the same issue. You may want to consider cleaning the tank if it happens again.

Anyone who is having the fuel level gage drop to empty issue, really needs to treat the fuel system with Techron or Sea foam throughly before sinking tons of cash into level sensor replacement. Even if the chemical treatments don't work, you can remove the level sensors and clean them by hand.

I had to run multiple (X 3) cans of Techron through my system over a period of time before it fixed the problem. Once the problem was fixed once, I never had the issue again.

BC

bighank

I had a sending unit replaced at the dealer under warranty first time time guage went to zero with about 7/8 tank full. Lasted about 3 years then happened again. Now out of warranty I didn't relish taking the tanks down just to clean the sensors. Used both Techron and Seafoam and Chevron gas (with Techron in it). Now with the tanks TOPPED OFF I get only 15/16 full on the guage. It USED TO READ SUPERFULL... LIKE WAY PAST THE FULL MARK. Won't disassemble the beast unless I HAVE TO. BIGHANK

HP_Addict

I do not think the 02s have a fuel return from the fuel line. i thought te operation was;
drv fuel tank - elec fuel pump - fuel filter- fuel rail
another line runs from the fuel filter to pass tank-jet pump- drvr tank

And I agree if the Techron does not work, then pull the pump and sesnor out of the drv tank and clean it. You do not have to drop the tank to do this.

MIKER

HP_Addict, thanks for your input. I stand corrected.
Once the fuel leaves the filter/regulator on its way to the engine it does not return.

This picture shows the fuel filter/regulator in my 2002 Vette. I labeled it for visual reference.

bighank

How do you remove the sender and its long filter from the tank without removing the tank? BIGHANK

HP_Addict

The sender and pump will slide out the rear of the tank. See this link:

http://www.cajundude.com/racetronix.htm

alini

I do stand corrected the left tank does remain full, since the left pump runs anytime the car is key is on fuel will always be siphoning out of the right tank, so there can be a difference between the two.

MIKER

Everything appeared to function normally for the first couple tanks of fuel, after blowing out the lines, and then the gauge tripped again.

I drained the tanks and pulled the pump and sending units to inspect for debris, etc. Both tanks appeared to be very clean. Sure enough, the right tank had much more fuel than the left which shows that the “jet / siphon pump” system wasn’t functioning properly.
Basically I just inspected for debris and again blew the lines with compressed air in attempt to clear any possible obstructions and put it all back together.

At ~150 miles into consuming the next tank-full the fuel gauge tripped off yet again. That told me that the jet / siphon pump still wasn’t transferring fuel to the left tank.

Using the 2002 Corvette Service Manual, “Fuel System Diagnostics,” starting on page 6-887 I performed what tests I could with the tools I have available.
The fuel pressure and leak-down test checked out fine. However, I noticed that when I would vent the pressure, the discharged fuel appeared to be aerated within the clear tubing. I’m thinking that the bubbles were formed when the gas depressurized from 55 psi to atmosphere it boiled. Can someone elaborate on this or is my fuel line constantly full of bubbles???

I tested the fuel supply from the left tank that feeds the “jet siphon pump” in the right tank. The flow volume matched the 300 ml/10 seconds of pump run time as per instruction.

I tested the fuel return from the “jet siphon pump” to the left tank. Absolutely ZERO FLOW. So, I pulled the fuel sending unit siphon pump assembly out of the right tank to inspect for blockage. After removing the jet siphon pump from the whole sending unit assembly I found it VERY difficult to blow air through. I used a small piece of wire to clear the orifice of debris. It felt like something broke loose but I never actually saw the debris. It seemed a little easier to blow through the orifice but being such a tee-niny hole it is difficult to blow through even when clear of debris! Could the blockage have been sulfur buildup within the orifice?

I’ve put it all back together and filled the tanks up. I could pull the fuel return line from the jet pump to test for flow but I’ve had my fill of gasoline showers so I’ll just wait to see what happens after ~150 miles of driving. If it fails again, I’ll tear back into it.

I took a few pictures for future reference:

brucemoose2

Man, that sounds like a major pain in the butt. I hope you've got it fixed now... Don't give up!

Bill Curlee

Outstanding documentation and pictures! Your an asset to the FORUM! Your info will FOR SURE help others!!!!!!!

WELL DONE!!

BC

LoneStarFRC

The answer to the fuel level(s) remaining the same (or at least close to one another) is because: as fuel is being consumed by the engine (as supplied by the left tank) the left tank pump never stops pumping fuel to the right side tank. The elec pump in the left tank continually pumps to both places. Think of it as a continuous "re-circulating" process in which each tank is, in effect, trying to "supply" the other.

When fuel leaves the driver's side (via electric pump) the line travels upwards and then makes a "Y". One leg (containing a check valve after the "Y") goes to the fuel filter/pressure regulator (to supply the engine with fuel). The other leg goes to the right tank to provide pressurized fuel for the siphon jet to operate. While you are correct in that the fuel in the right side tank is being pumped only over to the left tank, the left side tank is also continually providing some of it's contents to the right tank while it also feeds the engine. (The return line from the filter/pressure regulator also returns fuel only to the left tank but this is inconsequential to the above described process.)

HTH,
Robert

palmer302

Huh, so when I fill up with gas w/ 2 nearly empty tanks, how does the gas go from the the gas station fuel pump to each tank? is there a Y there also? Can it get overfull?

Bill Curlee

Theres a cross over tube between the two tanks at the top. The fuel spills over from the drivers side tank when you get the tank near full.

BC

Bob CTS

Excellent information and great post, thanks for sharing your research.