Plz help!!! Runnig really lean!

[ahraz123]

hey guys, just wanted some help/input from you guys out there that have come across this problem.

my rb20det was running fine for the longest time (what a surprise lol)
but recently under wot it gets really lean. at idle my aem wideband reads between 12-14 jumping around, and under full stock boost the gauge starts climbing to ~17 or 18 or sometimes even beyond the gauges reading capabilities.
i just received a new walbro fuel pump, thinking that it might be case, but no luck.
idk what else it could be.

the help is greatly appreciated!! thanks guys

ahraz

[Skym]

Lack of correct voltage to fuelpump = lean engine. Make sure you have wired fuelpump correctly.

Faulty FPR, exhaust manifold to head exhaust leak or intake manifold to head airleak (stock narrowband 02 sensor + ECU usually makes engine rpm rise, fall at idle when airleak is bad enough) could make engine run lean.

Also at idle the fluctuation in A/F ratio is due to stock narrowband o2 sensor making ECU run engine lean, rich. That's normal. If revs rise and fall alot at same time it's not.

If exhaust has a leak, oxygen can enter exhaust and get inaccurate readings on wideband. The fact that engine hasn't blown up with that lean A/F ratio says it could be an exhaust leak. Common gaskets to blow on exhaust manifold are turbo to exhaust manifold, head to exhaust manifold.

[ahraz123]

my rpms are constant, they dont move around at idle.
im not sure about exhaust leak(but i do know that 2/3 bolts on my turbo elbow are broken/stripped), cuz when i floor it it goes strong and then i can feel it slow down a bit around the 6000rpm mark.

thanks for your reply, makes alot of sense, but how would i go around checking the gaskets? would i have to just take them off one by one and check or is their a way around that??
thx

[Skym]

I assume you mean the elbow on intake side of turbo with 3x bolts??? There's a small gasket there. Can use a drill, easy out to remove those bolts. If on exhaust side they are known to snap when undoing them to remove outlet pipe / dump pipe. Some soak with CRC to help loosen them up.

If it's the cause, just replace all the gaskets, exhaust studs (studs should be done every 10 years or so), skim exhaust manifold to head flange on exhaust manifold (to make sure flange is flat as it does warp). That's including the turbo intake elbow gasket, exhaust outlet pipe / dump pipe gasket, oil return gasket, washer on inlet for oil feed on turbo, head to exhaust manifold gasket, turbo to exhaust manifold gasket. Nissan repair gasket kit for RB20DET has all the intake, exhaust gaskets including headgasket, camcover gasket's, etc.

[ahraz123]

i meant on the exhaust side, sorry for the late reply. caught up with school..
wouldnt a gasket leak result in a rich mixture?? having the o2 sensors make up for it by dumping more gas in???

[Skym]

The stock narrowband o2 sensor (0-1V) has lean, rich voltage triggers on ECU (software). If o2 voltage goes towards 0V (very lean) it hits the rich trigger on ECU that makes engine go rich. If o2 sensor voltage goes towards 1V (very rich) it hits the lean trigger on ECU that makes engine go lean. Those are not the exact trigger voltages ECU uses, but that's roughly how it works.

With more oxygen in the exhaust from exhaust leak the o2 sensor (o2 sensor voltage is going towards 0V) + ECU should make engine go rich then lean again and repeat.

When o2 sensor fails the voltage on o2 sensor is slower to fluctuate and makes ECU run engine rich longer (popping sound = flames from exhaust).

Wideband is a 0-5V sensor.

Have you checked voltage to fuelpump???

[ahraz123]

thx never knew it worked that way. learn something new everyday
i havent checked yet, im waiting for an "o" ring washer so i can install the new fuel pump.

[Skym]

From what I understand, need more voltage to Walbro fuelpump vs stock fuelpump. Wiring, relay needs to be changed. There's how to's on the internet on how to wire up the relay.

[fullthrottle]

Replace your fuel filter

Sent from my Desire HD using Tapatalk

[ahraz123]

fuel filter is about a month old.

@skym: ill have a look, thx for all the helpful info