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Thread: My split blm problem
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08-11-2020, 09:38 PM #21LTx Guru
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I still need to look at the log in more detail. That was just a quick scroll through. I'm working my way through a backlog of requests. Seems like somebody posted my name on other LT1 sites, and over at CamaroZ28.com there's new people signing up, and their first post is “Here’s my data log, can you take a look at it?”. Also happening on FirebirdNation.com.
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08-11-2020, 09:45 PM #22Xtreme Member
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Supporting Member2021 Charger Scat 392
1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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08-13-2020, 10:04 PM #23
I have 30# ford red top injectors. Yes I also have roller rockers. I emailed him about the BLMS and he said he enables the pcm to pull more fuel while he is trying to dial in a tune because some peoples setups need the wiggle room or something to that effect. The reason I am asking you guys is I tried to resolve this issue 7 years ago and he ended up assuming i had something mechanical to fix. So I wanted to run the logs by you guys to see if you could find anything glaring. He is also looking at them again (because he has forgotten me lol). Thanks for your help guys I am in no hurry.
1991 Z28
Engine: '94 355 LT1, GM hot cam, 1.6 RR's, Ported Heads, Dyno Don's headers, #30 SVO injectors, stock internals with skirted pistons.
Drivetrain: '95 T56, pro 5.0 shifter, hayes clutch, Stock 10 bolt with 3.42's
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The Following User Says Thank You to BCdawg57 For This Post:
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08-13-2020, 10:06 PM #24Xtreme Member
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Supporting Member2021 Charger Scat 392
1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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08-14-2020, 08:21 AM #25
Here is a link to the last tune he did
https://drive.google.com/file/d/1ciM...ew?usp=sharing1991 Z28
Engine: '94 355 LT1, GM hot cam, 1.6 RR's, Ported Heads, Dyno Don's headers, #30 SVO injectors, stock internals with skirted pistons.
Drivetrain: '95 T56, pro 5.0 shifter, hayes clutch, Stock 10 bolt with 3.42's
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08-14-2020, 11:23 AM #26LTx Guru
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Will be interesting to see what the injectors are set at. But if we look at the LTFT's for the most significant cells, on the average they are pulling out about 6% of the fuel. Using the stock injector constant (24.9) with 30# injectors would require a reduction of 20%.
The split exists only in the idle cell (16). That shouldn't exist with an LT4 HOT cam. There are places where the left bank goes as low as 88, and others where the right bank goes to 143. But all this disappears once the vehicle is driven. But in every cell, except 15, it is pulling out fuel. See attached chart.
On the three places where it goes into PE mode and uses Cell 15 with the 128 LTFT's, the average O2 readings are:
1 - L=0.932/R=0.923
2 - L=0.884/R=0.895
3 - L=0.900/R=0.903
The fuel MAY be rich, but there is no significant difference between the left and right banks.
A caution when looking at narrow-band O2 readings that show extremely rich - a narrow-band sensor is notoriously inaccurate at anything other than within the design range of 14.5 - 14.9:1 A/F ratio. Some sources even claim the range is +/-0.1 A/F units (14.6 - 14.8:1). Once you get above 0.700V the curve (volts on vertical axis - A/F ratio on horizontal) flattens. It takes a large change in A/F ratio to cause a small change in output volts. And complicating this is the fact that the operating temperature of the sensor can cause a larger change in the output voltage, larger than the small volts change caused by a large change in A/F ratio. They are just not accurate.
As far as the knock retard, in both instances of severe knock retard (12,6-deg, 12.0-deg) the throttle is hit and it takes several frames of data for the PCM to reach the programmed value of RPM/TP% go into PE mode. in that period of time, the O2 sensors are reading lean.
In one instance, the vehicle is coming out of closed throttle decel at about 3,600 RPM. As soon as the throttle is hit, knock counts jump from 1833-->12140. The retard occurs before it reaches PE mode. I think this may be a case of the PCM anticipating the knock based on the data it sees, and initiating the retard, rather than actually seeing knock.
In the other, the vehicle was traveling at constant throttle position/constant speed/3200 RPM for a period of time, and again, the throttle is depressed at about 3,200 RPM, the O2 sensors are indicating stoichiometric, and in the period of time before the RPM and TP% reach the point where PE is initiated, the knock counts bump from 12140-->16394 and the retard hits, before it reaches PE mode..
Possibly the transition points for PE mode are not low enough???? Or, tip-in problem????? I'm not a programmer... I just look at the data.
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08-17-2020, 03:43 PM #27
Thank you for the in depth breakdown. It dawned on me that the knock is probably the lower octane fuel that is currently in the tank. I also sent some logs to Solomon maybe he will have some new thoughts on the split at idle.
1991 Z28
Engine: '94 355 LT1, GM hot cam, 1.6 RR's, Ported Heads, Dyno Don's headers, #30 SVO injectors, stock internals with skirted pistons.
Drivetrain: '95 T56, pro 5.0 shifter, hayes clutch, Stock 10 bolt with 3.42's
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08-29-2020, 12:01 AM #28LTx Guru
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Maybe I missed it, but it would have been useful to know you are running low octane fuel.
There are two cases of weird LTFT's I'm involved with on CamaroZ28.com. Might want to look at these threads, particularly the last few posts on page 4 of the first one:
https://www.camaroz28.com/forums/lt1...-trims-887577/
https://www.camaroz28.com/forums/lt1...-888421/page2/
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08-30-2020, 09:47 PM #29
No, you didn't miss it. Just didn't think about it till now. I will look those over. Still have not heard back from Solomon.
1991 Z28
Engine: '94 355 LT1, GM hot cam, 1.6 RR's, Ported Heads, Dyno Don's headers, #30 SVO injectors, stock internals with skirted pistons.
Drivetrain: '95 T56, pro 5.0 shifter, hayes clutch, Stock 10 bolt with 3.42's
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