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I've had the EBL Flash for quite a while and am finally getting around to trying to finalize the tune. I have a good handle on WOT and most of the VE table above 30 KPa. Where I'm having trouble is the lower loads - 25-30KPa. I'm getting the dreaded "bathtub" or in my case a trench in the VE table. The more VE learns I do the worse it gets. See mods in sig and picture of VE table from last test drive below.
I started with the EBL TBI BIN. Currently set to open loop for WB VE learns. Replaced spark table with ARAP (no knocks), adjusted spark latency for big cap distributor and last adjustment was to adjust the injector corrections since my readings of posts indicated that this could help get rid of the bathtub. As best as I can tell, the change in injector corrections didn't help. I can say that cumulatively over 2 or 3 VE learns, the car appears to be running richer in the 20-30KPa area even though the VE table is leaning out. I've noticed that the cAFR and WB AFR have started diverging by quite a bit. Everything 35 Kpa and above is still fine.
Using Vette injectors and running 18 psi of fuel pressure.
Last edited by gheatly; Aug 22, 2019 at 12:35 PM.
Reason: remove BIN
It likely isn't learning in the 20 - 25 KPa area. Would need to manually adjust that area.
As for the cAFR and WB AFR diverging. Need to be careful at low manifold pressure. Real easy to go too lean and get misfiring. This is where open loop decel is helpful. Can bring the VE table up a bit, even if a WB reports it is richer then one thinks it should be.
This is due to the very small mass of air & fuel in the chamber, makes it hard to light-off.
Thanks! I have been manually revising the lower area cells every few VE learns - basically filling in the trench. Can I activate decel and still do WB VE learns? Is there a specific place to do that or do I just adjust the parameters so it is reactivated?
Don't fill in the trench so much - flatten the low MAP areas under it. The VE learns can't take place in those areas because the engine won't ever have 0-25 KPa @ 400 RPM in the manifold under normal conditions - except closed throttle coasting at higher RPM's (the decel RBob mentioned). Take all that garbage in the 20-25 KPa range and bring it down so there's at least no bathtub there in the map. And it would be best to err on the side of rich so fill in the "bathtub" some to avoid going lean on hot starts, etc. It's OK if the idle is trimming a little negative on the BLM's. On a cold start when you hit closed loop it's not that big of a deal with a speed density setup to be around 124 to 127. With a speed density system you are going to have variations - better they be trimming for a rich condition than a lean one. Even at 120 BLM on a cold start that's only 6.25% negative trim. Which is fairly normal even on a MAF system. It is widely accepted that +/- 5% fuel trim is normal and expected ambient fluctuations.
And when you get close like this - it seems to work better to use the narrow-band VE learns and set the smoothing down to 0. You're working on an entirely closed loop area of the map, so the NB is going to be dictating the trims here. The wideband is great but they don't always exactly agree.
If you have headers or anything like that and are trying to perform NB VE learns in the idle area - remember that the O2 can drop below temp and cause issues. I found it was very helpful to switch to a heated three-wire O2. The other issue is the IAT sensor - to not have wild idle fluctations in VE learning you need a stable IAT that isn't subject to heat soak.
GD
Last edited by GeneralDisorder; Aug 22, 2019 at 05:40 PM.
I figured that it was getting time to switch to NB learns, which is why I wanted to clean this area up. I have trouble with anything below 1,000 RPM due to my torque converter.
I figured that it was getting time to switch to NB learns, which is why I wanted to clean this area up. I have trouble with anything below 1,000 RPM due to my torque converter.
Why is the torque converter a problem for you? I'm very curious about your theory because my car has a 3500 stall converter (B&M holeshot) and I hadn't thought it was causing me any tuning troubles other than I had to correct some AE due to the large, rapid RPM climb to get up against the converter..... I'm open to hearing any theories that might explain problems I didn't know I had though!
I mentioned it in the context of low RPM/KPa tuning. When I accelerate from a stop, engine RPM rises to around 1,000 RPM before the converter "hits" and starts moving the car quickly. It will creep a little if I let off the brake, but I cant really load the engine below 1,000 RPM. Above 1,000 RPM don't know its there.
Well that's interesting..... I've never noticed any low RPM aspects of my converter that were..... significantly different than stock I guess you would say. I've had two different converters (as well as the stock unit - so three I guess) - one was an unknown (but likely quality) 12" 3000 stall converter, and then when I swapped the trans to the current Ligenfelter unit (built 700R4 from a 92 Camaro) it came with a 3500 stall B&M 10" converter. But both drive like stock at part throttle as near as I can tell. It sounds like there's an issue with the converter if it's not giving you any torque transfer for 400 RPM from idle to 1000. That doesn't seem right to me. I'm no expert but what you describe sounds like a mechanical problem that shouldn't (or at least doesn't have to) exist.
