Troque and Gear Ratio
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
I had the cruise set on 84 mph.
Burning Brakes
Joined: Apr 2009
Posts: 1,228
Likes: 10
From: That one city...you know that one. Idaho
I decided to look it up in OnDemand, and there is a 3rd O2 sensor listed there. I admit I was not expecting that.
I still doubt it not being there would cause any performance issues, or fuel economy issues.
I still doubt it not being there would cause any performance issues, or fuel economy issues.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Huh, I guess I was wrong. The LT1 has true dual exhaust; which pipe has the 3rd O2?
IDK that I get my best mileage at 84 mph; that was just the speed I picked for that trip, b/ it was 9 over.
IDK that I get my best mileage at 84 mph; that was just the speed I picked for that trip, b/ it was 9 over.
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
I have heard of more than one case where someone changed the exhaust in one way or another (larger exhaust, shorty headers, etc., etc.) and had to get a re-tune due to changing the back pressure. The engine was tuned originally with a set amount of back pressure... change that and you will change the fuel/air mixture. Removal of the aft one in my case may not have an effect on the fuel/air ratio... but I am not sure on that one. Someone must have changed the programming because I am not getting an error code!?
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
IDK that I get my best mileage at 84 mph; that was just the speed I picked for that trip, b/ it was 9 over.
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
Hey, guys, it is after midnight here on the east coast in NC. I will have to pick up with you tomorrow!
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Sorry, but what is IDK? If your rear tires are the same as mine 285/40ZR17, then your tire diameter is 26 inches and at 84mph you would be turning 1957rpm in 6th gear (http://www.4lo.com/calc/gearratio.php). I am not trying to say "I told you so", but you are proving my point. At ~2000rpm this engine is more efficient that at lower rpm. At 84mph with increased air drag you get better mileage than at lower speeds! I think this is great!!!!!
My data from that one trip "proves" nothing, except that you should be getting better mileage. I already stated clearly that "84 mph" isn't the magical, optimal speed; it just happened to be the speed that I chose on that particular trip...9 over the limit.
I've also gotten ~30 mpg traveling to and from work, when I lived in Telluride. All secondary roads, very mountainous, 30-60 mph speeds on that 44 mile commute. Now that was using all fuel saving techniques; driving brainlessly, I'd get ~25-27 on the same commute.
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Burning Brakes
Joined: Apr 2009
Posts: 1,228
Likes: 10
From: That one city...you know that one. Idaho
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
Exactly what I had (hence the dangling connector), listed as such in Chilton's, and a previous post attested to this as well. If the car did come with dual exhaust, then why only 1 O2 sensor after one cat?! I sure do not know!? Thanks!
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
Nope. I have seen it on other vehicles using 2 cats. The cats are placed as close as possible to the exhaust manifolds (to catch as much heat as possible) with an O2 sensor in front of each, come into 1 pipe, and then the 3rd O2 sensor. Had a 2001 Pontiac Montana with this configuration.
Burning Brakes
Joined: Apr 2009
Posts: 1,228
Likes: 10
From: That one city...you know that one. Idaho
Nope. I have seen it on other vehicles using 2 cats. The cats are placed as close as possible to the exhaust manifolds (to catch as much heat as possible) with an O2 sensor in front of each, come into 1 pipe, and then the 3rd O2 sensor. Had a 2001 Pontiac Montana with this configuration.
It is common for OBD2 vehicles to have O2s after the cats, but not so much OBD1.
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
Interesting!? And baffling, esp. if we are talking about dual exhaust!
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I have heard of more than one case where someone changed the exhaust in one way or another (larger exhaust, shorty headers, etc., etc.) and had to get a re-tune due to changing the back pressure. The engine was tuned originally with a set amount of back pressure... change that and you will change the fuel/air mixture. Removal of the aft one in my case may not have an effect on the fuel/air ratio... but I am not sure on that one. Someone must have changed the programming because I am not getting an error code!?
With the lower MPGs you are getting, I would wonder if the tuning was done correctly and if missing feedback is circumventing proper fuel trim.
Also, backpressure is a common "misnomer" often objected to when talking about exhaust systems. There isn't a change in backpressure so much as in increase/decrease in the "siphoning" effect of pulling exhaust out of the motor. (Small, insignificant detail that doesn't affect understanding of your point though...)
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
I am talking without my 94 Helms in front of me (and in fact as the 94 was sold over 15 years ago, my Helms may be long gone) but the 94 Y body was interesting. It had a 16 pin OBD2 ALDL connector but was OBD1. So I had to get an OBD2 to OBD1 gender changer to work on the computer. I can't remember how many sensors it had but I will go with 3. However I kinda remember that it was plumbed wired for 3 but the 3rd wasn't included as the PCM had no provision to use an after cat O2 sensor data.
I have an EE def file for TC so would be happy to read your bin (or LT1) file to see if it is stock if you can pull it and email to me. However I can't find any table in any of the 94 files I have that take input from a 3rd O2 sensor.
I have an EE def file for TC so would be happy to read your bin (or LT1) file to see if it is stock if you can pull it and email to me. However I can't find any table in any of the 94 files I have that take input from a 3rd O2 sensor.
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
I currently do not have any way to pull the program from the PCM. I want to get this ability, but I do not have it at this time. Got suggestions?
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
In my experience the least expensive as well as the best (including after purchase support) is TunerCat by TC. Google will get you there.
You will need the 16 pin ALDL female connector and wire to your computers usb port. That is also available on the TunerCat website. Might as well get DataMaster also, which is your logging software. That is by TTS, but also avail through the website.
You will need the 16 pin ALDL female connector and wire to your computers usb port. That is also available on the TunerCat website. Might as well get DataMaster also, which is your logging software. That is by TTS, but also avail through the website.
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
Also, if you have a bung welded into the exhaust manifold behind one of the cats you will see it as it would be capped by what appears to be a 7/8ths inch bolt. At least the 02 sensor is 7/8ths of an inch, so I expect the bung cap would be also.
Hopefully you don't have an open bung in the exhaust system. <g> Might get a bit of CO in the car when you are parked.
Hopefully you don't have an open bung in the exhaust system. <g> Might get a bit of CO in the car when you are parked.
Thread Starter
Instructor
Joined: May 2014
Posts: 152
Likes: 1
From: Fayetteville NC
In my experience the least expensive as well as the best (including after purchase support) is TunerCat by TC. Google will get you there.
You will need the 16 pin ALDL female connector and wire to your computers usb port. That is also available on the TunerCat website. Might as well get DataMaster also, which is your logging software. That is by TTS, but also avail through the website.
You will need the 16 pin ALDL female connector and wire to your computers usb port. That is also available on the TunerCat website. Might as well get DataMaster also, which is your logging software. That is by TTS, but also avail through the website.
Obviously, it will take me a few weeks to get that bin file, but I will and I will contact you at that time. Thanks much for that offer.