92 corvette tuning tips and questions.

[steveo]

it doesn't populate VE it only puts BLM in the table.

one thing you need to understand about tuning fuel is you're rarely populating a table with new values, you are adjusting the existing values based on feedback.

in simple terms the ECM says "5!", but your o2 sensor says "...but we had to add 2% of fuel there" so you might change the value to "7" and then try again.

in real terms, since you're tuning a VE table, the ecm actually says 'for 2000 RPM and for 50KPA of MAP, the engine is 43% efficient'.

it then injects its fuel on the assumption that the engine is actually 43% efficient at that RPM (there are other things affecting fuel but just worry about the VE table for now)

you then get feedback as a BLM from the trim system that says "trim in this area is 150"

since 128 is 0% trim, we can calculate the trim as 150/128=1.171 (17%) (in other words 150 is 17% higher than 128)

so the ECM had to add approx. 17% extra fuel to achieve the proper mixture.

since we had to add 17% of fuel, we can assume that instead of being 43% efficient at that RPM/MAP value, it is actually 50% efficient. so you could change that value to 50.

but a better way to tune would be to get multiple data points from that area and average them together, because big piston engines are not a precise instrument.

you then have to 'interpolate' or 'guess' the values to smooth the table in between your adjustments, because there's no way you'll have good data for the entire table.

if this sounds time consuming, and like it's something a computer could do for you with way less effort, that's why i wrote trimalyzer (but then you have to learn to use that properly, too, and have some common sense in case it makes a mistake.)

the other reason tools like trimalyzer are good is because you can't always trust trims, you can only trust them once you are in closed loop, and the engine is warmed up, and you aren't in power enrichment, and whatever else. trimalyzer is good at filtering data.

edit: it's also good at taking HOURS of logs and crunching the whole thing...

[BlackW1dow]

So I am messing around with the ve tables and my car is getting hotter than normal. Not sure if it’s bc I removed the EGR and air system or the tables..

[NomakeWan]

So I am messing around with the ve tables and my car is getting hotter than normal. Not sure if it’s bc I removed the EGR and air system or the tables..

Removing EGR and AIR should have nothing to do with engine temperature.

If you want to know if your VE modifications are having an adverse effect, revert them back to what they were and see if the problem resolves itself. If not, then something else has changed. Is it hotter out? Did one of your fan relays die? Are you just doing a lot of testing while the car is sitting still rather than driving around at speed? The C4's cooling system isn't the greatest, and if any part of it isn't working at its full potential, things can get out of hand pretty easily. I found that out from experience, hahaha.

[LeMarky Dissod]

Is it hotter out? Did one of your fan relays die? Are you just doing a lot of testing while the car is sitting still rather than driving around at speed?
The C4's cooling system isn't the greatest, and if any part of it isn't working at its full potential, things can get out of hand pretty easily.
I found that out from experience.

Don't know about the LT1 OE fan-on thresholds for '92 & '93, but they were set so high from '94-'97 that the powertrain usually runs considerably much hotter in stop'n'go traffic than on the highway. NomakeWan's observations about the cooling system are absolutely spot on.

I can sort of get why GM would prefer LT1s to run 32°F hotter in stop'n'go than on the highway (except for sedans & wagons with big ol' mech fans that cost 10 peak horse), but this is easily fixed by lowering the fan-on thresholds to keep temps more consistent across driving conditions.
If both fans are on by 212°F / 100°C instead of 235°F / 113°C, it's one less thing to worry about, and a much larger safety margin.

[NomakeWan]

According to the stock BIN, the fan thresholds for the '92 Corvette are 219F Lo 227F Hi for 0MPH, and 227F Lo 235F Hi for any speed over 0 MPH.

[LeMarky Dissod]

219°F Lo 227°F Hi = 0MpH
227°F Lo 235°F Hi >0MpH
GM's $EE Y-LT1 fan-on thresholds are identical. The $EE F-LT1 & $EE B-LT1 fan-on thresholds do not change based on MpH, but are also too hot for me.

Given that:
LT1 cars' OE programs lead to running hotter in stop'n'go than on the highway
LT1 sedans and wagons with V08 mech fans run cooler than LT1 cars with electric fans

I don't see a reason against lowering the fan-on thresholds so that coolant temps remain consistent across environments, especially if this can be done without a mech fan.

[BlackW1dow]

So after throwing all my logs into trimalyzer, thank you steveo, I came out with this graph. i know there is a smooth button on tuner pro, but what's the best was to smooth it? do I smooth everything up on the right side to match the rest or should I leave it the way it is and do some more logging?

Does the logs just never touch those cells and that's why it isn't changed? I have attached the graph from trimalyzer as a reference to what I'm working with after about an hours worth of logging.

[lionelhutz]

I'd keep the fixed part for now. The rest that never got touched I would pull up. Pick those cells only and multiply them all by 1.13 first so they all come up close to the corrected part. If that correction isn't right then do another one until you get them close. After that, hand blend them into the corrected part to make the whole curve look nicer in the area transitioning between the corrected and the not corrected parts.

As for the corrected part, it looks pretty good. It doesn't have to be smooth, factory VE tables aren't. Just hand knock off any big peaks or valleys a bit which you really don't have to do here right now.

[NomakeWan]

What lionelhutz said is correct. Once you take the suggestions from Trimalyzer and put them into your tune, open the graph in Trimalyzer and just smooth any sudden jagged edges by hand. It may help to open a stock BIN and look at how its 3D graph is laid out to get an idea of what GM deemed acceptable. Getting the suggested changes from Trimalyzer is science. Smoothing the table transitions visually, that's art.

[stew86MCSS396]

After pulling my stock tune it matches the bin I was tuning with. I can about 99% sure rule out the cylinder volume as the issue which leads me to the injector flow rate. The rate in the bin I was using matches the stock rate. That being said I know the injectors have been changed but I have no idea what brand or flow rate they are.

I have looked up the numbers on the injectors but it comes up with like 10 different options. how do I determine their flow rate so I can correct in the bin?

Well gee...perhaps someone who's more web savvy can search the make and part number if you would post it.

Edit: If any one caught what I had posted/edited out, hind sight thought...if you're running lean based on the trim graph^^^you posted then my suggested increasing the injector constant is going to make you leaner.