Using Tunercat and the PE tables I was only able to get the PCM to add fuel to a certain point in the PE tables until I had to adjust with the PE (coolant temp) tables and maf tables. The PE value was around -20 and the inj duty cycle was around %80 and any more PE adjustment and the duty cycle didn't change. So still being lean at %80 I had to go to other tables. This is on a boosted 1995 LT1 with the MAF maxing out around 4.8k. Anyone else run into this?

 

I found something similar, but the other way around:
I was trying to lean out Idle doing the PE Idle thing and was able to lean it out just a bit. There seems to be a limit as to how much enrichment/leanout you can apply.
I dont remember the exact amount. I gave up trying to run CL with my cam.
I run an open loop tune now.
This was using LT1 Edit though.

RG

 

maybe -20/+20 is the limit?

It's good to know about this, so if we find ourselves nearing this limit we can adjust other parameters, like the fuel injector constant or MAF tables.

 

Is the value negative 20 or positive 20 in the PE table? LT1 edit will it let you do up to about +40% in the PE table. Will it not go any larger than 20?

 

What I mean is, perhaps the PCM ignores any value past -20/+20. Maybe it's a hardcoded limit. I'm speculating here, though.

There's no real good reason to have to adjust the AFR at WOT that much if the rest of the PCM is well-tuned in. If one is finding they need to go more then +20 or -20 in the PE table, it might be a good idea to look at some of the other values (e.g. fuel injector constants, MAF calibration, VE tables). Chances are something's far enough off the PCM is having to do a LOT of correction to keep it running properly, even in closed loop.

 

I have an OBD2 97SS 383 D1. I use LT1 edit v2.2 to tune. The max limit on PE vs. rpm is 48 in the table. I have zero-ed PE vs. temp table. I do not know what the max is on an OBD1 PCM? Anyway, I am running closed loop with the MAF. Some of the things I have done are...
Use of wideband dynojet afr to tune.
Boost ref fuel regulator.
Adjusted MAF cal 2% lower and raised BLM update 60kpa for low speed fueling afr.
Adjusted PE vs rpm curve @ WOT for AFR of 12.0
Running 72# injectors. (peak & hold type)
Run full timing with spearco intercooler and h2o/ meth Inj.
Zero-ed knock table.
Raised MAF threshold frequency to maximum.
Adjusted low speed fueling and Inj offset time vs. voltage.
Hope this helps.

 

It seems there must be some type of limit. Adjusting from -20 to -25 actually showed slightly leaner and no change at -30. This was verified by seeing no significant change in the injector duty cycle. So went back to -20 to -15 range, scaled the whole afr down with the coolant PE table then did slight adustments to the RPM PE table and up top on the MAF tables to get it right. So it seems you have to do some scaling with the coolant PE tables and MAF to keep the RPM PE tables in a working range.

 

% Change To Fuel/Air Ratio Vs RPM at WOT. Is this what you are calling the PE Table? If so, I don't see why you would ever want to have -15 or -20 in that table. With those values all set at 0, you will be commanding an A/F ratio of 12.7:1. At -15 you would be commanding 14.6:1 and at -20 you would be commanding 15.3:1.

 

Is it 12.7:1 or 14.7:1? On the Gen-III tuning software packages it says the PE multiplier vs. RPM is based on the PCM's programmed stoichiometric air/fuel ratio, which by default is 14.7:1. Maybe its different on Gen-II. I guess it doesn't matter as long as its possible to get the AFR where it needs to be for a given setup.

 

Yes, for the Gen 3 programs there is a PE Enrichment Table vs RPM that you use 14.7/Value in the table cell for comanded A/F ratio. For the OBD1 and OBD2 LT1s you use either of the following formulas.

(1 - ([# in Temp Table] + [# in RPM Table])/100)*14.7

14.7/(1+Number in the Cool temp table/100+ number in the RPM table /100)

I have a couple of excel programs that figure it out for you by just copying and pasting the values from the temp and rpm tables into them. I don't have any way of hosting them or I'd gladly share them.