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L28 ok when cold, running rough when warm and stutters at 1400 rpm


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Need help! I'm no expert so I need a little advise. I've searched and tried several suggested fixes, but the car won't run properly.

 

Engine: 1977 280z stock L28

 

Symptoms:

Car starts easily, idles great and I can easily drive the car out of the garage. As soon as it get hot the car won't rev properly and backfires. When throttle is increased the car stutters at 1400 rpm and drops till it dies. The car at this point doesn't have enough pull to be driven back into its garage. It still idles and revs above 3000 fine though.

 

The car worked fine, except cold start problem, two years ago when the car was set to work on. During the 2 years of work on it (engine related) it has pulled the AC (just pump and plumbing), replaced all bosch connectors, replaced all fuel lines, replaced distributor cap + rotor + plugs + wires, fitted k&n intake filter, 6-1 header, fuel filters.

 

The cold start problem is now gone (because of new bosch connector), but it now hesitates to much when hot to the point it's undrivable.

 

I think it basically runs to lean, so I've checked all connections (new), fuel pump, tank (recoated inside), vaccum, and it all looks good. The AFM looks like it works great and I just cant seem to find the cause. The water temp sensor isn't dead since the engine dies when I pull that connector, so it must give some sort of signal.

 

Any ideas or suggestions on what it could be?

 

I have the Haynes manual and the FSM, but I can't seem to find a solution.

 

Thanks!

Edited by HaaJeHaa
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My first thought was AFM but you say no. I can tell you that I had a 280zx that would run like a champ until it got hot, then it would sputter out and die. I would wait for it to cool off and it would be fine until it heated up again. It turned out to be the fuel pump. Once I replaced that it was fine.

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Popped the cover off the AFM and all connections seems fine. The mechanics is also in working order...

 

I've actually ran the fuel pump on my workbench in diesel just to see how it behaves. Steady stream of fuel for 10 minutes, so its not that.

 

I have no idea what could be wrong....

 

It ran perfectly before I began work on it, so it's either something that's wrong to the parts fitted or it didn't like to sit for 2 years.

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