load decreasing at WOT

[TXEnginerd]

As the title indicates, I'm seeing what is to me a weird result when logging load at WOT. It jumps up to a good number when I hit the throttle but instead of continuing to climb, it decreases throughout the pull.

The load seems a little low to me as well. My displacement is set at the stock value and I'm not technically using either scaling or BP method. I just had to load my injector files and the scaled MAF value file (which doesn't scale anything else) and only had to do minor tweaking after that.

03 Cobra AMZ2
2.3L Whipple @ 17psi
E85
FRPP 80#s
custom return system @ 50psi base
VMP 3500 slot sensor MAF
logged with SCT X4

Datalog (click to open full-res image):


I'm really not sure what to check for this situation. Any input/suggestions welcome.

 

[watman02]

What gear are u in for this? That will affect load.
Load is just a calculated figure I wouldnt worry about what it is at. The only thing u need to know from it is where to adjust fuel and spark tables and to comand o/l. I wouldnt be concerd as long as the car is running well and Afr is good and smooth

 

[TXEnginerd]

Thanks for the reply. In the screenshot I included both a 3rd and 4th gear pull. The right pull is the 4th gear one - load shoots up to 1.51 then tapers down to 1.18.

I'm not overly concerned about the load being lower than I was expecting. I am concerned that it decreases instead of increases though. That does not seem normal to me and these WOT pulls felt weaker than they should have with my mods.

 

[watman02]

What is the red and blue lins in your screen shot? It looks like your maf flat lines(blue line) thus causing ur load to drop off sharply what are your maf counts at this point? Are you hitting the 63.9lb limit in the ecm? and the red line is spark advance?

 

[TXEnginerd]

What is the red and blue lins in your screen shot? It looks like your maf flat lines(blue line) thus causing ur load to drop off sharply what are your maf counts at this point? Are you hitting the 63.9lb limit in the ecm? and the red line is spark advance?

Not hitting the limit but someone on SCT forums pointed that out too. Here is what he had to say:

It looks like restricted airflow to me. LOAD is basically MAF divided by RPM (times a constant), so if MAF flat-tops and stops increasing, then LOAD will decline as RPM increases, which is exactly what you see on the datalog. So, if you look at the MAF trace, RPM is climbing faster than MAF for the first bit, so LOAD trends down a bit, then MAF stops increasing and LOAD declines even faster.

Something is restricting airflow.

The only other cause would be if the MAF sensor was out of range, but if that was happening your lambda would go lean and it doesn't.

That makes perfect sense to me. I recently swapped to a smaller filter to be able to accommodate a new maf housing and sensor in between my current intake tube and filter (the intake tube has a slot for a MAF but not a slot style). I noticed a couple psi drop in max boost so I am pretty that is the problem. The new setup is too restrictive.

Thanks for the help!

 

[TXEnginerd]

Just wanted to update everyone on the resolution to this problem. It turns out it was belt slip after all.

I added a Metco tensioner pulley brace and replaced the gatorback belt with a smaller Gates HD belt and this was the result:



Thanks everyone for your time and input, and especially cj428mach for the solution!