DOUG @ ECS

A code is thrown when the fuel trims are 25% off, that does not mean that 24% off is OK.


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romandian

still dont understand. the maf is a mass sensor. so if engine is getting colder air and more of it the maf will register that. are you saying positive fuel trims from the s/d map are added to that at wot? and engine is running to rich? well how rich can it be to lose substantial power? will putting the iat sensor into a warmer location (or tweaking its output) be a solution in that case?

enoniam

Positive trims come from both the VE table (s/d map) and MAF calibration. The vararam affects the MAF's reading since it affects how the air flows through it. Positive fuel trims, particularly for fuel cell 15, are added at WOT. (15 because that is high manifold pressue, high rpms.) Whether or not the engine is running too rich will then be very dependent upon how accurate the MAF calibration is at WOT. It will have to be VERY rich to lose substantial power. I would want the iat sensor located where it sees the air temps going into the engine - downstream of a turbo or supercharger and any intercooler if possible. That is to make its reading accurate relative to what the engine is getting. To fix the rich / lean issue you should tune with a wideband o2 sensor(s), starting with the MAF calibration and then the Power Enrichment settings.

tblu92

Moving the IAT sensor is 1990 technology---Today's tuning software allows you to "desensitize" the IAT sensor so it does NOT remove timing from false high IAT temps----Any tuner knows how to do this and it's a common practice---
I agree with the other poster You always prefer to get your P/T fuel trims at "0" or slightly negative----as a negative FT will always lock on "0" when it comes to WOT---
Again if not clear the positive fuel trims are added to your WOT fueling---The actual place the positive fuel trims lock on at WOT IS
"Just before going to WOT"
So you can carry a + fuel trim from idle all the way to WOT !!!
That is why a tune is needed with a CAI because even a + fuel trim at idle can affect your WOT fuel
Does not sound like it means much --However a STOCK tune usually has about an 11.5 AFR at WOT so if you have a +20% fuel trim added to that from a CAI that takes your WOT AFR to a pig rich 9.6 !!
That's got to hurt the power----- Dedicated race cars are set up about a 13.0 AFR---- weekend racers about a 12.6--12.8
and a safe daily driver about 12.4--12.5----So a 9.6 AFR is horrible for a N/A engine---

romandian

having tuned a m8 motec before, i wonder where the fuel trims come from. motec runs wideband closed loop at wot and gererates stft and ltft. now, the lt1 ecu runs open loop at wot and some ft seem to be carried over from closed loop.

but concerning a cait, where do they really come from? the maf will measure the air mass correctly, look it up in the table and inject the correct amount. right? what trims? the sd table will be corrected for temp (while maybe not for humidity) and should yield the correct value also. what trims? what do i not get?

as an example i have done this:





car pulls 0.35 g in second gear regardless of cait.

i tweaked the ait sensor. adjusted it at wot from 3500 to 700 ohms and nothing much happened. thats a 15% leanout if my thinking is correct. so, how can a tune help. my conclusion is: all caits are b.s.

enoniam

I can tell by your statement "the maf will measure the air mass correctly" you are giving the MAF sensor WAY too much credit. It is not a laboratory grade instrument. It's output is a frequency which changes due to the temperature of some heated electrical components in the airstream that run hotter at low airflows and cooler at higher airflows. They are very dependent upon the flow right up next to them, hardly dependent at all on air flowing away from them. When you drastically change the air plumbing configuration as you have you most likely affect the portion of whatever air is flowing through the entire MAF body that is in direct contact with the actual sensing elements. Hence your MAF calibration is probably off by a good deal.

GM knows the MAF sensor are crude devices so they have long term fuel trims to adjust for the inherent errors in the measured air flow. The fuel is trimmed in closed loop to give a stoich AFR. Since running richer than stoich at WOT is a good thing, and since wideband sensors cost more than what they want to use in mass production, they add fuel and any applicable positive long term fuel trims and run open loop at WOT.

The C5 comes with a cold air intake stock. The C5 aftermarket CAIs aren't addressing provider colder air as much as they are focusing on less overall restrictions in airflow.

Besides fueling, air flow calculations by the PCM also affect ignition advance. Hence getting the airflow data right is also important to getting the spark advance where it needs to be.

romandian

well, when i read this, the question is: why do they use a maf at all. it looks to me, two widebands are cheaper than the maf. also cai stock? my c5 pulls air from a closed compartment. how is that cai? also i have 400 mm of straight pipe before the maf.

im looking forward to getting efilive and understanding things better. but no cais for me.

enoniam

It isn't MAF versus widebands. GM could have used a MAF with a wideband setup that wouldn't have forced them to go open loop at WOT.

Compartment isn't fully closed, otherwise engine would choke. It isn't pulling most of its air from within the engine compartment which is why I say it is a CAI. Most CAIs on the market for the C5 are just different filter and tubing arrangements located in the same compartment as the stock airbox. Air temps are the same, just offering the possibility of more max airflow.

tblu92

The MAF in a stock system --- closed loop/open loop- is like the previous poster says is NOT the main sensor to set fueling ---
It can be used to add fuel at WOT but is not the correct way to do so--rather just a band aid
---The front 02's are the measuring device that READS the oxygen content in the exhaust at P/T-- and based by that reading it makes corrections to the P/T fuel using a LTFT correction--this correction is made by the injectors "on or pulse time"
The MAF table is just another input that the ECM uses but a reader of airflow and not the corrector--
Tuning 101 dictates ---make changes in the MAF table only when the airflow is somehow changed around the MAF actual location--If power enrichment is off--make changes to WOT in the PE table---
Make changes to the injector flow rate only when changing injector sizes or fuel line pressure
PS: only exception is that on an auto trans the trans sets the base line pressure based on load--and it does this using the MAF table---It's not uncommon to install an aftermarket MAF without re-tuning and it will fry your trans---because it sends false load values to the ECM and to the trans line pressures---
It's all rather complicated---

enoniam

I think we must have had different Tuning 101 instructors, LOL!

My preference is to get the MAF reading close to being correct. From the PE table you know what the AFR should be. Adjust the MAF calibration table to get the measured WOT AFR to what's programmed in the PE table vice changing the PE table values - to me that is the bandaid...

MAF does affect transmission shift pressures and spark advance. Why not get it right...

romandian

is there some kind of write up on the c5/ls1 ecu somwhere, that i could study? what is "101 tuning"?

enoniam

101 in my mind anyway is referring to how colleges in the US number their courses.

100 series are generally first year courses, 200, 2nd year, etc. 101 courses are usually first semester, first year introductory courses. So when we say Tuning 101 we are referring to basic-level tuning that is generally appropriate.

I've got a 25 page Word document on LS1 tuning that I read before I got started tuning - I'm sure I've tweaked that document's "101 process" some over the years in my own tuning. I'm not sure the source of the document but I'll forward it to you on an as-is, use at your own risk basis if you PM me your email. It will give you some good info on tuning the LS-based engines.

romandian

i got it. thanks a lot. will study that. is it hptuners based? the abbreviations are killing me. still deciding if to get that or efilife. the latter has the problem, that for the 2000 ls1 i first have to change to the 2002 os and then replace it with a cos. (i like to keep things simple.)

enoniam

I haven't looked at this in years, but if you look on page 21 you will see that it references needing HPTuners. It looks like page 21 should be page 1 - not sure why they put what looks like the introductory material at the end...

tblu92

Well there are several thoughts on tuning and you'll never get 2 tuners to agree on a "procedure" on how to attain a same result
The way I was taught---was --when making internal mods on an LS1 engine (hds/cam /Lt's/manifold etc )-------Your COMMANDED WOT fuel ratio will not match the ACTUAL WOT fuel ratio---- To correct this correctly would be to change the VE table because the VE is what has been changed----We were taught to only make changes to tables that were directly affected by bolt on mods ( change your injectors or fuel pressure make a change to the IFR table-----Install a CAI or aftermarket MAF or T-Body make a change in your MAF table----
It is a band aid to change the MAF table if internal mods have increased the engines VE--
VE is directly related to major airflow increases to the mechanical engine--So if the Commanded AFR does not match the ACTUAL AFR---You need to correct the VE table
The VE table is used as a reference only during "rapid changes in airflow" The ECM will take the VE % Plus the MAF numbers to get an average between the 2 to set the Fuel during this transition-----If you only change the MAF you are only getting the average from 1 table and not both---so you may develop a lean/rich transition and most likely a BOG or stumble---

romandian

interesting. sound like you know what your talking about.

i just looked at the main ve table in a 2 bar cos (hpt). why are the values between 23 and 94, and not something like 23 and 180? the values for 1 bar and 2 bars are 79 and 94 (4800 rpm). an increase of 19%? doesnt make sense to me.

enoniam

Only MAF input is used above 4000 rpm.

I datalog the % difference between MAF airflow and dynamic airflow. That helps to identify which input is contributing the most at any point in time. If you get the MAF and VE table too far off it will show a consistently large delta even at steady state operation. Get it close enough and MAF is running the show at steady state.

All Commanded WOT fuel is doing is telling the PCM how much additional fuel you want there relative to what it thinks it would need to run stoich. Since with narrowband sensors it doesn't have a clue what it is doing other than if it is lean or rich relative to stoich it is pretty much running blind at WOT - hence the need for doing WOT tuning with wideband O2 sensors.

enoniam

The numbers are relative to how much air would be going into the cylinders compared to assuming 100% efficiency. The effect of boost and/or vacuum is already being taken into account before applying the VE multiplier.

Joshboody

Hey guys, I'm fairly new to LS1 tuning and reviewing a thread on LS1Tech, have a question based on the attached tune and datalog.
http://ls1tech.com/forums/pcm-diagno...e-tuneing.html

This engine is highly modded in heads, cam, etc. As you can see in the log MAF and dyn airflow are relatively close. In the tune the MAF/Hz has been changed drastically, BUT the VE table is relatively stock in higher MAP. How can MAF and dyn air follow so closely in this case?

I assume there's some scalar/calc that was changed. Thanks for any insight.

ps. apparently CF doesn't allow hpl files, so have to rename the txt extension.

EDIT: I understand it now. Dyn is filtered/final, VE airflow is MAP based... didn't realize this was a channel.

romandian

o.k. but where? maf table?