Ls1 5.7 ve tuning, having problems when activating short term fuel trims

[jnrdownunder]

Hi all

I have been tuning my ve table i have got my ve table reasonably rich by 5 to 10 % across the bord.
I am running a aem wide band gauge and have it connected to my hp tuners with serial port on my laptop. The problem i am having is when i re enable short term fuel trims and drive down the road then all of a sudden i am getting all these lean cells car starts to hesitate when it gets lean and it is showing lean on the wide band gauge Aswell but once you turn short term fuel trims off the car runs really good again with no problem. any thoughts help would be apricated.

sorry forgot to mention running engine on map disabled maff

[SiriusC1024]

Tune and log plz.

[abc]

Modifications? Have you changed the engines ability to move air?

[Alvin]

Hi all

I have been tuning my ve table i have got my ve table reasonably rich by 5 to 10 % across the bord.
I am running a aem wide band gauge and have it connected to my hp tuners with serial port on my laptop. The problem i am having is when i re enable short term fuel trims and drive down the road then all of a sudden i am getting all these lean cells car starts to hesitate when it gets lean and it is showing lean on the wide band gauge Aswell but once you turn short term fuel trims off the car runs really good again with no problem. any thoughts help would be apricated.

sorry forgot to mention running engine on map disabled maff

There becomes a point especially on older Gen ECM's that the stock o2's don't get along with the cams overlap/ reversion.

What is the build? Specifically cam

[edcmat-l1]

Ah, this is another guessing game right? Like the one in the GEN4 section?

[abc]

Ed, you may need the magic 8 ball for the Gen 4 section issue, but you could probably start with the crystal ball here!

[jnrdownunder]

Hi guys thanks for your time i have attached a log file with 02 sensors on and log file with 02 sensors off i have all so uploaded tune file. car runs no CATS 3 inch high flow exhaust with extractors. I am going to check for exhaust leaks in case that is causing problems.

CAM SPECS : Duration @.050 - INT 231 - EXT 243
Lobe separation 113 + Adv
Valve lift INT 0.617 - EXT 0.623

[bk2life]

3 inch high flow exhaust with extractors.

probably getting fresh air in there--
how long are the extensions?

[SiriusC1024]

Which wideband are you using? There are two PIDs in the log that read way differently.

You forced 5-10% rich with wideband tuning. With CL re-enabled yes there will be some hesitation and error until LTFT's settle in.

Tune the VE table stoichiometric. I applied the CL corrections and they make a VE table I'd expect from your specs. Don't force rich. That's asinine. Use PE when needed.

[jnrdownunder]

I am running AEM 30-0300 wide band gauge the sensor is just before cat in the exhaust and 02 sensors are just in front closer to engine. I have been tuning with AFR that's what was on gauge and what i could see in the PIDs but i did see the lambda above it and it is not giving the same reading as my AFR gauge. i am happy tunning in AFR. also i have long term fuel trims turned off all the tuners i have been talking to locally say they leave long term fuel trims off and only run short term trims. i have put new exhaust gaskets and moved my wide band onto passenger side exhaust bank. I'm going to try get the ve table closer to 14.7 AFR and see what it does i did want it runing a little on the rich side as its going to remain in speed density all the time not using maff sensor.

[SiriusC1024]

30-0300. Knew it. Narrowbands indicating stoichiometric and wideband registered lean 16's, which is what happens when the 30-4110 channel is used with the 30-0300.

Tuning AFR is fine because the math works out either way. I'm talking about the non-stoichiometric part. Doesn't matter SD or not. If you tuned it right then it's right.

[jnrdownunder]

so should i change setting on my gauge ? what is the easiest way to do that ?

[SiriusC1024]

No the gauge should be right. What's in the log is what I'm talking about. Wrong PID.

I know you said the gauge read lean, but I'm seeing for myself in the logs. Sometimes it was indeed lean, but usually not during CL.

[jnrdownunder]

so my best bet is to re tune my VE table and try to get it all with in 5% an when i turn short term trims back on it should work ?

[SiriusC1024]

Yeah pretty much.

[jnrdownunder]

Thanks i will give that a go

[jnrdownunder]

Forgot to add i am road tuning the car

[abc]

There is no way to tune closed loop to be rich with the factory PCM, at least not significantly rich, that I am aware of. If you want it to be rich and stay rich, your gonna have to stay in open loop. In my opinion, I would tune the light load drivability with the NBO2s', in closed loop. If you want in on the rich side, raise the switching point of the NBO2s'. If you want it to be significantly rich, you can invoke PE sooner and have control over the VE table in open loop or go whole hog and turn all fuel trims off and run it in open loop.
Your cam is gonna have enough overlap that it will cause exhaust stream dilution issues. The O2s' are gonna be semi saturated with the unused air and register as lean and therefore the PCM will add fuel in attempt to solve the sensed lean condition. In your case, you have attempted to manually solve the sensed lean condition by adding the necessary fuel to make the gauge read where you want it and when you give control back to the PCM, it is sensing significantly too little air and in turn, removes fuel, causing your seen and felt lean condition.
Any camshaft choice is a series of compromises. With your cam, I would shoot for a read value of 1.0 to 1.05 lambda (14.7 to 15.3 AFR) during light load drivabilty, below 2500 rpm. That will likely mean your NBO2s' switching points will be around 275 mv in the light load areas. As load increases you can raise the NBO2s' switching point to near normal or above, say 500 to 600mv. This will make it richer just before you enter PE.

I'm sure the pro's will tell me if I'm way off my rocker, am I? Should we just keep it simple and run it in open loop?

[jnrdownunder]

Thanks for the information.

I'm going to try re tune VE table and try get everything under 3000rpm 14.7AFR then tune everything above 3000rpm a little richer and try turn the short term trims back on and see how it behaves. want to try get the most drivability out of it as its going to be daily driven.

Engine tuning is all new to me Aswell so everything is going to be slow and a lot of trial and error

[Alvin]

This cam is definitely on the line for a GEN 3. It's entirely possible that trying to use the stock o2 and letting fuel trims control fueling might make it drive worse.

I didn't read everything but saw talk of maybe you using the wrong transform on the wideband. Address that first, dial in your VE table, Then allow fuel trims to work again. It's OK that they don't come back at 0/0 after wideband tuning. But after you get the fuel trims back to 0, if the car drives worse.. it will likely end up in OL.

You can fix surges induced by O2 swing but often in a situation like this is the reversion is tricking the narrowbands into hitting targets that are usually too rich in reality. So the fuel trims drive the car back rich.