L83 Swap w/ Idle LTFT -18 or more

[modularfox]

Hi, Ive finally got my 1987 Silverado swap on the road and it needs to be tune and was looking for information on how to adjust fueling at idle to put some solid shake down miles on it before it gets tuned by a professional. The l83 pcm is way different than the ls1 and doesn't have the same table that I'd say I'm more use to seeing to tweak the fueling. I don't have a wide band, but I've had goodluck with the 14point7 setup on my ls1 swap. If needbe, i could invest in a 2nd setup if its going to be necessary.

L83 6l80e from 2015 Tahoe
stock engine internals, long tube headers, catless 2.5 exhaust, k&n filter, 5 bar fuel regulator w/stock fuel pump control module.
new A/C Delco mass air flow sensor and pre cat o2 sensors (from amazon)
Ive tried connecting the crank case lines together w/5/8 hardline then single 5/8 hardline to intake tube, but cant tell if it makes a difference, the long term fuel trims still go -18 or more, then hover there and since the short term can correct fueling at that point.

other things that I've notices is the idle rpm does not match commanded when the LTFT are maxing out, say 500 rpm when commanded 620 ish.

attached is a short idle log, reset fuel trim prior to recording
attached is the tune file
tune file is stock engine with a small bump in idle with changes to vats and vats related, gearing and fan controls

appreciate time taken to read and would greatly appreciate advice on how to correct this issue. Monday I have to work and will smoke test the exhaust to see if I have any leaks







thanks,
Clint

[5FDP]

I think figuring out your extreme negative timing is more of concern than it running a little rich. But that is likely the cause for the trims yanking fuel because the timing is no negative.

Other settings still need to be done with this swap. You need to disable COT (cat over temp), the cat diag test in the engine diag tab as well.

Disable the flex fuel feature if you did not retain the factory sensor too.

Do those changes and start logging some of your torque tables and spark correction tables. Need to see what is commanding the timing to go so negative.

[modularfox]

I think figuring out your extreme negative timing is more of concern than it running a little rich. But that is likely the cause for the trims yanking fuel because the timing is no negative.

Other settings still need to be done with this swap. You need to disable COT (cat over temp), the cat diag test in the engine diag tab as well.

Disable the flex fuel feature if you did not retain the factory sensor too.

Do those changes and start logging some of your torque tables and spark correction tables. Need to see what is commanding the timing to go so negative.

thanks for you reply. I will disable the COT and relash. I do have the e85 sensor wired into my build as I have the fuel tank setup for e85 (no rubber inside tank) As far as tables go, I don't recall seeing that sort of table available, probably a custom one? If you had have a few minutes to tell me which paramater to choose and which table to copy the values I could log it and post for review? again, appreciate the help. Feels good to drive the truck again, been a while.





thanks,
Clint

[kevin87turbot]

Your MAF numbers are really high at idle. Once you sort out the MAF curve, the timing will very likely come around to proper values.

[ahmedabri97]

To solve the negative timing issue:-
1. Press on throttle cleaned in VCM scanner.
2. Dial in your MAF curve.

[modularfox]

Thank you for the replies. I found a video which happens to be a gen5 engine to tune the mad and looks like I will need the wideband Afterall.
Is there a way to do it with no wideband or would it be a waste of time to attempt it any other way.
Thanks,
Clint

[modularfox]

I only have the base model hptuners, no pro box. On my ls1 bmw, I used the 14point7 controller and sent the output to the a/c pressure sensor which worked great. So I was thinking of using the Fuel Tank PSI sensor input just so i can tune with the a/c on.. anyone with more experience think that would be a bad idea? or would it be best to go through the a/c pressure switch? not sure what consequences of the data going through the ecu and what the ecu might do when it sees different voltages..try and activate the purge valve that's not there ?
The a/c psi signal I can see it just activating the FAN on at different %

Thanks again

[5FDP]

Just buy the AEM OBD2 wideband, it works on all CAN-BUS vehicles like this harness/computer is running.

No extra wires, no extra fooling around. It's as simple as hooking up the sensor, power/ground and the OBD2 dongle, then finding the wideband channel in the channels list.

[modularfox]

Ill look into the AEM OBD2 wideband once i get back inside, Im back outside fooling with it.

So, after watching the video

https://www.youtube.com/watch?v=7IoWmLEmlvE

and I cannot get the values as he is with the math parameter I have (the one that I used on the LS swap VE table). my values needs the decimal 2 places to the left and that might be it, but since I dont know if that would be right to modify the equation Id like to see if someone could see and tell me what I'm doing wrong. I spent about 1 1/2 hours ouside in the LS swap trying to replicate the values he was doing before I remove the wide band and controller from it.

so the math parameter I have for the 14point7 setup is

([7101.10]/.5)+10.085 and is set to Air-Fuel Ratio (14.7 Stoich) gasoline for Unit, Decimal 2

[7101.10] is the A/C pressure sensor on the LS1 ECU

so the math parameter similar to the wideband one but with the wideband sensor changed to the a/c pressure math
100*(([6420.10]/.5)+10.085)-[50118.238])/ [50118.238]

also dont know which to use, Lamda or 14.7 as the unit

It displays correctly when its set up for the gauge and graph, but cant seem to get the values to be the histogram equation to be the error ratio

He does a Transform function to the AEM unit he has, but its not an option for the A/C pressure sensor..

so instead of reading 14.09 for example, its reading 1409.. I don't get the math and how to display error ratio, mostly the parentheses in the math... Ill fool with it a while more then look up the AEM one 5FDP recommended. I see why tuning costs so much lol so much knowledge goes into it

so if i take the 100* out of the math, the value looks similar to the video... this is confusing ... anyone know what makes the math equation work ?

again, thanks for replying!!
clint

edited again for the 3rd time sorry
so the formula is for stochic value, not lamda... its too late to start the car again so ill fool with it tomorrow and see if i can get the histogram to populate.
thanks and appreciate your patience as much as your advice when you take the time to help

also dont know which to use, Lamda or 14.7 as the unit

it didn't matter, its the same number in the equation so it just didn't matter. I got math to work through the a/c pressure witch on the LS swap car with the 14point7 setup.

([6420.10]/0.511)+10.07904622

(updated to reflect wideband reading only with new math to match spec sheet)

Was the math I used and works. The error value Last count is almost the same number when dividing the wideband display by the commanded afr. Gonna move forward and update once the MAF values are around 1-2% ish.

[modularfox]

thank you , 5FDP, kevin87turbot and ahmedabri97!! spot on. After adding a bung to the header for the wideband sensor, set the tune up like in the youtube video/instruction and started logging the MAF eq error. that and with the wideband was showing rich rich... (like the long terms were saying all along). based on those numbers from the scan just at idle, pulled 10%, flashed and instantly fixed the idle rpm, timing and exhaust note due to both of them!!!

Drove it several times while logging and making the little changes, but man, cant thank you guys enough for helping and pointing me in the right direction!

I do have another question about the MAF tuning. Is there a recommend drive cycle / drive style? all logs were light on the throttle to avoid any sharp throttle spikes.
Thanks again,
Clint

[grandam75]

thank you , 5FDP, kevin87turbot and ahmedabri97!! spot on. After adding a bung to the header for the wideband sensor, set the tune up like in the youtube video/instruction and started logging the MAF eq error. that and with the wideband was showing rich rich... (like the long terms were saying all along). based on those numbers from the scan just at idle, pulled 10%, flashed and instantly fixed the idle rpm, timing and exhaust note due to both of them!!!

Drove it several times while logging and making the little changes, but man, cant thank you guys enough for helping and pointing me in the right direction!

I do have another question about the MAF tuning. Is there a recommend drive cycle / drive style? all logs were light on the throttle to avoid any sharp throttle spikes.
Thanks again,
Clint

Try to lock it in a gear when tuning the maf. When I did my L83 6L80e swapped vehicle the biggest issue for me was that the trans is messing a lot with timing during shifts which gives false data, especially at wot. I changed trans parameters to make it stay in 3rd gear (no upshift ot downshift after 3rd gear engaged) Then all that was needed was 2-3 wot runs to get it very close.

[modularfox]

Thank you for the input. I will do that and see what it does.. man now that the truck idles like it should, and dives like it should, holy cow it's so fun..