| Hi guys, First things first, my 300zx is a manual transmission 1990 Twin Turbo (with JWT ECU upgrade and Stillen Intercoolers). I've owned this vehicle since 2003 and I do all the work on the car myself. The last Timing Belt Service was done by me approximately a little less than 2 years ago. At that time I also replaced the fuel injectors. The car had been running just fine since then... no issues whatsoever. About 10 days ago I started the car one morning and I got really rough idling and hesitation/stumbling while driving (as if some cylinders weren't working). I did a quick balance test and none of the cylinders appeared to stand-out as the culprits. I did a compression test followed by a leak-down test on all the cylinders and below are the results (please note that I did all this while the car was "cold" so I expect these numbers to be on the low-side, nevertheless they appear to be reasonable). (Cylinder #)___(PSI)___(Leak-Down % _ compressor PSI / cylinder PSI) ____1________150______2.6% _ 78/76
____2________150______5.1% _ 78/74
____3________149______2.4% _ 82/80
____4________149______5.1% _ 78/74
____5________149______2.5% _ 81/79
____6________149______6.3% _ 80/75
I looked at the self-diagnostics (mode 1) and I got a code 55 (no errors). I did self-diagnostics (mode 2) to see if there were any issues with the O2 sensors; they appeared fine (left/right sensors properly flashing very frequently within 10 seconds at 2000 RPMs). I hooked-up my USB ODB connector and run the Conzult diagnostic software (this can be seen in the video link below). All the values look reasonable in the Full Data Monitoring window. Conzult also didn't report any errors in the Diagnostic Trouble Codes window. From here I looked at the Nissan Service Manual, specifically section "Engine Fuel & Emission Control System" (EF & EC, pages 67~79) and performed the tests (nothing seemed out of the ordinary). Here's what I have looked at so far (all these items appear to be functioning just fine): - checked fuel pressure (got ~37 PSI at idle... the fuel pump, regulator and damper are relative new) -> no issues - checked EGR valve (did not stick and it also functioned when manually applying vacuum) -> no issues - checked the Idle Air Control valve (IAA) and it appeared fine (no carbon buildup and both solinoids were activated when 12-volts were applied to them). I had a spare unit that I switched it out with (just "in-case") but that didn't make a difference (see picture here: "https://ibb.co/W3GTYLh"). -> so no issues with this either... - checked the IACV air regulator and it appeared fine (partially open but when applying 12 volts for a couple of minutes then the valve would properly close, see picture here: "https://ibb.co/W3GTYLh"). -> no issues here... - checked a few of the injectors and got 12.7 ohms resistance (they were relatively new and so I didn't expect them to have failed) -> no issues - note, I have replaced the engine wire-harness several years back (brand new from Courtesy Nissan), so the wires are soft and not corroded. - I tested the Power Transistor Unit (PTU) as per Service Manual (EF & EC pages 120~122) and found no issues. Since I also had another spare PTU I switched it out but that also didn't make a difference. - I did a vacuum leak test (as described here: "http://www.thumper300zx.com/z32/boostleaks/boost_leak_guide.htm"). I used about 5~7psi and I had no leaks. - I checked the Fuel Temperature Sensor and the (ECU) Coolant Temperature Sensor. The resistance of both sensors checked-out fine under hot/cold conditions (they were also in agreement with each other). -> no issues here... - The Throttle Sensor Idle Position was checked via Conzult -> no issues - The car is at 15 degrees BTDC at idle (reported by Conzult and I also verified this with a timing gun).
One thing that I noticed is that if I disable cylinder #4 (by pulling-out the coil wire) then the driver's side exhaust would always have a misfire (as expected and you could feel that with your hand at the exhaust), however, the passenger-side exhaust would be nice and smooth, just the way it is supposed to be! Similarly, if I enable cylinder #4 again but now I disable cylinder #3 then the passenger's side exhaust would always have a misfire but the driver's side exhaust would be relatively smooth. Having all cylinders enabled would cause misfires on both exhaust sides. Please see the quick video that I made here: "https://youtu.be/eLStfNEoTdk".
At this point I think that the timing belt may have slipped a tooth or two. That's my best guess... my next step is to take the timing cover off and see, however, I wanted to hear your opinions and also seek suggestions of "other" things to check before taking things apart. I also have a spare CAS that I may try to use but I don't know if that would make a difference (I may also need to look into this "http://www.jimwolftechnology.com/wolfpdf/VG30DETT_CAS_COUPLING_MISALIGNMENT.pdf"). One question that I had was regarding the Intake Cam Sprockets... it seems that there is a bunch of oil around the timing covers and alternator (see pictures here: "https://ibb.co/WkG8YM4" and "https://ibb.co/W043b6X"). Since the cam seals haven't been that long since they were replaced, I am thinking that maybe the Intake Cam Sprockets may be leaking (see "problems" in the CAM section here: "https://conceptzperformance.com/wiki/index.php/Variable_Timing_Control"). I have had the "VTC rattle/tick/knock" ever since I can remember but that never caused any issues (other than being annoying). Can the Intake Cam Sprockets fail in such a way that they could cause the rough/hesitation/misfire issues that I have been having? Is there any way of testing this??? I would imagine that the VTC solenoids probably wouldn't contribute to my current problem, correct? Additionally, I know that the oil leak could also be attributed to a malfunctioning PCV valve... they were replaced during the Timing Belt Service ~2 years ago but I will check them too (I haven't done that yet).
Thanks guys... any suggestions would be greatly appreciated it. Sorry for the rather lengthy message but I know its best to be as thorough as possible. Thanks again.
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01:54:26 08/25/20
