Newbie's 1st Log 1994 LT1 Corvette, Can you have a look?

[dave w]

I wanted to bump this and ask specifically; Why are my trims are so out of whack? It looks like it PCM is compensating for a lean condition at anything above light load. I don't need the exact answer, but if someone could point me in a direction that would be great.

I used a sample EEHack data log to show / analyze the Fuel Trims. (see screen shot below)

I used TunerPro to show the VE Table (Fuel Table) from a Camaro LT1 .bin file. (see screen shot below)

Generally, adjusting the VE Table will correct fuel trims.

Generally, slightly rich fuel trims work better for E10 fuel.

dave w

[Joshie225]

Dave W,

Thanks for chiming in! I ran the EEHack analysis myself which is how I knew the PCM was adding as much as 17% extra fuel. I was wondering if this is common on MAF equipped cars on E10 fuel or if maybe I have an issue that some preventative maintenance might solve? I think the thing to do is install my new O2 sensors and go for another datalogging drive. I also think that I should clean the MAF. I can see the MAF values changing, but if they are lagging it could explain the hesitation I've experienced and high fuel trims. I'll do some work and report back.

Joshua

[dave w]

MAF output Frquency (Hz) will vary with the amount of AIR flowing through the MAF.

$EE definition shows both fuel and spark tables are "MAP" vs "RPM" or aka "Speed Density".

It's challenging to understand what $EE is doing with the MAF frequency input. The $EE Hack (Post #5): http://www.gearhead-efi.com/Fuel-Inj...rmation-EE-EEB will possibly help with MAF functions. Possibly the MAF frequency output is a modifier for Injector Base Pulse Width? Possibly the MAF frequency output is a modifier for Spark Advance? Possibly the MAF frequency output is a modifier for both BPW & SA?

It's likely a good plan to verify the MAF is working correctly.

dave w

[steveo]

its not really challenging at all

its a dual mode ecm. when the maf works, ve tables in ee are unused

it takes maf freq and translates to airflow afgs with the maf table, and uses that for its base airflow calc.

ve tables are only backup for when the maf dies

[dave w]

its not really challenging at all

its a dual mode ecm. when the maf works, ve tables in ee are unused

it takes maf freq and translates to airflow afgs with the maf table, and uses that for its base airflow calc.

ve tables are only backup for when the maf dies

Thanks for the info.

dave w

[Joshie225]

its not really challenging at all

its a dual mode ecm. when the maf works, ve tables in ee are unused

it takes maf freq and translates to airflow afgs with the maf table, and uses that for its base airflow calc.

ve tables are only backup for when the maf dies

This is interesting. Does this mean that if I want the speed density tables to be accurate that I need to disable the MAF before tuning?

[spfautsch]

Affirmative.

In all honesty until you change your cam or add some other big airflow improvements I wouldn't suggest messing with the stock VE table. Improving on what the factory did is going to be a tall order unless you've got access to a load cell dyno. You can make global rich / lean adjustments by scaling your cylinder volume constant.

EDIT: Oh, and another possible cause for more air getting into the engine than the MAF is measuring is... vacuum leak?

[Joshie225]

Understood. I won't mess with the VE tables while in the stock configuration.

Vacuum leaks are much more influential under light load and the fuel trims are fine there. I've had the MAF sensor off the car for cleaning and the rubber boots look to be in very good condition so I doubt air is bypassing the MAF. If it were lean everywhere I might fiddle with the cylinder volume constant, but it's only above 40 kPa between 1000 and 2500 RPM that it seems to be lean. I'm going to go for a drive to see if cleaning the MAF had a positive effect.