| I assume if a compression test turns out to be well within spec that there is nothing that can possibly be wrong with the valves to create a lean misfire of some sort? When I look at the pistons through the spark plug hole I don't see any out of the ordinary carbon-build up. My NA Z has been having quite high NOX levels of 1300ppm and a popping noise from the exhaust which indicates to me it's misfiring. Although when I do a power balance test the cylinders drastically run rougher. On a separate note I used a vacuum gauge to test the engine's condition and the reading was a flicking needle that smoothed when acceleration occurred. This indicated to me it was valve guides, which then made me think this was the whole issue. Thing is, I tried the same gauge on my non-misfiring Z and the gauge also flickered similarly although the pressure was about 4 psi less. The suffering Z had vacuum readings that were quite high, 21-23", flickering of course. I've changed the injectors due to a whole bank reading out of spec after multiple visits to the smog shop. I thought they could be firing insufficiently and causing a lean condition. I haven't gone back since because I've been trying to figure this misfire noise out. I've speculated the o-rings could be leaking and causing a misfire, although I then thought this couldn't be because of the lean issue, but have re-seated the injectors multiple times. Anyhow, I've tried everything possible short of getting new heads/engine to figure this NOX/misfire issue out including: -cleaning entire EGR system out
-3 new injectors
-new cats
-new o2's
-changing PTU
-changing CAS
-gapping plugs
-pressurizing intake for leaks
-testing fuel pressure (This one gets me because the gauge drops after a few minutes...I'm suspecting a faulty check -valve, but hey, it could be an o-ring)
-fuel injection cleaning via on-car tool
-seafoaming a few times
-adjusting throttle plates I looked at the plugs and they all look great (tannish white) except for cylinder 2 white is blackish. So as you can see, there are things that are contradicting each other...some show signs of lean misfire, others rich misfire. I'm going to remove the plenum and pressure test the injectors on the rail and look for leaks. At the same time I will do a leak down test...
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