240ZRX Posted May 1, 2007 Share Posted May 1, 2007 I have a situation on my 72 240Z/355SBC where the fuel pump gradually stops pumping fuel. It is a Holley 125 Black pump. original pump was a Welborn in line that I ran with a bypass regulator. the car will run all day around town, but when I go on the high way it basically runs out of fuel and stops. here is what i have done to date. - Drained tank/fuel is clean nothing at all/tank was treated and lined/gas tank renu. - All vent lines on tank not crimped/fuel line to pump is good/fuel filter not clogged. - originally pump was drawing from stock location on the 240Z tank(72) - I am now drawing fuel from the drain plug hole (sort of a more gravity type set up) have not run car on highway since this change, so i do not know if this was the cure. - Am presently running a toggle switch from the battery thru a fuse, and temporarily by passing the relay. (car did same thing with relay hooked up or bypassed) - Even drilled vent holes in fuel cap, but pump still stalled out. i am running out of fixes so any suggestions will be helpful. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted May 1, 2007 Share Posted May 1, 2007 Sounds like the fuel volume is low for some reason. You hit all the usual suspects. Could be a failing pump too. Your post confuses me a bit. I guess you were running a Welborn pump with a bypass regulator and had this problem. You are now running with a Holley pump and still having this problem? You say the "pump still stalled out". Do you mean you know the pump is no longer turning or just that the car quit running due to the lack of fuel? Did the car ever run right? Or is this just something that has happened since you changed your setup? Quote Link to comment Share on other sites More sharing options...
240ZRX Posted May 1, 2007 Author Share Posted May 1, 2007 The pump (holley and welborn) did two things. They would just drops fuel pressure and then at times it stops all together. The welborn pump I hooked up to a battery and it spun like a clock extremely smooth, but intially on the car it also did not deliver fuel while on the highway. both pumps would at times completely stop,. I thought they might be overheating and shutting down, but both pumps when this happens are cool to the touch. Also with the pump on there was no fuel pressure to the gage when this condition happens (even though you can hear pump running) The only thing I can think is that the stock pick up tube on the 240 tank was too much of a draw for both pumps (even though the pump was mounted as high as top of pick up tube. That is why i now have pick up line coming out from drain hole. Just getting expensive to pay 45.00 everytime I have to be towed.... Pressure at gage is 6lbs constant. Am running an Edelbrock 750, so the pressure is high already for that carb. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted May 1, 2007 Share Posted May 1, 2007 So I guess you are saying the pumps stop pumping (i.e. no fuel flow), but don't stop running? Cause if they stop turning there is your problem. I don't think it is too small of a pickup tube. Even the stock fuel system should provide enough fuel for 70 MPH cruising. That should be true no matter how juiced your engine is. Or by "on the highway" do you mean flat out as fast as you can go? If the lines were too small you might stall at wide open throttle, but the pump should catch back up when you go back to an idle (or restart). How long do you have to wait before the engine runs again? Also is your fuel filter on the inlet or outlet side of the pump? One thing, you want to mount the pump as LOW as you can, not high. You also want the suction side of the pump to have as few restrictions as possible. Pumps are better at pushing fuel than sucking it. But even with that you are suppose to have a filter on the suction side to keep stuff from clogging the pump. You might want to pull your pump apart and check for debris. Pumps usually have some type of inlet screen. Maybe there is something there cutting down the fuel flow. Also cut open your fuel filter and check for crap, especially if it is on the inlet side of the pump. Quote Link to comment Share on other sites More sharing options...
240ZRX Posted May 1, 2007 Author Share Posted May 1, 2007 Okay the lines are 3/8" all the way. I have two filters a small inline on the suction side and a spin off type between the pump and carb. Both are clean as a whistle and there is no debris in canister. with the line coming from the drain hole in the tank, the pick up port on the pump is about 1" higher than the tank outlet. Highway driving is 70-75 and when I do gas it up there is never any hesitation. it only happens when I am at a constant cruise speed 50-65. Pump sometimes shuts of altogether (stops running) checked all wires/ground/voltage all is good. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted May 1, 2007 Share Posted May 1, 2007 Whoo man, I don't know. I guess if I were you my next step would be to hook a hand held voltmeter across the wires right at the inlet to the pump and run the lines into the passengers compartment. If you still have over 12 volts across the pump inlet when it happens, then you have ruled out all electrical problems. How do you know it stops turning? Put your hand on it and not feel any vibration? I guess one other possible solution is to always stay on the gas Quote Link to comment Share on other sites More sharing options...
240ZRX Posted May 2, 2007 Author Share Posted May 2, 2007 When this situation happens I am able to go under the car and both hear and feel the pump. Now tonite I took it out for a ride around the area (3-4 miles) all types of driving situations and the car had no problems at all. so let me run this by anyone and see if it makes sense. originally the car had a fairly stock 350/600Edelbrock/small Crane fireball cam. with this set up there was never any fuel problem (welborn pump) over the winter i had head/cam/lifters/complete MSD box/distributor installed. I also had a 750 edelbrock carb and high rise air gap intake installed. could this new set up have been to much for the way the pump was set (high) and that it was drawing from the original fuel outlet pipe which is set high on tank and draws fuel from bottom of tank up to the outlet. could it not have been supplying enough fuel. now that I lowered the fuel pickup to the tank drain hole I am figuring in this position fuel flows easier with a better volume to the pump. Could that be a good guess??? HUH! Quote Link to comment Share on other sites More sharing options...
Teekass Posted May 2, 2007 Share Posted May 2, 2007 Are you losing any other electrical items when the fuel pumps quits running? I don't have a schematic in front of me, but was wondering if the fuseable link that supplies current to the fuel pump had a loose connection, and was intermittently quitting. If that was the case, you would also lose whatever fuse panel items that fuseable link supplied power to. The fact that it always quits at the same time (during higway driving at constant speed ) leads me to believe it's something else though.....sorry, but I'm out of ideas. Quote Link to comment Share on other sites More sharing options...
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