Thread: Why am I all the sudden running lean?

Hey whats up guys,

I have a n62 maf in a billet maf box from turbo tank, I didnt seal it 100% originally and moisture killed it. I have since replaced it and my car
will now rev flawless at idle. But now if i drive and get on the gas its really lean ( 16-18 AFRs ) obviously its not safe and I got into boost for
a brief moment before getting off the gas.

What else could be the issue? I had a bad maf which I replaced, Nothing else changed I havent changed anything on the car at all.
The wideband is reading lean and the plugs look like you would expect for a lean condition.

Vacuum looks like what it should be and the tune hasnt changed and also the maf is the same as it was.
Also checked for boost leaks which appear to not exist ( whole piping is done with brand new couplers and t-bolts ).

• Idle = FINE
• Rev = FINE
• Driving = LEAN / Bog ( bogged with out adjusting plugs )
  

The car will drive fine off boost im wondering if my Walbro is sh|tting the bed, I have a fuel pressure gauge but its under the hood.

I will attempt to data log but would also like to hear your input, Wanna get back to enjoying my car..

If the only part you changed was the air flow meeter, than its very likely to be the air flow meeter.

The mafs that we use are getting very old and they all read slightly different.

You likely need a retune.

MAF you replaced with is where I'd be looking first. The N62 FSM probably has a test procedure for the MAF I'd try to find.

Ok I will have to research a test procedure, I dont have a Z32 FSM.. Ill also try cleaning the sensor and testing with my laptop ( nissan data scan ).
Just want to drive this car again.. Figured it would just be a direct swap N62 to N62, I mean if i had a JWT ecu which I dont they just want to know the
MAF model and the tunes usually work flawless.

http://www.nicoclub.com/FSM/300zx/1994/ec.pdf

MAF diagnostics begin on page 113

Thanks Brotha!

I will look tonight have people seen variations between N62 MAFS? to make this much of a diff?

Cleaned MAF / Tested with Nissan Data Scan + Multi-Meter everything looks good. Anyone think my 1 Year old Walbro also is crapping the bed
or is it time to get an adjustable FPR? Check the following Vids, Again car idles and revs fine its behaving like when my stock pump was dying.

AFR's go wacky at idle it will be 16-17-16-17 then just go 14 - 12 - 14 - 16 wtf

Fuel Pressure Gauge



AFR's on Wideband ( randomly go rich ) this is what my failing stock pump was doing.



While this is going on idle is fluctuating a little im working on that ( 1000 - 1200rpm ) but pulling 20 vacuum the whole time.

If I take for a small spin it drives almost fine but if I poke throttle into boost it use to jump to 11.8ish AFR now its pegged lean 17-18 (unsafe )
and trust me the 1-2 times while testing I let right off, Im not cooking my motor out of stupidity.

Anyone one else have any input? MAF appears to check out fine, Could it be the FPR or Walbro taking a crap its only a year old and 7k miles or less old.

i had a walbro fail on me less then 24hours an only a few miles, my fault i guess i was low on fuel, not out but really low like 1-1.5 gallons.. i had just installed it an i didnt wanna do it with a buncha fuel in the tank lol

Think its showing signs of a failing pump? Ive been working on cars a while and this has me stumped.. Parked car one day and wouldn't start, Determined MAF got moisture in it.. Fix that and now it revs and appears to be the same as it
was before except... ITS SUPER SUPER LEAN so and the AFRs go up and down and pressure seems low.

Leaning towards pump dying, Its behaving like when my stock pump was dying... Does that fuel pressure look low?