I have read the prior thread on this but it was not ever resolved. I have a '93 SSE. When thfuel tank is at 1/2 it will stall at idle and will buck and miss at full throttle but as soon as you fill it up this stops. The stall at idle occures when the car is not even moving. I am sure the fuel guage is accurate because filling it back up agian takes betwwen 8 and 10 gallons.

I replaced the fuel filter and a running fuel pressure test shows normal pressure and it holds when engine is shut off. This should exclude a fuel pump but I am not convinced. During a time when the problem occures the fuel pressure is down.

What could cause the fuel pressure to drop if the tank is 1/2 full?

I have purchased a new pump and plan to put it in on thursday. What I want is ideas of what else to look for in the tank and fuel pump assembly while I have it appart for an answer as to why this is happening.

Good call. That'* the first thing I'd look for in that situation (but only becuase it happened to me once, and I'd forgotton about it until just now). You should have paid about 100 bucks for the pump.

I was thinking along those lines too. I actually got an entire assemby from a wrecked 93 with 13,000 miles on it. Its a chance I know but since I have on ly had this car for the last 10K and it has 170k on it I never know what I will find. Maybe someone replaced it once before and put the wrong pump in or broke the tube the pump connects to. Also the entire assemby only costed me $20.
Do you think its worth the risk putiing in a used low miles pump?

By the way I also took the engine and trans from that car. Got them both for a total of $300. Now I have spares!!!

I'd inspect that new assembly very carefully. The worst thing you can do with a car is not drive it. My car was garaged for 5 years, I bought it a year ago with VERY low miles, and I'm STILL fighting dry and cracked hoses, belts, etc.

That one from the wrecker could be worse than yours because it was sitting so long. I'd be tempted to power it up with a car battery and test it with water before you put it in. Make sure all the water is out before the install though! This will give you a general idea. Gasoline molecules are smaller than water, so it'* not a gaurantee, but it'll find anything obvious.

That or the Fuel Level Sensor module is starting to act up causing sporatic problems when under 1/2 full.

I got hold of a scope with an amp probe and gave a look at the fuel pump. I noticed a spot with no upward curve in the waveform that would seem to point to a bad armature on the pump. I replaced the pump with the used assembly I got out of that wrecked '93 and put it in on Saturday. The PSI on a runing test went up 5 lbs. to 40 and the car runs alot better. Also for the first time since I bought the car it will run with less that 1/2 tank. Problem resolved.

Way cool! Chalk another success story up. How did the old unit look? What about debris in the bottom of the tank? Did you get a look? Oh, and how long did this take you? I'd be curious if you learned any tricks we could post in Techinfo to make this easier. Our cars are getting older. More of us will see this soon. Makes me wonder if some of the other cars stumbling with low tanks may have the same problem.

Ok first I would sugest that anyone with the problem where the car stalls or stumbles with a low tank to test the fuel pump with a scope and amp probe. This will show you any signs of failure and also show you pump RPM. If you dont have access to this equipment go to a shop that has it and knows how to use it. Here is a link with more info on this. http://www.vetronix.com/pdf/masterte...rtech_tt_4.pdf

Next the trick I learned. First the entire car needs to be lifted. I did this by using ramps on the front and jackstands at the rear. Both rear tires shoud be removed for easier access to the fittings and clamps. Buy a fuel line tool from the parts store, mine costs $3.99 at Auto Zone and was worth every penny. Buy new fuel line clips while at the parts store, again $3.99. Use a floor jack to slowly lower the tank and to put it back in. There is a pesky wire that goes to the ABS sensor on the driver side, undo the connector on the passenger side and remove the clip holding the wire tight, this will give enough slack in the wire so it doesnt snag on the tank when its going back in. And remove the two hangers on the muffler so the exhaust hangs down several inches, just rest the muffler on a bucket. This allows room for the tank to clear the exhaust.

Emptying the tank is the tricky part. I only saw one way to do it and that is to remove the vent pipe on the filler and siphone from there. The total job was about 2.5 hours including smoke breaks (away from the car!!).[/url]