'92 Miata, surging problem, 85,000 miles.

Good move. It's cheap and fairly easy to replace. If it's original, 85k is well past its service life.

FWIW, my fuel pump still works fine at 143k. I change the filter every

60k. There's another filter at the pump, inside the tank, but they rarely if ever need attention.

Hello,

I used to have an automotive repair garage in another life and remember that once I had a VW that acted like you describe. I tried a new filter which is usually the cause, without success. I then took the fuel tank out and drained everything out including the piece of cloth that someone had put into the tank. When the demand was high the cloth would block the suction tube and when off or at low demand it would float free and the engine would act normal.

In your case, I think you may have a reoccurring problem if the inside of the tank is rusted and flaking off. If a new filter helps for awhile then the problem comes back that is a sign of internal contamination. Water always goes to the lowest point in a fuel tank and depending on the internal coating it may be rusting there. Older VW tanks were famous for this problem. They had a low spot that sometimes just required a light tap to break through and start leaking.

Good Luck

Don

To the OP, based on what you say about the water in the tank, I'd replace the pump and at least look at the filter in the tank, there could be huge amounts of rust in the tank so you'll need to look at it with the idea of maybe having to replace the tank as well, if you don't the tiny rust particles will continue to clog the fuel system forever, I speak with the voice of experience, I may be the world's foremost expert on futile attempts to get rid of rust in a fuel tank!

There is a cheap fix that often works: remove the tank and coat the inside with a plastic sealant.

Yes, one of the many "futile attempts" I mentioned.

I've never tried it personally on a car tank. But it worked well on a leaky steel motorcycle tank for me. Pour it in, rotate the tank to cover all inner surfaces, let cure overnight.

You left out the next step, watch coating peel off and, along with remaining rust which couldn't be cleaned out, clog fuel lines.

That was a Honda 750 I got real cheap. I finally gave up and sold it real cheap. Putting a of cup of light oil (kerosine consistency) and a handful of pebbles and shaking vigerously for a few hours scoured it completely clean and shiny and allowed it to run trouble free for about two days before the tank was covered with rust and began clogging fuel lines again....

FWIW, I had the gas tank treatment done on a car that had been sitting and it seemed like it worked well.

Hi,

KBS-Coatings markets a fuel tank repair and coating kit for large and small tanks. It will seal small leaks as well as terminate more rusting of the inside. it is a three step process and the tank should be out of the car of course.

Disclaimer: I sell these products.

Don

Thanks for all of the input. So far I haven't done anything. The next day it ran fine. I drove it 5 miles, stopped for 1/2 hour, and then drove it 5 miles back all with no incident. It ran normally, and continues to run normally on short trips. I haven't taken it more than 5 miles out since my post. Does this help any in the diagnosis? Thanks, Mike

If you haven't replaced the ignition wires and plugs, this is a good place to start.

Just something to check: There has to be a venting valve to allow air to go into the tank while fuel goes out to the engine. If air has trouble to get in, you'll get fuel starvation. Hope this helps.