rev limiter at 2000rpm (leans out), leans out under boost and rough idle

[Keith_Bergen]

First of all, the car has a s15 sr20det in it, hks bov, fmic, hks poncams, and splitfire coilpacks, plugs were replaced last year, and i'm running fresh premium fuel.

The problem i'm having is the car has a rough, stumbling idle, it completely leans out at 2000rpm and is difficult to get past. once past that, under boost it leans out to about 17-18, stutters and only boosts about 5psi. Driving down highway at consistant speed the engine runs perfect.

I have disconnected the o2 sensor to run open loop which changed nothing.

I checked maf signal - blue wire has 1.2V at idle, and 1.8V at 3000rpm under no load which is where it should be, pink (ground has ~0v), and black/white wire has 12V.

I can't find any vacuum leaks anywhere.

Cam's are timed

ignition timing is dead on 15 degrees btdc

Any help or idea's would be much appreciated as i've been trying to figure this out for weeks. Also, please no "Search" comments, as i've searched for days and can't find anything quite like this.

Thanks in advance for any advice.

[Keith_Bergen]

So the only things i can think of that could possibly cause this would be:

MAF input into the ECM (wiring)

Vacuum leaks (could it be the iacv-aac not closing?)

throttle position sensor?

ECM

Bad injector? or bad wiring from ECM to injectors

bent valve? i'll check compression tonight

Anything else that i could possibly check? I'll try to check fuel pressure tonight too.

[Keith_Bergen]

has ~135-140psi compression on all cylinders, disconnecting tps doesn't change anything, pinched off line to iacv-aac, doesn't change it. fuel pressure gauge i got didn't work but am almost certain that wouldn't cause it.

[Keith_Bergen]

So, Tonight I graphed the maf input into the ecm which was perfect, graphed the cam position sensor inputs (1 degree and 180 degree signals) into the ecm which also look perfect, as well i checked the knock sensor voltages.

The only one that seemed a little odd to me was the knock sensor was reading about 4.8v which seems really high as the specs at idle are supposed to be around 2.5 volts. I cut the wire near the ecm and checked voltage on both sides of the break. The output voltage from the knock sensor was right around 2.5v when i cut the wire. I checked the wire from the ecm and it showed the 4.8v even if only the ignition was on and not running. As the knock sensor is a 1 wire sensor I'm under the assumption that the piezoelectric element was all that created a voltage in the system and the ecm wasn't supposed to put out any voltage itself. or is the ecm supposed to put out a reference voltage for it somehow. Please give me some advise on this as i'm not 100% sure how it's supposed to work.
I'm also a little disappointed as my buddy posted the same problem on his rx8 forum and they've given a lot more advise about it then zilvia which is pretty much a nissan/240sx specific forum.

[Keith_Bergen]

Any other idea's? I can't seem to figure it out

[g35gabby]

17-18 is real low vac for it to have no leaks(not impossible, but...). I would think one of your couplers isnt clamping perfectly and under load the increase in pressure is causing the un-clamped connection to expand and allow pressure to excape.

beyond that FPR or fuel pump would be high on my list of things to check.

I would def make yourself a vac leak detector if you have access to an air compressor(specially to check things like the BOV) and figure out the fuel system situation.

PS what are you using to check A/F? are you able to read the OBD2 system or use a Dash hawk like system to data log?

[Keith_Bergen]

I'll try to check my vacuum, maybe an evap leak smoke detector may find a leak, or i have an adaptor that i might be able to hook up to the compressor, fuel pressure is good, so it isn't the fuel pump or fpr, it seems more like it's missing. like no spark at 2000, and sometimes at idle. I'm just using a wideband a/f gauge to check a/f, but if it's missing, the excess o2 in the exhaust would cause the gauge to read lean. Still working on trying to hook up the obd2 connector.
Thanks for the input!

[Keith_Bergen]

There are No vacuum leaks as i pressure tested and smoke tested it all yesterday. Also, drove it around a little more, definitely seems like it's not getting enough fuel under boost. I'm gonna check fuel pressure.

[g35gabby]

check your fuel system + your MAFS.

[drift213]

check for bad injectors O'rings?

[Booost]

When you pulled your plugs what did they look like? Check all of your couplers on your charge-piping/intercooler piping. Check resistance of all your injectors and compare to factory resistance on your injectors (or correct/optimum resistance for your injectors). Check fuel pressure. What kind of fuel pump are you running? If you have a test light, find a good ground, disconnect the plug to your coil packs (be sure to do all four), have someone turn-over the motor and check to see if your getting power to the coil packs. Also check your ignitor as well.