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

[Joshie225]

I got my SparkFun FTDI breakout to 16-pin ALDL cable assembled last night and was soon communicating with my 1994 Corvette. Today I took it for my first ever data logging drive.

The log begins with the car reasonably well warmed up, driving out of my neighborhood on city streets, shutting off the car to run an errand, restarting the car and doubling back to the freeway heading North. I chose the wrong exit and sat idling on the off ramp for nearly 10 minutes before I could get back on the freeway South bound. I hammered it up the on-ramp, cruised a few miles on the freeway and exited into my neighborhood.

https://drive.google.com/open?id=1Mwr9fsmOO1OkyeafgTnjxnTWbxcYfJwE

During the warm up I blipped the throttle a couple of times while connected with EEHack and experienced some hesitation off-idle. With higher RPM, 1000 or so, I did not experience the same hesitation. I don't recall this hesitation when not logging, but I will double check.

It looks like my car is running lean whenever there is much load. I can see the O2 sensors responding, but still wonder if I have 25 year old sensors that respond slowly. I have new ones to go in so I can get before and after logs to compare.

I would appreciate feedback from any of the experienced sages.

Regards,
Joshua

[dave w]

Hi,
I'm in Vancouver WA also.

dave w

[F-Body Speed]

Dave w, familiar with 93 LT1 stuff any? I am in Portland, hope to move into my new shop in Oregon City in couple months.


Vince

[dave w]

Hi Vince,
I've only worked on a couple 93 LT1's. I've had success crunching data logs and reprogramming the chips. In the next couple days I'll try to set aside time to look at the .xdl posted above.

dave w

[spfautsch]

Do you have your wideband connected yet? Also, you might want to specify what mods you have if any.

I'm no sage but it seems like your O2s might be a bit lazy. Did you clear any codes before you started logging?

[Joshie225]

From what I can tell the car is 100% stock other than a K&N drop-in air filter that came with the car. The wideband is not yet installed. When I get the car on a lift to change the O2 sensors I'll see if I can add a bung for the wideband sensor.

The only DTC set in the PCM was for low coolant temperature and that code didn't activate the SES light. I cleared that code the night I got the cable together, logged the next day. The "SYS" message I'm getting persists. Through the process of elimination it appears the "SYS" message is not due to the code set in the PCM, but in another module. This is frustrating as when I previously entered CCM diagnostic mode I found no codes. I'll try CCM diagnostic mode again and see if it still gives me "ERR" when it queries module 4 (PCM) or if it shows any other DTCs.

[spfautsch]

Good luck with that. My CCM has been acting strange since I got the car - door locks cycle open for no apparent reason and two days ago the courtesy lights started switching off and on in a similar manner. I suspect there's a loose ground somewhere but I'm not quite ready to tear the interior apart yet and found nothing when I had the dash out 3 years ago.

[Joshie225]

My CCM appears to function well except when communicating with the PCM in diagnostic mode, and perhaps at other times, leading to the persistent "SYS" message. I had forgotten about the CCM code 81, invalid vehicle configuration detected (engine types do not match). I strongly suspect that the recent CCM replacement and reprogramming was not 100% correct which leaves me to research how to reprogram it. Anyone have a Tech-1A they would loan/rent?

What I'd hoped to get from this thread was feedback on the datalog. The corrections seem a bit large for E10 fuel and I was curious to hear the experience of others with similar vehicles.

[Joshie225]

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.

[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-Injection/showthread.php?335-16188051-and-16181333-PCM-Information-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.

[spfautsch]

Just to clarify, the cylinder volume constant only impacts the speed density calculations. I believe the MAF fueling calculation doesn't need to know anything but the injector constant.

[spfautsch]

Another idea just crossed my mind - has your MAF had the honeycomb removed (aka descreened)? That would throw the calibration off.

[Joshie225]

MAF screen is intact.

I was thinking about fuel pressure and checked the vacuum line to the regulator. But if the pressure were high at low load the PCM would have to pull fuel then rather than add fuel under load.