1976 Running rough, sputtering, backfiring

[TritleZ]

I picked up a 1976 280z that had been garaged since 1998 this past winter. Just recently I've been able to work on it. I started by draining all the old gas from the gas tank. Drained and changed the oil and coolant. After I installed a new fuel pump, and plugs I was able to start the engine. It initially ran fine (maybe a minute) but now everything I start it the engine sputters and back fires and will eventually die. I can get it to idle but it only idles at 500 rpms.

 

My first thought was that it was getting too much gas and loading up. I checked the plugs and everything looked clean. I then proceeded to pull the injectors thinking that one may be stuck or something. All the injectors didn't appear to be stuck open when I used compressed air through them hooked to the fuel rail (unless I didn't do something right) So I re-installed the injectors. I purchased new injector clips and installed those tonight. But I am getting the same results.

 

Is there something I am missing? It looks like the previous owner may have tried to do some work on the engine as I can see a few missing vacuum hoses, but not sure what goes where. Could it still be old gas running through the system? I have over 2 gallons of fresh gasoline in the tank. Is it a fuel pressure problem? My next step is to check the FPR, and then to check the AFM.

 

Any help/suggestions would be greatly appreciated. I will try to upload a video to YouTube to show what's happening.

[Zincolumbus]

My 76 had sat for a while also I did pretty much same as you maintenance wise. I did not pull the thank and clean it that is were my problem was. I could put new fuel filters on and it would run fine for a few minutes then sputter and die. My problem was junk in the tank kept clogging the filters it only took a couple minutes to clog them tight. Hope this helps some also download the fsm from xenon that should help with hose routing.

[TritleZ]

Thanks for the reply. I'll check the fuel filter today. And I just downloaded the FSM, thank you again.

[TritleZ]

I replaced the fuel filter. Not really much difference. Took a little bit to get it started again. Maybe just took a bit to get fuel back to everything? Here is a video of the engine running for about 2 minutes (longest I've had it running this smoothly) before it sputters, back fires, and then stalls and dies.

 

[Zincolumbus]

I would check your fuel pressure sounds like its starving.

[stravi757]

reading the fsm is a great start. Once you read how the efi system works on this car its much easier to diagnose problems. I would start with checking the fuel pressure, Are you running to rich or lean. Also make sure to clean every electrical connections in the engine bay. I would also just go ahead and replace the water temp sensor. do the plugs wires and all of that. look for vacuum leaks! if you said the hoses look like they have been messed with that could be the problem.

[Guest ttoude]

The other half of the rusty gas tank story is that small flakes of rust traveled down stream and are probly lodged in the hard fuel lines.

 

I used a bike brake cable to "snake" the hard lines.

 

My tank is clean but the motor was from another car.

 

If I let it sit for LONG time it will run, for a moment. My FPR fuel return line was blocked shooting 95psi to the injectors causing low rpm + sputtering and a cool PLOOM of fire out of the down pipe.

 

 

Edited April 4, 2010 by ttoude

[UPSMT280Z]

hey trtlez i have a 78 and had the same problem it wasnt the main fuel filter it was crap in the tank getting sucked into the screen on the intake side of the fuel pump. I pulled the pump cleaned it all out and then the problem went away never been seen since.