Surging Fuel Pump...

[unclebilly]

So it's 90° here in Calgary today. On the way home from work, my car started doing something new...

The fuel pump in my car is typically quite loud (this is the 3rd pump I've had in there in 2 years of ownership) - none have quit but all have been loud.

On the way home, it was louder than ever and it was surging, every 3 seconds or so. Originally, this had no effect on the engine. I tried to leave an intersection and the car just about died. There was no power until the fuel pump surged again. A few stop lights later and it started to have a minor effect on the idle (similar to the surging you get from the car being too rich) and was maybe a second behind the surging of the pump.

It nearly died on me a few more times at stop signs before I got it home. The car was running at about 170° at the time.

Any ideas? I'm thinking bad fuel pressure regulator - where is this?

Why would the fuel pumps in my car be so darn loud? There was just over a quarter tank of fuel in the tank too.

[Jim Sims]

I can think of several things:

1.) Hard or worn rubber mounting bushings between the pump bracket and chassis.

2.) Cavitation (boiling on the low pressure or suction side) due to hot fuel; being down to 1/4 a tank or lower (depending on accuracy of fuel level gage) on a hot day makes this a definite possibility. The CIS system returns hot fuel from the engine to the tank gradually increasing the fuel temperature. Try filling up with cool gasoline and note if there is a change in the sound.

3.) Is there a possibility the connections to the return and supply fuel lines were swapped and you're pulling fuel through the smaller return line which also doesn't pass through the deaeration baffling in the fuel tank?

Cheers, Jim

[unclebilly]

Any other ideas?

[MURF]

pull of the tank output line and test for flow also check for rust and debris..sound like pump has to suck too hard to get the fuel...probably boiling out fuel tank needed

[unclebilly]

I looked in the tank last year expecting to see rust and debris but it was very clean - shiny steel everywhere.

I wonder if maybe the fuel and return lines are hooked up backwards - but would the car still run? It runs great except for this latest problem. I haven't driven the car since.

[unclebilly]

I will pull the line at the filter and try to back flush the system with air to see what happens.

[MURF]

do not backflush as you pu tit ..on a porsche the filter is after the fuel pump..you will damage the pump!!! you can blow out from the pump forewards but be sure to remove gas cap to relieve pressure..what i wanted you to do is remove fuel line from pump and run fuel into container and judge the fuel flow does it come out freely and fast enough..the bottom of tank has removable hex plug..we pull it to check tank condition

[unclebilly]

From when I've changed the pump (2 times) it flowed pretty nicely unless something new has gotten in there.

[unclebilly]

I kinda have a suspicion that my car has the wrong WUR installed - I haven't had it off recently but do plan to pull it verify the part number. The WUR was nearly new when I bought the car and the car has always had te warm start issue. As I mentioned, I've replaced the pump twice and have changed out the accumulator once. I've replaced a few injectors that looked suspect. I took the WUR apart last year and it was spotless inside, the resistance was 21 ohms across the terminals.

I've set the plate in the throttle body according to the Porsche CIS troubleshooting guide and can't find any vaccum leaks.

I'm wonder if the wrong WUR would have the pump trying to put out too much fuel pressure (loud pump) and would continue to cause poor warm starting. Just a thought. The previous owner's mechanic was quite a master in the trade...