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Old 04-10-2004, 05:37 PM   #1
squeeks
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01 GM6 i think
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Default Intake Leaning out Air/Fuel mix on EJ25...

So I know you've all seen many posts about this before, but I am looking for some more technical information..

I know that CAIs can lean the air/fuel mixture and over time, this can cause harm to the engine, but my question is this... What internal harm is exactly caused to the engine?? (i.e. what part of the block/head/whatever part is damaged)

Anyone know?

I've had the Cobb CAI on my car for around 30K miles w/ no ECU adjustment to fix the problem, I just bought an Apex SAFC2 to manage it better, but haven't installed it yet.

I'm just hoping to get a little more technical information an what exactly could be going on INSIDE my engine, or what could happen in the future if such a problem was left alone for a longer time than 30K miles.

Thanks!
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Old 04-10-2004, 07:22 PM   #2
Storm
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Leaning conditions increase exhaust temps, which cause more wear on valves, guides, pistons, etc... Generally, it's harder on the parts.

A simple rise in fuel pressure will easily counteract any leaning due to an intake change. Simple being, after you decide how you want to change your fuel pressure. Many have modded the stock FPR by crimping it in a vise to put more pressure on the relief spring. This is kinda tricky and irreversable. Others have modded stock FPRs into adjustable by drilling and ading a threaded bolt to adjust spring pressure. Again, kinda tricky unless you know what needs to be done.

An Apex-i SAFC also will increase injector values based on altered signals from the motor. Easy to tune, but later ECU's will learn around it, requiring frequent ECU resets.

Jay Storm
www.sourcemotorsports.com
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Old 04-10-2004, 09:38 PM   #3
SjYankee006
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Default

I was wondering the same thing... I recently had an 02 sensor go bad on me, and my tech said that it was because my car was running too lean. He said my CAI and high-flow exhaust were allowing the engine a breath too much and overworking/frying the sensor. Is an SAFC the only way to go to fix this? I don't mind increasing fuel to get better performance/less wear. How frequent ECU resets are we talking about here, once a week, once a month?

On a side note.. how much does a good SAFC go for?
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Old 04-11-2004, 05:56 AM   #4
squeeks
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Modacar.com has the Apex-i SAFC-II for $315. That's where I just bought mine from. How much did the replacement O2 sensor run you?

Thanks for the info Storm! I'm also very curious as to how frequently you should have to reset the ECU. Not a difficult process, but it might get a little old if you had to do it every week!
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Old 04-11-2004, 03:12 PM   #5
Storm
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I couldn't tell you how often you'll need to reset. We run a 98 w/the SAFC. Do a search in the engine management section for that topic. I've seen it discussed quite a bit. Some cars and settings are more finicky than others.

Quote:
Originally posted by squeeks
Modacar.com has the Apex-i SAFC-II for $315. That's where I just bought mine from. How much did the replacement O2 sensor run you?

Thanks for the info Storm! I'm also very curious as to how frequently you should have to reset the ECU. Not a difficult process, but it might get a little old if you had to do it every week!
Jay Storm
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Old 04-11-2004, 08:05 PM   #6
bigpaulo
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Default aren't 2.5's notorious for running rich anyways?

Isn't it true that the 2.5 NA Subie engines run notoriously rich anyways? Wouldn't you just be bringing things a little closer to stoichiometric by adding a CAI?
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Old 04-11-2004, 11:11 PM   #7
SjYankee006
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Quote:
Originally posted by squeeks
How much did the replacement O2 sensor run you?
The O2 was $100.... plus $100 for installation (I would have done it myself, but at the time I didn't have a choice).
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Old 04-11-2004, 11:22 PM   #8
SjYankee006
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BTW, does anyone know what the difference is between the SAFC-I and SAFC-II? Is it just a newer version of the same thing? And are the newer features worth the price or should I try to find a used SAFC-I? hhmmm..
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Old 04-13-2004, 02:27 PM   #9
Storm
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I wouldn't say that. Of course I've believed that when I started getting into this game. We tried leaning out our settings about -10% and found ourselves running with CELs, mediocre power and just chaulked it up to the 2.5 having decent but not awesome power. We also, with the same settings, got gas in KS and ended up misfiring and completely blowing any chances of a good result during competition.
Quote:
Originally posted by bigpaulo
Isn't it true that the 2.5 NA Subie engines run notoriously rich anyways? Wouldn't you just be bringing things a little closer to stoichiometric by adding a CAI?
After frantic troubleshooting and pleads for help from folks who actually know what they were doing, we richened things up across the board to the tune of abour +12-15% and we literally had so much more power that we then blew the rest of our runs re-learning how to tame the beast.

Right now we run with a true CAI(routed from the front bumper w/a simple foam prefilter), no cats, and very minimal exhaust. With our SAFC settings we have no CEL believe it or not, and we make enough power to spin all 4 wheels upon launches _every time_.

You guys can hem and haw about running rich-lean-stoic all you want. I know what works for us. There are videos of these facts on our website.

No offense to anyone directly. I'm only sharing what I've learned works versus what people preach as the gospel online.

Jay Storm
www.sourcemotorsports.com
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