I have a 83 280zx turbo and have been having timing problems. I replaced my l28et with a new motor, since it overheated due to a bad head gasket. On the new motor I set timing to 20 degrees and the rpm was about 800. At this point the engine had already been running for about 10 minutes. After setting timing I let it idle for about another 5 minutes, when all of a sudden it began to run poorly. I tried revving the engine and it began to backfire. I looked at the rpm and it was at about 200. I checked timing again and now it was at about 35 degrees. I played with the distributor and the best I could get it was 30 degrees. I turned the engine off and then started it again and timing was still at 30. I took the bolts out that held the distributor in place and got timing back to 20, but the distributor was in a position where the bolts could go back in. I know that I can take out the oil pump and reset timing, but I am trying to figure out why this happened. I don't want to be driving and this to happen to me.

I recently replace the cap and rotor for the distributor. And all spark plugs are with in spec and are firing. Also when the timing was set. the line on the crank pulley held its spot without any movement. There was not grinding or any other bad sounds when the rpm dropped. The chain on the motor looks fine. I don't think its the tensioner either because the time would be constantly moving. Thanks for the help.

 

Is it possible the bolts aren't holding? Mine did the same thing and I narrowed it to the bolts on the rotor not holding.

 

The bolts are holding. I notice that when the engine is cold the timing is fine, but when the engine begins to warms up it jumps.

 

Replace or test the vacuum advance.

 

I have a turbo car, so there is no vacuum advance

 

Hey kid, i'm a z-car tech and i live in the east bay. Send me a p/m with your e/mail if you would like me to come out. Later !

 

My experience stops here... But hey I tried.

 

Thanks for the suggestions Twiggs280zx. PM sent.