Karmakanix VW Audi Berkeley CA

Fuel Pump: Intermittent Failure

Gear case (3)Long ago last century, a fuel pump failure meant the car stopped and usually stayed stopped. If the tow truck driver kicked the fuel pump, it might start again. Not any more. The vast majority of the fuel pumps we replace at Karmakanix are because of intermittent failure, and for the pump just slowing down, not stopping. Usually, the customer reports that he just looses power on the road, sometimes the car stops, but restarts. Sometimes we will hear that the engine took several tries to get started. And when we scan the ECU, no diagnostic trouble code, or DTC, shows up. Most mechanics just tell you they cannot duplicate the problem, and just want to stop looking because they are worried more about their time than your safety. Most of the pumps we condemn are in cars running perfectly right in front of us, and most of them drive just fine, for a few miles. Or a hundred miles. Here’s how we find the problem.

fuel pump  DSC07585 120x92A fuel pump, like most motors, starters, etc., has an electric signal. We can see the failure happening by graphing the signal. When we do the math, the armature speed is too low. Normal rpm for a decent fuel pump is around 5400 rpm. We find usually 4200 to 4500 when the fuel pump is in the process of failing. The signal often shows an uneven and jagged pattern. We replace the fuel pump before you can go out and get stranded again. Ever hear a story that good? Our techs at Karmakanix really are the best.

The modern pump of the Fuel Stratified Injection systems has a twist. It has a power control which shows up as a duty cycle on the sine wave of the amperage current. So it’s a wiggle on the squiggle, so to speak. But that does not slow us down. We just adjust the oscilloscope to a faster setting, and the same rules apply.

Gear case (3)