280z Cold Starts, dies when warm.

[Shoetotheface]

Ive been having trouble with my 280z. My last Z was a 72 240z so fuel injection was pretty new to me when I started working on this. Ive been slowly learning the nuances to the L Jet system. The problem was a bad idle and not staying runnning. Old owner said it had bad gas in it so I dropped the tank and looked in and there was an inch of sludge. I rinsed all the sludge out of the tank and treated it for rust. Tank was perfectly clean when I put it back in. I also put in a new fuel filter, fuel pump, and just to be safe I swapped out the injectors and rail for the fuel rail and injectors from a running car. I also blew out the lines. Car still ran like crap. I got a fuel pressure gauge hooked up and my pressure is around 30psi to 28psi. Ive replaced the AFM as well. Car starts and idles around 1600. Idle drops after around a minute to 1k. Sometimes it holds sometimes it drops to 800 and gets really rough and dies. I drove it down the road once and under load it stutters hard and I hear a pop from the intake. After checking my plugs they are white. So my best guess is im leaning out somehow. Ive checked for vacuum leaks and couldnt find any. Any help is appreciated thanks

[siteunseen]

I had a hard to figure out problem with a '77 I'd bought. After a month or so I read about a recall on those with egr. My egr tube had come loose under the intake manifold where it connects to the egr tunnel. No telling how long it had been like that but it had rotted out a hole as big as a golf ball under there. Take a handheld mirror and look under the manifold close to the windshield end. Happen to me so it's a possibility. Good luck.

[Shoetotheface]

Mine is a 78. The EGR is on the intake but the car has headers. So its not connected to anything....

[Zed Head]

2 hours ago, Shoetotheface said:

I got a fuel pressure gauge hooked up and my pressure is around 30psi to 28psi.

Engine running or not?  Supposed to be 36.3, engine not running.

[Shoetotheface]

Engine running

[Zed Head]

2 hours ago, Shoetotheface said:

Car still ran like crap.

Sometimes it holds sometimes it drops to 800 and gets really rough and dies.

I drove it down the road once and under load it stutters hard and I hear a pop from the intake. After checking my plugs they are white. So my best guess is im leaning out somehow. Ive checked for vacuum leaks and couldnt find any. Any help is appreciated thanks

The idle problem and the popping problem might be from different causes.  But the fuel tweak might help the popping and stuttering.

http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

[Shoetotheface]

Would replacing the temp sensor fix this? Or would I still need to do the tweak?

[S30Driver]

Although you say you checked for vacuum leaks, I would get a gauge and check the reading,  see where you are at..   As a quick test, when warm and running at idle, unscrew the oil cap, remove, and see how the motor responds.  Its a sealed system, if no change, you have a significant vacuum leak.

As an example, when you changed injectors, did you replace all the seals with new ones?

Before changing more parts, if you have not done so, run the all the efi system checks in the 78 shop manual, record the info and report back.  Many members here can help you interpret that information.  

[Shoetotheface]

I did the oil cap test and the idle didn't change as far as I can tell. However it runs like such garbage it's hard to tell at all. I did the yogurt cup vacuum test and it passed. I don't see how I could have a vacuum leak but the oil cap removed didn't make a difference. 

[Zed Head]

4 hours ago, Shoetotheface said:

Would replacing the temp sensor fix this? Or would I still need to do the tweak?

Replacing the temp sensor would probably have little effect.  The tweak is a cheap way to see if you are running lean, and to fix it.  For whatever reason many of the old 280Z's run lean, maybe because the EFI system was tuned for 70's gasoline.

[Shoetotheface]

On 6/11/2020 at 2:11 PM, Zed Head said:

The idle problem and the popping problem might be from different causes.  But the fuel tweak might help the popping and stuttering.

http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

The fuel tweak didn't help. In fact nothing changed. I can completely disconnect the temp sensor and the car still idles the same

[Zed Head]

On 6/11/2020 at 2:11 PM, Zed Head said:

The idle problem and the popping problem might be from different causes.  But the fuel tweak might help the popping and stuttering.

http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

The fuel tweak was for the popping and stuttering, not the idling.

Are you sure that you're disconnecting the sensor?  There is also the cold start (thermotime) switch and the temperature sender in the same vicinity.

Edited June 15, 2020 by Zed Head