I've had this sound coming from the backend of my blazer for quite a while. Any ideas on what is causing this? It runs fine and the whining is the same when in park and driving. I haven't been able to pinpoint it but it can be heard near the rearend. Thanks.


whine - YouTube

 

Sure sounds like the fuel pump to me. What year is your Blazer? 2 door or 4 door?

 

Sorry. 2002 LS 2 Door. And I had the fuel pump replaced 2 years ago.

 

Normally you can't hear the pump when the engine is running, if you installed a good brand of pump, (and there's only one of them ).

First things to check are fuel pressure, leakdown, and maximum pump output pressure.

 

Ok. I'm a newbie with little tech experience. I had the fuel pump replaced through a mechanic so unfortunately not sure what brand was installed. How do I go about checking the above measurements? Thanks!

 

At the rear of the intake manifold there are two steel fuel lines next to the distributor on the driver side. One of them has a service port for checking regulated fuel pressure and leakdown rate.



Most auto parts stores rent/sell fuel pressure testers. Connect the tester as indicated above. On your 2002 in the underhood fuse panel there is a vacant terminal:



Connect a fused jumper wire from the battery positive terminal to the pump prime terminal, this will activate the fuel pump. Fuel pressure must indicate 60psi to 66psi. Disconnect the jumper wire and the fuel pressure will drop. It must remain above 55psi for at least 10 minutes. Check this first and post your results.

Checking fuel pump maximum output pressure, and leakdown at the pump, requires some "creative plumbing" to attach the fuel line at the fuel filter to the fuel pressure tester.

 

And if this is reading outside of the recommended parameters then the pump may need replaced? If so, what brand/model should I look at purchasing?

 

If it fails one or both parts of the test, further testing is necessary to pinpoint the problem. AC Delco or Delphi pump only if it needs replacement.