Ok here it is. When my fuel tank is half full or less, while driving there is a high pitched 5 second "hum" coming from the fuel pump/fuel filter area ONLY when driving. Will do it constantly some times. Not a set pattern. Just a Hum--5 secs--stop---1 min nothing--Hum-5 secs-stop---30 secs--hum. I changed my fuel filter about 20,000 miles ago and fuel pump still pumps out 72 psi when shorted at "fuel pump jumper pin" on passenger strut. Why would it only do it when half full or lower???? What about evap system?? Return line??? HELP PLEASE!!!

 

My Last Se did this. Found out had small leak at fitting on pump causing it to cavitate. May or may not be your problem.

 

I had the same issue with my SE. You need to replace you muffler bearings! Cut a small access hole in the bottom to get to them. NAPA sells them cheap!

 

LOL, thats the best thing Ive seen on here in a long time...

Come to think of it, thats the one thing I havent checked out on my 7s... time to get out the ol cut off saw!

 

Do you know if they carry them for the Turbo motors?

 

20k on a fuel filter, time to change that out for a new one.

 

+1. I could probably use one too..

 

+12,398,712,345,543,215 Your fuel finter should be changed every oil change. Every other at max...

 

Normally I would agree that the fuel filter in a Carb'd rotary should be changed atleast every 6k to 12k depending on where you live in the Country. Wetter/snowy areas that are damp more frequently.

However this is a Se with a F.I. motor. The recommended factory service on the fuel filter is 30k. In Ca and other dry climates this is more then sufficent. Again in wetter climates then 15k-20k would be better.

 

My bad, I checked the service intervals and it is 30k, I was thinking it was 15k instead. I do wonder if his noise isn't because the fuel filter is near service limit though.

 

fuel might be sloshing due to loss of baffles causing it to pick up some air.

 

I'm going to have to call you out on this one for an explaination or justification. How familiar are you with the internals of the tanks, baffles and sump cups, (SE only).

If you need a refresher, here is a thread I posted a while back. https://www.rx7club.com/1st-generation-specific-1979-1985-18/84-85-fuel-tanks-facts-416682/

 

i know that they have baffles, and i know that baffles in most gas tanks are know to rust away with time, especially when people dont keep the tank full. ive had that happen to me in my old VW. i know that there is the cup thing (ive stumbled across your thread sometime in the past) but if the baffles did rust away, and there isnt alot of fuel in take some air might get in. but possibly too the intake line might rusting and a hole might exist above the 1/2-1/4 fuel level sucking in air.

 

Good point on a rust hole on the pickup tube, didn't think of that one. One of the main causes of the inside of a fuel tank to rust is continuously running a low fuel level. The more often the tank is filled and kept full, the less the inside of the tank will rust. I have what looks to be a perfectly good looking 2nd gen tank in the garage. It sat for an extended period of time 1/2 full. The lower 1/2 of the tank still shows the rust free galvanized coating. The top half is badly rusted and most of the galvanized coating is gone.

When I first had the widebody on the street, I had an odd fuel supply problem. Took me a long time to find it. Turned out that the short hardline that mounts to the backside of the bin, the one between the tank and the pump, had a pinhole leak underneath the mounting clamp, due to rust. For some reason the problem was intermittent, never did figure out why it wasn't a constant problem.

 

this would make more sense than the tiny leak at the fuel pump by rx7doctor mainly because I stated this only happens at 1/2 tank or below. Below the half hark could be the hole....

alright since you guys are more smart then the general forum member heres my other noise: https://www.rx7club.com/1st-generation-specific-1979-1985-18/rr-wheel-area-weird-noise-596890/

 

Mine did it at about 1/4 tank or less. I figured that since there isn't as much free-flow from the tank at that level the pump had to work harder, therfore with the small fuel leak it started to suck air and cavitate.

 

ill have it up on the lift tomorrow as I'm going to be replacing the one tire. On my cross country move I ended up with a flat. No one in Orlando carries a 205/55R15 in stock so I now have the replacement...

rx7doctor..did u just notice a damp spot near the fitting or was it enough to drip? Did you have to replace the whole pump or just repair the hose?

Thanks for all the help

 

It was a small drip only noticed after I removed the cover. It was one of the ends that screwed into the pump. Aftermarket Airtex pump. Just resealed it at the fitting.
I had also noticed in 4th gear going up with we call "The Grade" outside of SLO it would start to buck when the tank was 1/4 tank or less also. This all went away after the resealing.