fuel pump problem & testing 1996 C1500

[markqc]

Had a problem with the fuel pump. Replaced twice at GM dealer within 15 months.(of course the warranty was only good for 12 months) What is the correct procedure for checking for a bad fuel pump and for fuel pressure? (before the fuel filter or after) In other words how would it be determined to be a fuel pump problem rather than a blockage?

Thanks
Mark

[RABarrett]

Simply, the method requires elimination. Checking before and after the filter simply eliminates the filter from the equation. If the pressure is low after the filter, check before the filter. If it is restricted, the pressure will rise to normal. My concern is that something may beoverlooked during assembly, including the pulsator, the oneway valve, or possibly electrical connections causing voltage drops in the system leading to misdiagnosis. Ray

[markqc]

Thanks for your reply Ray. My concern is misdiagnosis as you are suggesting. The dealer diagnosed the problem as the fuel pump, and I told them to go ahead and change it. (engine was running rough and sporadic, cutting in and out making the truck "buck") When they called me to pick it up they told me that they changed the filter as the fuel pressure reading was still showing a little low. Originally they said pressure was 5 lbs, after changing the fuel pump it was 33 lbs, and then they changed the filter and it was 38 lbs which is apparently normal. My concern is that maybe there could have been a temporary blockage in the filter causing the low pressure and they changed out a good fuel pump due to misdiagnosis. I requested to keep the old pump. Do you know a way of checking the old pump to see if it is ok?

Thanks,
Mark

[RABarrett]

The only way to check it is to duplicate its operating mode. This could become tedious as the only fluid that should be used for testing is fuel. It provides the necessary lubrication and insulating qualities necessary to protect the pump. Test for the correct volume of fuel delivered and the pressure at which it is delivered. The pulsator and oneway valve in the same assembly could also contribute to the problems you are encountering. It is also possible for the fuel you are using to add to the problem if the lubrication or insulating qualities are not appropriate for the pump used. I strongly recommend that the correct octane fuel be used from a name brand station that moves plenty of volume through its pumps. You can check these things by looking for the appropriate logo on the servicing truck, and it should be making frequent stops at the station from which you purchase. Ray

[markqc]

Ray,
Thanks for your input. I usually buy the higher octane gas (91) only from name brand stations. I never fill up when I see a tanker has just off loaded gas. Usually the octane ratings in the vehicle manual are listed as minimum. The manual usually states to use a higher octane fuel when you hear a "pinging" noise from the engine during acceleration. (I assume that the octane rating is 87 minimum for this vehicle but I will need to check the manual) What type of problems would occur when using the higher octane gasoline.
Thanks
Mark