capt_furious Posted May 15, 2009 Share Posted May 15, 2009 I was troubleshooting / correcting issues with the Z today and encountered a VERY strange phenomenon: I replaced some hoses and improved some small bits of my fuel system. Part of the troubleshooting was determining if the car cuts out the fuel pump at random intervals, and to correct what I suspected was a small air leak into the hoses at the tank connection(oversized hose on the fitting). I disconnected the electrical connection for the pump so I could test the voltage at the plug. I fired the car up out of curiosity just to see how long it would take to starve. It didn't. Fuel pressure dropped to zero on the inline gauge I've got just upstream of the fuel rail, but the car kept running and would even rev without cutting out. I reconnected the fuel pump and pressure came back up. Wow. So, do SUs actually create suction on the fuel line? I've never heard of a carb creating suction and feeding itself, or a car running with zero fuel pressure, but there you go. I didn't put a load on it or drive it around that way, maybe I should give it a try. Quote Link to comment Share on other sites More sharing options...
bschiltz Posted May 15, 2009 Share Posted May 15, 2009 How long did it run? I'm not familiar with SUs, but on my Quadrajet there is a pretty big float area that can let an engine run for quite a while. The first time I started my engine, I just dumped some gas in the float before I put the carb all the way together, then put it on the engine, then started it. Not the safest or smartest idea but it ran for about a minute with a coupel revs. Or maybe you just figured out the new alternitave fuel idea, engines don't actually need fuel, they just like to have it around! Quote Link to comment Share on other sites More sharing options...
Stealth-Z Posted May 15, 2009 Share Posted May 15, 2009 Just out of curiosity, is the mechanical fuel pump still attached to the head? Quote Link to comment Share on other sites More sharing options...
AK-Z Posted May 15, 2009 Share Posted May 15, 2009 Just out of curiosity, is the mechanical fuel pump still attached to the head? thats what I was going to ask Quote Link to comment Share on other sites More sharing options...
zeeboost Posted May 15, 2009 Share Posted May 15, 2009 I had an anti-theft killswitch for the fuel pump on my v8 280zx. It was just a normal 670 Holley carb, but there were a couple of times that I would drive off for about 30 or more seconds until the engine would start sputtering out. Initially I would freak out and wonder wtf broke this time, but then I'd remember and flip the switch, while coasting as long as I could before I felt it was safe to release the clutch pedal and get the engine going again. How long was it running? Quote Link to comment Share on other sites More sharing options...
thrustnut Posted May 15, 2009 Share Posted May 15, 2009 Dito that, my Carter will run for a couple minutes befor cutting out. I installed a fuel switch when I put the new engine in and forget at least once a week to turn it on before driving. I need a buzzer or somthin...(hey stupid, turn the fuel on) Quote Link to comment Share on other sites More sharing options...
zeeboost Posted May 15, 2009 Share Posted May 15, 2009 I thought it worked great for anti-theft, though, because say if a criminal just stole the car, he'll be driving off at least a good half a block or so, thinking he made away with it, and then BAM - unless he finds the hidden switch, he's screwed. Quote Link to comment Share on other sites More sharing options...
auxilary Posted May 15, 2009 Share Posted May 15, 2009 he has a block off plate for the mechanical pump, if memory serves Quote Link to comment Share on other sites More sharing options...
capt_furious Posted May 15, 2009 Author Share Posted May 15, 2009 The mechanical pump is still on the block, but it's not hooked up. I ran it for about a full minute or so last night. I'm going to try it again tonight and see how long it lasts. If it was just running off of the fuel in the line / bowls, there's a lot of fuel in there! Quote Link to comment Share on other sites More sharing options...
thrustnut Posted May 15, 2009 Share Posted May 15, 2009 The first time I forgot the switch was leaving the DMV. I got about half a mile away when it cut out in a roundabout and I thought WTF...another gremlin. I was still coasting with enough speed to pop the clutch, look down, flip the switch, let it prime for a sec. and re-start it. I would just let it go for a while and see if it dies, it wont hurt anything. Quote Link to comment Share on other sites More sharing options...
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