manifold pressure vs load - SDS and datalogging

[Nigel]

Stats:

L28 Turbo, T3TO4b, SDS EM3-6F, RX-7 440cc injectors, Walbro 255lph pump, ScottieGNZ down pipe, 3 in mandrel exhaust, Techedge DIY WideBand O2, ~9psi boost...

 

Earlier this year, I set up the Techedge to datalog 02, RPM, MAP, Throttle Position, and Air Temp. Last week, I installed an Aeromotive adj. FPR, and I'm now in the process of retuning, because the stock regulator was obviously too restrictive.

 

I discovered something interesting when looking at the AFR with the new regulator. I hope to post some screen shots soon, but in the mean time, here's a description of what I'm seeing...

 

What I'm doing is logging a run in 3rd gear, full throttle from around 2500 rpm to 6000 rpm. Boost builds in a linear fashion, and I reach peak boost around 3750rpm. After I installed the new regulator, when I stomp on the gas, the AFR would dip to < 13:1 then started to rise in step in boost up to around 14.5:1. Just as I reached peak boost, they droped down to 12 - 12.5:1. But my RPM FUEL values are fairly close together around the RPM range this occurs, and my MAP values were rising at a constant slope. I had to dramitically increase the slope of the MAP FUEL curve as soon as I started to make boost, and then level them off as I approached peak boost (Since the peak boost MAP value is fine). So, for example, my MAP fuel value at 5 psi is nearly as much as my value at 9psi. Even then, I still haven't been able to get AFR's to go below 13:1 until I reach peak boost.

 

In other words, it's looking like I need as much as or more fuel while building boost, then while actually maintaining peak boost.

 

Does this make sense?

 

Nigel

'73 240ZT

[Z-Gad]

First, what is your fuel pressure set to? I think stock is ~37 psui, but most larger injectors prefer ~ 42psi.

Next, it may be your accelerator enrichment settings and not the map values. From the main screen, use the left arrows and you'll see the settings. If you increase the fuel values there or adjust the sensitivity, it may make up the difference. Also, you may want to turn the boost down to 6-7 psi (if possible) and do a coulple of runs there to see what the car is doing.

[Nigel]

My base FP is set at 40psi. I can raise it up a couple more psi, but I think all that will do is result in my having to offset all my RPM fuel values down. I’m aware of the accelerator pump feature, but to the best of my knowledge, that’s just a brief extra shot of fuel lasting for only about a second. And indeed my AFR’s drop when I floor the throttle. The issue is that they start to climb back up as boost increases then drop once peak boost is reached. It seems that the demand for fuel is not increasing in proportion to the increase in boost.

 

Here’s the theory behind my tuning:

 

At maximum boost, the MAP FUEL values are pretty much constant as that boost level is held pretty much to redline. So, achieving my desired AFR should be done through RPM FUEL values. And I’ve managed to get very consistent AFR’s based on that. Now, the rpm range while building boost is around 1200 to 1500 rpm (in otherwords, it takes 1200 to 1500 rpm to go from 0psi to ~9-10psi) with peak boost arriving around 3750 rpm. My theory is that if RPM FUEL values in that range are fairly close together, and are not that far off the peak RPM FUEL values, then achieving my desired AFR should be done through MAP FUEL values.

 

Just out of curiosity, how many people have watched their AFR’s while building boost?

[Z-Gad]

I do... constantly as I have the LM-1 in the daily driver...

Anyway, I seem to remember that I had some odd RPM fuel values to compensate for something similar to what you are describing... It seemed after the car made peak torque, I actually had to slightly ramp my RPM fuel values down a few points to get even AFR's ... somewhere around 5000 rpm's, maybe the first point by 4750..