I am the owner of an Auto Repair Facility and we have a 99 626 2.5 V-6 that had a hard start problem every morning. We found that fuel pressure was bleeding off very rapidly after engine was shut off. We blocked off the return line to isolate the pump and to take the regulator out of the equation. The pressure still bled off very rapidly. At that point I ordered a new Delphi pump from World Pack and installed it along with a new strainer. After starting the engine a loud hum could be heard inside the car. We checked all lines to make sure they were not contacting the body of the car. We installed a new filter and also check the lines for blockage.The regulator does not have any fuel coming out of the vacumn port and the pressure rises as it should at WOT.The next step was to obtain another pump but we still have the noise even with a different pump. I guess my next step is to order a pump from the Mazda Dealer and try it. The onlything is that at this point I am having a hard time believing that the pump is the culprit since 2 different pumps were tried. What if the dealer pump does the same thing. Can you shed any light on this problem.
Thanks, Duke

 

Have not been very happy with aftermarket pump performance in the past so only use OE. Have had some aftermarket pumps that were noisy for two reasons. Crappy build and new pump was slightly longer than the OE which allowed the bottom of the pump/screen to contact the bottom of the fuel tank resulting in vibration transfer which made a horrendous amount of noise when pump was running. The only other problem I have seen with pump noise being transfered into the car was when a customer installed pump one screw off of where it should have been and the pump body was contacting the slosh bin. Rotating the pump back to where it should have been solved the pump noise concern. Hope this helps. Your diagnosis of the original problem sounded to be very through and accurate.

 

Have not been very happy with aftermarket pump performance in the past so only use OE. Have had some aftermarket pumps that were noisy for two reasons. Crappy build and new pump was slightly longer than the OE which allowed the bottom of the pump/screen to contact the bottom of the fuel tank resulting in vibration transfer which made a horrendous amount of noise when pump was running. The only other problem I have seen with pump noise being transfered into the car was when a customer installed pump one screw off of where it should have been and the pump body was contacting the slosh bin. Rotating the pump back to where it should have been solved the pump noise concern. Hope this helps. Your diagnosis of the original problem sounded to be very through and accurate.

 

Yes, I thought of the pump possibly hiiting something inside but it is not so I guess I will install yhe OE part and get back to the forum with the results. Thanks for your input.
Duke