What Would Keep the Fuel Pump From Pumping?

[cgrossl]

I have an 85 Chevy SWB, 2WD with about 150,000 miles on the original 305. Over the last month or two, I have noticed that every now and then, it randomly acts like it is running out of gas. It would do this for a few seconds then go away. At first, this happened very rarely. Over time, this problem got worse. It started happening more frequently and when it did happen, it happened for a longer period of time. Finally, I decided it was time to look into it.

The first place that I thought to look was the fuel filter so I replaced it, no change. Then, I replaced the fuel pump. After replacing the fuel pump, it isn't pumping a drop of fuel. I can manually fill the float bowl with gas, and the truck will run about 30 seconds, just fine. While it is running, I can completely disconnect the fuel line and not a drop of fuel comes out. This had me completely baffled. I thought, maybe the fuel line going from the tank to the pump is clogged. So, today, I disconnected it from the pump, then shot compressed air into the tank. Fuel spurted wildly all over the floor. Definitely not clogged. But, I tried running it again anyway, no change. I should also mention that when I replaced the fuel pump, I checked the oil and it didn't even register on the dipstick. But, I am still getting oil pressure.

I figure that I have one of two possible problems,

1. The new fuel pump that I bought is defective. I don't think that this is very likely though,

2. Due to the low oil level and high mileage, the fuel pump lobe wore off of the camshaft. I seem to remember reading somewhere that engines of this era were bad for that.

Am I missing anything? Is there something else that could be wrong?

[magnethead]

I'm thinking camshaft lobe.

[beaterC10]

Not to insult you, but have you verified the rod that rides on the cam lobe is in contact with the fuel pump lever, or in other words did you get the pump installed correctly? Might also make sure the lever on the pump is not broken. I know from my own experience either one will keep the pump from pumping.

[cgrossl]

No insult taken. Is it possible to get the pump installed, without the pushrod contacting the pump lever? I didn't think that there was enough room to the get pump lever in there beside the pushrod.

[f.monroe]

If it were my truck I would run the inlet side of the fuel pump to a gas can with a short piece of hose . If it still doesnt pump .... lobe worn, bad pump, etc . If it does then I would look at the rubber lines from the tank sending units to the hard lines under the truck . Mine dry rotted on the truck I had in high school and it did some of the same things . I replaced them and the problem was solved . Frank

[79BIG10]

To go along with Frank's post above if it still isn't pumping I would look at the sending unit as well. Turn the key over to get power to the system. This will get the sending unit to get the gas started to the pump. While you're at it check for any fuses to them being bad as well.

Do you happen to have dual tanks on this? You could have a problem there as well.

[blaserman]

Is it a mechanical pump or electric? This would help a lot to figure what is going on.

[cgrossl]

Its has a mechanical pump and a carburetor. The lines from the tank to the pump are clear. I a little compressed air into the tank filler neck while the line was disconnected from the pump and fuel sprayed everywhere.

[60-66 Nut]

I don't think I've ever seen a fuel pump lobe wear completely off, but I'm sure it's possible. I have seen the push rod get so sludged up that it would stick. I have also seen too long of a bolt being installed in the upper hole on the front of the block and binding the push rod. Don't know if any of this helps, but good luck anyway.

60-66 Nut

[RunTMCfan]

I posted a very similar problem just about 30 days ago on this forum.

One thing I found was my fuel line was clogged. Pull off the line from the tank to the pump at the pump. Blow into it to see if you've freed it of any guck. I think you can lightly pressurize the tank via that line with a small nipple on an air compressor. This should create back pressure and at least get gas to your pump.

Everything you are checking is great. But if gas isn't even getting to the pump your efforts will be futile.

[SCOTI]

If the fuel issue was intermittent w/the old pump..... put it back on & see if you still get absolutely no gas.

If that's the case, more than likely you'll figure out what went wrong when swapping or you'll figure out it just might be that 'new' fuel pump (bad diaphram?).

[mhicks]

You should be able to push the lever on the pump with your finger or thumb with the pump off of the block and eliminate bad pump or or clogged line. If it won't pump by hand put a short line on the pump into a gas can. This will eliminate the clogged line or bad pump.

[magnethead]

people- are you not reading that they already eliminated a clogged line using an air compressor

However, i'll put my .02 in here. Your sending unit may or may not be at fault. My truck has just started going whack on the left tank....(will open new topic)

[SB406]

Old fuel lines = Cracked Line or Hose
If the line from the tank to the pump has any leak, the pump will suck air, lose prime, & Not Work.

As suggested above, put pump suction directly in a can of gas & try it.

[scotto0609]

Make sure fuel tank is ventig properly, to check loosen gas cap. When you loosen gas cap listen for suction, hissing. Then try running truck with cap loose and see if problem persists, if so I,m out.

[centsless]

Like sb406 said, If the fuel line between the pump and the tank has a small hole in it, the pump will not draw fuel from the tank. When you disconnected the line and pressurized it, that did verify no blockage. Leave the fuel line hooked to the pump and pressurize it again. Then inspect the lines for a wet area. If you find one, replace it and see if that fixes it. You would be surprised how one little hole from dryrot will do this

[us111]

hello,as already been stated run a house from fuel pump inlet to gas can,if it runs then you have elimanated everything from there to carb and can start going back from there,just one note,had pretty much same problem and the line was sucking air,but when i had hose in gas can i had to prime carb 4 times to get pump to start drawing,so make sure and try it enough times,first 2 times it wouldn't pump i was cussing a blue streak!

[magnethead]

did you check for a pinched fuel line? That's what it appears to be on my truck.

[84 400]

man i know just were you are. my first truck (77 dodge powerwagon with the 318) had the same thing happen to it. i just gave up with the pump and whent to auto zone and bought a block off plate and an electric pump. wired the pump to the run position on the kep and ran it threw the oil pressure switch that shuts it off when the vehical gets in a crash(for safety) It ran fine and i never looked back unless you want to fix the lobe(new cam) i would co buy a low volume (7psi???) electric pump a pressure regulater and a block off plate.
Good luck
ian