Starting Problem

[mr_man21]

For the longest time i thought i had an overheating problem. But after replacing the thermostat, water pump, fan clutch, and radiator i dont think that is the problem. i think i have a hot start problem. The car after getting to running temp is doesnt like shut off because its to hot, but once i turn of the car it gets tricky. in order to start the car. i have to turn the key and give it gas. and it will start. but everytime i start the car cold i dont have to give it gas. This is the weird part. The first time i try to start the car while it is hot and i dont give it gas it will almost start then sputter dead. if i would have given it gas it would have started but maybe i forget to. So after the first time i try to start the car without using gas and the engine is hot it wont start. the key turns over and the engine turns over and over but wont start. i have to wait until the car cools way down before i can start it again. If anyone has any idea or suggestions please let me know as soon as you can. Thanks everyone.

[Victor Laury]

Andrew, Ya need to tell them that this is about your 79 ZX. Otherwise, they might tell ya to tune your SU's ::

[hls30.com]

-or welcome you to the vaporlock club-which still sounds like it may be in order!

Is the injector fan still inplace? If not, get one and put it back!

Will

[mr_man21]

Yeah, I just put the auxillary fan back in when i started using the car. about a month ago is how long i have been able to drive and work on it.

[zbane]

Yeah, I know the feeling. I too have a '79 zx and you are experiencing the beautiful thing called Vaporlock. I have been able to suppres the VL problem a little by removing as many constrictions to the fuel line as possible. The PO (previous owner) had installed fuel lines that were too tight. I changed those after I changed the filter, and this seems to help, a little. Check to see that your fan is working, and try to find some of that insulating wrap for your fuel rail.

[=Resurected280=]

My '78 280Z does this too, does anyone have a picture of this auxillary fan setup? My car always does this in embarassing situations, like when running errands, and i would love to find a way to fix it.

One other thought, I've seen people wrap their fuel rails in what looks like header wrap before has anyone tried this or know if it works? Thanks in advance =)

[=Enigma=]

The engine continuing to run after being shut off id called run-on or pre-ignition. This is generally caused by heat stored up in excessive carbon deposits within the combution chamber, which causes fuel still left in the combution chamber or soaked into the carbon deposits to ignite and keep the motor running after you turn it off. In carbureted cars it can run for a while as he vacuum created by the rotating motor continues to pull in fuel.

Assuming you vehicle is still fuel injected, this is unusual, but may point to bad injectors that are leaking fuel, and may also explain the reason for the carbon deposits. If it's bad/leaky/clogged injectors and you fix those, the carbon deposits will get burned off over time and the pre-ignition will go away. Pre-ignition can also happen while the car is running however, and can in some cases cause very serious damage to your vehicle. I would get it taken care of as soon as possible.

Failing to start when it's hot is as explained previously due to vapor-lock. Looks like you have two problems here.

[zbane]

JC Whitney may be a good place to find that thermal wrap, should you decide to go that route. Someone had mentioned to me that a plumbing shop might have something compatable, but I felt that plumbing supplies may not be appropriate for an engine bay.

[sblake01]

I don't understand this. First of all, I doubt that vapor lock could occur at the 36.3 psi that the efi cars are regulated to. Secondly, I live in So Cal, and drive my 78 280Z in 100+ degree weather w/o ever experiencing this problem. No auxiliary cooling fans, no thermal wrap etc. I really don't think that the 280ZX injector cooling fans accomplish anything and note that you don't see them on any of the later cars. I would tend to lean more in the direction that Enigma went.

[=Resurected280=]

Thanks for the pics zbane I always wondered what those black things the ZX's have on their valve covers were , now I know.

So far as mr man 21's problem goes I think Enigma is right that this is a two part problem. The "running on" is one and the vapor lock is the another.

I have a suggestion on the vapor lock issue though, as this is something I've wanted to try for a while but I havent done it yet. I wanted to wire up a switch to disable the starter motor on my car so that I can turn the key like I was trying to start the car and run just the fuel pump (this is easier than it sounds). My hope here is that running just the fuel pump for maybe 10 or 15 seconds would prevent the "try to start-->sputter, sputter die" symptom by getting fresh fuel from the gas tank moved through the system. Does anyone have any thoughts on this or know whether or not this could work??

Mind you that i'm not positive how vapor lock works exactly but this was just a thought that I had.

[=Enigma=]

Derek, why would you need to disable the starter just to get the fuel pump pumping? The fuel pump should run just by turning the ignition to the "Run" position. Am I missing something?

[zbane]

Agreed, Enigma- The pump SHOULD pump automatically when the key is turned to the on position.

Derek, if you are having problems with sputtering, and you think it is pump related, perhaps you have a leak in the system somewhere which is allowing the fuel system pressure to drop.

Regarding Vapor lock-As I understand it, here is what happens

1-during driving, the fuel lines (metal and rubber) warm up.

2-air flow is not enough to cool the lines.

3-the lines get hot enough to boil the gasoline. Since gas expands as it evaporates, it creates a blockage in the system, one that liquid gas cannot get around and the fuel pump is not powerful enough to force through the system.

4-since the liquid gas is now trapped behind gaseus gas in a very hot fuel rail, the liquid gas boils and becomes gaseus, thus putting more back pressure in the system.

The only way to deal with vapor lock, once it occurs, is to allow the engine (and lines) to cool enough to allow the gas to condense into its liquid state.

I know I probably don't have the process 100% correct, but that is how vapor lock has been explained to me in the past.

hope it helps