Hey everyone, wondering if someone here can help me out with this issue
My 1990 300zx tt has been running rough, the idle is fine but at about 4000 rpm power starts to fall off and it acts as if it’s hit a limiter, jerks around and puffs a lot of black smoke out the exhaust. If I turn the boost up and keep it floored it will hiccup at 4000rpm, push past and pull hard all the way up to redline
I thought it was running way too rich so I checked for boost leaks... didn’t find much, installed a wideband o2 (on the driver side exhaust pipe) and that is pegged at 14.6, on a cold start it gets close to 14 but no lower
So I started thinking it was an ignition issue
Tested the coils, all were between 0.7 and 1 ohm
Pulled the plugs (less than 1000 miles on them) and all had black soot on the base ring, ground strap showed they might be a bit hot heat range on some of them, no signs of detonation and gapped to .035
Plugs are ngk heat range 5 iridium cant remember the number but they’re not the “special made vg30 plugs”

Any idea what’s going on? Could it be as simple as getting a heat range 6 plug? I’m pretty confident this is not a single cylinder issue
I’ll see if I can attach a picture of a plug

By looking at the plug I was almost certain it was an extreme rich condition causing this... is it possible my o2 isn’t reading correctly? I followed the instructions for installing, 24 to 36 inches downstream of the turbo and I have catless downpipes
With the engine warm there is absolutely no fluctuation in the gauge, it reads 14.6 steady

Any luck figuring it out?

sns00 wrote: ↑

Mon Jun 01, 2020 1:00 pm

Any luck figuring it out?

Yeah I actually started another thread after this one, after pulling the motor, replacing every gasket and hose, and rebuilding the turbos it had the exact same issue
Turns out it was the maf sensor all along even though all the tests came back positive with the multimeter and the diagnostic software
Runs like a dream now with a new maf