NO-OPTION-2002

iTrader: (2)

Posted by horist...
So... lets start this here. This is a topic that is very interesting to me and to many others. The problem is there are very many "opinions" and seem to be very few "hard facts" on the subject.

Another problem is the lack of information on what goes on in a computer. What I would like to find is a credible reference as to what GM OBD-II computers do with all these inputs - i.e. what inputs and tables affect each other.

I have read every published source I could find on these subjects including "Automotive Electronics Handbook" by Ronald K. Jurgen (900+ pages IIRC), and "Corvette Fuel Injection 1982-2001" by the late Charles O. Probst.

The problem with these sources is all they tell you in general is "The sensors supply signals to the PCM. The PCM takes these signals, makes it's calculations, and tells the Actuators what they should be doing."

Really? Wow! Well that was 900 pages and 1 week wasted!

So if any one can help either with "quality" sources and/or supply any helpful info here on this forum (without getting into trouble with YOUR sources obviously), I think we all would be greatly appreciative!

Hey, maybe we all can learn something.

horist

OK... well one useful piece of info is from Chris @ hpt posted here
http://www.hptuners.com/forum/YaBB.p...num=1078851555

LS1 VCM Main Airmass Calculation (taken from the VE sticky)

I'll let the experts come in here though... I'm not a tuner and don't pretend to be one I'm as eager as everyone to learn more, so if anyone has useful information please contribute.

I will go through the various tables in HPT and post up after work about which we may want to focus on ... sounds like we've overlooked a few things

NO-OPTION-2002

iTrader: (2)

Awesome!

That is exactly the type of post I think people are looking for.

Please keep this going.

PS - That must have been burried because I've been all over HP Tuner's site and I don't think I have ever seen that before. Thanks horist!

XLR8NSS

iTrader: (4)

I've always wanted to see a complete map of the PCM, something that shows a table and then shows what other tables it's linked to and how the information is used between them. That'd probably be a HUGE undertaking, kinda like mapping the Human Genome.

I think it would be very valuable in helping people learn how to tune.

BJM

iTrader: (1)

If you want to know what tables affect what you will have to read the rest of the code in the PCM. For my Grand National I spent last winter reading every line of code in the ECM, it took all winter reading a couple hours every day. It took me a while longer than some might because I had never programmed in assembler before. Mind you its only 12k of binary so its do-able. I think you will find that a disassembly of these PCMs is in the hands of only a few people and they will probably not be terribly forthcoming in making it public. They would consider it their competetive edge. But that is what it will take is for someone to start breaking down chunks of code.

horist

TTT anyone have more insight on tuning for MAF and tuning SD only or combo of both? We're not talking about disassembling the PCM here... just methods given our current tuning alternatives that we can use to get a better SD or MAF tune

P Mack

iTrader: (6)

This is my process, not including idle & spark stuff:
- disable maf
- tune ve table in speed density and open loop using wideband, desired a/f =13.0
- refine ve table for part throttle in speed density, closed loop using ltrims
- enable maf
- tune maf table using wideband in open loop, desired a/f - 13.0
- refine maf table at part throttle using ltrims

I'm not saying it's the only way or only way, but I like it and it makes sense to me. If you have an auto or don't have wideband, you're gonna have to use some different steps.

NO-OPTION-2002

iTrader: (2)

OK, how about this?

Has anyone looked into the Society of Automotive Engineers (www.sae.org)? They have many, many books available covering any automotive topic know to man. Problem is they are *very* expensive. Has anyone read/browsed through any of these? I am willing to try this route *if* I feel there will be a decent return for the money.

Also, I've noted that the sources i've found are a little too general. If I get into these SAE materials, what are the chances they might be over my head?

For reference I have no engineering background, just a solid GM automotve training, and basic electronic self teaching.

Thanks for any insight!

SScam68

iTrader: (20)

NO-Option-2002

I actually have a whole stack of papers/journals from SAE that I would like to look at but since I am not a student anymore I can't get them for free from the university library.

I do have one though titled

"Comparison of Air Meter Interface Strategies for Engine Management Systems" by Mark H. Svoboda @ Delphi.
Electronic Engine Controls 2000: Modeling, Neural Networks, OBD, and Sensors.

PM me your email and I'll send it to you. Its a pretty involved paper and in all honesty I haven't had a chance to really sit down and read through it but it seems to cover a lot of the basics and then some. At a minimum it should provide some insight as to whats involved with these sensors.

One thing that my friend and I were trying to figure out was what exactly the MAF transfer function takes into account, shape functions?

Maybe we can discuss it over the forum

Frank

NO-OPTION-2002

iTrader: (2)

PM sent.

Thank you!

Kelly

NO-OPTION-2002

iTrader: (2)

Frank (sscam68),

Thanks, I recieved the paper. I'm at work now so I will read it tonight. I looked it over real quick, and I may have to brush up on my math to keep up with it.

Thanks again,

Kelly (NO-OPTION-2002)

Corpsvette

P MacK

I am currently doing this following a post on HPTuners board. I am very confused about open loop and closed loop. Right now I have the MAF disabled and commanding 13.0 and tuning my part throttle loggings to an AFR of 13.0. I am basically there. When you say refine VE table for part throttle in SD, closed loop using ltrims, what do you mean. How do I command open or closed loop. I thought once I had my VE table dialed in to run 13.0 AFR and plug the maf back in, I then adjust the MAF by adjusting the MAF FREq table until ltrms are 0 or slightly negative. Thanks,

Jim K

P Mack

iTrader: (6)

So you've pretty much done your entire ve table using a wideband already, right? It's not really necessary to refine your ve table in closed loop using ltft's, but since the narrowband o2 sensors are much more sensitive (around 14.7), you may be able to get your ve table a few % closer to perfect. To do this, just enable closed loop, go logging and turn on your ltft histogram in the scanner. The numbers it displays should be close to the % your ve table is off, so adjust accordingly.

Yes, after you finish your ve table you can tweak your maf table until your ltrims are 0. But keep in mind ltrims will not help you at w.o.t. so you'll still have to use wideband to tune your maf table at the higher flows.

Keep in mind mafless is not the same as open loop, some people get confused on that. Let me know if this answers your question or not.

Corpsvette

Thanks P Mack,

My only confusion is how do I enable closed loop. How do I know when I am in open or closed loop? What is my indicator? Thanks again for the help. I do understand the WOT part.
Jim K.

P Mack

iTrader: (6)

The easiest indication of whether you are in open or closed loop is to look at the fuel trim cell. 20-22 are open loop and the rest are closed loop (see the picture). Normally your car is in closed loop except when warming up, wide open throttle, etc. You can switch to open loop by either unplugging your o2's, or the easier way, in the editor go to engine>fuel control>open and closed loop>closed loop enable and change the temps to something you'll never reach.

pekkaz

If you unplug MAF... how is the ignition timing calculated ? Looking at the tables it seems to be based on airflow...

P Mack

iTrader: (6)

Airflow (g/cyl) can be calculated using maf and rpm, or using ve, air temp, and Map (speed density). Normally it uses a mix of both but it can use just speed density if the maf is disabled.

pekkaz

OK, is it possible to log gms/cyl with a scanner when MAF is unplugged ?

Magnus

iTrader: (4)

Insert Dynamic airflow PID.

Remove the MAF parameters from your table display in the scanner and your histograms will all update normally..

I tune my car in 100% speed density. I haven't had a MAF on the car in a very long time. I often tune in open loop, ... I really don't use closed loop much, but I also have my laptop in the car with me every time the car is operational.

- Keith, HP Tuners

P Mack

iTrader: (6)

Magnus, if I check the LTFT off button under fuel control, is that the same as putting it in open loop? Or do the STFT's still work then so it's not true open loop?