Alright kids... I need a brainstorming session w/ ya'all (requires some reading).

So last fall I decided I needed to up the fuel pressure a lil, as my L28ET would lean out at full throttle above 5000rpm. I was looking for a RR FPR, but before I bought one, I decided to make sure it was the fuel pressure making it lean out. I clamped off the return line after the fuel rail & took it for a run... ran very well, then it burnt out my fuel pump control modual... I got another & since then, it's run SUPER LEAN... For example: it idles fine, but the second I step on full throttle, the air/fuel gauge drops to the lowest red, and it knocks & pings like crazy. It won't go over 4k rpm at full throttle & it sounds like the engine is going to jump right out of the engine bay.

So I start the diagostic session: (steps done in the following order)

-swap turbo ecu's... no difference.
-swap fuel pumps (stock turbo for Walbro 255)... no difference.
-added RR FPR w/ fuel gauge (fuel pressure @ 35psi)... no difference
-swap fuel injectors... no difference.
-tested volts going to fuel pump (9.5v at idle, 12.5 at full throttle).

-today, pulled the head temp sensor connection... won't idle of course, but rev's BEAUTIFULLY because the ecu is dumping fuel in if the head temp sensor is unplugged. So... swapped head temp sensors... no difference.

-So, my conclusions... Not an ecu prob, not a fuel pressure prob, possibly a sensor prob?

WHAT AM I MISSING?

 

I'd check both the AFM. It and the head temp. sensor are the two main factors in the amount of fuel your ECU dumps in. I'm assuming you've already checked the o2 sensor

See when you pulled the head temp sensor it sent the ECU into closed loop mode. Which means it wasn't taking a reading from either the AFM or the o2 sensor. Only the temp sensor and TPS. So that right there should tell you the problem is one of those two items. The AFM flapper may be functioning properly but check to make sure the air temp. sensor is still working good.

 

Alright, I'll swap AFM's next. I did unplug the O2 sensor... no change as well.

 

also on a long shot check out your fuel pump relay its in the fire wall by the BATT.under the plaistc cover ...just a thought if the afm thing doesnt pan out.........

 

Wow Id Check The New Modual, Just Cause Its New, Or New To The Car Doesnt Mean It Will Work Correctly, As Well As The Other Ideas Listed Above^^. My Car Has Been Running Way Rich Lately So Im On The Opposite End Of You.

 

I'm bypassing the module altogether. I'm running a quiter pump anyways so it's no big deal to me. I'm also rewiring the pump with a new relay and some 10 guage wire to power the pump. That way I know my pump will have plenty of voltage all the time.

 

What kind of pump? I thought my Walbro 255 would be loud as hell, but it's vey quiet.

 

It's a NOS pump. They rate it in gallons but converted it comes out to 254 lph. But the entire pump is insulated and it's claimed to have quite operation so... But I haven't actually run it yet. Once I get the engine back together I can test the validity of their claim. I'm going to use my old NA pump to build a fuel injector cleaning station

 

Alright... I had time to work on the Z for a few today.

I swapped AFM's & that didn't make any difference... so I swapped mine back in, and it rev'd much better, but still leans out above 5k rpm @ full throttle.

So the major problem seems to be the AFM connector (possible corrosion & loose wire connectors), which I'll have to wait till next weekend to check on. But the lean prob is still there. Dammit!

 

I know this post is incredibly old, but I've had these exact same problems and have tried all of the same solutions. How were you able to finally fix the issue? Thanks! Peter