Alright, I am stumped.

[Alisaihin]

I have a 1990 240sx. It's a 5 speed, KAE, and it's got a serious attitude problem.

I have a feeling it might be running really rich somehow (blown FPR?). From off-idle to about 2500 it's like it should be. Runs great. Once you start easing past that it begins to lose power bad. Now, there are two conditions that adjust how it behaves from about 4000-4500 and up.

Part throttle-it'll climb until it can't anymore. Kinda picks up a little as it climbs, but still feels weak as hell.

Wide-open? It dies here. It stops giving power to the point where it only seems to be able to keep firing ENOUGH to not sieze up and make the car skid to a stop. If you keep your foot into it it winds down until about 2500 and then begins the acceleration anew. Lift off, and it'll allow renewed acceleration.

When you wind it up high under part throttle, or let it hit that cut point, it belches an immense amount of smoke, which smells heavily of fuel.

I've removed emissions, nada. Redid the ignition entirely, nada. Fuel pump and filter replaced, nada. Rebuilt the intake, replaced an injector on #4 (it was likely just a bad O-ring but eh), STILL NO CHANGE. Due to intake rebuild I know I have no vacuum leaks. I also even have my 4th and 5th gear switches disabled. Nothing.

Another note, the car tends to stumble initially upon cold-starts. I need to gas it some to get it to live. After the initial gassing necessary it idles fine, perhaps set a wee bit low (I need to correct that, uff).

Anything else I'm missing, or is this an FPR issue and I've been absolutely silly not to look into that? I really want a second opinion before I dive into this engine again.

[Dillinja666]

Unplug MAF and see how it runs.

[Alisaihin]

Unplug MAF and see how it runs.Been there, done that. When unplugged while running, dies. If started while unplugged, 3500 limit.

TPS is also fine, it's new. (I felt like I was forgetting to mention stuff...)

[CamberWear]

Definitely check knock sensor. It seems you have symptoms of a broken one. It will retard timing and affect your a/fr.

[Alisaihin]

Definitely check knock sensor. It seems you have symptoms of a broken one. It will retard timing and affect your a/fr.
Ohhhhh, Makes sense. I will give it a look.

Edit: ...does the KA24E even have one? it seems that it doesn't from a search.

[Alisaihin]

Would a dying crank position sensor maybe cause it to do this? I really don't wanna mess with that because it's part of the dizzy...

[frankies1390]

u check coolant temp sensor, chased down a ton of electrical on mine. turns out the coolant temp sensor was not only shorting out but bad. super rich!
also pinch ur fuel line to see if your idle changes (which it should) unplug your vacuum line off of fpr to see how it acts? u might be dead on with the fpr?

[Alisaihin]

I am certain the coolant temp sensor works. I've seen the actual sensor element (When the manifold was off, it was shiny and looked rather new), and experienced it doing its thing when the motor borderline overheated after the radiator gave me a rude awakening (car was retarding the timing bad, dumping fuel in, and looked to see my temp was rising. Pulled over and it blew a bit of a hole near the upper rad hose).

I did unplug the FPR and plugged off the vac line so there wouldn't be a vacuum leak, it acted...exactly the same. Same symptoms, same idle...the only reason I'm hesitant is because I've read often times bad FPR's will leak gas back through the vac line.

I won't be able to check the car until maybe the 1st at least from now, I'm gonna be flying out 1400 miles away from my Apartment...so yeah.

[Alisaihin]

I have returned from my hiatus. I've noticed now that it's colder the initial steam from the exhaust when it's started up is thicker white and heavier. I had my little lady watch it after it warmed up and saw nothing streaming from it (This includes normal driving-she DOES have 20/20 vision, btw), so I'm theorizing that it's likely residual fuel coming from it (I don't notice consumption of coolant-I've checked levels after drives and it's constant).

Hopefully that gives more idea as to what I'm handling here.

[OddyseusDSM]

Ignition timing too far out can cause it to break up at higher rpms. I mistimed once and had that same symptom. Double check with a light if you ever touched it without one. You should be near base timing at WOT and at idle.

In cold light gray smoke is fine, white sweet is bad

[Alisaihin]

Ignition timing too far out can cause it to break up at higher rpms. I mistimed once and had that same symptom. Double check with a light if you ever touched it without one. You should be near base timing at WOT and at idle.

In cold light gray smoke is fine, white sweet is bad

Well, it seems that a lot of those initial problems were a battery just absolutely crapping out (stumbling at a start, in particular). I put in a new one and it starts up like normal.

I still have the throttle issue, so I can check the timing again. If the timing is off I'll be pissed because it was retimed by a Nissan Dealership (I don't think I'll ever have any dealership's service department diagnose my cars ever again. Past few years they all seem to have gone to shit.).

I'm literally here right now just to bounce ideas around but common thing I'm reading is timing must be screwed up somewhere.