[kevm14]

I think the only way to adjust MAF-mode BLMs is to change the MAF airflow/frequency tables...

I'm interested in testing the AE fueling hypothesis. You're saying with the VE tables zeroed out (or set significantly lower), the car drove exactly the same? I suppose I could try myself.

 

[Ram Air 383]

Anything that affects fueling at part throttle in a closed loop such as MAF tables, injector constant, engine displacement constant, etc. will have an effect on BLMs and O2 readings. If it doesn't, it has no effect on fueling.

O2 sensors are not used at WOT and in open loop so short term fuel trims are not updated at that time.

I do think that VE tables are used in open loop. Reducing values in the 800-1200 rpm range cleaned up the exhaust smell in open loop. So do the experiment with VE tables when the car is warmed up. When I zeroed out VE tables, the car was warmed up and I didn't notice any difference in how it was driving. I reprogrammed it back after 5 minutes.

 

[kevm14]

I find it odd that VE would be used in open loop but not closed loop. The MAF sensor has nothing to do with the O2 sensors and I don't see why it couldn't be relied upon regardless of operating condition, cold or hot (except a brief period after engine startup).

Open loop fueling should be controlled by the open loop fueling tables, as well as the measured airflow input from the MAF sensor.

This snippet from TunerCat has me thinking:

Under changing conditions where the vehicle is accelerating, decelerating or the load is changing significantly the PCM essentially goes into speed density mode and uses the VE tables to calculate the required fuel. Once conditions stabilize the PCM goes back to using the MAF sensor readings. I believe this is done because the MAF sensor are relatively slow to react to quick changes in air flow.

If this is true, then it doesn't matter if the PCM is in open loop or closed loop mode. It still needs to calculate AE fuel when required.

Of course, TPI cars from 85-89 come to mind. They had no MAP sensor. But they had explicit AE tables, whereas LT1s don't seem to. So once again, they've either not been found by the makers of LT1edit and TunerCat (after how many years???) OR the PCM calculates AE from something else, like VE.

Or that's all wrong and it DOES use the MAF for AE. Doesn't seem like it would react fast enough. The engine kinda needs fuel the moment the throttle is cracked, not moments later after the pressure wave registers on the MAF element a foot down the intake tract.

I may still experiment on my car...

 

[Ram Air 383]

Originally posted by Kevin Moore:
I find it odd that VE would be used in open loop but not closed loop. The MAF sensor has nothing to do with the O2 sensors and I don't see why it couldn't be relied upon regardless of operating condition, cold or hot (except a brief period after engine startup).

This was surprising to me as well. It's something I read on camaro forums. My only proof is the car seems to idle cleaner in an open loop which is very apparent with an LE3 cam. It would be interesting to test this with a wideband O2. I didn't notice any difference otherwise adjusting VE tables. VE tables may have an effect in closed loop as well but I haven't noticed ANY difference through logs or seat of the pants. One day I may buy a wideband O2 kit and see what happens.

 

[kevm14]

And I can't say that I noticed anything either. Of course, my car is nearly stock, but the VE did change a little. The O2s aren't brand new, though (maybe 35k on them).

So, unfortunately, this leads us to doubt rich91080's experience. Was he imagining things? I doubt it. I believe what he says was happening was really happening. But why and how?

The fact that this 12 year old PCM is still mysterious is hilarious!

 

[Ram Air 383]

Joe Georger, the creator of VE master claims that VE tables do nothing in MAF mode for an EE pcm tune.

http://home.comcast.net/~jgeorger/vemaster/

Tunercat creators claim otherwise. I'll try to find a way to test the changes on a wideband dyno. But VE tables definitely do not affect short or long term trims.

 

[producers_kid]

But VE tables definitely do not affect short or long term trims.

Could you confirm/clarify what you mean? Did you mean DO or DO NOT affect short or long term trims? Do you mean that if you plug in, say, "20" into each VE cell that it will not have any effect in closed loop?

Maybe this is one of those things that, if you believe it works for you, great. If not, great. However, it remains either a true or false belief.

 

[N0DIH]

Question. SD Mode.

Is this simply disconnecting the MAF, OR flashing it off through TunerCat, datalog, then flash back on?

Originally posted by aknovaman:
How about this theory. For OBD2 cars, run a OBD1 conversion PCM, datalog in SD mode with DataMaster, fine tune the VE table using the BLM #'s, revert to non-SD and tune MAF tables using the BLM's. Copy the OBD1 file tables into the OBD2 file tables and prog your OBD2 pcm.
Viola! Now you have a perfectly tuned OBD2 car or am I totally off the mark.

AkNovaMan

 

[Ram Air 383]

Originally posted by producers_kid:
Could you confirm/clarify what you mean?

Record a datamaster log. Look at the short and long term blms (obviously in a closed loop). Run VE master or just change VE table values. Record a data log again. Notice the difference in fuel trims or a lack of.

 

[kevm14]

Originally posted by RamAirRocket:
Question. SD Mode.

Is this simply disconnecting the MAF, OR flashing it off through TunerCat, datalog, then flash back on?

I'd recommend flashing to SD mode. Unplugging the MAF throws an SES, and runs both fans.

But yes, then you would datalog and reflash with the new VE data. I'd recommend doing at least one or two more iterations like this, in SD mode. For the last flash, just uncheck the SD mode switch and you should be good to go.

I support Ram Air's claim that VE does not affect MAF-mode LTFTs, however I am still unsure if AE may be calculated from VE, even in MAF-mode.

 

[kevm14]

Been reading through my FSM for my Camaro (specifically drivability and emissions) and among other interesting tidbits, I came upon this interesting section regarding fuel injection modes, relevant to our discussion:

Acceleration Mode
When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the PCM increases the pulse width to the injectors to provide extra fuel during acceleration. The amount of fuel required is based on throttle position, coolant temperature, manifold air pressure, mass air flow and engine speed.

Where are the damn TPS-based AE tables??

 

[Ram Air 383]

There is a VE vs %TPS vs RPM table. The question whether it is used in MAF mode remains.

 

[kevm14]

Yeah but all previous GM speed-density ECMs have had both the 3D VE tables and separate AE vs TPS and AE vs MAP tables. To date, we have not seen the last two in the 8051.

 

[N0DIH]

What is "AE" mode?

Has anyone ever changed all VE tables to say 50 across the board and driven it? That would prove beyond a shadow of a doubt if they are used in MAF mode.

 

[kevm14]

AE is just another term for "pump shot." It stands for acceleration enrichment.

I have not changed my VE and driven the car in MAF-mode.

Based on what I currently know, the LTFTs will NOT reflect such a change to VE.

 

[Ram Air 383]

It's called PE (power enrichment) in our PCM. We have 2 tables "AFR vs Coolant Temperature in PE" and "AFR vs RPM in PE". PE only happens at high throttle openings (over 90%) so PE vs TPS% would not be very useful.

 

[kevm14]

I wasn't talking about PE. I'm talking about pump shot, which is AE, and is transient fuel.

 

[SoCalChlln]

Most people don't like OBD II. i do and the more i understand it the easer it is to tune it. I am about to start working on tuning my MAF soon.

Hello Rich.
I’m also a 96 LT1 owner that wants to keep it OBDII and still tune and datalog.
I currently own the Jet DST tuner but don’t know which data logging programs will work with both an OBDII pcm and my DST.
If you can outline or advise me on how to connect my Laptop to my ALDL port, and you’re saying (if I’ve read it right) the EFILive program does this and datalogs a 96-97 pcm correctly for use with an OBDII tuner like DST right?
I’m new to the tuning arena, so you might have to dummy it down a little for me. But I pick up things very fast when properly directed with accurate and concise information.
THANK YOU for your time and any information you can offer.
It will be much appreciated !!!

 

[SoCalChlln]

It's called PE (power enrichment) in our PCM. We have 2 tables "AFR vs Coolant Temperature in PE" and "AFR vs RPM in PE". PE only happens at high throttle openings (over 90%) so PE vs TPS% would not be very useful.

You do know the Corvette has the PE button and circuitry to use PE mode.
The Impala/Caprice/Roadmaster does not, so without fabrications to the circuitry and a switch, PE mode does not come into play when tuning on a non corvette model.
If I’m mistaken please correct me.

 

[cappy p]

Epic necrobump