Need Some Help - Backfire, Misfire, etc.
 

I recently bought a '76 280Z that had laid up for about a year. After changing out the fuel injection relay, throttle position relay and fuel pump, I get a relatively stable idle. When the car is under acceleration, it misfires, skips, or backfires. A local mechanic (note desperation) tried a new distributor, only to inform me that the timing jumps. The ducting between the air filter, mass airflow sensor and throttle have cracks, (anyone know where to get these?) which I'm sure doesn't help. Does anyone out there know what this problem is? I'm familiar with situations like this from a carburetted view, but this is my first fuel injected Z. If it helps, I can drive the car, but not far & it's nerve wracking. :confused:

When you tried a "new" distributor did he use the same cap, rotor , and plug wires? A cracked cap or old wires will cause cross firing. Check all your engine ground wires. Make sure your vacuum advance is working.

Any air leak in the system will cause severe problems due to the air to fuel ratio being out of whack. Sounds like the engine is running lean and that can be a cause for backfiring, etc. The EFI can't do its job and will cause the timing to shift, this due to the reports from the various sensors in the system.

Since you have to repair the intake system, due that first I bet that resolves your problem.

Any QUALIFIED Z specialty center can sell you the parts you are needing and also help with advise.

I am also currently being a 76 back to life, my local guy is a great help!

By the way make sure you change out the fuel filter, if clogged it will cause much of the same symptoms as you discribed.

Keep in mind, i had the exact same problem on my 260z, I replaced my NGK Spark plugs with some Bosch Platinums and that problem magically disappeared.
I think you may have some fouled plugs. Check those first, as they're the cheapest thing to replace.

You gave us the most reasonable cause by informing us about the cracks and leaks in the intake system. Easy enough to test.

I have run various sparkplugs in my Z's over several decades and I usually begin with NGK when working with a car that is new to me. My Nissan competion engine runs with special Champion plugs, overall I rather like the NGK products

Hard driving, such as gymkanas and timed track events, calls for different setups. But lets be practical, our cars are 28 years old and are antiques in many states. You have to pay attention to the original engineering of the vehicle if you wish to have a great running engine.

You can easily see the function of the plugs and injectors with a scope.

I had a 82 turbo with the same symptoms..i tried everything .still no luck...but come to find out there was a small inner filter where the gas tank line connects to the fuel pump ...it was completly clooged with trash from the gas tank..once i cleaned it everything was back to normal...i know you already changed your fuel pump,but maybe it is starving somewhere else for fuel?

Try replacing the two boots on the intake. You can get them at Motorsports-www.zcarparts.com Have them send you a catalog. It has alot of OEM, replacement, and performance parts.