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1995 Firebird LT1 Auto
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Discussion Starter · #1 · (Edited)
I have a modified LT1 car that is new to me, unsure of history, has some bolt on’s like a Holley throttle body, headers, intake manifold, not sure if anything else. I just got scan 9495 to work with a home made cable.
That said, I’d like to explore the ability to save my original and modify the car’s tune for some performance mods, tire size, etc. car has a strong gas type smell and blows a bit of black smoke at high rpm. Also I’m not sure if this is relative or not but I’m located around 3500’ above sea level. Which is a big deal for carburetors but not sure on fuel injection.

Is there any software that you guys have experience with or recommend for a beginner? I see some free stuff called is available like Tunerpro RT. Thoughts?
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Here's a decent introduction to LT1 tuning, with info about available software. Worth a quick read through, to see what you would be getting yourself into. The person who owns that site is a tuner, offering mail order tuning services. I can offer another tuner that I usually recommend, if you develop an interest in a mail order tune. They can be amazingly effective if done by the right tuner. In order to have a mail order tune done effectively, you need to know ALL the engine modifications.


For example, what size is the Holley throttle body, what brand/style/size are the headers? Any modifications to the heads and cam? If it's just the bolt-ones you listed, it gets simple. Because your 95 has a mass air flow sensor, the improvements to engine breathing are seen by the PCM, and it makes adjustments to fuel flow. To answer your question about the impact of elevation, the main effect of elevation is the reduction of air density, and the need to reduce the fuel flow. The mass air system fully accounts for that.

What intake manifold do you have? It is very unusual to replace the stock LT1 manifold unless the engine has extensive internal modifications. There is an Edelbrock intake manifold available, but it really doesn’t improve anything.

If you can run a data log using Scan9495 I can review it for you and look for the source of the strong gas smell.
 

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1995 Firebird LT1 Auto
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54 Posts
Discussion Starter · #3 ·
Here's a decent introduction to LT1 tuning, with info about available software. Worth a quick read through, to see what you would be getting yourself into. The person who owns that site is a tuner, offering mail order tuning services. I can offer another tuner that I usually recommend, if you develop an interest in a mail order tune. They can be amazingly effective if done by the right tuner. In order to have a mail order tune done effectively, you need to know ALL the engine modifications.


For example, what size is the Holley throttle body, what brand/style/size are the headers? Any modifications to the heads and cam? If it's just the bolt-ones you listed, it gets simple. Because your 95 has a mass air flow sensor, the improvements to engine breathing are seen by the PCM, and it makes adjustments to fuel flow. To answer your question about the impact of elevation, the main effect of elevation is the reduction of air density, and the need to reduce the fuel flow. The mass air system fully accounts for that.

What intake manifold do you have? It is very unusual to replace the stock LT1 manifold unless the engine has extensive internal modifications. There is an Edelbrock intake manifold available, but it really doesn’t improve anything.

If you can run a data log using Scan9495 I can review it for you and look for the source of the strong gas smell.
sounds great. I feel I owe you a bunch of beer, thanks for all your help. I’ll look at the intake and throttle body, snap some pics and run a scan and post back.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Further thoughts....

The minor bolt-ons you have listed (if that's all there is) are not enough to require a tune. The PCM should have been able to adjust for them. If it's running rich, its a problem with the O2 sensors, or can be things like a leaky injector, misfires, leaking exhaust, faulty MAF, etc. You don't fix those with a tune. You investigate the source of the problem, and a data log is the best tool. Then correct the faulty component.

For a vehicle with limited mods, the most productive change to the tune it to reduce the excessively rich target A/F ratio the PCM calculates when the combination of throttle position and RPM forces the PCM to operate in power enrichment (PE) mode.

When the car is being driven moderately, the PCM programming attempts to maintain the A/F ratio at 14.7:1. That is the A/F ratio the gives decent gas mileage, and produces the least emissions (the cleanest combination of unburned hydrocarbons, carbon monoxide and oxides of nitrogen). There are corrective actions taken, using feedback from the O2 sensors. But 14.7:1 is too lean to produce the higher HP desired in more aggressive driving.... think wide open throttle (PE mode).

In PE mode, the PCM looks at several parameters and calculates a richer A/F ratio required to maximize power. Typically, the calculation with the factory tune yields a target A/F ratio of about 11.7:1. This is on the excessively rich side, but is used to prevent the risk of detonation (knock) if using the wrong octane fuel. Traditionally, you make more HP/torque closer to 13:1. Using tuning software, you can alter the target A/F ratio calculation to produce a result closer to 13:1. If you look through the tuning guide I linked, he explains how to do that. This simple change can increase power by 10-15 HP.
 
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1995 Firebird LT1 Auto
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Discussion Starter · #5 ·
Further thoughts....

The minor bolt-ons you have listed (if that's all there is) are not enough to require a tune. The PCM should have been able to adjust for them. If it's running rich, its a problem with the O2 sensors, or can be things like a leaky injector, misfires, leaking exhaust, faulty MAF, etc. You don't fix those with a tune. You investigate the source of the problem, and a data log is the best tool. Then correct the faulty component.

For a vehicle with limited mods, the most productive change to the tune it to reduce the excessively rich target A/F ratio the PCM calculates when the combination of throttle position and RPM forces the PCM to operate in power enrichment (PE) mode.

When the car is being driven moderately, the PCM programming attempts to maintain the A/F ratio at 14.7:1. That is the A/F ratio the gives decent gas mileage, and produces the least emissions (the cleanest combination of unburned hydrocarbons, carbon monoxide and oxides of nitrogen). There are corrective actions taken, using feedback from the O2 sensors. But 14.7:1 is too lean to produce the higher HP desired in more aggressive driving.... think wide open throttle (PE mode).

In PE mode, the PCM looks at several parameters and calculates a richer A/F ratio required to maximize power. Typically, the calculation with the factory tune yields a target A/F ratio of about 11.7:1. This is on the excessively rich side, but is used to prevent the risk of detonation (knock) if using the wrong octane fuel. Traditionally, you make more HP/torque closer to 13:1. Using tuning software, you can alter the target A/F ratio calculation to produce a result closer to 13:1. If you look through the tuning guide I linked, he explains how to do that. This simple change can increase power by 10-15 HP.
i have a scan log file today. How do I upload it for you to check out?
 

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1993 6-spd T/A - 1996 C4
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Type out your message, then look at the bottom of the box you typed in. There are some letters and symbols. See the paperclip? Click it.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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See post #5 in this thread for my recommended tuner:

 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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I'll see what I can do with it.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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14,975 Posts
Opens but can't change extension. I'll send you a private message with my email. Send it as an attachment.
 

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1995 Firebird LT1 Auto
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Discussion Starter · #11 ·
Opens but can't change extension. I'll send you a private message with my email. Send it as an attachment.
Hi Fred, so to change directions on the thread back to tuning, I ended up buying a custom tune from moehorsepower. Haven’t driven it yet since uploading as the weather sucks. Anyway my brother in-law has the same car as me 95 firebird LT1, however he has different gearing RPO code GU2 so a 2.73 gear I believe and also a different tire size. Do you know if there is software or directions that I can use or follow to modify the tune to change these things to work for his car?

thanks again!
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Go back to post #2 and click on the link. The first full paragraph on page 1 of the document covers three available OBD-1 tuning softwares. Kind of cluttered paragraph, but the info is in there.

Not sure, but you may have an issue with the VIN when trying to load the new program into a different vehicle than the file is for.
 
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