What is really LV8?

[GN owner]

What is LV8 and what is the formula for it? How does the ECM calculate it and from what factor does it uses to do its calculation? The reason I am asking is that my 87 GN shows an LV8 of 128 and according to specs should be between 50-60 on an idling engine. The chip is a JC94 and the car is basically stock except for a 237 fuel pressure regulator and an exhaust system. Thank you for any info on this complicated subject.

 

[bruce]

Originally posted by GN owner

What is LV8 and what is the formula for it? How does the ECM calculate it and from what factor does it uses to do its calculation? The reason I am asking is that my 87 GN shows an LV8 of 128 and according to specs should be between 50-60 on an idling engine. The chip is a JC94 and the car is basically stock except for a 237 fuel pressure regulator and an exhaust system. Thank you for any info on this complicated subject.

LV8 is a way of determining engine load.
It's a function of grms/sec, and RPM.

An idle LV8 of 128 is really off. Just off hand, all I can think of is a bad MAF. Any codes?.

 

[GN owner]

I've changed the MAF with a known good one and the LV8 is still the same. It appears to be fixed! I can rev the engine, put it in gear and even turn on the A/C and nothing seems to be able to change it. The MAF reading will go between 6 to 8 g/s.

 

[bruce]

Originally posted by GN owner
I've changed the MAF with a known good one and the LV8 is still the same. It appears to be fixed! I can rev the engine, put it in gear and even turn on the A/C and nothing seems to be able to change it. The MAF reading will go between 6 to 8 g/s.

This isn't adding up.
6-8 at idle is fine.
What is your idle rpm?.
IAC count?.

 

[GN owner]

My idle RPM goes between 775 to 900. The IAC count is between 11-17. I was thinking of putting back the stock chip and see if that changes things. I guess I need to be going back to square one and see what it looks like and start from there.

 

[terryk]

LV8 is "Load Variable 8 bit" (vs LV16 which is the 16 bit calculation.) LV8 is used whenever an engine load value is needed.

LV8 = (Mass airflow/RPM) * scalar (scalar is usually near 1).

Terry

 

[GN owner]

I'll be putting in the stock chip and then see if the LV8 will be fixed or not. Does anyone uses this parameter to help in tuning their car?

Thank you all for your response!

 

[dennisL]

Although it doesn't solve GN Owner's problem, I thought I might add to the LV8 formula portion of this thread. When looking at the code it appears that LV8 = MAF Table value X RPM X LV8 Scaler (1.04) X MAF Table Scaler. The result is capped at 255.

Just last night, I read in Ken's TLink user guide that LV8=airflow/rpm and then today see the same formula again here. Since this doesn't match what I see in the '86 - '87 TR code, can someone shed some light on this? I'd like to use this calculation in a spreadsheet and just want to get it right. Thanks.

 

[GN owner]

Update on the LV8 problem!

I finally had the time to work on the car and found out that the problem with the LV8 data being fixed is attributed to the JC94 chip that I had installed. The LV8 data varies with all of the other chips that I installed. These included the KB9006, stock chip and Thrasher 92 chip.

Also have a problem with the car when idling it tends (sounds like it) to go rich with the symptoms of the RPMs dropping to 650 to 700. Isn't the idling RPMs determined by the chip? I cleaned the TB and IAC but it didn't change anything. I'll probably be changing out the O2 sensor and get an adjustable FPR to see if it will cure this problem.

 

[TurboDave]

Originally posted by dennisL
Although it doesn't solve GN Owner's problem, I thought I might add to the LV8 formula portion of this thread. When looking at the code it appears that LV8 = MAF Table value X RPM X LV8 Scaler (1.04) X MAF Table Scaler. The result is capped at 255.

Just last night, I read in Ken's TLink user guide that LV8=airflow/rpm and then today see the same formula again here. Since this doesn't match what I see in the '86 - '87 TR code, can someone shed some light on this? I'd like to use this calculation in a spreadsheet and just want to get it right. Thanks.

Not so sure in can be MAF times RPM. That would yield some pretty big numbers real fast. Example 100 gps airflow times 2500 rpm = 250,000 X the scalers which are both more than "1".
The smallest maf scaler is 10, the largest is 255

Sooooo, I'm confused now!!!

 

[boostcreep]

I heard that someone used a curve fit program on some of the data in the cal docs and came up with the formula to calculate LV8. Has anyone tried that?

Nick

 

[Eric Stage I]

Here I go again...

Code as translated on gnttype:
3A0C: CE 00 44 LDX #$0044 X = #$0044 ; InjectorPW
3A0F: B6 34 35 LDAA $3435 A = 'MULT' Load Variable Scaling Factor (1.04) (E = N / 128)
3A12: BD FD 1F JSR $FD1F ; Apply (0-2) Multiplier
3A15: 96 AA LDAA $AA A = Current MAF Table Scalar Divide Value
3A17: BD FC 85 JSR $FC85 ; D = InjectorPW * Current MAF Table Scalar Divide Value
3A1A: 4D TSTA if (A == 0)
3A1B: 27 02 BEQ $3A1F goto $3A1F
3A1D: C6 FF LDAB #$FF B = #$FF
3A1F: D7 23 STAB $23 Filtered Load Var = B
3A21: 7E 38 CA JMP $38CA

Looks like the inj pw is multiplied by some scaling factor (1.04) and then its multiplied by the current maf table scalar.

So does that mean if the pw is 3 ms (say, at idle) and mult by 1.04, which is 3.12, then mult by the current maf table scalar (10), we get an lv8 of 31? I seems alittle low?

Geek Stage I

 

[TurboDave]

Originally posted by Eric Stage I
Here I go again...

Code as translated on gnttype:
3A0C: CE 00 44 LDX #$0044 X = #$0044 ; InjectorPW
3A0F: B6 34 35 LDAA $3435 A = 'MULT' Load Variable Scaling Factor (1.04) (E = N / 128)
3A12: BD FD 1F JSR $FD1F ; Apply (0-2) Multiplier
3A15: 96 AA LDAA $AA A = Current MAF Table Scalar Divide Value
3A17: BD FC 85 JSR $FC85 ; D = InjectorPW * Current MAF Table Scalar Divide Value
3A1A: 4D TSTA if (A == 0)
3A1B: 27 02 BEQ $3A1F goto $3A1F
3A1D: C6 FF LDAB #$FF B = #$FF
3A1F: D7 23 STAB $23 Filtered Load Var = B
3A21: 7E 38 CA JMP $38CA

Looks like the inj pw is multiplied by some scaling factor (1.04) and then its multiplied by the current maf table scalar.

So does that mean if the pw is 3 ms (say, at idle) and mult by 1.04, which is 3.12, then mult by the current maf table scalar (10), we get an lv8 of 31? I seems alittle low?

Geek Stage I

I honesltly don't remember what my LV8 is at idle. But isn't it somewhere in the 30's?

Must be something else being done. I just checked my 87 on the scanmaster (cold idle @1200rpm). It showed inj pw of 3.5-3.6, and the LV8 was hovering at around 41. I didn't look at the MAF flow to ensure I was sitll in table 1 though.

 

[dennisL]

Okay, I figured it out! So get ready, put your helmet on and fasten your seatbelt. (The helmet is an old geek trick that keeps your head from exploding.) Oh, and Eric ... armed with this knowledge, you're eligible for a promotion to "Geek Stage II".

The code to calculate LV8 actually starts at $3A00. Here the Reference PA value is read to represent RPM. For this project, we want to determine LV8 for a given RPM and airflow, so we need to convert RPM to Ref PA count. The formula for this is:

Ref PA = 120/(RPM*6)*65536
Using 1200 RPM as an example, the Ref PA would be 1092 (decimal). By the way, this formula answers my question from earlier regarding where does RPM figure into the equation.

Okay, now we have to multiply the Ref PA with the current MAF table value. Let's assume the reported airflow is 7 or 8 gm/sec. This puts us in MAF table #1 with a value of C3 (decimal 195).

Now here's the tricky part. The ECM has to multiply a 16-bit number (Ref PA) with an 8-bit number (MAF table value) but the result can not exceed 16-bits. To accomplish this it discards the least significant 8 bits of the result. These 8 bits have a value of 256, so if we divide the 8-bit multiplier by 256 prior to the multiplication, we will arrive at the same result.

E = Ref PA*(MAF table value/256)
E = 1092*(195/256)
E = 1092*0.761
E = 831
This is the value Eric called Injector PW because its stored in $83 & $84. Technically, its not the Inj. PW yet, but it will become that at $3EB1.

Next we have to scale the LV8 so we get $3435 [85]. The conversion for this is LV8 Scaler = N/128. So our scaler is 1.04.
Scaled LV8 = E*(LV8 Scaler/128)
Scaled LV8 = 831*1.04
Scaled LV8 = 864

Lastly, we have to multiply this with the current MAF Table Scaler but this is the same deal as before. We need to divide the MAF Scaler by 256 before we multiply. Since we determined the reported airflow has us in table #1, the Scaler is 0A (decimal 10).

LV8 = Scaled LV8*(MAF Table Scaler/256)
LV8 = 864*(10/256)
LV8 = 864*0.039
LV8 = 33

"And that's all I have to say about that." (Forrest Gump)

 

[TurboDave]

Too late, mine's already exploded. Forgot my helmet before reading

 

[dennisL]

Dave, I put a warning message at the beginning! Well I'm sorry to hear about your blown head gasket. From now on, I'll put a *CAUTION* in the message.

 

[Eric Stage I]

Dang...

So now we know. The next time someone asks how to calc LV8, just tell them:

LV8 = ((120/(RPM*6))*65536)*(MAF table value/256)*(1.04)*(MAF Table Scaler/256)

Its as simple as that

I'm not too proud to say it would have taken me a LONG time to figure that out (maybe never), but I'm glad you did, Dennis!

Hmm, time to think up some more questions...

Thanks,
Eric

 

[Scott231]

Next we have to scale the LV8 so we get $3435 [85]. The conversion for this is LV8 Scaler = N/128. So our scaler is 1.04.
Scaled LV8 = E*(LV8 Scaler/128)
Scaled LV8 = 831*1.04
Scaled LV8 = 864

Eh...typo?
If LV8 Scaler is N/128 then in line 1 above, you should have E*(N/128/128) which makes no sense. So if Scaled LV8 = E*(N/128), and you arrived at 831*1.04, you must have used N=133, where did you get that?

 

[dennisL]

Yes, 133 (decimal) is the LV8 Scaler value used in the factory EPROM. Its located at $3435 and is hex 85. I should have been more specific.

 

[dennisL]

LV8 Trivia

This might be a good place to post some LV8 trivia for those who are interested. We've already established that LV8 is a number from 0 - 255. Its purpose is to be an indication of how much load is on the engine. A low number (0 is not really possible when the engine is running) means a light load and the number goes up as the load increases.

Here's how the ECM uses LV8:
1. Its one of the parameters that determines the amount of spark advance.
2. If it ever drops below 25, Learn Mode is turned off.
3. If it drops from at least 39 to below 15, deceleration enleanment (DE) is turned on. This happens when you lift your foot a little from the gas pedal, and car is now "coasting". In DE mode the injector pw is reduced 10 - 25%.
4. When you lift your foot a lot so the TPS is now <2%, the ECM goes into DFCO (deceleration fuel cutoff) if the LV8 is >34. This mode causes the injectors to be turned off. If the LV8 goes back up to 52 or more, DFCO is turned off.
5. LV8 is used to determine the EGR solenoid duty cycle.
6. LV8 is one of the parameters that controls turning the charcoal canister purge (CCP) solenoid on and off. It won't energize if the LV8 is >128. If it is energized and the LV8 goes above 134, it turns off.
7. Power Enrichment - this is the mode we like the most! Well, to enter PE either the TPS has to be >45% or the LV8 has to be at least 160. If the LV8 drops below 110, PE is turned off.
8. There is no error code for LV8 but it is checked before a speed senor (code 24) or EGR failure (code 32) is reported. Code 24 needs LV8 to be 50-99 and code 32 needs <129.
9. In open loop and the coolant temp >25F, extra fuel is added based on LV8.

All this is based on the factory 86-87 program.