hitting/kicking fuel tank starts pump working

2002 Astro AWD 4.3 eighth letter of VIN is X

After shopping the vehicle would not start. It would crank just fine. Ever since we bught the vehicle the gas gauage has been sporaticly jumping from empty to the approximate gas level, and sometimes to a full reading. So I added some gas. It still would not start. A old fellow came by on his way in to the store, said he just retired from owning his own repair shop. After he kicked the bottom of the tank under the pump, the vehicle started. He said the pump was failling.

Is he pulling my leg? Or is this an old timers diagnostic trick when test equipment is unavailable?

This is a wonderful forum. I have received excellent help in the past and I thank all of you who pocess the skill and knowledge for your willingness to help the rest of us.

Actually, the "old fellow" is probably partially correct. The problem may not be the fuel pump itself, but the electrical connections to the pump (and the gauge sender). That particular series can suffer from poor connections at the exterior connector at the top of the in-tank unit, the interior connector at the same location, and the ground connection above the tank. The in-line connector above the tank and the connector closer to the front of the vehicle are usually reasonably reliable. The undervoltage and poor pump performance can result from the resistive connections at these points.

This is how the connectors overheat and fail:

http://mysite.verizon.net/strey/files/PumpConnector.jpg


The resistance created causes lower than normal voltage to the pump, resulting in inadequate fuel pressure to start and run the engine. The CPFI system requires a minimum of 61 PSIG to operate the injector poppets, although I've seen some barely start and run as low as 58 PSIG under just the right circumstances.

Unfortunately, the repair will still require removeal of the fuel tank to access the pump unit in the tank:

http://mysite.verizon.net/strey/files/AstroFuelTank.jpg

http://mysite.verizon.net/strey/files/AstroTankTopUnit.jpg

Also unfortunate, but just as true, is that the only good way to repair the connector is to replace it. I've tried repairing the connector alone, and ended up replacing the "repaired" connection and entire pump unit a year later with a new assembly. Even if the pump is intact (as mine was), the connector will never get better. The replacement in-tank units include a new pump, and a new level sending unit, which is why the "old fellow" remarked that the pump is failing (even thought it may not actually be the pump portion itself). The better replacements have a revised design electrical connection which does not suffer the resistive heating problem:

http://mysite.verizon.net/strey/files/InTankUnitNewB.jpg

Thank you Blue Bowtie, very much for your super informative posts. Not only to my questions, but also to many of the other threads I read here in this forum.

I don't know if a final/closing post is expected, but I just wanted to let you know I replaced the fuel pump with one that came with the wiring harness piece as illustrated in your photo. Everything works wonderfully now. No more bouncing/eratic fuel gauge either.