After setting the timing to 15 degrees @ 850 rpm the car hits a flat spot and misses at around 60k when accelerating under normal street driving conditions. Car is running a 10% UD pulley. When adjusting the CASS it is in a similar position (within a couple of degrees) of original marks. The TPS however to get the 4.5 reading seems set differently than the original marks. Almost at the ends of the slots. If the ignition timing is advanced to say 30 degrees it runs better if you are gentle on the throttle. Turbos are working fine after changing a couple of vacuum lines. Whats up here?
Could be any number of problem, maybe not even timing. Don't advance your timing without having a qualified person do it. You run the risk of detonation and engine damage. Might feel great at low rev but not so at higher rpm. Timing belt could be out a tooth, or could be an unrelated issue...vac leak etc. Pretty common for TPS be almost fully adjusted....don't know why. Most of my Z's have also been like this. Nistune or stock ECU?
Hopefully that was a typo and you meant 0.45. Have you checked the ECU for fault codes? Have you worked through all the basics for a misfire problem, spark plugs, coil packs, PTU, dirty AFM or dodgey contacts on all of the above? Did you end up checking the timing mark on the pulley against the piston and checking the ECU timing at idle?
The TPS obviously increases the voltage as it is turned. As Fists spotted the 4.5volt setting is hopefully a typo, but if it isn't? well there's the problem. You have maxxed your TPS, but then you would have hit the end stop postion and it would not turn anymore unless it is easy to bust and overshoot the TPS contacts and kick the car into a failsafe mode. I know of one member who has one of his cars at 0.22volts TPS. I have run at 0.18v and currently at 0.34v. The TPS could be worn on one part of the contact track from overuse at that throttle position and that flat spot (triggers failsafe mode) will shift to a different rev range with a lower voltage setting at idle. Seems like you have discovered that scenario.
How goods your timing light? Do you trust it? I know mine has to be held just right to work properly on the zed. You can get a better signal by pulling the number 1 coilpack and putting in a spark plug wire between the coilpack and plug. Also, car wasn't converted to manual from auto?
Based on his other thread car is still auto although it was having some issue with the auto, I did mention that codes from the auto gearbox control unit can throw it off.
Yep, typo should have said set at .45 now at around .42. Spark plugs all new. Coil packs checked. AFM new, swapped with original unit no change. Contacts were all cleaned and replaced as required. 2 only. All connectors cleaned and treated. Re ECU don't have the equipment (Consult) Checked timing with extension lead on No1 engine running set at 15 degrees @ 850 again. No change.
Need to check that with my gauges but they are at work. Seems ok when doing a physical inspection. No strange noises from motor, no vac leaks no puffing, sounds excellent. Fault is similar to blocked primary jet on a motorcycle when coming onto the main jet and it stumbles. Once the car is through the stumble the car is fine?
Good quality light & yes I trust it. You don't have to hold your tongue at a special angle to get it to work. Used the extension HT lead. Car has always been Auto trans.
I can get access to a diagnostic tool as used by pro's with all the connectors would this be of any use? Still have auto hunting but not as bad as before. How long does the ECU take to relearn after say 3 years inactive?
Can you check the RPM that it starts to misfire at? There are a few points that give you a hint, 2.5krpm is typically an AFM fault as this is a safety mode limiter when no AFM is detected. Ignition problems tend to manifest at about 4.5krpm, at a guess thats because peak torque is around there.
A dignostic tool would be very useful, although note that an OBD2 type unit won't work, you want something Z/Nissan specific for this era. The main thing to check is that the ECU isn't deliberately changing timing for some reason, if the ECU is trying to fire at 25degrees and you've got the light flashing at 15 then you're 10 retarded through the rest of the range although I don't think that would cause a severe miss (that's how my car was set when I got it, once I got ECUtalk I figured it out) You can check each computer for fault codes without the tool but its a bit more work, the ECU and gearbox control will be relevant here, the ABS and steering control units also have diagnostic sequences. you should be able to find the codes and procedures in the tech section.
First thing I would do is to check the top dead centre marks on your under drive pulley ,by turning over your engine to get number one piston to top dead centre then check the pulley top dead centre mark lines up to the pointer. If mark does not line up to the pointer at top dead centre the outer pulley vees has spun a little bit on the inner boss. [outer vees & inner boss sometimes are press fit together] If this is wrong a timing light is useless the only way to set the timeing is to use ECUTalk or a lectronic turne setup while engine is running.
