Tuning the MAF curve today getting everything pretty well smoothed out. Still in open loop MAF only I wanted the check the A/F at WOT in PE. Looking directly at the wideband everything seemed OK until I looked at the scanner log.

At around 6000 I was at 12.54 AFR then It creeped up to 13.87 around 6400 RPM! It was there a brief second unbeknownst to me when I got out of the throttle. Seeing the scan though was a little upsetting

I'm running a small cam, headers n/a with 50 lb/hr injectors with a 10 year old Delco OEM pump.

Looking at the Walbro 255...

Does this sound like running out of fuel pump??

Couple pics between 6000 and 6500 RPM (wideband highlighted top left column)

 

Fuel pressure is the tell tell sign.

Have you tried to add more fuel to it?

 

Really don't know where to add fuel without making the tables rich below that spike. It's perfect 6100 and lower but at 6400 it starts to go lean (rev limiter is set at 6500). It's kinda worrisome seeing that quick lean spike at high RPM's.

I'll feel more comfortable knowing the old Delco pump is replaced with a pump with more headroom. Plus the check ball in the old pump looses prime (return type), I have to cycle the key twice to start. Been putting off doing the pump as it's a pain in the ***, pulled the bed and replaced it around 10 years ago... yep It's time.

 

I’m more of a seeing is believing type of person.

You could always put a gauge on the rail and tape it to the windshield to see.

I’m at 222k and some change on the factory FF pump but I’ve got a BAP on mine.

It'll die a horrible death and leave me on the side of the road when it goes.

But that’s what AAA is for. Lol.

 

Go ahead and put a new one in, but you need to check the fuel pressure. There are other things that can cause a lean condition at high rpm. What happened to me, for example:

I had some injectors with incomplete data. The lower voltage area of the data was too lean. If I wasn't monitoring system voltage, I might never have figured out that my alternator was shutting off (the brushes will bounce at high rpm on some rebuilds) at the same rpm that my wideband went lean. A factory new alternator fixed my high rpm lean condition. I since have new injectors with good data.

I don't imagine that this is your problem, I am just showing something other than a fuel pump that can cause a lean condition.

 

Why not log injector duty cycle, Fuel pump requested Fuel pump commanded DC, Desired fuel Pressure. I doubt your running out of injector with 50 pounders, but Id also question the injector data.
Personnally, I like making trucks richer because of the weight and load

 

Actually really great advice. Sometimes we overthink things.

 

It's a year 2000 truck, fuel pump duty cycle and desired pressure are not available. Injector duty cycle won't differentiate whether the injectors are too small or the fuel pump can't keep up.
I think Tampa is overthinking it. A simple fuel pressure gauge should be the first step, OK? yes, check injector duty cycle. No, suspect fuel pump. And just because of the way it suddenly drops at a certain rpm, I would log system voltage, too.
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This. All of this.

 

The injectors are indeed in question. They are GEN 4 Flex injectors scaled to GEN III data, so I'll have to trust the numbers my original tuner deciphered. I have found matching data (gen 4 to gen 3) in the injector sticky over at LS1tech.

Everything is new on the truck engine, belts, hoses, transmission, rear gears, radiator, battery, tires, brakes, shocks etc. About the only old parts that may leave me on the side of the road (normal wear & tear) is the fuel pump and the original universal joints.

After the pump is replaced I'll troubleshoot more if the issue still continues.

Thanks for the input guys!