Timo,
I have quite a bit of experience with the VG from my Maxima days, and the Z31 is very similar, although they don't have a fuel temp sensor.

the service manual should have resistance readings for all of the temp sensors at cold and hot temps. you should be able to check the temp sensors with a multimeter.

when you say the fuel temp sensor tab is broken, do you mean the sensor's tab, or part of the wiring harness going to the ECU?

My thought is that the fuel temp sensor isn't necessarily important (not every car has one and they all run, right?), so I'd grab a resistor from the parts bin that corresponds to the fuel temp at reasonable temp (anywhere from 50 to 100F), and plug that into the harness to fool the ECU into thinking the fuel temp sensor is connected.

If the coolant/head temp sensor is bad, it will cause all kinds of ugly things- usually that causes the engine to run really rich, to the point of flooding the engine. they often only run at full throttle or high RPM because of it.

You say all emissions stuff is removed? do you have an oxygen sensor? If not, can you plug one back in? Nissan ECUs really like to have Oxygen sensors on them. if not, they go into a failsafe mode and dial back timing and run full rich to make sure the engine stays cool.

also, the engine is looking for an O2 sensor signal while it's in closed loop mode, which isn't a huge issue for the car on track- you're usually either at full throttle (open loop mode) or off the gas (don't care what mode it's in long as the engine doesn't die).
But an Oxygen sensor will cause the ECU to do stupid things. they're cheap enough to reinstall or replace, so you might try it.

IIRC, factory timing on a Maxima was around 15deg BTDC. On 93 octane you could run about 18* or so and get better throttle response and more power, but watch your engine temps under track conditions--- I don't think it's an issue in the fall but when it's 100deg outside, that'll cook an engine in a hurry.


A backfire through the intake sounds like a timing issue to me.. these old distributors have been known to "wear out" internally where the gears and such get just enough play in them to cause erratic readings to the ECU. If that's the case, the ignition timing could be off and cause the backfire through the intake. If you have a spare distributor, it probably wouldn't hurt to try it. (you can probably get them cheap from a junkyard if you can still find one. I'm not confident a Maxima dizzy will work though- I think they're slightly different.)


So based on the stuff you've mentioned, it could be any of those thigns.. fuel/engine temp sensor, oxygen sensor, crank position sensor..

the airflow meter could also be an issue if you've knocked it too car out of calibration. I don't know what turning the screws in the meter do since mine always worked and I left it alone. I believe there's a setting in the manual that it should be like 0V with engine off (key on), 0.5V at idle, and 3.5 or 4V at full air flow. the problem is that's pretty hard to check at WOT without having the car on a dyno...

hope that helps some..