Manual Fuel Pump Test
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Senior User
Joined: May 2010
Posts: 350
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From: Spartanburg, SC
Manual Fuel Pump Test
I just replaced the tank (Advanced Auto), sending unit (LMC), and fuel pump (Advanced Auto) in my 300 4x4 with manual transmission. Now the truck runs like crap. It acts like its missing at idle, does good at full throttle, but if you 1/3 throttle, it will begin bucking and missing. Could this be the new fuel pump? Is there a test to see if it is working properly?
Elder User
Joined: Aug 2010
Posts: 567
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From: Vancouver, WA
To test your fuel pump you will need to put a pressure gauge on it to see how much pressure it has and how long it holds the pressure. Did you replace the fuel filter too? Did you get all the hoses on the tank put back correctly?
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Senior User
Joined: May 2010
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From: Spartanburg, SC
Only two hoses, one going to the fuel pump and one for the vent. Both went back with no problems.
I did not replace the fuel filter. It was fairly new before the tank replacement. The reason for the tank replacement was because it was beginning to separate at the seams.
I did not replace the fuel filter. It was fairly new before the tank replacement. The reason for the tank replacement was because it was beginning to separate at the seams.
Elder User
Joined: Aug 2010
Posts: 567
Likes: 1
From: Vancouver, WA
A vacuum gauge is what to use, but I also test the pressure side to see if it holds the pressure needed. The pump is a pressure device, not a vacuum device and so the fuel systems works on needing constant pressure to meet demand. It's possible you are sucking air at one of your hose connections that you changed in the system. Make sure all connections are good and tight.
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Senior User
Joined: May 2010
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From: Spartanburg, SC
Well the way I tested it was to take it back to Advance Auto and tell them it was bad. They gave me another one and I just finished putting it on and still the same, no change. I'm going to get some di-electric grease and make sure the plug to the sending unit is connect really good. The only other option is to change out the sending unit with the one out of the old tank. Its rusted up pretty good, but I know it at least worked. The tests go on...
Cranky Old Guy
Joined: Mar 2008
Posts: 3,562
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From: Raphine, Virginia
Sending unit will not effect how the engine runs if you have replaced it. Only thing that go wrong with it is gauge won't work, or fuel sock on pickup tube is clogged. Doubt your new one is clogged since you replaced the fuel tank.
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Postmaster
Joined: Dec 2006
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From: Spokane, WA
Small hint...don't buy the dialectic grease. Next time you are at the grocery store or a pharmacy buy a tube of petroleum jelly...the store brand is usually the cheapest. I use the stuff on everything electrical plus anywhere else a light grease is called for. Since it is recommended for the high corrosive environment of boats, it certainly is good enough for cars.
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Senior User
Joined: May 2010
Posts: 350
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From: Spartanburg, SC
Thanks Harte3, a little petroleum jelly on the connection and new fuel line from the front to the back.
Thanks to GFW1985, I was wondering about the sending unit. I guess, if the truck is running at all, the sending unit is working. I'm beginning to think I have a vacuum leak somewhere. From the manifold vacuum tree, I have:
1) a line running to the brake booster
2) a line running to the bottom connection of the PVC valve on the back of the valve cover (the top connection is has a rubber cap on it)
3) a line running to the firewall for the A/C
4) a line running from the top of the carb to the EGR valve
5) a line running from the bottom of the carb to the vacuum advance of the dizzy.
Am I missing something? Everything else is capped off. Could this be the culprit of it missing?
Thanks to GFW1985, I was wondering about the sending unit. I guess, if the truck is running at all, the sending unit is working. I'm beginning to think I have a vacuum leak somewhere. From the manifold vacuum tree, I have:
1) a line running to the brake booster
2) a line running to the bottom connection of the PVC valve on the back of the valve cover (the top connection is has a rubber cap on it)
3) a line running to the firewall for the A/C
4) a line running from the top of the carb to the EGR valve
5) a line running from the bottom of the carb to the vacuum advance of the dizzy.
Am I missing something? Everything else is capped off. Could this be the culprit of it missing?
Elder User
Joined: Jun 2010
Posts: 509
Likes: 4
From: Casper, Wyoming
Small hint...don't buy the dialectic grease. Next time you are at the grocery store or a pharmacy buy a tube of petroleum jelly...the store brand is usually the cheapest. I use the stuff on everything electrical plus anywhere else a light grease is called for. Since it is recommended for the high corrosive environment of boats, it certainly is good enough for cars.
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