L28 Misfiring?

[Indey]

My 76 280Z has the original l28 in it, it has an issue that happens somewhat randomly. Sometimes when I start it, it will act as though it's misfiring, and not hold an idle, to solve this, I generally have to hold the gas for a period of time, and it will finally "kick in" and not misfire anymore. It will also randomly die when I'm driving along, and when I restart it (If it restarts) It's doing the same misfire, and I have to hold the gas again till it runs correctly.

 

Now the particular thing about when it does this.

 

It generally happens when it is very hot outside.

It also generally happens when I've gone somewhere and gotten back in the car relatively quickly to go somewhere else.

And finally, when it does this, it throws a good deal of smoke out of the exhaust.

My mechanic has been unable to recreate the problem, so he cannot figure it out.

 

So i was wondering if anyone had ever had a similar problem with their motor

 

Thanks in advance.

[tecreatta]

Sound like the cold start sensor my be acting up sometimes it'll flood a car if malfunctioning at idle and cause a backfire due to excess gas in the manifold. Check your plugs if there are black you definitely have a fuel problem.

[NewZed]

It's possible that your fuel injectors are leaking. The gas pools in the intake and has to get burned off.

 

You could install a pressure gauge and monitor fuel pressure, before you replace expensive injectors. If it happens whenever fuel pressure drops, that would be a fairly good clue, assuming that the FPR and the check valve are in good shape.

[Jackbat]

I had the same problem. It turned out that my fuel injectors were leaking (and others not letting enough fuel in, leaning it out to much.)

Check you plugs. If they are fouled (rich) or white (too lean,) you should buy a remanfactured injector from an autoparts store. (usually about $30.)

Replace the injector at one of the messed up plugs, and the plug itself.

 

If you notice a difference in how it runs, its a good bet that you have some bad injectors, and can go ahead and replace all 6.

I replaced mine one at a time, and everytime it got slightly better until I replaced the final 2 injectors and it fixed it complete;y.

[rossman]

I believe your injectors are getting heat soaked. After the car sits for a few minutes, heat from the manifold radiates on the injectors causing the fuel inside them to vaporize. The car will run like crap until the fuel pump forces all the fuel vapor out of the injectors. If the car sits long enough, the fuel condenses again and the problem doesn't show itself.

 

Things you can do to help alleviate the problem:

 

1) Re-install the heat shield between your manifolds if it's gone

2) Wrap your injectors and fuel rail with reflective insulating tape

3) Install an injector blower from a S130 (280zx)

 

Also, download a copy of the EFI Bible. It's highly likely that you have multiple FI related issues. Make sure you clean all of the FI connectors.

Edited July 10, 2011 by rossman

[TimZ]

I believe your injectors are getting heat soaked. After the car sits for a few minutes, heat from the manifold radiates on the injectors causing the fuel inside them to vaporize. The car will run like crap until the fuel pump forces all the fuel vapor out of the injectors. If the car sits long enough, the fuel condenses again and the problem doesn't show itself.

 

Things you can do to help alleviate the problem:

 

1) Re-install the heat shield between your manifolds if it's gone

2) Wrap your injectors and fuel rail with reflective insulating tape

3) Install an injector blower from a S130 (280zx)

 

Also, download a copy of the EFI Bible. It's highly likely that you have multiple FI related issues. Make sure you clean all of the FI connectors.

 

You are describing classic heat soak/vapor lock symptoms.

This is a common problem on FI Z's that many don't seem to know about, to the point that Nissan added a blower fan on the ZX's to address the problem, as rossman pointed out.

Edited July 10, 2011 by TimZ

[Indey]

So a few months later just to add to this..

 

I finally ran across a few specific things about the problem.

 

To which first off, thanks to everyone who contributed info!

 

Now I had talked to another member about it and he of course also suggested vapor lock, and suggested that I move to 91 octane since it's less volatile, and he also suggested the webbed intake manifold that nissan came out with to replace the open runner n42 manifold that's currently on the car, in another effort to get heat away from the injectors.

 

Then I ran across something where someone said they had the same sort of issue that I did, and they removed the filler caps rubber seal, and the problem went away. So being that I was stuck in my works parking lot today with a Z that wouldn't start, I figured, "hey what can it hurt to try?" So i removed the filler cap, and went to start the car. lo and behold, it fired up instantly. I put the filler cap back in place and drove home, where I am now. I called my mechanic and asked him about it, and he said that it's possible that an injector wasn't closing, or something to that effect, and it was allowing pressure to build in the gas tank, which would prevent the car from starting. Naturally when I released all the pressure the car was able to start again.

 

So for a temporary fix, if this continues to work, I will be happy with it for now. However I am going to get that webbed intake manifold, since I'm going to redo my exhaust system I figured why not just put a redone already cleaned manifold on, and save myself the hassle of having to clean my own, and if it can also reduce the injector temps due to the extra webbing then great! I also figured that at the same time I would go ahead and just replace all 6 of my injectors because well. If you're going to do something, do it right.

 

Anyways thats the current bit of my story for this problem. Hopefully people with the same problem will be able to search and find this and it can help them!

[bryand2]

Did the OP ever figure this out? I seem to be having the same problem. Car misfires only when being started while warm and at idle. As soon as the car is under load and moving it goes away and it only happens when the car is warm. I thought maybe I had a leaking fuel injector as well but im curious about this gas cap rubber seal and built up pressure in the gas tank. My situation is a little different because I am always able to start the car but when it is warm and start it, it runs on 5 cylinders until the car starts moving, any ideas?