Starting Problem

[=Resurected280=]

Thank you, this does help, this is how I thought vaporlock worked too but I wasnt sure. The reason I wanted to get the pump to run by itself is because I was hoping that having just the pump running like that would push the air out of the lines and back to the tank, and therefore put fresh gas in the fuel rail. My fuel pump does work correctly (its only a year old) but I think it only runs for a few seconds when I turn the ignition to the on position. I also dont have any leaks that I know of, the only mechanical problem my car has is on hot starts it does exactly what mr man 21's car does.

Sorry for the confusion here. I guess what I was trying to ask is would the fuel pump be able to on its own push this air out of the fuel rail? I was thinking that this would bring fresh fuel into the rail and avoid the hot start problem.

Just as an additional question, can vapor lock happen while a car is running? I wouldnt think so but I'm not as sure about my knowledge of vaporlock as I was =)

[zbane]

Yes, I know from experience that vapor lock can happen while you are driving.

Not safe, and Not fun. The pump will not be able to push the vaporized fuel backto the tank because the vapor compresses but does not condense. It also has the nasty habit of rising to the highest point available in your fuel system, and getting it to move down the line is just too much for the pump.

Good luck.

david

[=Enigma=]

Many fuel pumps on EFI systems are on a timer that runs for a few seconds when you first turn the key ot the "ON" position to prime or pressurize the fuel system to ensure fuel delivery. My 4runner is like this. It stops after a few seconds in case all you wanted to do was turn the ignition ON to power lights, radio, or other accessories. Once the engine is started it should resume running and continue to run as long as the engine does. If it does not, there is something wrong with the timer circuit assuming one exists. Perhaps a 280ZX owner can chime in on this.

Please note I originally thought it operated like my carbureted 73' in which the pump continues to run as long as the key is in the "ON" position, regardless of whether the engine is running or not.

[sblake01]

Again, I'll state that I've not experienced vapor lock in either of my EFI cars and I live in So Cal. And niether of them have those stupid cooling fans. You guys are discussing cars that have had some apparently bad maintainence/modifications performed on them by previous/previous owners. And then suggesting that you do more bad mods like wrapping the lines in thermal wrap which accomplishes about as much as the ZX cooling fans. Note that the ZX was the only car that Nissan chose to put those on. Not the RWD Maximas, 810s etc. There are some misconceptions posted here about vapor lock. An EFI fuel pump is powerful enough to 'force through the system' at it's regulated pressure. If it's working properly. If you were discussing carbureated cars, there might be some validity to this discussion. Again, I say forget about vapor lock and look elsewhere. OUT!

[=Resurected280=]

Okay then, suggestions? Me and Andrew are obviously not the only ones with this problem and my car in particular has been family owned since new and my uncle informed me that it always had this vaporlock problem (or whatever it is), even after repeated visits to the dealership trying to remedy this.

[sblake01]

I really don't have any suggestions other than ruling out vapor lock. I've never experienced it is either of my efi Datsuns and my long time friend and owner of a Z shop says that efi Datsuns don't vapor lock. Acting up when hot can be a myriad of different things from a bad temp sensor to a bad efi relay. A bad air regulator, cold start valve, thermotime switch, coil, even a bad fuel pump check valve. All of those are things that work better when cool than when hot. Those, I've been through and solved.

[RogerZ]

If you turn off the radio and you can still hear (which I can't) turn the key to run and listen. You will hear the fuel pump run for a few seconds and then stop (times out). this on 81 turbo, 83 turbo, 83 na, 85 z31. CAn't hear it on my z32 but might be my hearing deficit. Thirty years in the engine room of a large cargo ship does wonders for your hearing.

[hls30.com]

Many fuel pumps on EFI systems are on a timer that runs for a few seconds when you first turn the key ot the "ON" position to prime or pressurize the fuel system to ensure fuel delivery. My 4runner is like this. It stops after a few seconds in case all you wanted to do was turn the ignition ON to power lights, radio, or other accessories. Once the engine is started it should resume running and continue to run as long as the engine does. If it does not, there is something wrong with the timer circuit assuming one exists. Perhaps a 280ZX owner can chime in on this.

Please note I originally thought it operated like my carbureted 73' in which the pump continues to run as long as the key is in the "ON" position, regardless of whether the engine is running or not.

There is no timer! What is going on is the sensor for intake air is detecting no air flow through the intake(In a a fuelinjected Z(X) the sensor is a part of the AFM), and the ecm cuts off the fule pump. With out this feature if the car were in a wreck that cut a fuel line and stopped the engine, the pump would empty the fuel tank and add to the fire hazzard of the wreck.

There is a check valve in the fuel pump that enables it to keep prime, and in conjuction with the fuel pressure regulator, keeps the system pressurized. It could be that you have a leaking injector, that is allowing pressure to drop below what the car needs to run by putting fuel in after shut down(explains the after run) and making the fuel system act as if you must reprime the tank on the next startup. I would put a suitable fuel pressure gage in under the hood and check what happens from startup through running and then to shut down-I think your fuel pressure is dropping to 0 after sitting a little while, and it should drop only slightly at shutdown.

Will