Hey guys, I thought I'd create a thread that can perhaps go sticky that we can all add troubleshooting tips and tricks to to help newbies with their zeds. My posts will be specifically for the z31 and z32 as I have had no experience with the earlier zeds but anyone who wants to add anything for these models, feel free!
I think before I continue I should let everyone know that YOU WILL DIE IF YOU DON'T TAKE PROPER CARE. UNDERSTAND THE OPERATION OF THE ENGINE BEFORE ATTEMPTING ANYTHING. Fuel air mixtures do explode. High voltages do arc. Gears and pulleys do catch fingers. This post is only meant as a basic summary of troubleshooting procedures that I have personally performed. I have performed each and every operation I've listed here without personal harm but I may have just been lucky. If you have any doubts, take it to a mechanic. All operations listed here are dangerous and shouldn't be performed if you are unsure you can safely perform it, or if you don't have proper protection. Use your head.
Also, a great resource is the service manual. There is an excellent Haynes one for the z31 and there is an official nissan one for the z32.
The haynes is worth about $70 AUD new, and the Nissan z32 one cost me $200 (its actually 2 books) but its saved me time and time again from mechanics fees. Buy the service manual for your car. Its well worth the money.
ECU error codes
With almost any engine issue, you should first consult your car's ECU. Your ECU has many checks in place for each and every sensor that indicate it's not doing its job properly, which the ECU can then relay to you. The ECU does this by a series of flashes from a led.
<insert ECU checking prodecure here>
<insert ECU codes here>
It must be understood however that the ECU is only operating on the values it's reading from the sensors, so if the ECU says that a sensor is reading out of the normal operating range, don't immediately assume the sensor is faulty. Consider what might be making it read that way before you go replacing anything.
Eg. your ecu is saying that your O2 sensor is reading faulty. This could be that the sensor needs replacing, or that your fuel pressure regulator isn't working properly, giving a super high fuel pressure, causing far too much fuel to be injected, causing the O2 sensor to be reading out of range.
Your ECU codes should only be taken as a guide as to what sensors are affected, rather than what sensors are faulty.
Exhaust smoke
Smoke coming from your exhaust comes in a variety of different colours.
Black: This is fuel. This indicates that the fuel isn't burning completely. This could be a result of a number of things involving both the fuel system and the ignition system (too much fuel, or too little ignition?). See the fuelling and ignition systems sections.
White: This is steam. This can be something relatively harmless (like water condensed in your muffler) or could be coolant getting into the combustion chamber (cracked head, warped head, blown head gasket) which is really quite bad. Easiest way to check this is take your radiator cap off while the engine is running (only when the engine is cold of course! You don't want 8th degree steam burns from opening the radiator cap hot). If you see bubbles coming out of the coolant and you've got white smoke, take it straight to the mechanic because it's getting quite serious.
Blue: This is oil. There are several places around the combustion chamber that oil runs through. Firstly, oil is splashed onto the bottom of the piston to lubricate the cylinder wall as well as cooling the piston down. Oil could get into the combustion chamber from here if your piston rings aren't sealing well enough. Secondly, oil runs up through the head gasket up to the head. If your gasket is blown, or if your head is warped, oil can leak past into the combustion chamber. Thirdly, oil is used in the head to lubricate the valves. There is a possibility that oil is leaking past the valve into the combustion chamber. All 3 are quite serious and you should take it to a mechanic.
Also there is a possibility that oil is coming out of what is known as the PCV system into your intake. PCV stands for Positive Crankcase Ventilation and its a way of passing air through the block in order to help alleviate pressures building up from the pistons moving about the place. You have 1 inlet to the crankcase, and 1 outlet (z31) or 2 outlets (z32) into the engine intake. The reason it dumps the oily air back into the intake is for emissions purposes as oily air isn't too good for the environment, the atmosphere or the other road users should oil splurt out.
Installing a PCV catchcan is a great idea (yet normally slightly less-than-legal) as heavy cornering may actually cause oil to spew into your intake. This is basically just a can with 2 holes on top. One goes to your pcv outlets, and one goes to the atmosphere/intake. Venting to the atmosphere is illegal in most countries, but if you don't tell anyone, I wont.
Fuelling system
Your fuelling system has a feed line and a return line. Fuel comes from the tank up the feed line to the fuel dampener (to help even out the flow from the fuel pump). from here it goes to your fuel rail which all your injectors hang off. Also attached to your fuel rail is a fuel pressure regulator. This keeps the fuel rail at a constant pressure and it does this by allowing some fuel to return back to the fuel tank via the return line.
Your injectors are opened and closed via signals from your ECU. Your ECU consults various sensors to determine exactly how long to open each injector for. your throttle position, the intake air flow and the oxygen sensor in the exhaust are all consulted and your ECU has a lookup table which it will get a value from.
The amount of fuel to inject must have pinpoint accuracy as if it doesn't inject enough, the engine can overheat and detonate (pinging) which can seriously damage your piston, valves and your head gasket. Too much fuel and your spark plugs will foul and your catalytic converter and muffler will get clogged with soot. Also, you won't have all that great fuel efficiency.
We use the terms 'rich' and 'lean' to describe too much fuel and too little fuel respectively.
Rich:
Firstly, if your engine is running rich, you'll notice black smoke in the exhaust. You may also notice that slightly pinching the fuel feed line (with the engine running) will cause your engine to idle a little better. Pinching too hard WILL CAUSE YOU TO DIE from too much pressure in the fuel system, causing a burst somewhere, causing you to get covered in fuel, CAUSING YOU TO CATCH FIRE AND DIE.
You can check your spark plugs too. If your engine is running rich, the spark plug(s) will be coated in black soot.
This can be caused by a number of things. Your FPR may not be working correctly, sending too little fuel back down the return line, causing too much fuel pressure in your fuel rail. It could be caused by the ECU opening the injectors too long because of an incorrect sensor reading. eg. Your AFM/MAF might be telling the ECU that there is more air coming through than what there actually is, causing the ecu to tell the injectors to inject far too much fuel to burn with this air, causing the engine to run rich. Check the ECU codes for sensors reading out of range.
Lean:
You can check if you're running lean by slightly pinching the fuel return line. This will cause more pressure in your fuel system which will cause more fuel to be injected. If you notice that pinching the return line causes your engine to idle better, then it's running lean normally. WARNING: PINCHING THE RETURN LINE TOO HARD WILL CAUSE YOU TO DIE. read previous warning in 'rich' secton.
Running lean will also cause your engine to 'ping' or detonate under load. If you have a detonation sensor (turbo engine only) this will be going nuts and your engine will retard the ignition timing to help protect the engine. This will result in a loss of power though.
This is what your spark plug looks like running lean:
Note the broken/blistering insulator. Excessive electrode wear will also result from running too lean.
This can also be caused by your FPR sending too much fuel down the return line, causing insufficient pressure in the fuel rail. A dicky fuel pump will also not be able to maintain pressure in the fuel rail. Incorrect readings from sensors will cause the ecu to underestimate the amount of air coming in, causing it to inject too little fuel.
Check your ecu codes.
Injectors:
Injectors generally either work or they don't. I've never seen an injector that 'half' works. This is because the injector has a tiny hole that fuel is sprayed out of, and any conceivable piece of grit that is going to clog the injector is going to clog it completely.
A real simple way to check if each injector is working is to go through each cylinder and disconnect the spark plug lead (z31) or ignition signal lead (z32). WARNING: With the spark plug lead, don't put any part of your body too close to the metal tip, and don't touch any metal part of the car, as there are serious voltages we're talking about here. Should an arc form between the ignition lead and your body, YOU WILL DIE.
if disconnecting the lead causes the engine to run worse, then it means that that cylinder is working normally. If disconnecting the lead doesn't do anything then it means that the cylinder isn't running normally and either the injector or the spark plug isn't working he way it should. Try to isolate the cause down to ignition by reading the next section. If you can't, its the injector.
Ignition system
The z31 and z32 differ quite significantly here. The z31 uses a distributor/coil based system whereas the z32 uses signals from the ECU to drive individual coils for each spark plug.
Z31:
In the distributor style approach, the ignition timing is mechanical in nature. A metal contact spins around the distributor at half the speed of the engine. In addition, each spark plug has a contact too inside the distributor. As the centre contact turns, it touches the spark plug contacts, completing a circuit and allowing the coil to discharge through the spark plug, causing ignition.
Distributors have a manual advance/retard adjustment which can be done by loosening the adjustment nut and rotating the entire distributor. Advancing will increase chances of detonation (but create slightly more power) whereas reatrding the ignition will do the opposite.
I remember when i used to have a z31 engine, i'd put a wingnut on the adjustment stud, so that if i put in higher octane fuel, i could quickly change the ignition advance to take advantage of it but if i was stuck out in the country and they had cheap shitty fuel, i could retard the timing so my engine didn't detonate.
Z32:
The Z32 utilises a separate coil for each spark plug. These are controlled by the power transistor (mounted on the front of the timing belt cover) which is controlled by the ECU.
Unfortunately though, all coils must be almost exactly the same impedance or it will damage your power transistor. As such, its advised by most that if you replace one coil, you should replace them all.
Because your ECU controls the sparking, there is no manual adjustment here and you have to leave everything up to the ecu.
Spark plugs:
WARNING: The ignition system contains very high voltages and can kill a human in the right circumstances. Use care when handling various components, even when the engine is off.
You can check each spark plug is getting the right signal by taking each lead out in turn and holding it close to a piece of metal on the engine. WARNING: Holding the lead at the end, or touching any part of the engine or chassis whilst holding the lead WILL CAUSE YOU TO DIE. The voltages coming through the ignition system are enough to kill a human in the right circumstances.
Holding the lead close to a metal part of the engine should cause an arc to come from the end of the lead to the engine. Don't do this all day as its no good for your ignition system as a whole. Its just a quick check to see its all operating the way it should.
If a lead doesn't cause an arc with the engine, it could be that your distributor isn't working (z31) or a coil isn't working (z32). If they all arc with the engine then its time to check the spark plugs. With the engine off, take the spark plugs out and inspect the contacts. If necessary, regap them and clean them.
If AND ONLY IF you have a spare spark plug around can you procede with the next step. WARNING: Doing the following proecdure without adequately blocking the spark plug hole in the engine WILL CAUSE YOU TO DIE.
Take a spark plug out of the engine and put the dodgy/spare spark plug back into the engine. Start the engine. Attach the coil to the spark plug you're testing (the one you've just taken out). DO NOT hold the spark plug or the coil with your bare hands, but use a suitable insulator. Now hold the spark plug so that the bottom 'L' shaped contact is touching a metal part of the engine, You should see the spark plug arcing between the contacts. If you don't, replace it.
The reason you should only do this if you have a spare spark plug is because if you don't, you've got a hole into the combustion chamber that is still getting fuel delivered to it. As a result, every compression stroke is actually spewing out fuel and air into the atmosphere. Controlled combustion is great inside the cylinder, but you don't want to be pumping fuel vapour into the immediate vicinity, especially when you're testing spark plugs.
Lubrication system
Oil is drawn up from the sump at the bottom of the engine, through the oil pump, then to the oil filter, and then distributed to the bottom of the pistons, and to the heads. A simple way to check your heads are getting oil is by looking inside the oil filler cap (with the engine off of course) after you've just taken her for a run. You should see the intake camshaft (z32) or camshaft (z31), and if it looks bone dry, you've got big issues.
Oil pumps are tremendously expensive ($600 AUD for a z32 one from Nissan) If you suspect the oil system isn't functioning, take it to a mechanic as you don't want to go throwing around that kind of cash unless you absolutely need to.
A great modification for maintenance and troubleshooting purposes is to install a remote oil filter kit. This effectively moves your oil filter away from the engine and to an easier-to-access location in the engine bay. With this sort of system, you can even run sections of clear tubing so you can see the oil running past if you want. Make sure you're using proper oil tubing though, the pressures can get pretty big. This modification will also allow you to check and change the oil filter easier, which will cause you to do it more often, which will extend the life of your engine considerably.
I'll add those ECU procedures and codes when i find my service manuals.
-Mike