Hey all,

I was hoping I could get a few tips on part-throttle tuning my 90 6-speed. The engine is running fine with no noticeable mechanical issues but during datalogging I can see that my BLMs are not great - fairly rich overall. No major knock events though thank goodness.

I already know how to use TunerPro and my Autoprom to change settings and burn chips for simple things like fan temps, injector constants, EGR flags, etc. but I haven't really messed with the VE or spark tables. I'm not planning on using a Wideband until I get my feet wet a little.

I've read that starting with getting the VE straightened out first is the way to go - then spark then back to VE. How do you guys get decent data to find the VE changes? Take a long drive then mull over the thousands of data points? Short drives targeting certain regions of the tables? What's the best way you've found to calculate the changes?

I've got a nice long trip coming up this week so if a long drive is the way to go then I'm set. If I know what to look for in the data, I'd probably write an app to do most of the figurin' for me.

Thanks!

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The wideband is good for WOT tuning, or for tuning a car that is openloop only.

The problem with a wideband, is if you go ahead and dial in the true AFR, while in closed loop, the narrowband sensor is going to change the AFR because it won't agree with the wideband.

You can use the wideband's 'narrow band output', and try to play with the o2 thresholds to get the ECM to play along but I've found it to be futile..

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It's like cat and mouse. I usually get the car fired up and in closed loop, then while running disable closed loop with the 'coolant threshold enable' constant. This turns off the correcting, but allows BLM reporting.

Then I have someone drive, while I directly make changes to the VE table. Choose and RPM and map value that is rich, and take out some fuel. Keep working at it until the BLM is close to 128. The more fuel you take out, try adding some cruise advance. A lean highway cruise in the low 40s is not unreasonable.


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10 years ago, I used whatever was available at the time (winaldl, moates, datamaster) to save CSV files, I'd then use my VE spreadsheet to make the conversions, burn a prom, go drive around again and spend all week.

Now, with an emulator, and a pilot, I can dial in a VE table in an hour or two.

-- Joe

Using an emulator would be the way to go but, unfortunately, I don't have access to another driver so I have to do things the old-fashioned way.

Thanks for the tips on adding advance as the fuel is pulled.

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No problem.

LEAN AFR's need more advance to get the fire light than rich AFR's. In fact, a condition with not enough advance will show up as a rich condition on the BLM because of incomplete burn.

-- Joe

Wouldn't an incomplete burn show up as lean? Incomplete burn = less oxygen used in the burn, so more oxygen in the exhaust. The O2 sensor would see that, and report lean, right?

You know more about than I do, so I'm sure you're right, but I was wondering if you explain the nuts and bolts of it. It seems counter intuitive to me.

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O2 sensors sees the extra fuel and reports low BLM. It's one of those strange conditions that causes the tuner to keep pulling fuel because the BLM reports like 108 or something silly, and makes the problem worse.


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The narrowband is not perfect.


Things get all sorts of crazy when you had a big cam into the mix, because the overlap period is havoc on the 02 sensor. Anything with more than 224 degrees duration, I usually just run open loop and get it dialed in with the wideband. While we'd like to think EFI is great for weather corrections and all that, with such modified motor and 80s technology the corrections hurt more then they help.

The true benefit of EFI over CARB is:

1) You can play with crank fueling
2) You can modify timing, idle, fueling without opening the hood
3) You can log RPM vs LOAD vs MPH for WOT fueling at the track, to get an idea of where to add or pull fuel/timing. Since we know that dyno tuning an engine hardly EVER prepares it properly for the track, since a dyno can't accurately simulate progressive load and drag coefficient of an individual vehicle.


"Closed loop" is a great idea, and works well on stock motors. When you go crazy with cams and engine combos it's not reliable.

-- Joe