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Discussion Starter #1
I've started to notice that the inside of my exhaust pipes and the arse-end of my car have become very sooty as of late...this, along with the noticable drop-off in fuel economy (at least 1 to 1.5mpg average) point to my LS1 running way too rich. I had suspected it before the transmission failure, but it is obviously much worse now... while it was in for the warranty problem, the dealership performed a fuel system maintenance (cleaning the fuel rails and changing at least one of the fuel filters as to partially recompensate me for their first-time screwup.

What is weird is that with the Accel Blue flat air filter (essentially a European K&N filter) and JHP/HSV MAF tube I added ~10-12k miles back, the car should be getting more air. I haven't popped off the airbox cover yet (I will shortly), but there's no way the filter is dirty enough to restrict airflow this soon. Even assuming that the EEPROM computer did not properly adjust to these new additions, shouldn't the car be running leaner? Can an intake leak somewhere cause weird airflow problems that actually restrict airflow?

So-- I'm looking for suggestions. Should I buy a programmer and lean it out myself (ka-ching), or drag it back to the dealership and tell them to recal the EEPROM since I suspect their fuel service knocked the mixture further out of whack?
 

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If you're still under warranty, I'd just take it back to the dealership and see what they say/do. Maybe they can at least tell you exactly what will be happening... it sounds like the cheaper option than dishing some of your money to take care of it yourself. Even if you're not under warranty I'd take it to them and just see what they say is wrong.
 

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From what I've read, even just a CAI will cause it to run rich.

I won't know until I get the car tuned. Finally, got a good tuner close by.

We got Houston Goat Herd dyno day Saturday and got 17 signed up. These are all '04 and '05 GTO's. Some modded, most near stock.

I've decided on a tuner rather than experimenting with edit myself.
 

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Discussion Starter #4
I've disconnectected the negative terminal of the battery to allow the PCM to reset itself...we'll see what that does.

It just seems counterintuitive to me that a CAI setup would make the car run richer...oh well.
 

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Groucho said:
I've disconnectected the negative terminal of the battery to allow the PCM to reset itself...we'll see what that does.

It just seems counterintuitive to me that a CAI setup would make the car run richer...oh well.
The computer senses that you have leaned out from the intake. It's answer is to throw all the fuel it can at the situation. That ends up leaving you on the rich side.
I know you hate them, but I had the same situation with my Z28. I spent $485 for a dyno tune and picked up 1-2 tenths in the 1/4 mile and my mileage went from 26-27 hwy to 29-30 hwy. It also improved some driveability issues.
With how much you drive the dyno tune is the way to go. I would not do it till you are done modifying the car though, as it will need to be reset each time you add something to the car. Also if you go to the dealer you will need to let them know not to reflash your computer. You will have basically voided any emissions warranty you have too.
Your best bet for tuning is to find somebody that specializes in the LS1. That means you are going to have to go where the mullet-heads with the F-bodies go. Sorry to share that piece of bad news with you, but anything less and you will be disapointed. Check out GM High Tech Performance magazine to see if they have any tuners listed in your area. That's how I found Stropes Speed Shop in Washington, PA, near Pittsburgh, they weren't cheap but definately the best.
 

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Discussion Starter #9
fergyflyer said:
The computer senses that you have leaned out from the intake. It's answer is to throw all the fuel it can at the situation. That ends up leaving you on the rich side.
I know you hate them, but I had the same situation with my Z28. I spent $485 for a dyno tune and picked up 1-2 tenths in the 1/4 mile and my mileage went from 26-27 hwy to 29-30 hwy. It also improved some driveability issues.
With how much you drive the dyno tune is the way to go. I would not do it till you are done modifying the car though, as it will need to be reset each time you add something to the car. Also if you go to the dealer you will need to let them know not to reflash your computer. You will have basically voided any emissions warranty you have too.
Your best bet for tuning is to find somebody that specializes in the LS1. That means you are going to have to go where the mullet-heads with the F-bodies go. Sorry to share that piece of bad news with you, but anything less and you will be disapointed. Check out GM High Tech Performance magazine to see if they have any tuners listed in your area. That's how I found Stropes Speed Shop in Washington, PA, near Pittsburgh, they weren't cheap but definately the best.
LOL!

I can suck it up. I think I have a Def Leppard t-shirt somewhere...if I hack a wig just right I'll fit right in.

:rofl:

I'm done modding the engine. She's a daily driver, after all. Is there a cheaper way than buying LS1 Edit or a Superchips flasher to "store" a tune, should it need to be reflashed back to factory settings?

I've hooked the battery back up and drove it around the block. Felt pretty good....but I haven't noticed a performance drop off to begin with...
 

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Discussion Starter #10
Looks like the computer reset has done the trick. I tried to keep the drive "typical," which essentially means a 80 mph cruise over the 4100' mountain on the 115 mile drive home.

The soot build-up on my clean "test patch" looked clean when I got home.

The end result: 76mph average speed, 22.5 mpg...a 3 mpg gain. I burned a gallon less of gas than on the way to work. That may not sound like much, but if this holds true it'll save ~$5.50 a day in gas...

Gonna keep a close eye on it.
 

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Groucho said:
Looks like the computer reset has done the trick. I tried to keep the drive "typical," which essentially means a 80 mph cruise over the 4100' mountain on the 115 mile drive home.

The soot build-up on my clean "test patch" looked clean when I got home.

The end result: 76mph average speed, 22.5 mpg...a 3 mpg gain. I burned a gallon less of gas than on the way to work. That may not sound like much, but if this holds true it'll save ~$5.50 a day in gas...

Gonna keep a close eye on it.
I'm glad.... you drive entirely too much to not worry about mileage. :cheers
 

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Discussion Starter #12
GTODEALER said:
I'm glad.... you drive entirely too much to not worry about mileage. :cheers
Yes I do.

It held for the drive back to work this a.m., in slightly heavier traffic- 115 miles, avg speed 69.5mph, avg mileage 22.3mpg...1 gallon less burned.
 

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Groucho said:
Yes I do.

It held for the drive back to work this a.m., in slightly heavier traffic- 115 miles, avg speed 69.5mph, avg mileage 22.3mpg...1 gallon less burned.
I'm sure that you are more concerned with the enviroment than your wallet, right?
 

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Discussion Starter #15
Well...it's a week down the road and I can already see my MPG dropping and the soot increasing again.

I've been discussing this with the blokes on ls1.com.au - this is not an unknown situation.

The bottom line is this:the stock MAF is sensing too much airflow, and the PCM is constantly trying to compensate for this by dumping more fuel into the mixture. The problem lies with the MAF data itself, not necessarily the PCM tune.

BTW I called Granatelli Motorsports, makers of the high-performance mass-airflow sensors. They say that my adding the HSV intake tube and Accel filter has created an ersatz CAI that causes the stock MAF to send bogus data. They have a product to sell, obviously, but they reccommend one of their aftermarket MAFs. They state that the stock MAF's firmware cannot be flash-modded.

Is this the case?

The cost of their MAF is not insubstantial ($415), making me wonder if this little excursion is worth it, or if I should just say the hell with it and drop in a stock air filter ... :rolleyes:
 

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Stock filter is a cheap test. Experience with Grans MAF is that unless you got mods such as heads / cam or Nitrous, the gain is minimal. Now, with a tune and the Gran MAF, I can see good gains in your future :cheers

We dynoed 15 GTO's saturday, and there was even one 04 A4 that was running real rich, blowing some black smoke at high rpm's The guy's engine bay looked like it was never cleaned, but the car had definate problem.
 

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Groucho said:
Well...it's a week down the road and I can already see my MPG dropping and the soot increasing again.

I've been discussing this with the blokes on ls1.com.au - this is not an unknown situation.

The bottom line is this:the stock MAF is sensing too much airflow, and the PCM is constantly trying to compensate for this by dumping more fuel into the mixture. The problem lies with the MAF data itself, not necessarily the PCM tune.

BTW I called Granatelli Motorsports, makers of the high-performance mass-airflow sensors. They say that my adding the HSV intake tube and Accel filter has created an ersatz CAI that causes the stock MAF to send bogus data. They have a product to sell, obviously, but they reccommend one of their aftermarket MAFs. They state that the stock MAF's firmware cannot be flash-modded.

Is this the case?

The cost of their MAF is not insubstantial ($415), making me wonder if this little excursion is worth it, or if I should just say the hell with it and drop in a stock air filter ... :rolleyes:
A speed shop that I dealt with told me that with a basically stock car, no major mods like heads, cam, headers, tb and such, that the MAF's on the market do more harm than good. Of course he's selling dyno tunes and they use the data the MAF throws at the computer and manipulate it to work properly based off of the exhaust content. I still think you would do better to get a good dyno tune. That really improved my Camaro. I had the soot on the pipes 30 minutes after starting it from just doing an intake and exhaust. My Corsa had real nice chrome tips and the soot was an eyesore. Not to mention the car did not run it's best.
I guess for an analytical thinking another benefit is they give you the data so you can see the improvement in black and white. You'll get more power, better mileage, less emissions and no soot on the pipes.
I moved from Pittsburgh to San Luis Obispo, and I had to get my car Smog Checked. Well at first they weren't happy with the intake, but I got them CARB #'s so they had to test it at least. They started the test and part way through the computer stops the test and tells the tech to check the exhaust. They checked to make sure the exhaust was connected and not leaking and started again. Part way through it shuts off again. They could not get it to register on the emission level it was designed for. I had to go to a referee station and get them to test it. They cheked the exhaust real close for leaks and then ran the test, same thing. They had to bump the car to the next level up, ULEV I think, to get it to register for the smog check. I think it ran that good because of the dyno tune.
 

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Discussion Starter #20 (Edited)
Thanks Fergy- that's cool!! I may have to do that...

BTW I got this answer to my question about tunes and edits over on the Aussie forums...it's best, clearest explanation of what an edit is that I've read yet!

Mongy said:
All a modified maf does is try to trick the PCM further. It is old technology before direct editing of the PCM tables was available to the masses. Your best option is to spend your money on either getting a professional edit, be it mail order or from a recognised shop. It is not a simple explanation but most of the tables are what would be described as "static" tables, i.e. they don't change. With Edit you can go in and modify these tables to reflect the changes you have made to the hardware, that way you can reduce the STFT correction percentage which is not a static table. When the STFT reaches the upper limits of its settings it then transfers it to the LTFT and the STFT then resets back to 0 and the process starts all over again so it is making long term changes to your PCM. A positive LTFT makes the PCM think it is running lean so it will add fuel and as a precaution even if it is not running lean on WOT and showing a negative percentage it will not remove the added fuel it is putting in on part throttle. The way around resetting these LTFT changes is to do a PCM reset, this is one reason why a car with an aftermarket intake or exhaust will gain power immediately after a reset, but it will then just start it all over again doing its corrections and the gains will be lost very quickly until you go in and edit the base tables so that the STFT corrections are as close to 0 as possible, that way your engine will be getting the correct quantity of fuel to run a good AFR at any throttle position and continue to deliver good power and use less fuel. Not sure what the situation is in the States with edit but most of the shops in Australia that are in the forum sponsors section can offer a mail order tune service to anywhere in the world. It is hard to try and explain it in writing but I hope this helps.
 
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