Fuel system diagnostic help.

[Doyt W. Echelberger]

A noisy fuel pump (yes, under the floor of the trunk) will be heard from 
inside the car. It is really loud and anyone can hear it within 50 feet.

I have an 87 5ktq, and when mine did similar power-loss tricks, I went nuts 
for a week trying to find the cause. Checked for vacuum leaks, ignition, 
plugs, loose wires, etc. The car would lose so much power that I would pull 
over to avoid being run down in traffic.

It turned out to be a failing oxygen sensor.  Replacing it totally fixed 
the problem.

When the oxygen sensor fails, it does so in an overly rich mixture mode, 
which makes the car burn fuel poorly and die.  I found that the car ran 
pretty well when I cracked the throttle wide open in second gear. The extra 
air leaned out the mixture for a moment, and the car surged ahead for about 
two seconds.  If yours does this also, you have a supporting piece of 
evidence pointing toward the oxygen sensor.

Your mechanic can test the oxygen sensor with a special instrument. It 
should be producing a particular frequency, and as the thing fails, that 
frequency moves toward zero. Mine worked for a few minutes when the engine 
was started, and then slowly fell off to zero.

Let me know how it turns out.

Doyt Echelberger

 >>>>>>>>>>>>>>>>>>
At 06:50 PM 12/22/00 -0800, you wrote:
>I replaced the cap and rotor.  I was just at the store to buy a spark plug
>socket.  I will hopefully replace the plugs tonight.  I can't hear the
>fuel pump.  It is located in the gas tank, right?
>
>- Marcus