Hello, I have a 85 nissan sentra that is carbureted, with a mechanical fuel pump. It wants to stall after a freeway run. What could be causing this and how do I check it? I have replaced 3 autozone fuel pumps in it(they last about a year) and not sure if its the crappy zone pumps or something else that is causing them to go bad. I bought a clear universal filter for it that I want to install inline on the inlet to the pump but not sure how many filters I can install with out hurting the pump. I have had the tank out and didnt see any sediment in it. this pump has 3 lines to it, inlet, outlet and the return line.

You should do a fuel pressure check once you have a new pump in. You should be getting 3-4 psi from that system and anything less and the engine may come on but sputter and die. Its also posible that the carb might need priming again. Just drop a small amount of gas straight into the carb (have the throttle open when you do it). Make sure all of your lines are connected at the right ports.

Whats the temp of your coolant after running it on the freeway? How is it after just driving for a couple minutes? How long are you running it on the freeway? I've had about the same amount of trouble with Autozones Master fuel pumps as any other brand so its more than likely a problem elsewhere. Its rare to get 3 bad parts in a row from the same place (though I will admit it has infact happened to me).

Regards and good luck,

Dylan.

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1997 BMW M3 - 3.2litre Inline 6 cylinder

Just a thought, check your gas cap, maybe it's not venting and building up pressure in the system, try loosening the cap and drive it again?