While I am still diagnosing the root cause of why my car is losing fuel pressure overnight, I have what appears to be a "separate" fuel issue.

I usually refill my tank when I get down to between 1/4 and 1/2 tank on the gauge and it usually takes about 11 gallons to fill up.

A few weeks ago, I completely ran out of gas for the first time while driving down the highway, but the fuel gauge still showed I had 1/4 tank (no codes). Had the car towed home because I did not think it was a fuel issue (based on the gauge and the tow truck charged more to deliver gas than to tow the car 6 blocks).

I finally picked up 1.5 gallons of gas in a gas can and added that to the suspected empty tank - car fired right up. Therefore, it is reasonable to at least assume that the left tank was completely dry when it shut down.

Tonight, I finally got the nerve to try and drive it to the gas station and fill up just to see how many gallons it would take (still just had about 1-1.5 gallons in tank and gauge showed just over 1/4 tank?). The car took right at 12-gallons to fill up (and the gas gauge now shows FULL).

So where is the missing tank capacity? Since it took at total of 13-14 gallons to fill up from completely empty, it the rest of the capacity maybe trapped in the right tank? If so, why is the right tank apparently still using some of it's capacity?

 

Your running out of fuel and taking 12 gallons of fuel to fill up would normally be a symptom of fuel not transferring from right tank to left tank.

The puzzler is that the PCM normally would drive the gauge to zero and throw a CEL and a code when this happens. I don't know why it wouldn't unless you have more than one thing wrong, such as bad jet pump and bad sender.

 

And checkout all the threads about the use of Techron to keep your sending units functional.

 

I use Techron every other tank fill-up - always have. Also use BG BK-44 once a year.

 

Yeah, but since it is taking on 13-14 gallons from the pump running dry in the left tank last night, it is like the jet pump must be working to empty at least half the right tank before shutting off?

Then again, maybe the Jet Pump just finally happened to clog half-way through transferring gas the last fill-up cycle and a few gallons were just trapped in the right tank? If that is the case, I am running solely off the left tank now and last night it just topped off the right tank and I no longer have access to it??? That may also explain why the gas gauge still showed 1/4 tank when I ran dry - there really may have been 1/4 tank trapped in the right side and the cause was right?

 

Techron is great stuff, but you don't HAVE to run it. In fact running it too much can damage the lining of your fuel tank. I would say no more than 5 bottles per oil change max is a good rule of thumb.

Seafoam is also a good product, and can be used to clean the fuel system by putting it in your gas tank. It also works as a fuel stabilizer if you don't drive the car very often. You can also put it in your crank case, but should change your oil soon after doing so. You can also feed it into your vacuum lines. This will really clean things out as evidenced by the thick smoke that you'll get coming out of your exhaust after doing this.

To the OP, the C5 holds a total of 19 gallons. If it only took 13-14 gallons, then I would say your fuel gauge is correct (you still had 1/4 tank left). It does seem unlikely that your pump would clog if you're using Techron every other fill up though. Good luck. I hope you're able to figure out the issue.

 

The car has 2 jet pumps. We are concerned with the passenger side jet pump. It seems strange that the car didnt trip the MIL. The pump orfice is extremely small. You take it apart and try to blow through it. Some cars had a recall because of plastic bits from the factory clogging the jet pump.

 

don37-- your explanation of the jet pump and it's small orfice getting plugged makes sense to my problem except I've been using Tehcron additive to every tank since I started having problems last year. Is there any other reason that you know of that the siphon pump wouldn't transfer all the fuel in the pass tank to the drivers tank? My issue is not being able to get a full load of fuel, or conversely it only takes 14 gals from being actual out-of-gas to full (overflowing). I've narrowed the fill issue as not being the filler hose or a backpressure issue; and it seems to be confirmed by the sensor voltage readings taken at 3/4, 1/2, and 1/4 gauge readings: respectfully primary tank at 1.9, 1.5, .7v and pass tank at 2.57, 1.8, 1.7v. Guage went to zero within 2 miles after taking these readings and was out-of-gas within a couple hundred yards.
There are not many shops around who will tackle this kind of work and since I'm on an island I don't have a lot of choices. The dealer didn't even have a technician who knew the vette had two tanks!!!. My go-to shop wants to drain and pull both tanks in order to diagnose problem. His estimate is $1500!! There has got to be a better way of narrowing the possibilities and your comments on the forum gave me some hope.
And wisdom you could pass on would be appreciated. jim

 

your voltages are dropping. this is correct if your car is 2008 or earlier. techron wont help clogged orfice on siphon jet pass side due to plastic bits. i physically reamed the orfice and couldnt get it clear. as a temp fix i built a siphone jet out of steel fuel line and a carburetor jet. if you search online u can find really fancy annodized orfice jets. my bet is to replace pass side pump assy and be done with your nightmare. which island?

 

don37:
Thanks for your quick reply.
Vette is 02 so your suggestion makes sense. So I will focus on the pass tank. Actually, I pleased to narrow my areas of search as I already had the drivers pump replaced (twice-first time with aftermarket brand which failed in less than 6 months) with a Delco OEM. What a rabbit hole that was!!
Maybe a bit more help? The replacement pumps are no longer made. Tried an aftermarket brand (the only one I could find) and they sent me the 03 late version (didn't have the 99-03 version) and it is not interchangeable due to the different flange configuration and welded metal components. The only parts which would swap are the electrical innards. That was another one of the rabbit holes!
So reaming out may be my only option.
But you referred to an orfice that is anodized and might be available online. How would I search for such a unique item? Any suggestion might help. I tried being specific and got nothing back.
Again, thanks for your prompt feedback. You have been most helpful.
BTW: my problem is partly because I'm on Maui and there are virtually no vette skilled techs here!
Thanks, jim

 

kihei akahi grade 7 xmas break 1982 ish! still there? give me an hour and i will pm you a drop box link with info/pics

 

Don37: for pm you need my email right? Not sure how you get that that unless I publish it here. Jim

 

Don37:
Couldn't figure out how to respond to your pm. Kept going in circles.
Anyway, been down the backorder issue in past. In fact with a dealer in Canada. Problem is that part has been discontinued even though it doesn't show such on some dealers inventory lists. Had confirmation from at least a dozen sources.
really appreciate your efforts to help.
If you can recall where you might have seen the nozzles (assuming they are replaceable) please let me know. Otherwise I'm going to try your reaming repair and a clean flush of system.
Thanks again. jim

 

In West Texas they want $1,500 just to swap out the fuel pumping the left tank! So I will have to do it myself.

What 3rd Party fuel pump failed you? Delphi?

 

radium engineering. pm sent

 

easy answer. the bottom jet pump unclips. simply replace with the guts of a c6 jet pump.

 

Yes, Delphi. Searched all around US and Canada until I found a Delco in stock.

 

Now that makes sense if they are the same mechanically. Even could go back to company that Herko who sells 03 late units that I bought and sent back as the mechanic couldn't figure out what needed to be fixed.