LuckyRPS13

This is in my Baby sisters first car which is a 92 Nissan 240SX hatchback. She wanted to have a car like her big brother. we picked it up off a car lot cheap because it had been broken into about 6 months ago. the thieves stole the Maf, battery and random parts like the mirrors privacy cover ect. I have chopped up many 240's so I had plenty of known good working parts to get it back up and going again. enough of a back story.

When you rev the motor black smoke kicks out the exhaust. Driving you don't see it as bad unless you are WOT. Then you will see it down low and almost disappear at higher RPMs. It runs and drives just fine, but the fuel MPG is drastically lower than it should be.

I have swapped out 3 known working MAf's, 3 ECU's, 2 temp sensors, 2 fuel pressure regulators, 4 used and good working order injectors. All the replaced injectors have good o-rings. Did a complete tune up the weekend we picked it up. I moved the Vac lines for the FPR are going directly to a nipple on the intake after the first fuel pressure test was showing it at 40psi at idle. Now the Fuel pressure is reading 34ish psi at idle and about 43ish psi WOT.

Only thing left to change that I can think of is the O2 sensor, and the intake manifold gasket. It seems like there is a slight vacuum leak around runner 4 into the head.

running out of Ideas here.

LuckyRPS13

No one has ran into this before?

Tantwoforty

Sounds like you have the skills to find it sooner or later, Id double check injector seals, pull the codes ect. but id guess its the O2 sensor if its none of the other things. a vaccume leak normally wont make it run rich, it will just idle high and be lean if anything.
good luck!

Nikeboy355

As 240s get older, I don't trust old parts...

I am dealing with a low fuel pressure problem right now and this is how I am dealing with it:

1. Fuel pump - I am just going to replace and purchased a Deatchworks pump
2. Fuel pressure regulator - Purchased from Autozone for $69
3. Injectors - I'm taking them to RC to get serviced for $114 total

That way the fuel system is for sure 100%...

If that doesn't solve the problem, then you have a sensor or calibration problem...
Sometimes working with old parts will make things more confusing...
It's better to isolate the problem using "new" or "tested" parts...
"Tested" professionally that is...

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LuckyRPS13

well waiting on her to bring it back by with an O2 sensor. I will keep every one posted when I find the issue. Maybe will help some one with the same problem down the road.