Symptoms of a bad mechanical fuel pump

[78C10BigTen]

So my 350 has been running odd lately, i recently took the eddy off to clean it hopin that was it but it was not. So at a slow cruise like 10 to 20 mph not excelerating it seem to kind of miss persay... its purring then blurp purr blurp purr. Would a weak (dying) mechanical fuel pump cause this? Today when i got home i sprayed ether all around the carb to find maybe an air leakage but none. While running i did notice the fuel filter damn near empty wich it never has been before. Anybodys input helps.

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[Blue Ox]

Would tee-ing in a fuel pressure gauge be out of the question?

 

[78C10BigTen]

Would tee-ing in a fuel pressure gauge be out of the question?

Where do i put it and what does involve? Id do it...

 

[Blue Ox]

In that hose between the filter and the carb. You will need a Tee fitting and a few more clamps. Mechanical fuel pump probably only puts out about 5 psi so a 15-20 lb gauge should have you covered. If you can I'd set it up so you can see it while you're driving. Outside the cab obviously. If that's when the problem manifests itself that's when you want to be able to see if the pressure drops.

 

[78C10BigTen]

In that hose between the filter and the carb. You will need a Tee fitting and a few more clamps. Mechanical fuel pump probably only puts out about 5 psi so a 15-20 lb gauge should have you covered. If you can I'd set it up so you can see it while you're driving. Outside the cab obviously. If that's when the problem manifests itself that's when you want to be able to see if the pressure drops.

It does it in gear idling at a stop also after ive driven a few miles

 

[78C10BigTen]

Also what pressure is ideal for my eddy? Its a 650 cfm

 

[Blue Ox]

It does it in gear idling at a stop also after ive driven a few miles

If you can open the hood when it's happening then, naturally, you don't need to hang it out on the cowl.

I'd guess 4-5 psi is probably adequate for a carb. Usually if you get fuel starvation issues the pressure drops to near zero.

 

[DoubleDingo]

I've never used a filter like that, and many will tell you to discard it and run hard line so you don't burn your truck to the ground. But, I cannot make out what the word is inside the arrow, however, the arrow seems to be pointing the wrong way if it's supposed to "flow" towards the carb. It appears to be flowing the wrong way unless it's looping around.

 

[78C10BigTen]

I've never used a filter like that, and many will tell you to discard it and run hard line so you don't burn your truck to the ground. But, I cannot make out what the word is inside the arrow, however, the arrow seems to be pointing the wrong way if it's supposed to "flow" towards the carb. It appears to be flowing the wrong way unless it's looping around.

Ive always been told to use that kind of filter instead of a glass type because the o rings dry up, leak and start a fire.

 

[1987 GMC Jimmy]

You can pull the line and do a volume test. I’ve been told a mechanical pump should fill a 20 oz. Coke bottle in 8 seconds. I’m thinking metal canister filters and not glass or plastic. We’ve had a couple people on here with Delphi pumps that put out double what they’re supposed to, but if you’re just now having issues, that’s probably not to blame. Those mechanical pumps are pretty tough. I’ve seen them take a lot of sitting and still work fine.

 

[78C10BigTen]

You can pull the line and do a volume test. I’ve been told a mechanical pump should fill a 20 oz. Coke bottle in 8 seconds. I’m thinking metal canister filters and not glass or plastic. We’ve had a couple people on here with Delphi pumps that put out double what they’re supposed to, but if you’re just now having issues, that’s probably not to blame. Those mechanical pumps are pretty tough. I’ve seen them take a lot of sitting and still work fine.

The reason i use plastic over metal canister is so i can visually verify theres fuel there.

 

[1987 GMC Jimmy]

I get that. Maybe one day they’ll make them out of transparent aluminum, but until then, I’d stick to the metal ones for safety’s sake.

 

[78C10BigTen]

I get that. Maybe one day they’ll make them out of transparent aluminum, but until then, I’d stick to the metal ones for safety’s sake.

Honestly having both plastic and the glass tube ive never had any issue with either but id rather be able to see my fuel level.

 

[1987 GMC Jimmy]

Maybe there’s less to that hesitance to stay away from those filters than people think there is, but I’d rather be safe than sorry. I’ve heard of some people running plastic and glass filters for a very long time with no problems, but I’ve seen stories of people having them bust or leak out of the o rings on the glass ones and cause a fire. I cant speak from personal experience. All my filters have either lived in the carb or on the frame rail somewhere.

 

[78C10BigTen]

I've never used a filter like that, and many will tell you to discard it and run hard line so you don't burn your truck to the ground. But, I cannot make out what the word is inside the arrow, however, the arrow seems to be pointing the wrong way if it's supposed to "flow" towards the carb. It appears to be flowing the wrong way unless it's looping around.

It says to carb and its in the right direction

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