I have a 1990 L98 corvette, when the fuel tank is at half a tank. The car will bog down or act like it's getting starved of gas. If you turn the radio off you can hear the fuel pump screaming.
Know if I go to the gas station and fill up past , a half of tank or if I fill the tank. The car will not bogg down or act like the car isn't getting fuel. My question is ? Is it the fuel pump it's self or is it the little rubber thing in the pick up line/ diaphram.

 

Crank and run your engine and see what your fuel pressure is while running...then you need to check your fuel pressure when the engine is turned off...make sure that the pressure stays. If it drops like a rock...you can either have a problem in the fuel pump check valve, sending unit tubing or pulsator....or even leaking fuel injectors.

DUB

 

its the lil rubber thing.

The pulsator often gets loose or leaks and allows the system to get air or loose the tension when the tank gets low enough. This phenomenon is also caused by the PP windage tray in the tank bottom. As fuel sloshes around the pump sucks air.
I designed a "fix" for this issue that's been in several threads. Do a search and see if you can find a thread with the term "tank well" or pump-well. If I can C&P the text I'll send it pm asap...

that is, IF you are willing to go IN the tank to cure this issue.l

 

If u can find it, great. I'll look also

 

I bookmarked Lee's fix, so here ya go:

http://forums.corvetteforum.com/1583102051-post11.html

 

Thanks

 

I get the pulsator tomorrow . So hopefully it will cure the problem. It's a a/c delco, my parts manager found it for me. Wish me luck.

 

knowing the problem ONLY takes place at 1/2 tank, that does not say pulsator. The ONLY thing a bad pulsator can do is let some of the fuel pressure leak out of the pressure line and back into the tank...that's letting the pressure fall off but that would happen at ANY fuel level.

IF the pulsator were in the suction side of the pump (its not) THEN and ONLY then could it cause this problem....

its more likely that this is about windage. Fuel sloshing around and letting the pump suck air briefly. If it gets worse or happens more as the fuel level drops.....then you need to go to the well.

I am going to be doing some work in my tank as soon as I get a decent day, with semi human temps to work in, and I will take some pics for all those that have ask about this "fix" for the low fuel starvation problem that we all end up with sooner or later.

 

I double checked my theory and filled up this morning and it's still doing the same thing if the tank was half full. Also the fuel pump is very loud when at half a tank. It's gets a little quieter when u fill all the way up. Unfortunately this car is my daily driver.

 

Have you checked your fuel pressure as I wrote in post #2 ???
It can make a difference. Because the fuel system is pressurized...it does no make sense that the car runs fine of a full tank versus a half tank. Except for possibly the pump is getting hot and beginning to loose pressure. Usually a pump is either "good" or "bad". On very rare occasions I have seen the pressure drop when the pump gets hot.

DUB

 

well....in some cases, this is grasping, the pump strainer can clog up and starve the pump even with fuel covering the whole assy.

With MORE fuel and its weight, that equates to greater pressure on the strainer, that might be helping fuel to get thru the clogged strainer....as the level decreases the strainer can pull less and less fuel thru and THAT is the sound that you hear, a pump that's starving for fuel. The pump is at the bottom of the tank and it only takes maybe 1/4 tank to cover it. So at 1/2 tank its well under the fluid level. If its making noises and starving with 1/2 tank I would say the strainer is clogged and causing the problem.
That is exactly why I am going into mine this week. Its got a clogged strainer and does pretty much the same thing. But I know from the symptoms that its the strainer. It gets a new strainer and pump as the cure. Its died a couple times at idle and if I try to restart immediately, I hear the pump howl from being dry...even with a full tank of gas. If I wait 10 seconds the fuel seeps back thru the clogged strainer and it re-pressurizes again and starts and runs fine.

hearing the pump howl is the key to this diagnosis. A noisy pump is a dry pump. Its near silent when its submerged in gasoline.



BTW, a pump that runs dry more than an instant is a damaged pump and WILL fail;. the impeller is rubber or plastic and it MUST be wet when it operates for lube, otherwise the dry running burns it up...quick. If you can hear the pump, its not sucking fuel. I would BET that if there was a fuel pressure gauge attached you would see the needle bouncing around giving a clear indication that the pump is starving and running dry...even with half a tank.
as Dub says, do the pressure test. If the needle on the gauge bounces ANY, that shows pressure loss. The gauge needle should move around gently and smoothly, any flickering is telling you that the pump is starving and is dying.

 

Went into work today and changed the strainer, fuel pump and pulsator . The strainer on the fuel pump was loaded with crap and the strainer on the fuel pump was crapped up also. Once I replaced everything the car came alive. Thank you all who helped me.

 

Cool !

Glad to hear that you solved the mystery.

This really is fairly common. The strainer should be changed almost as a maint thing instead of waiting for a problem to develop. Its much less stressful to deal with it before it becomes a problem.
I think we ALL believe that some of the gas we buy is crap and loaded with trash. If your fuel FILTER down the line has junk it it, remember, all that trash had to go thru the strainer/screen first ! That should make you wonder how bad the strainer is ! ...and the poor pump has to chew that stuff as well if it made it as far as the filter.

Rule of thumb:

if you can HEAR your fuel pump when you have more than 1/4 tank of gas....then your pump & strainer need attention. Pumps should always be silent when submerged.

 

Food for thought, I'm a very happy camper.

 

You got to "LOVE IT" when a "plan" comes together.

I hope you (noticed them) and re-installed or replaced any of the small rubber "O" rings that were on the bolts that secure your sending unit to your fuel tank. IF not...I would highly advise it...along with a very small amount of anti-seize on these bolts also. Just a thought...because I service many fuel pumps and the previous tech who worked on it do not do either...and water gets under the head of the bolt and gets to the threads...and the bolts get rusted in..."snap-off" and ruin the fuel tank.

DUB