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Discussion Starter #21
And you are not reading the replies. He only said to zero out the VE to demonstrate a point he was not suggesting that as a permanent thing.
 
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Discussion Starter #22
His point is floored; if you tune them you will see my point. Like I said before yes VE tuning is for SD, and the computer uses them in MAF also no mater ODBI or ODBII. If I am wrong and you know where it says "under no circumstance does the computer look at the VE tables when the MAF is connected." Then I will let it die, and no it can’t be your own words it has to be creditable source, and also i have numbers from 3 different cars where it worked and also my brother has tuned other peoples car (VE tuning that is with the MAF connected).

If you build it they will come.
 
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Discussion Starter #23
I found some formulas
http://www.slowcar.net/LT1Edit.htm

Volumetric Efficiency:

It was determined by John Lamb that the value is defined by the following relationship.




VE = Actual airflow(MAF)

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(RPM/120 * Air Density * 5.733)



Air density can be determined using:



(MAP – Vapor pressure(H2O))

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0.287 * IAT(in Kelvin)



This is simply a re-arrangement of PV=nRT (ideal gas law)

When the value in this table is increased at a specific point fueling at that point will be increased, and vice versa. This table is used typically in closed loop mode to adjust the long term fuel trims so they are around 123-125.
 
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Discussion Starter #24
BPW = BPC * MAP * T * A/F *VE * BVC * BLM * DFCO * DE * CLT * TBM

Where

BPW - Base Pulse Width

BPC - Base Pulse Constant

MAP - Manifold Absolute Pressure

T - Temperature

A/F - Air Fuel Ratio

VE - Volumetric Efficiency

BVC - Battery Voltage Correction

BLM - Block Learn

DFCO - Decel Fuel Cutoff

DE - Decel Enleanment

CLT - Closed Loop

TBM - Turbo Boost Multiplier

In the above equation, any term that has a value of 1 is essentially not contributing to fuel delivery or neutral. It is not taking away or adding to the fuel quantity.

BPW - Base Pulse Width means the pulse width under steady state engine conditions. Extra fuel is added when the throttle is juiced for acceleration. This is called asynchronous mode and will be discussed later. The above equation only consists of the synchronous mode contribution.
 
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Discussion Starter #25
You problem is you're reading sentences out of context. It seems to apply to everything you read on this topic.

I said the car will not run with VE tables zeroed out if the MAF is disconnected (= speed density) because one of the formula parameters becomes 0. You know that n*0=0 where n is any number, right? If you connect the MAF the car run just fine if it has an OBD-I PCM. I'm not saying you should keep the tables at zero. This is just to illustrate the point that these tables are not used WHEN THE MAF IS CONNECTED ON A OBD-I CONTROLLED CAR.

Have you noticed that you're doing all your readings on speed density systems? How do I know? It says so in most of the links you provided and the formula above is missing the MAF reading. Maybe you're the one that is slow.

I'm done.
 
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Discussion Starter #26
sometimes i am slow
anyway try tuning your VE tables in SD and then connect your MAF back up and get back to me on how the car runs. don't tell me it will run the same. just try it. it won't hurt.
 
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Discussion Starter #27
Rich, I am in fact planning to tune my VE tables using VEMaster in speed density mode after a dynotune. The reason is I want to be able to drive the car if something happens to the MAF sensor.

Most popular tuners do not tune VE tables in OBD-I program. The reason for that is you can easily keep the BLMs around 128 in the closed loop by adjusting (or just using proper) injector constant, MAF tables and possibly injector offset. It's the PCM job to keep the air fuel ratio at 14.7. If the BLMs are at 128 +/- a few percent, then the air fuel ratio is very close to 14.7:1. The VE tables will not make it run better. Ask Bryan or any other tuner if you don't believe me. Even though this does not prove that VE table values are used or not, it proves that you do not need to tune them for the car to run optimal in the closed loop.

If you're worrying about the open loop which occurs while the O2s are still cold, there is an "Open loop AFR...." table that can be adjusted. This needs to be done on a dyno with a wide band sensor since O2 sensors are useless in the open loop.

So if the VE tables are used at part throttle and I compensated for not modifying them with other tables values, my final AFR should be off once I adjust them. I'll let everyone know the result.
 
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Discussion Starter #28
Cool I see we are getting closer to understand each other. You are right about everything you said, and you mad a good point you’re tuning just to cover your ass if you MAF fail. But I noticed a performance increase during part throttle acieration. I also noticed better gas mileage. if you had a 1996 i would have you come to Staten Island and let me tune your car. by the way i just purched 2 books on fuel injection. i will post the names later i letf the books in the car.

Also I learned people with big cams need or have to tune there cars in SD and them connect the MAF to complete the tuning process. They do this to get better drivability during part throttle.

Am I right about this?
 
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Discussion Starter #29
Originally posted by rich91080:
Also I learned people with big cams need or have to tune there cars in SD and them connect the MAF to complete the tuning process. They do this to get better drivability during part throttle.

Am I right about this?
It's a very good way to tune an OBD-2 controlled car starting with speed density.

I have a cam with more duration and overlap than most off-the-shelf cams including CC306 and GM847. I tuned the air fuel ratio using MAF tables, injector constant and offsets and PE tables. The BLMs are steady at 126-130 without any splits. There is no knock retard and cam surge is almost non-existent. It's a 95 Caprice with an OBD-I.
 
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Discussion Starter #30
Originally posted by rich91080:
i have numbers from 3 different cars where it worked and also my brother has tuned other peoples car (VE tuning that is with the MAF connected).
3 different cars, ok. How many of them have '8051 PCMs (94-95 B/F/Y-cars)?
 
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Discussion Starter #31
Originally posted by rich91080:
But I noticed a performance increase during part throttle acieration. I also noticed better gas mileage.

Also I learned people with big cams need or have to tune there cars in SD and them connect the MAF to complete the tuning process. They do this to get better drivability during part throttle.

Am I right about this?
Ok a couple comments since this can 'o worms has apparently reopened.

Why do you think you would notice an improvement in part throttle acceleration but NOT in full throttle? Perhaps it's because there are no transient throttle conditions that would require acceleration enrichment (pump shot). So, if the '8051 DOES actually use VE, perhaps that is how it controls AE! There are no tables for pump shot in Tunercat. Yet when I drove around with my MAF disconnected, the car drove great.

Maybe the 8051 PCM actually calculates pump shot based on VE. Of course, this still doesn't account for transient TPS movement but maybe between a faster PCM (to check the MAP sensor more frequently) and this dynamic AE calculation that I am proposing, it doesn't need the %TPS AE like previous GM ECMs.

Speaking of previous GM ECMs, as you guys likely know, there were two versions of TPI: MAF and speed density. MAF was used from 85 to 89 and GM switched to speed density for 90 and 91 on the C4 and 90-92 on F-bodies as well as all 93 LT1s.

The MAF version of TPI did NOT have a MAP sensor. There were NO VE tables. The spark tables were done by airflow (LV8) vs RPM. They also had AE tables.

The SD version of TPI did NOT have a MAF sensor. There were ONLY VE tables. Spark was done the way LT1s are. There were AE tables.

SD LT1s also had AE tables. But these ECMs were less sophisticated than the successor '8051 PCM (no sequential EFI, for example).

So far, this supports my theory. I think the MAF in LT1 cars DOES handle AE to some extent, but it may also use VE to refine the calculation. This would explain enhanced part throttle drivability, though I'm a little confused on the claimed fuel economy gains.

Thoughts?
 
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Discussion Starter #32
though I'm a little confused on the claimed fuel economy gains.
That’s because my impala was running pig rich at low RPM my fuel trims were like
-20% for both banks.

Also if I would sit in the car and let it idle, I could damn near watch the gas gage go down, it stunk and also right before I did tuning I was getting a code for cat efficiency. And yes I replaced the 2 front O2. I thought the cats were going bad, but it was because the car was rich. This also tells me that the computer is not that good at making correction.

One think I learned is you can tune your MAF and get the same results as tuning the VE tables. I got a lot of reading to do I got books.


:D


 
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Discussion Starter #33
Careful with the Corvette book by Probst. There are some known discrepancies. I believe it had something to do with the MAF. Check on Camaroz28.com or the LT1edit list.
 
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Discussion Starter #34
Are there any books at all that cover GM OBD-I and OBD-II programming? Most aftermarket systems are more versatile and operate in speed density mode.
 
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Discussion Starter #35
The only way to know for sure other than experimenting with an 8051 in a car is to actually dig in the code and see if the VE tables are used for ANYTHING when the MAF is working properly.

The Tunercat guy (John?) might know.
 
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Discussion Starter #36
I read most of that corvette book last night i was up till 4am and i had to get up at 8:30
and I did not find what I was looking for. It is like fuel injection for dummies. it explanes the basic function of the sensors but not in details. I highlighted one pragraph.

When you step on the accelerator, the Throttle Position signal increases before the Manifold AIr Pressure (MAP) or Mass Air Flow (MAF) signal is increased. So the TP signal can cause an enriched mixture, as the throttle is beging opened, something like the accelerator pump of a carburetor. In a way, it contributes to calculations about load, as signaled by the MAF or MAP sensors.
I am going to look into the MAF more.

I really want to know in details what the computer does when it need to compute values and what affect does each table have on the computer and other tables. I guess what I am looking for is a programming index.

for example i want to know

the computer get the value from the MAF and it converts into digital then what? where does it go what tables look at it what calculations are done?

Or where, when and, what are the VE tables used for? i know in SD but i'm sure it is there for other reasons.


 
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Discussion Starter #37
I typed a whole long thing out and accidently refreshed the page which erased my post.

So now you get the abridged version.

That book isn't going to tell you anything you or I don't already know from what's out there.

The people that know the answers either work (worked) for GM, or make software like Tunercat or LT1 Edit. Even Bryan Herter probably isn't looking through 8051 code but might have a relatively educated guess from years of tuning.

You understand pump shot (acceleration enrichment - AE) right?

Any engine with a throttle restricted air intake needs AE. The '8051 ($EE mask in Tunercat) PCM doesn't have explicit AE tables. This is part of my theory that VE might have something to do with transient fueling.

the computer get the value from the MAF and it converts into digital then what? where does it go what tables look at it what calculations are done?
Actually the way the MAF works on LT1 cars (and I believe successive GM MAFs) is not the same as they used to. It is not an analog 0-5V input that an A/D digitizes. The MAF outputs in terms of frequency (0 to 11+ kHz), which I think allows for easier future growth (no 5V max for airflow into the engine) while implementing superior output resolution (11kHz corresponds to ~445 g/sec which is roughly 445rwhp vs 5V on a TPI MAF corresponding with 255 g/sec).

Hopefully you learned from that book that the PCM's fueling job consists of calculating and recalculating the pulsewidth of all injectors between ignition events. It has no problem doing this. So understand that any fueling calculation is done with the goal of obtaining new injector pulse widths.

That said, it simply uses a lookup table just like a TPI ECM to figure out what the MAF signal translates to in terms of airflow into the engine. With that number, the PCM takes the cylinder volume, injector constant, desired AFR tables, correction tables based on other sensors (AE from the TPS, MAP and MAF sensor falls into this category) and closed loop corrections to determine the final pulse width for the current ignition cycle.

How's that for the abridged version.

Does that help?
 
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Discussion Starter #38
Originally posted by Kevin Moore:
The only way to know for sure other than experimenting with an 8051 in a car is to actually dig in the code and see if the VE tables are used for ANYTHING when the MAF is working properly.
I agree 100%.
 
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Discussion Starter #39
that does make sence.

The only way to know for sure other than experimenting with an 8051 in a car is to actually dig in the code and see if the VE tables are used for ANYTHING when the MAF is working properly.
i will try to contact him. The Tunercat guy (John?)
 
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Discussion Starter #40
I emailed john today and i will let you guyes know as soon i do.
 
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