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runs really bad on freeway


mattchew

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so ive got another wierd problem with this 72 240z of mine. when i get going abut 60 mph it soundslike a lawnmower and boggs down till i get to maybe 45 miles an hour. But it cruises just fine at about 50-55. oh and it does this up hills too. i can take hills only about 25 mph. all of my emmisions crap is removed. ive replaced my fuel pump and filter, flushed my lines and cleaned the parts on the tank that the fuel comes out of with a clothes hanger and compressed air. pulled my carbs apart and cleanedthem out. steve at z therapy set my float bowls for me. and i replaced my points and checked my timing.. still does it... anyone have any idea what i should try next? someone suggested that i need a new distributor and that pertronix kit would fix this. But its pretty out of my budget right now unless i have to. well any advice would be appreciated:) oh by the way it idles good and drives just fine in the city.

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Have you checked the the last chance filters in the carbs ? Su's run best slightly rich, also the stock fuel filter is a restriction. Another thing to check for is kinks in the rubber portions of the fuel lines and dents in the metal portions. Fuel system problems are often mistaken for ignition problems, no fuel of course there will be no ignition Doh!

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I agree with Zforce. It sound like fuel starvation to me. New anything does not mean it can't be bad out of the box or suffer infant mortality. Check fuel flow rate and pressure. It sounds like your car is stock so the factory service manual specs and procedure apply. I attached the fuel system section in case you don't already have it. Perform the diagnostic procedures for the fuel pump. Also, check the screens at the inlet to the carbs as Zforce said, they are not included in the fuel pump diagnostic procedure.

EF Engine Fuel System.pdf

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Why would it even out after 50MPH if it's starved for fuel at 45MPH?

You didn't read it quite right. He says when he tries to go 60+ the car chokes and dies slowing to about 45 before it catches again. The 50 mph is max speed without dying out.

That is the classic sign of fuel starvation. If you are still running a mechanical pump, check that the lobe on the crank pulley is tight, and that you have the pump installed with the correct spacers.

Since the pump is new, my bet is a pinched hose or as someone else said the "last chance" filters in the float bowls.

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so i robbed the coil and resistor off my parts car put them on there and it started to run a little better on the freeway. I could get it to about 75 before it did this. I started driving down to a friends house to get an electronic distributor he had laying around and on my way over it stopped getting fuel pressure and i could barely get it to run at all. im thinking that my gas tank is a lot worse than i thought. im gonna rob the tank out of my 74 260(parts car) and hopefully that will fix it. im gonna clean it out really good before hand though. so between the electronic distributor and the gas tank im hoping this will fix it!! this car has givin me so much trouble its earned the name duh'z's:p

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