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Discussion Starter #1
My Z car is in very good condition, but it has an issue that I am not sure of how to fix, as I don't know what the problem is. However, I can explain what happens.

On cold starts the Z fires right up! But it may not idle very good at first. Once it warms up a little 1 min or 2 mins it idles steady at about 700 rmpm.

Now, If I turn the car off and start it right back up it fires right up.

If it turn the car off and let it sit for more than 5 minutes, when I go to start it again it takes a while and then it fires. But when it starts the idle will bounce between 500 and 1000 rpm, and finally after a short while it will idle fairly smooth.

Also when driving sometimes it idles at around 700 rpms, sometimes around 1000. There does not seem to be anything consistent.

The car seems to have a little hesitation sometimes at low rpm < 2000 (it is not much, maybe just a little).

The car does run very well when over 2000 rpm.

The only thing not stock is the fact that the charcole canister was removed by the previous owner. The hose is just left open. Is this how it should be or should it be plugged? I did not think it should be plugged, but I am not sure.

I have recently installed new plugs and wires, cap and rotor. I have not checked the timing, but it seems good.

Exhaust is fairly new, but not the cat converter. I was thinking maybe that cat is plugged, but it runs very strong in higher rpms.

Thanks for any help,
Dan Didier
 

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idle sounds like you have a cold start valve stuck open. 2000rpm hesitation sounds like vacumn advance
 

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Re: What year is your car?

What year ?? Is it carberated ,injected turbo ??? It would help greatly if more info was given. Gary Portland
 

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Discussion Starter #5
Re: Strange Problem - 1980 zx

Sorry about that - the car is a 1980 and it is fuel injected.

I don't think the line for the canister should be plugged, but I am not sure.

Thanks for all the replies.

Dan
 

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Re: Strange Problem - 1980 zx

You should have 3 hoses that connected to the charcoal cannister. Vapor, Vent/purge, and Vacuum signal. The Vent line to the tank is the only one that could be left open (of course that would let fuel fumes into the engine compartment. Can you say 'CAR-B-QUE'?) The Purge line and the Vac Signal line should both be plugged off. If not they will create an air leak and would cause some of the problems you are seeing.
 

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Re: Strange Problem - Heat Soak/Vapor Lock

I've had this problem in my 75 and 77. And the solution was to isolate the fuel rail from the engine block.

Don't know if your 80 came with the fuel rail fan, but it is ugly, and some say dangerous. It's purpose was to solve the very problem you are having. It is supposed to turn on after the engine is shut down, and the engine gets hotter (no water circulation, or air flow). The fuel gets so hot in the rail that it vaporizes. You probably noticed that the stumble/rough idle goes away after you get on the gas good. That means you have flushed the vapor and are sending liquid gas again.

You can fix this problem by finding every point that the fuel rail touches the intake manifold, and the head (lines that cross in front of head get real hot) and adding some sort of isolation between the rail and other metal. This prevents the high temp cycle that the engine goes through when you shut down from being felt on the metal fuel lines. It really did work for me.

Or you may want to invest in the fan that ZX's used. Some posters here claim they are a saftey hazard. If you have any sort of fuel leak, and the fan cuts in after the car has sat for a minute, the spark from the fan can ignite the fuel vapor. Sounds bad. Your call.

You have other problems. I think your idle is too low. Setting it slightly higher may produce a more smooth idle. Fix all vacuum leaks. Do you have the fast idle device? It should idle your car slightly above 1000 rpms during warm up cycle, then it shuts down and idle returns to normal. Is it working intermittently? Check for corrosion on your sensor connections.

Get a Factory Service Manual. If used properly, it will answer most all of your questions. Then you can ask the truely bizarre stuff here!
 

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Okay didierd and John

With that fuel vent line - what do you do with it? I've been looking for a definitive answer as to what to do with the fuel tank vent, and the expansion tank in the rear of the hatch. I run tripples with no fuel return so I've got that plugged, the expansion tank is in place with all hoses connected but then I have that vent line left over. Do I need the expansion tank or is there another way to vent the tank and do away with the expansion - I don't recall running into these expansion tanks in other vehicles?

For Didierd, could your fuel injectors be leaking, causing a slight flooding state after sitting for a few minutes. I had an RX7 turbo that did this, after it was shut off the injectors were worn or dirty and didn't close completely allowing fuel to drip into the chambers then it wouldn't start for a while. Just a thought, seems you've replaced the other basic tune up items dealing with spark and timing so fuels the main thing left. Coils also get heat soak and don't work very well, but its usually after being run for a full warm up at least.

Matt
 

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Discussion Starter #9
Re: Strange Problem - Heat Soak/Vapor Lock

My car does have the fan that kicks on! and it works (it goes on anyway)

it has been that way for 180,000 miles - doubt it is too dangerous.

I will check into all the things you guys have said. I will report back.

Thanks!
 

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Discussion Starter #10
Re: Strange Problem - MORE INFO

Hi guys.

Take a look - I have some pictures for you.

You can see in this first picture where the canister used to be. You can see how the line is just bipassed. You can also see where I plugged the other line.

http://didierd.pointclark.net/PA260199.JPG

This other picture shows the distance of the fuel lines from the head. The fuel vaporization theory sounds like it to me, but this car has been like this from factory, why would it change now?

http://didierd.pointclark.net/PA260200.JPG

And this picture is just for good measure - in case you may notice something here - http://didierd.pointclark.net/PA260201.JPG


If you are interested here is a couple pics of my car during it's paint job and after I painted it.


http://danspage.sunyit.edu/pics/z/6-25-01/P6250008.jpg
http://danspage.sunyit.edu/pics/cars/z/Zapart.jpg

Again, thanks for all the replies.
Dan
 

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Re: Strange Problem - MORE INFO

You have the vacuum line going directly to your vapor vent line(the one bypasing the carbon canister) which I would thing would be a vacuum leak. Try pinching that hose with a pair of vice-grips and see how it runs then.

Charles
 

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Re: Strange Problem - MORE INFO

>This other picture shows the distance of the fuel lines from the head. The fuel vaporization theory sounds like it to me, but this car has been like this from factory, why would it change now?

First off, it is a theory, but credible, since Nissan recongnized that their FI cars could indeed suffer from performance problems related to heat soak, and created that fan to solve it. People used to say that FI cars shouldn't be affected since the fuel is under pressure. Well, true enough. Higher pressure will mitigate the affect, however our fuel rails do not STAY at the higher pressure at shutoff. The pressure drops, and if your fuel system has any problems, it will drop faster.

That may explain why you are just now having problems. If your fuel pressure drops immediately after engine shut off, you are more succeptible to heat soak problems. (Fuel pump check valve, Fuel Pressure Regulator, leaky injectors, leaky cold start valve, leaky fuel line).

Or, your thermostatic switch could be on the way out. They do fail every now and then. Or you could have corrosion on the contacts of the switch. Not sure.

Your problem could be unrelated to the heat soak issue, but it sure sounds exactly like it.

About the safety issue. I was just passing on what I've read about here. Evidently, someone who knows posted on this issue after losing his car, and investigating others. It does make sense, too. You park your ride. The slight leak vaporizes fuel that wafts around your engine bay. Fan cuts on, and WHOOSH! Like I said though, you make the call. Hope you get it fixed.
 

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Could be the Cold Start Valve. It increases the amount of fuel and air that enters the engine during a cold start until it is warmed up.
 

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Which is the problem??

I think that the fan should'nt be to blame for that cenario - If you got vapours or spiled gas under your hood, you've got other problems on your hands
 

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Re: Strange Problem - MORE INFO

Three things I see and would fix. Vent line from tank should not go directly to the manifold. That would create an air leak or it could create a negative pressure situation in the fuel tank and restrict fuel delivery. Second, since the EGR appears to have been removed, I would make sure that the ports on the bottom of the throttle body are securely plugged. (Also, it may be my eyes but I can't see a vac advance on the dizzy?). Along with that the port into the intake manifold for the egr must be plugged. Third, I would relocate the coil to dizzy wire so that it is farther away from the AFM. Perhaps a right angle boot and a longer wire that loops away from the afm. It can induce odd signals into the injection system.
 

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Re: Strange Problem - MORE INFO

Try rubber grommets. You may have to drill the hole through the rail bracket slightly bigger to accept one that will pass your bolt.

Or you could try something like teflon strips on either side of the rail bracket, making sure that the rail bracket itself does not touch the bolt.

The part of the rail that goes around the front of the engine is trickier. Pay a visit to your local hardware store, and see what they have to offer in their specialty washer section. There are washers that have a sleeve that extends into a hole, used for electrical applications, that keep the bolt from touching what it is fastening. Maybe Radio Shack?

I was able to use rubber, but I know that it won't last forever. It does work, though. I haven't had the problem PERIOD since I made that change.
 
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