In accordance with my post from yesterday, this afternoon I removed both fuel pumps and dissected the dead fuel pump I brought back from Beaver Run Motorsports Complex. The executive summary based upon my observations is as follows:
The main pump's final failure mode was the pea-sized blob of plastic coating that protected the solder bump that connected the positive lead from the in-tank fuel pump to the back of the in-tank fuel pump's screw fitting. The blob was sucked into the main pump and ground to tiny bits in the bearing of the main pump. Consequently the electric motor seized.
The in-tank FP is composed of two primary pieces - the pump itself and the screw fitting. The two pieces are connected by a roughly 1-inch length of fuel hose. The hose is held to the two pieces with two one-time-only hose clamps. In my case the hose had disintegrated at the clamp closest to the screw fitting. The positive lead from the in-tank pump to the screw fitting had broken free from the screw fitting. When I removed the in-tank pump pieces I assumed that the screwing-out process had broken the hose and broken the positive lead. But, that assumption was to be proven false. Next, I turned to disembowelment of the dead main pump. The outer metal sheath of the pump is crimped around the outlet end cap. Using a BFH, Big f'ing screwdriver and a small chisel I uncrimped the sheath and pulled out the guts of the pump. I confirmed my suspicion that the motor was seized on the spindle. (My suspicion was due to the last diagnostic test conducted at BRMC in which the main pump was drawing 12 amps directly from the battery while making no sound at all.)
I proceeded to dismantle the guts of the pump so as to get to the bearing. A couple of removed c-clips and four torx bolts allowed access to the bearing assembly in which I found lots of little bits of hard red plastic that exactly matched the color and consistency of the coating on the in-tank pump's remaining solder bump.
The hose connecting the in-tank pump to the screw fitting failed due
to the combination of a decade of deterioration and the pressure of
the crimp. The in-tank pump - held to the fitting only by the two thin
wires - then began moving around in the tank due to the sloshing of
fuel and general movement of the car. At some point the positive
lead's solder bump twisted loose. The bump proceeded to get sucked
into the main pump where it eventually found it's way into the bearing
race and got ground up against the five small roller bearings. Good
thing that the other wire was still attached or I'd have had to go
Not a too-bad way to spend an afternoon. Maybe I can put all that copper wiring to use. The hose connecting the two major bits of the in-tank pump will eventually break. Soon thereafter the main fuel pump will fail. Add the in-tank pump to the list of items that should be replaced prophylactically every 8 to 10 years.
-- David Chamberland
91 928GT (Amazonagrunmetallic: Green. NO! Blue! Ahhhhhhhhhhh!)
89 928GT (Black/Black - "Walt")
928 Owners Club Charter Member (http://www.928oc.org)