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?

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?

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.

Actually, you need to use a vacuum gauge to check a fuel pump. Connect the gauge to the inlet of the pump and make sure you have 7 inches of vacuum. if you do, you're golden.

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.

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...

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.

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.

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?

No offense to the previous poster, but please don't do this. Petroleum jelly isn't even close to the same or as effective as dielectric grease. It burns, swells rubber, and wears off much faster that petroleum jelly. Leave the vaseline in the medicine cabinet and use dielectric grease for electrical connections; you'll be happy you did one day. I dunno WHO reccommends it for boats, but I'll bet no automaker does.

Thanks guys. Wyo, I ended up going to the parts store and picking up a tube of dielectric grease and shot into all of my connections. Thanks for the heads up.