Symptoms of a bad mechanical fuel pump

I had a similar issue the other day but when it started to feel like it was stalling out I switched tanks and it would take off again. If I switched back to the original tank while cruising it would be ok for a while. After screwing around like that for a while I finally pulled over and looked at it. The filter was almost empty but then it would get a surge of fuel. It idled fine like that but didn't work under load. I have an electric pump and a hokey fuel routing and it was almost 100 out so I was thinking my problem was that the fuel was boiling off on it's way to the carb. I kind of ruled out the restricted line because when it cooled off it works as intended.

After I read this I don't know if you can get anything useful to help diagnose your problem but I'm not deleting. Never go backwards!!

Its messed up because today it ran the exact same way but the filter was full.... im confused other then thinking its spark...

1987 GMC Jimmy said:

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.

Click to expand...

I was one that ran a glass one for years without problems. Now I am a metal canister and carb-filter guy.

DoubleDingo said:

I was one that ran a glass one for years without problems. No I am a metal canister and carb-filter guy.

Click to expand...

I never had a glass one leak or cause fire but the fear of it i switched. Especially since ethanol eats rubber o-rings.

I ran a glass filter when I was younger. Then one cold morning, it started puking fuel everywhere. Haven't run one since. But I have run a bunch of those plastic filters without any failure. They are always mounted above the intake and in a way that doesn't cause them to vibrate.

The problem sounds like it could be fuel or spark. What do the plugs look like?

Big Chip said:

I had a similar issue the other day but when it started to feel like it was stalling out I switched tanks and it would take off again. If I switched back to the original tank while cruising it would be ok for a while. After screwing around like that for a while I finally pulled over and looked at it. The filter was almost empty but then it would get a surge of fuel. It idled fine like that but didn't work under load. I have an electric pump and a hokey fuel routing and it was almost 100 out so I was thinking my problem was that the fuel was boiling off on it's way to the carb. I kind of ruled out the restricted line because when it cooled off it works as intended.

After I read this I don't know if you can get anything useful to help diagnose your problem but I'm not deleting. Never go backwards!!

Click to expand...

I ran into the same type of problem with the same setup. My line, rubber hose, and slipped down and was on the valve cover so it was getting hot and causing a vapor lock. I am of the same mind set that inline filters and rubber hoses can be a fire hazard but they have been that way for years on our trucks. I keep a fire extinguisher in my truck just because of that reason.

Mine has rubber line and a clear filter like that.

Id like to switch to metal and will someday.

Need to pop a new filter on it haha

78C10BigTen said:

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.

Click to expand...

The problem with your setup( fire wise) is you are running a fuel filter, clamps and rubber hose over the top. A pinhole in a fuel line will start a fire, and the pinhole will feed fuel to the fire all the way until the fire has burned the plug wires up or the fuel line in 1/2. So you won't know anything until it's too late. Mount the filter low, down by the pump and run a steel line from there,if you have to use rubber you should only need very short pieces as couplers. This way a leak at the filter is a leak under the truck not fuel all over the top of the engine,and hope fully a leak starting would be noticed as a puddle under the truck,not a small unnoticed leak on top of the engine, for a week before the fire.. Sorry I didn't read all posts,to test a fuel pump test output volume and output pressure,check inlet vacuum if all 3 pass you are barking up the wrong tree.

I think Ricko1996 has the right answer; the filter should really be down in the rubber line that feeds into the fuel pump. However, I've never seen anyone do it that way, maybe because it seems to be easier to reach when you put it up near the carburetor.

I bought a fuel line T at the auto parts store and used it to run a temporary line to a fuel pressure gauge. The fitting I bought was a metal block with a 3/8" barb fitting on each end and a threaded hole on the side. I had to find a third barb fitting to screw into that hole so I could attach the hose for the pressure gauge. I ran the temporary line for the gauge right up through the hood gap and to the bottom of the windshield so I could see the gauge through the windshield. The T fitting was a similar design to this one. https://www.summitracing.com/parts/...MEUjk3Ke5efUkIPH98p52I52n97HdepQaAnbAEALw_wcB

75gmck25 said:

I think Ricko1996 has the right answer; the filter should really be down in the rubber line that feeds into the fuel pump. However, I've never seen anyone do it that way, maybe because it seems to be easier to reach when you put it up near the carburetor.

I bought a fuel line T at the auto parts store and used it to run a temporary line to a fuel pressure gauge. The fitting I bought was a metal block with a 3/8" barb fitting on each end and a threaded hole on the side. I had to find a third barb fitting to screw into that hole so I could attach the hose for the pressure gauge. I ran the temporary line for the gauge right up through the hood gap and to the bottom of the windshield so I could see the gauge through the windshield. The T fitting was a similar design to this one. https://www.summitracing.com/parts/...MEUjk3Ke5efUkIPH98p52I52n97HdepQaAnbAEALw_wcB

Click to expand...

Mines down there,and it's steel all the way from the filter to the carbureator. I've already had a fire from a pin hole in a rubber line. I got very lucky,I wasn't on the road I was backing out of the garage,noticed smoke between the cowl and windshield got the hood up,the fire out,had my kid fire it while I watched, poof as soon as it started cranking had a pinhole squirting fuel like a squirt gun right on the distributor. On the road I wouldn't have noticed the smoke,and by the time I got to the side if the road hood up etc. I'd have never got it out. Oh yeah,my filter is right after the pump,I don't know how I feel about a filter that close on the pump inlet,afraid any air that gets in the filter might break prime on the pump,momentarily.