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Old 11-16-2001, 01:56 AM   #1
Scooby Newbie
Member#: 8721
Join Date: Jul 2001
Location: Colorado Springs, CO
1999 2.5 RS
Rally Blue

Question Tuning questions

I recently bought and installed an S-AFC for my 99 RS and I need to know what kind of gauges are neccesary for tuning. I know either EGT or A/F ratio, but which is hinestly better? I have done several searches but I could not find any good answer. I don't need it to be absolutly accurate, but enough so that I can have my car running well. Would an A/F gauge be sufficient for this? Or does their location(after the cat) render them completely useless? Is the EGT really worth the extra money and install difficulty? Thanks for any help
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Old 11-16-2001, 10:47 AM   #2
Richard L.
Scooby Specialist
Member#: 8465
Join Date: Jul 2001
Chapter/Region: NWIC
Location: Puget Sound, WA
'00 2.5RS Coupe, AW
'93 GMC Typhoon AWD


You might need a special A/F gauge for the front wide band O2 sensor. A standard A/F gauge will not work. Hooking up an A/F gauge to the rear O2 sensor will not give you an accurate reading since the sensor is located after the cat. I personally like the EGT gauge since installation is pretty easy. Just install the gauge, run the thermocouple lead through the firewall, drill a hole for the probe, and you're done.

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Old 11-16-2001, 06:46 PM   #3
Captain Ding
Scooby Newbie
Member#: 5773
Join Date: Apr 2001
Location: Allentown, PA, USA
2003 Forester XS
Pacifica Blue


I also have a 99 RS with an SAFC and went with both gauges. I use the A/F gauge to find out how the car is running in 500 rpm increments and the EGT to see how it is overall. MAF cars have a hard time with aftermarket intakes. To give you some idea how hard of a time they have, I'm -3% at 4000, +12% at 5000, and +20% at 5500. Without the A/F gauge, I wouldn't have seen the engine lean out the way it does at 5500 rpm. On the other hand, even though the mixture now stays consistent all the way through the rev range thanks to tuning by the A/F, without the EGT I wouldn't know how close to stoic I really was. My A/F is an autometer hooked to the 2nd O2. When my A/F gauge is on the R in Rich (about 80% deflection), it's really running stoic (1425 degrees). If I was running where the A/F indicates stoic, I'd be walking home.
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