IM having weird problems with my fuel pump. I installed a Walbro 255 lph pump a few months ago so I hope its not going bad. At times when its running I can hear the pump skip a beat almost stop and start (at least the whine does). The rpms at idle when it does this will drop down and almost stall. I can hear it insync with the pump stalling. I happened to have my scanner on the fuel pump votage at the time it did this and you could see it drop from 13.4 to 12.5 volts. The 12.5 and could have been more i just happened to skip by it while monitoring the scanner. Also just recently twice the car will get really hot and then cool back down as quickly as it started. I checked the plugs and it looks like IM running lean when it does this. Everything in the cooling system is good, never had any cooling problems till lately.

I checked the fuel pressure with the gage to the window before it started doing this (a few weeks back)and pressure seemed fine. The car is stumbling and bucking under part throttle but wot throttle seems fine.

Could the computer be bad causing the pump to loose voltage? I did have the wire from the O2 sensor ground out on the header at one time.

Any thoughts or comments would be helpful, before it start swapping out parts.

 

When I went to a carb I pulled the pump out of the tank and put a holley pump outside the tank. I have the Pump wired to the stock wires. Every once and awhile it will die down Much like you described. I couldent hear the Old fuel pump in the tank but it probably did the same thing. I would guess it happens in a lot of our cars we just hear it when the pump is in the tank.
What causes it?

 

do you have a larger electrical load when this occurs?? like A/C, subs, or electric secondary fan?? Just an idea. Also, how hot does it get before it starts to cool?

 

I have a 1990 IROC 5.7 TPI that seems to be experiencing the same thing. I have not tested voltage. but. after long period of driving, could hear the pump start, spool up for a few seconds, then stop. It would repeat this cycle and the idle would correspondingly rise and fall with the pump running and stopping.

After towing it home, it now idles, but I have not had time to work on it. I let it idle for about an hour and no sign of the original problem.

Can you please let me know if you figure yours out? This is the 3rd fuel pump I put in over about 2 years (Napa replacements). If I resort to changing it out a fourth time, I am going to try the Walbro. Car is stock, but what the heck - it may not stay that way.
thanks & merrry Christmas