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Is my fuel pump bad?

76k5blazerr

76k5blazerr

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I was just driving my 72 c10 to get a new engine for the blazer and she died on me on the side of the road, fortunately I coasted into a gas station, anyway, popped the hood and the fuel filter had nothing in it, took the line to the carb off the pump and cranked it, no fuel. Before this I had noticed the truck bogging down a bit before acceleration off a stop. So, what's the first thing to replace. Fuel pump? I can only think of 2 things, fuel pump or a line is clogged, but truck has run great for the last 2 months I've owned it so I'm thinking fuel pump. This engine only has 2k miles on the rebuild and it doesn't look like the pump is new.
 
Ok. Update, so I got home with the truck on the wrecker, when we loaded it I couldn't get any fuel to the thing, wouldn't start. Get home, unloaded it and as soon as the driver left I opened the hood and cranked her for a few seconds and it fired up after a little pedal pumping. Now the filter is full. What is going on hear? Seems after 30 mins or so of straight driving the motor quits getting fuel or something? What do you guys think.
 
76k5blazerr said:
Ok. Update, so I got home with the truck on the wrecker, when we loaded it I couldn't get any fuel to the thing, wouldn't start. Get home, unloaded it and as soon as the driver left I opened the hood and cranked her for a few seconds and it fired up after a little pedal pumping. Now the filter is full. What is going on hear? Seems after 30 mins or so of straight driving the motor quits getting fuel or something? What do you guys think.
Click to expand...

Back when I was running a mechanical fuel pump, truck stalled on me at a light. Wouldn't restart. Luckily downhill, so coasted it into a gas station, where it proceeded to start. Drove another 10 minutes or so to work, parked it, came back out, no fuel. Replaced pump, problem gone.

Not really sure how you'd make sure it's not something odd like a plugged pickup tube in the tank, vs. just replacing the pump, filling the float bowl up, and starting it to see if the problem is resolved.

Since there is no fuel in the carb, and none getting to the carb, it's not a carb issue. Likely culprit IMO is the pump.
 
dyeager535 said:
Back when I was running a mechanical fuel pump, truck stalled on me at a light. Wouldn't restart. Luckily downhill, so coasted it into a gas station, where it proceeded to start. Drove another 10 minutes or so to work, parked it, came back out, no fuel. Replaced pump, problem gone.

Not really sure how you'd make sure it's not something odd like a plugged pickup tube in the tank, vs. just replacing the pump, filling the float bowl up, and starting it to see if the problem is resolved.

Since there is no fuel in the carb, and none getting to the carb, it's not a carb issue. Likely culprit IMO is the pump.
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Did you see my last post about getting the truck towed home and then it started? You still think it's the pump?
 
76k5blazerr said:
Did you see my last post about getting the truck towed home and then it started? You still think it's the pump?
Click to expand...

Yes, read that, still made me think of my experience. However, as mentioned above, if it's time-based vs. random, then I'd be thinking perhaps vapor lock as well. It's a known "issue" (whether it is in your case or not, who knows at this point) which is why GM went to the three-line fuel pumps on everything by the end of the production run.

Vapor lock is pretty hard to prove, but if if consistently starts/runs ok after it cools down, it's not the pump.
 
Yep, fuel pumps are super cheap and easy to change on those years, so I would not hesitate to throw one on. They depend on a spring inside the pump to return the plunger, so if its broken or something is sticking, then its not going to pump.
Not sure on yours, but Ford pumps of those years had pressed in valve modules. I saw one pop out internally, and it would not pump. After some jarring around, the valve would fall back into place and it would work for a while.
Also a weak or sticking valve would cause the same problem.

Since its a new to you truck, I would take a hard look at the fuel line. There may be a filter or a piece of rubber in the system somewhere that is stopped up or collapsing.
Just because the factory did not put it there..........
 
I had a '71 K1500 that had a small section of rubber fuel line joining the factory steel fuel feed line from the tank,right near the rear wheel,on the inside of the frame...all OEM..it looked like an inchworm...

I had issues with the truck stalling out on long uphill grades or when I'd boot it to get up to highway speeds sometimes--a few times it died completely,and I had to pull over,eventually after much cranking,it would start up,but sometimes not want to accelerate without bogging out again..you had to feather the gas pedal to keep it running..

I tried replacing the fuel filter(s) and took the paper one out of the Q-jet inlet fitting and added an external one you can see through,and when it stalled ,you could see no fuel was reaching the carb..
I also blew the fuel lines out at the carb back to the tank,with 125 psi of compressed air,to no avail..then I decided to install a new fuel pump on the engine..it didn't stall for 2-3 days,but then did it again..

I had noticed when I put the air hose to the fuel line,it seemed like at first no air wanted to go back to the tank,then whatever was blocking it blew free...
I was about to drop the gas tank to see if the sock filter was clogged or if any rust was in the tank,but while I was under the truck,I saw that piece of rubber hose,and it was all cracked on the outside--but not leaking...for the heck of it I took it off and replaced it,and I sliced the hose open with a razor blade,and found the inside liner was all collapsed and gooey like tar...

Todays ethanol gas can cause old hoses to fail in that manner,so I'd take a long hard look at any original rubber lines from the tank to the carb..

The truck never stalled out again after I replaced that hose,and ran much stronger over all too--I think it was half starved for fuel most of the time..
 
dyeager535 said:
Yes, read that, still made me think of my experience. However, as mentioned above, if it's time-based vs. random, then I'd be thinking perhaps vapor lock as well. It's a known "issue" (whether it is in your case or not, who knows at this point) which is why GM went to the three-line fuel pumps on everything by the end of the production run.

Vapor lock is pretty hard to prove, but if if consistently starts/runs ok after it cools down, it's not the pump.
Click to expand...
Ok, so I have a 3 line pump. Is that factory? And if not, what year truck should I use at the parts store to get this pump? Or can I put a 2 line on and plug off the other line?
 
You can go either way--buy a pump with the return line fitting (most 70's A/C equipped vehicles used them)--and you can plug off the retur line port if desired,I have done it on more than one fuel pump on GM's..
The pumps with return lines usually have a bigger "can" on them than the 2 port non return line versions..
 
Easy way to rule out vapor lock is to prime the carb and turn the engine over. If it starts, the vapor lock can be overcome. I used to have to do this on a regular basis with an old 305 with a worn cam lobe.
 
Can Can said:
Easy way to rule out vapor lock is to prime the carb and turn the engine over. If it starts, the vapor lock can be overcome. I used to have to do this on a regular basis with an old 305 with a worn cam lobe.
Click to expand...
So your saying if I have the problem again, prime the carb and if it starts, then vapor lock is or is not the problem?
 
diesel4me said:
You can go either way--buy a pump with the return line fitting (most 70's A/C equipped vehicles used them)--and you can plug off the retur line port if desired,I have done it on more than one fuel pump on GM's..
The pumps with return lines usually have a bigger "can" on them than the 2 port non return line versions..
Click to expand...
Went back to the store tonight and bought a 3 port pump, installed it and cranked her up, no leaks (not that I had any before) but I always check. Also it may have just been me, wanting to feel like I fixed the problem, but it seemed to me that the truck was running smoother than before. Old pump was pretty beat up. Hopefully this fixed the problem, geuss I will have to take a long drive and see. :dunno: This time I will have a gas can with me to prime the carb Incase it does again.
 
76k5blazerr said:
So your saying if I have the problem again, prime the carb and if it starts, then vapor lock is or is not the problem?
Click to expand...

Yes, vapor lock can be identified as an issue this way. However, what is causing the vapor lock still needs to be figured out. It could be a weak fuel pump, fuel lines too close to a heat source, or a combination thereof. It sounds like the new fuel pump has resolved your issue for now.

Is the C10 running a 305 by any chance?
 
Better to have the three line pump anyways.
Return line helps keep the pump and fuel cooler.
They were used to combat heat on early 70ish big block GM vehicles


Replace all your rubber lines from the fuel tank fwd also.
 
Can Can said:
Yes, vapor lock can be identified as an issue this way. However, what is causing the vapor lock still needs to be figured out. It could be a weak fuel pump, fuel lines too close to a heat source, or a combination thereof. It sounds like the new fuel pump has resolved your issue for now.

Is the C10 running a 305 by any chance?
Click to expand...
It's a 350
 
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