Hey guys, first post here so please be gentle

ive been learning to work on things with this truck (and man have I had some things to work on with it)

Ive been chasing a fuel issue for a few days now and I’m almost positive it’s the fuel pump. It’s the mechanical pump on the side of the engine, driven by the cam. I’ve looked up how to replace it and removing it seems simple enough but I get unsure when it comes to bolting the new one on.

the cam needs to be in a specific position to get the new one on there correctly. A few questions-
1. is there a wrong way to put the fuel pump on (I believe the pump arm needs to rest on TOP of the cam, not below it)?
2. Can it even be pushed forward and in with the arm BELOW it, and ultimately screw everything up? Or is it one of those “you’ll know something’s wrong, it won’t line up or go in right unless it’s correct.”
3. reading things on here, people say to manually crank the motor to get the cam where you want it. How do I know where I want it and when it’s there?
4. the crank pulley, from what I’ve read, is pretty obvious. I’m fairly new to working on things so as stupid as it sounds a picture would really help to know where to put a socket and a breaker bar to manually crank it.
5. I’ll disconnect the battery. Do I need to have it in neutral to manually crank it to move the cam?

thank you in advance for any help. Yall have already helped me a ton just in the archives of this forum.

 

Welcome to FTE. Some guys with lots of experience with the 300 mechanical fuel pump installation will be around soon. You do have to be out of gear to turn the engine by hand. If the plugs are out its easier. Have you removed the fuel pump yet? You might want to test the fuel delivery before affixing blame. New mechanical pumps have many issues and it would be bad to replace a good pump.

 

thanks! Unfortunately this is a newer one a shop threw on for me when it was in getting the rebuilt carb installed.

it’s a brand new gas tank, rebuilt carb, I just changed the fuel filter on the carb itself; only other thing it could be is the sending unit as I haven’t gotten to changing that yet. I didn’t realize it was separate from the gas tank and was in a pinch at the time to get it up and running. It’s on the list, but a fuel pump is cheaper than a sending unit and time to drop the tank so I’m starting here. I do believe it’s the fuel pump, but there’s always a chance it’s not.

technically the pump is “new” but I think something snuck up and into the carb fuel filter. When I pulled that off it had a rattle in it. The new one I just threw on didn’t. Fuel pump may have been damaged / compromised in all of this too.

Will prime the carb with the gas pedal fine, then start, but dies immediately once that fuel is spent.

 

Don't forget that the fuel line between the tank and pump is a "suction" line. This means that any loose clamp, tear in rubber, or steel lines will draw unwanted air in. It usually won't leak fuel so it makes it harder to find. This will make the fuel pump inefficient at pumping liquid. Same principle as drinking with a cracked straw.
I just experienced this personally. Chased my tail on my 80' 4.9l. Had the new pump in hand and then found a tear in the line at a clamp when disconnecting old one . Cut it back and reinstalled. Ran like a champ after that.
There are lots of issues with new pumps as well. I'd start with a simple inline gauge just prior to to carb. This will help troubleshooting. You'll want it anyway if you end up swapping pumps. Lots of folks talking about auto store pumps having differing output pressures.

 

good to know, I’ll give the lines a good look over today just to double check for cracking or any possible leaks.

 

Bigblue & Orange65 have some good points.

Before installing a new pump tell us why you think the pump maybe bad and what the truck is doing so we can make sure a new pump is going to fix the problem.
Orange has a vary good point on the fuel line and hoses. Hoses may look good on the outside but be bad on the inside.
They can break down and plug the fuel path and starve the motor of fuel, act like it is running out under load when fuel is needed the most.

As crazy as it sounds the wrong size rubber hose can also cause a problem.
Our 300 motor trucks use 5/16" rubber hose. I tried to use 3/8" with 2 clamps trying to pull fuel from a gas can set up on the inner fender just so I could move the truck as I was rebuilding it.
I evn replaced the pump thinking is dried out from sitting and still would not pull fuel.
It is not hard to do but I would replace all the rubber fuel hose. Now if you had a shop swap out the fuel tank for a new one you may want to check that hose if new and the right size.
The tank hose is the only one that will give you the most trouble to change as you are working above you and gas will come out.

Little trick get a bolt that will fit inside the hose pretty tight by pushing it in. Depending on how long that hose is you can either pull it off the metal line or cut the hose and then quickly put the bolt in the hose to stop the fuel from coming out.
Then you can cut the new hose to fit and fit it on the metal line first. Dont forgret to put the 2nd clamp on the hose then remove the old hose from the sender and quickly put the new hose on.
Again gas will come out but this should keep the amount pretty low.
You can do dthe same at the pump but you will keep the old hose on the metal line and stick the bolt in it toi stop the fuel from coming out.
New hose on the pump, 2nd clamp, pull old hose off the metal line and new hose on.
Pump to carb is not a big deal and you dont need to use the bolt trick.

If you do need to change the pump we can walk you though it as it is not hard and I have never turned the motor over to get the pump to install.
But again let us know why you think a new pump is needed like gas dripping out of the weep hole or you are making oil in the motor - it is filling the crank case with fuel and this is not good.
Dave ----

Edit - Welcome to FTE

 

Thanks for the welcome.

I’ll give some more context

Truck had a long history of issues, notably one where the gas tank was drilled and gas drained from it. Took me a while but with the help of my father in law we installed the new tank. Again, I didn’t know the sending unit was separate so it still has the old sending unit, and when we changed the tank we noticed the filter on the sending unit wasn’t even present. We noted that the sending unit needs done on a “when I can” basis. I’ve had to throw so much money at this truck since then that $150 on a sending unit has to wait because I’m constantly spending $ to keep it running at all.

I live in a SMOG state (unfortunately) and was having trouble smogging it. It was in a shop for a few months chasing an odd issue I had on top of that. essentially, the truck wouldn’t run past 45mph. Once it hit that speed, the load essentially vanished until it coasted down to 40-ish MPH. Then it’d sputter back up and climb back and repeat.

the shop tested mostly everything and ultimately said it was the fuel pump not pushing the right pressure. My carb also needed to be rebuilt as it was having a fuel issue as well. I rebuilt the carb. The issue remained. Replaced the pump. Issue resolved.

flash forward a month or so and I replaced the alternator and external voltage regulator. Took it for a lot of test drives and it ran fine. Maybe 4-5 days later, it died at a stoplight. Wouldn’t start again. Spoke to my father in law who said it seems like a fuel issue, and I agreed.

I assumed the carb was good so I started with the cheapest possible fix which was the inlet fuel filter on the carb. I yanked the old one and it had a rattle in it, which I found odd. The fuel filter got swapped out with one that doesn’t rattle.

the truck started, ran for 4-5 seconds, but once I touched the gas pedal it died. Now it’ll start for .5 seconds and die immediately. HOWEVER, if I press the gas while it is running for that .5 seconds, it runs in park. As soon as I let off the pedal, it dies. I have a feeling this is telling me something, I just don’t know what. My guess was that the pressure from the gas pedal is passing fuel through the pump but the pump won’t do its job to fill the carb.

my assumption is two possibilities, but three now:
1. Some debris in the tank got through the sending unit, screwed the fuel pump and screwed the inlet filter on the carb. Pump needs replaced. Inlet filter is done.
2. sending unit needs done (it’s on the list, but I need it running)
3. fuel line leak between tank and fuel pump, but I’d be surprised seeing as I didn’t touch the fuel lines and it ran fine until it died on me at that light

 

Additional question- the fuel lines into and out of the pump have two clamps on them. Should I consider removing the one furthest away from the attachment point? Is it redundant / restricting flow?

 

Yes, two clamps, is not normal. one should be fine.

Also, contact the repair shop, you may be covered under their warranty.

 

I’ll rip those off today and run just one clamp. I don’t know that it’ll be enough to get things running again unless one is over tightened, but we’ll see.

 

You mentioned that when pressing the accelerator you got fuel into the carburetor. You can verify that by looking down the throat of the carb. You'll see a stream of gas shooting down the throat. That means the carb is getting fuel from the fuel pump. You are in a smog state and I think your truck is equipped with a feedback carburetor. That can cause issues when not properly operating. Also make sure your choke is set up properly and operates well. You can do a test on the pump to see how the volume and pressure are doing. You can pick up a cheap test kit and see how the pump is doing. It's relatively new but today that's no guarantee it's still good. I also have never needed to turn the engine to install a fuel pump. If you remove it do it slowly and look inside to see which side of the cam the follower is on. Also the pump will spring back as you remove it. That tells you which side to be on. New pumps should be tested before installing. When you move the lever there should be resistance. If not it's defective.

 

I’ve seen a lot of information that these new pumps have issues. It’s a $30 part and everyone’s saying it’s easy to replace. But it’s interesting everyone here is pointing to reasons other than the fuel pump, as if the fuel pump is very reliable on these. Just seems conflicting.

yes, when I pump the pedal I get the carb primed. It starts. Immediately dies. If I hit the gas when it is started, she runs. Once it let off, it dies immediately.

does that point to fuel pump or another issue?

 

You can test the fuel pump. 5 psi pressure and 1 pint in 20 seconds flow. Or you can load the parts catapult PULL! And replace the fuel pump and see if that is the issue. Can you keep it running by pumping the accelerator?

 

It's a good idea to get a service manual for your truck. Hanes, Chiltons or manuals are available. Used good copies are around. Used book stores are a good source or ebay has them. Or new.

 

if I put my foot on the gas at all when it fires up for that split second, it runs. Mash it and it acts as it should. The second I let off the gas pedal, it dies instantly.