RB20 Ultra Lean. Please help!

**liquidus** · 10-05-2011, 01:03 AM

I need the help of the RB engine masters. Car is idling a little high and is very lean. Here's all the details.

At idle, wideband reads off the charts, 18:1 +.

If I unplug the MAF, car idles at around 11:1.

Tried a different MAF, no change. Checked voltage of MAF at ECU, showed 1.3v, with light throttle, went up to 2v. Seems to be okay.

Checked very diligently for vacuum and air leaks. Boost gauge shows vacuum at 20. Seems good.

Tried a different o2 sensor, no change. Checked the voltage at the ECU, showed around .5v when the MAF was disconnected (running rich), shows 0-.1v with the MAF connected (running very lean). Seems to be okay.

Checked ECU for error codes. Showed 55, all good.

Put fuel pressure gauge between fuel filter and fuel rail. Showed around 40 psi. Seems good.

I read on this very site that someone had their engine run lean due to the engine temp sensor, which seemed completely insane, but I tried unplugging mine, as that poster did. No change.

I'm really out of ideas. Maybe the ECU was tuned for larger injectors? Maybe there is some sort of nearly invisible vacuum leak. I've checked all around, and you would think it would need to be a decent leak to make the car this lean.

Considering the 11:1 ratio with no MAF, is it even possible that it is related to the injectors/coils/spark plugs? I'm starting to hate this engine

Please, please, please help me.

-Rob

**nimblestix** · 10-05-2011, 02:14 AM

Is it misfiring at all? When you rev the engine does it richen up?

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**Skym** · 10-05-2011, 01:30 PM

Checked wiring to fuelpump???

Check that there is no exhaust leaks as oxygen in exhaust (leaking exhaust manifold, common problem) = lean on wideband.

Same with intake plenum airleak (common problem, engine runs lean), but would have rev needle bouncing up and down due to o2 sensor making engine go lean, rich (when leak is really bad).

Higher idle points towards IACV, that's where I would look.

With narrowband o2 sensor your meant to hold at 2000rpm? and note how long it takes to switch between lean, rich voltage wise.

**clone** · 10-06-2011, 11:20 PM

Just curious, What fuel pump are you running?

**NISMONEWF** · 10-19-2011, 08:41 PM

what fuel pump has nothing to do with it .... if the rb is in a 240 and hes using the 240 fuel pump then it shouldnt be a problem unless hes running a much larger turbo ... and thats only when showing boost ... im with Skym on this one .... all of those are possible .. i have seen each and every one of those problems on many RB's .. its been a few years since i have turned a wrench on an RB but you never forget those pain in the ass leaks ....