Mechanical fuel pumps failing

[Dougefresh]

Ok guys new here and would love some help from you experts. 1984 sr5 corolla. Has a mechanical fuel pump that keeps failing. I think I'm up to 4-5th one in the last year or so. Car runs great after a new one is installed. Gas gauge is off. But does work. Only thing I can think of next is dropping the tank and maybe have a hose cracked or the pick up tube cracked sucking air?..??? Dunno just stuck gave this to my 16yr old who loves the car. Just frustrated to keep having this issue . Any help would be greatly appreciated.

[Glock30]

Ok guys new here and would love some help from you experts. 1984 sr5 corolla. Has a mechanical fuel pump that keeps failing. I think I'm up to 4-5th one in the last year or so. Car runs great after a new one is installed. Gas gauge is off. But does work. Only thing I can think of next is dropping the tank and maybe have a hose cracked or the pick up tube cracked sucking air?..??? Dunno just stuck gave this to my 16yr old who loves the car. Just frustrated to keep having this issue . Any help would be greatly appreciated.

When you say that it is failing, are you getting fuel out of the weep hole or is it just not sending fuel. I have not taken mine apart to know for sure, but I know that most cars have a in tank strainer. It's possible that you have debris in the tank and that is clogging the strainer. It happened to my Bronco recently and I had to clean out the tank. Also, when you are re-installing the fuel pump are you using the spacer? There is always the option of an electric fuel pump, but I have never tried one with the oem carb.

[jondee86]

I've not looked inside a 4AC pump, but every mechanical pump I have
played with worked the same. Two small spring-loaded disc valves and
flexible rubberised fabric diaphragm. This diagram shows how a typical
fuel pump works....



The pump is self-limiting, in as much as when the pressure builds up on
the delivery side, the diaphragm stays "down" and does not contunue to
build pressure. Pumping resumes when the carb requires gas to replenish
the float chamber. The only way I have ever seen these pumps give problems
is if one of the following happens...
- actuator arm wears down until the stroke is too small to pump
- bits of thread or other crud get stuck in the valves and stop them sealing
- the diaphragm ruptures due to old age

How do you decide that a pump has failed and needs replacing ? What
actually happens ? Have you ever tested one of the failed pumps to see
if it can pump gas out of a can if you work the rocker arm by hand ?

Cheers... jondee86

[davew7]

All it takes is one flake of rust in the valve, to prevent the fuel pump from working. It is worth a try to take and blow compressed air thru the pump to see if you can dislodge the rust. I would also put a low restriction filter [see thru type] in front of the pump inlet. Do the same, if you have to get a new pump. Depending on how quickly you $hit collect in the filter, you can then decide if you need to pull the fuel tank. DaveW7

[Dougefresh]

I do have see thru glass type filter on it. Has always been clean. Looked inside gas tank seemed to be clean as well. Going to go ahead and drop the tank tomorrow morning....thinking more it's in the pick up tube that's cracked or clogged.. Either that or a fuel line coming off the tank has a split in it, or something.. ...

[Dougefresh]

So sorry for not replying back with an update but here goes. I dropped the fuel tank two weeks ago all pretty much clean lines and pick up tube were clear. So we put it all back together and put a new fuel pump in her. Bam she drove fine...for about two weeks when pump failed again. Ok so last detail I left out which can only be the problem now is the header.. It's got to be giving too much heat from it. So I bought some fuel line insulator and wrapped it also got a fuel pump shield Toyota part # 23915-15011....which I got from Toyota where I work in the parts Whse. And we happen to have one one hand(rare), was told this helped the pump from creating vapor lock, so it's worth a shot also keeps heat off the pump, so the fuel lines are wrapped and pump covered. Hopefully this solves the issue if it goes out again the next step is too wrap the header. Which I didn't do yet as I heard they hold moisture and crack after wrapping. So we'll see how it goes.. Another last resort is to change manufacturer of the fuel pump. But I don't think that is an issue.. Thanks guys for the help and advice.

[Glock30]

That heat shield is basically a hard plastic unless they make a new and improved one. The heat shield is on the OEM manifold. If you are running headers it probably is too hot. That part is really to isolate the fuel pump from the head so that it doesn't draw heat from the head. If you have been running fuel pumps without it on there or without a plastic spacer the actuator arm is most likely bending because it is too close to the cam. The fuel pump is driven much like a lifter and has a special lobe. If it is too close it will ride on the cam wrong.