QuestionI have a 99 chevy that makes a loud buzzing noise from the fule pump. When the key is turned on the fule pump stays on and will not stop making noise for approx 3 seconds after turned off. Is this normal?
I also have a 91 chevy that I gave to my brother when I got my 99. Last week he went through a large water puddle drove it home and now will not start. I changed the cap, roter and the fule filter. I pulled the TB apart(I admit, I do not know A thing about TB on these newer rigs). When turning the key to the on position I hear nothing from the fule pump. Unlike my 99. After reassembly of the TB, I was under the truck (flustered!) hitting the tank. Low and behold it started several times but then resumed its absence of egnition. I have checked all fuses that I could find. Are both of these trucks in need of new fule pumps?
AnswerHello Russ,
Your truck....the one that buzzes all the time. Lets do it first.
When the ignition key is turned to run, the fuel pump in the tank should come on, and pump for two, to three seconds.
If there is a signal that the engine is cranking, it will continue to run.
When oil pressure builds to above 4 PSI, it will also recieve power from a switch in that circuit, and will continue to pump until the engine is shut off, AND the oil pressure drops to below 4 PSI.
So if the question is about it running after the truck is turned off, it would be the oil pressure switch, and I would say it is absolutely normal.
As to weather the buzzing is too loud, that could be caused by the bottom of the tank being bent, or for whatever reason, the pump touching the tank, or part of the tank assembly, and just resonating the noise, like if you lay a running electric razor on a counter.
But yes...it should run continuously.
You can connect a fuel pressure tester to it, and low pressure is an indicator of either a plugged filter, or a pump in need of service, but as long as the pressure is normal, meaning the engine is running fine under load, then it's a personal call if the noise is more than you want to live with.
Dropping the tank, or moving the bed back, is required to access the pump, and see if you can insulate it for noise.
The other truck, now....that one needs the pump accessed.
Believe it or not, on a regular pickup, if you don't live where there is a lot of rust, it is easier to move the bed.
Hitting the bottom of the tank is a test for a bad pump....doesn't always work, but if it does work, you can bet you will be in there before long.
You can replace just the pump....it isn't necessary to replace the complete tank unit, for which they want $300. or so. The pump can be bought at a parts house for about $80.
One thing I would like to suggest, though.
When you get the tank unit out, look at the wire connections where they are riveted to the inside of the tank unit. I have replaced a pump, only to have it act the same a few days later, and upon close inspection, found that the rivets for those wire connections were loose, and not making a good connection.
You can stick the pump into a bucket of clean DIESEL fuel, and use some jumper wires to a battery, and run the pump in the bucket.
If you connect to the connector outside the tank unit, you can wiggle those riveted connections and see if the pump slows down or stops. I soldered the connections on the one I had the problem with.
Use the diesel fuel because it won't explode like gasoline might if there is a spark, and the diesel fuel won't hurt the pump, or the engine if a tiny bit remains in it.
I assume you have checked the wire harness connector at the pump, and the GROUND wire that bolts to the frame just in front of the tank. Make sure it is clean and tight. If you live in the rust area, remove the ground wire, and make sure it is CLEAN and tight.
Van
