sr20 fresh swap and rebuild running lean

[socalbmxr06]

Hey guys looking for some insight into my lean running problem. After searching tirelessly for the past 3 weeks I decided to post up.
From my research it seems like these are the usual culprits:
-wrong spark plug gap
-fuel pump voltage
-fpr (and fuel pressure in general)
-maf
-vacuum or boost leak (usually pre turbo after maf)
-bad o2 sensor
-etc.

Well with all that I still can't pinpoint my issue. It runs lean at idle than gets extremely lean as I push down on the throttle and richs up some as I lift off the pedal and get back on it. Anything above 0lbs of boost and it can get rediculously lean above 17 afr to tapping out my aem wideband.

About the car:
Just got back from the shop with a fresh rebuild and idles and runs strong, but lean...
96 240sx with s13 blacktop sr20 (type-x) motor.
Just about Everything is brand new:
New Maf, new o2 sensor, New wiring harness(wiring specialities), New rebuilt engine with 86.5 mm pistons, cosworth headgasket, valve job, tomei m7960. Aem wideband, and aem tru-boost.
-tried 2 different fpr's(both tested and work fine), fuel pump is a brand new walbro 255 with proper s14 kit.

Things still to possibly check
1. possibly purchase an in line fuel pressure gauge to monitor under throttle?
2.Timing check again??? ( Checked twice already)
3. ECU swap? or tune?
4. Replace and/or regap plugs
5. Drain fuel tank and refill?

Questions to ponder:
1. Could vacuum line routing of the bov and wastegate being t'd together affect afr's??? (going to seperate the two with the wg being attached to bottom nipple). fpr already vacuumed lined to its own port.

[Mikester]

Things to check


the tune

Questions to ponder:
1. Could vacuum line routing of the bov and wastegate being t'd together affect afr's??? (going to seperate the two with the wg being attached to bottom nipple). fpr already vacuumed lined to its own port.

Your BOV & wg actuator can be tee'd; even though everything having its own source is better. So long as your FPR is NOT tee'd you are okay. Both the FPR and BOV need intake manifold vac/boost pressure to operate properly... The WG actuator only needs pressure from the charge piping.

Fairly certain that your BOV/actuator will not cause your AFRs to be bad.

You didn't mention injectors or tuning media... If you are running stock 370's, you are going to be lean as hell considering that the stock T25 even w/injectors at 100% duty cycle will still lean everything out past .8 - .9bar.

That M7960 moves significantly more air... it needs fuel & timing adjustments. In other words- Car likely needs to be properly tuned. Until then, I highly recommend you monitor AFRs closely & stay out of boost until then. Your fresh rebuild [and wallet] will appreciate it=)

On the note of fuel pressure... adjust it to OEM specs... and get a standalone & proper tune.

[socalbmxr06]

Thanks for the response really appreciate it. I'm curious now to find out if anyone is running the M7960 with a stock motor. I was under the impression that it was a mild turbo upgrade.

[Mikester]

^^It is- If you add bigger injectors & TUNE for it.

'Mild' upgrade is a very broad term; and is not synonymous with 'plug and play.' ;)

The M7960 will make roughly 330-340rwhp on a stock vavletrain w/appropriate supporting mods... You can't just slap something like that in and go to town... All that extra air needs fuel & timing adjustments to work properly/safely.