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First..I would like to Thank you guy's for the help you have given. This 1976 280z (fuel injection) has been a real education....The car runs great..However, when the car run's for a while, or it could be engine temperature. The car will put itself out of timing (or it seems). While test driving for about 30 mins. And try to accurate the car will start coughing. . When the car was pulled over and sitting still..the coughing continues. And, sounding like it's back firing though the air cleaner..we have walked though the Service Manual, and other books we have. It makes no mention of this type of problem..It's not over heating, when the car it cools, the timing is correct...
 

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You may want to consider the ignition computer. It is on the pass side kick panel (on my 78). The transistors in it will fail with heat as they age. Sooner or later you have to replace it. Ther eis no way to test for this. It is kind of an when-all-else-fails kind of thing.
 

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Thanks.John...that is where I'm at..tested all the wiring checked the computer and ect...The Ingnition computer has to be it...Since I'm at this point..would it be better to upgrade the unit..maybe a product from MSD and if so..which one would you use..??
 

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Two things to look at. First if I remember correctly the 76 has a dual pickup distributor. The different timing being actuated by a temp switch above the therostat housing. Check that circuit first. Also a major cause of backfire through the air cleaner is lean running. Look for vacuum and air leaks. An air leak will be accentuated as the car warms up. The f/i control unit automatically enriches the mix when cold so it can cover up a lean condition but it shows up more when warm. The early tran ignition boxes don't go bad nearly as often as the later ZX boxes so I wouldn't automatically condemn it. If you want to test the box you can try to duplicate the heating with a hair dryer blowing on it. Or, you can get a can of 'cool freeze' or something of that nature at an electronics store. It is designed to spray on electronics when they warm up to help troubleshoot. If you spray it on the ignition box and it gets better then that is the problem.
 

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'The eminent JohnH240 is likely more knowledgeable than I am. However, I think the dual pickup is more dpenendent on whether or not it is an automatic. automatics have em, sticxks don't. I thinik... It is easy to tell. Just lift up the cap and take a look. I put a dual on mine, one is simply disconnected. The rest of what he is saying would have been my first guess too, but 30 minutes is too long for the car to go through the warm up cycle for this stuff to have an effect. If the car runs well after the car somes up to temperature (5 minutes, 10 max) the problem would manifest itself then if it was due to those kinds fo things (vacuum things, tuneup stuff, etc). His ideas aon testing the box are good. as for getting a new one, especially a High performance One. I believe that the bottom line there is that there are no such high-performance boxes or chips available for this car. I think they might be avaioable for the later ZXs, but not for the Z. If you hear differently, let me know. I think ifyou call MSA they will just sel you the nissan unit. Make sure you know your production date when you order it., It makes a differenc4e. Good luck.
 
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