Catless/ strait pipe vs. cat effect on mpg?
#1
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Catless/ strait pipe vs. cat effect on mpg?
Hey guys, like quite a few other people on here I have a catless midpipe, and like everyone else it throws a code so the engines in limp mode.
My question is, how much of a difference in mpg would there be with a good cat not throwing a code vs the catless midpipe throwing one? would the better flow increase it at all?
My question is, how much of a difference in mpg would there be with a good cat not throwing a code vs the catless midpipe throwing one? would the better flow increase it at all?
#2
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sounds like you have a failure of a front o2 sensor. So it's not the catless midpipe it's the faulty sensor causing the car to go into limp mode.
https://www.rx8club.com/series-i-trouble-shooting-95/o2-sensor-failure-front-rear-192278/
https://www.rx8club.com/series-i-trouble-shooting-95/o2-sensor-failure-front-rear-192278/
#7
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it throws a code and indicates this with a check engine light, but it does not make the PCM go into "limp" mode. The engine will continue to operate normally in spite of the code. If you want to get rid of the CEL/code you will either need to install a cat converter or cheat the system by blocking the code with a Cobb Accessport. MPG just depends on how you drive or what cat you may or may not have. Some high end racing cats will flow the same as a cat-less midpipe.
#8
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If the Engine light is on, chances are it will not go in open loop, meaning it wont ajust for the best performance/economy it will stay with the base maping, where it is important to get flashed if your are to modify anyting on the engine to put this ''limp mode'' values where you want them to be... even cancel your MIL light for these normal occurances (having not cat)
#11
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it throws a code and indicates this with a check engine light, but it does not make the PCM go into "limp" mode. The engine will continue to operate normally in spite of the code. If you want to get rid of the CEL/code you will either need to install a cat converter or cheat the system by blocking the code with a Cobb Accessport. MPG just depends on how you drive or what cat you may or may not have. Some high end racing cats will flow the same as a cat-less midpipe.
Ive searched around, how exactly do you get a Cobb Accessport, I just got an agency midpipe off rotary to complete my exhaust and I'm sure it will throw a CEL
#13
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When I had my high flow cat and throttle coolant bypass I did notice the secondary air pump running all the time (high pitch wine during start up). Meaning it was trying to warm up the car/cat faster (open loop) and dumping more fuel. Ever since I put stock cat back for smog and undid the throttle bypass, I got way better gas mileage about 20-50 miles more on a full gas tank, but I did lose bottom/mid end power. Also my exhaust tip started to melt my shroud due to the excess heat .
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Having a midpipe will not throw your car into limp mode , just cause you to fail smog emissions with a static CEL. Blinking CEL will throw your car into limp home mode (something mechanically wrong). With that said, when i get my RB dual resonated midpipe I am removing my secondary air pump . power > mpg, gotta pay to play. I didn't expect good mileage when I decided to get a sports car.
#18
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When I had my high flow cat and throttle coolant bypass I did notice the secondary air pump running all the time (high pitch wine during start up). Meaning it was trying to warm up the car/cat faster (open loop) and dumping more fuel. Ever since I put stock cat back for smog and undid the throttle bypass, I got way better gas mileage about 20-50 miles more on a full gas tank, but I did lose bottom/mid end power. Also my exhaust tip started to melt my shroud due to the excess heat .
I'm not saying you're wrong I just can't see the connection.
1) The secondary air pump has no way of knowing the Catalytic temperature. It comes on when the car is cold and runs until a certain engine temperature not catalytic temperature.
2) The engine is NOT in Open Loop when trying to warm up the car/cat faster. I don't know where you got that idea.
3) The Throttle Body bypass you undid it? Huh you mean you put it back to stock? Anyways I still can't see the connection on the secondary air pump.
I honestly don't think the the TB bypass and the cat delete will largely impact the time for a vehicle to warm-up.
Maybe it was just colder when you had the mods vs stock setup?
Just say'n -- if you have more details I would like to here them. I'm ready to be convinced.
Having a midpipe will not throw your car into limp mode , just cause you to fail smog emissions with a static CEL. Blinking CEL will throw your car into limp home mode (something mechanically wrong). With that said, when i get my RB dual resonated midpipe I am removing my secondary air pump . power > mpg, gotta pay to play. I didn't expect good mileage when I decided to get a sports car.
It's not really relevant whether the CEL is on or flashing the code that is important.
For example you may have a Failed OMP which should put your car in to limp mode and throw a CEL (solid check engine light).
I can't think of a flashing cel that will put your car in to limp mode, maybe a misfire or knock event.
Last edited by wcs; 11-19-2011 at 07:37 AM.
#19
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@wcs
My car still has mods, only difference is the coolant bypass and the cat delete were removed. I'm thinking the reason I used more fuel was because more cold air was going through the engine, and colder air is more dense than warmer air, meaning dump more fuel, you are right on the money sir. And I realized there are other sensors mainly temp that determines open loop/close loop. I think the secondary air pump was going crazy since there was no cat? (maybe the ecu is triggering the pump to turn on to increase oxidation since o2 sensor is detecting alot of emissions, dunno just a speculation).
You are right with the flashing CEL, most of the time its a misfire, and the computer can try to adjust. I just remember my buddies truck who had a bad MAF and he kept getting misfires/weird fuel trim data and no power. Thing was the MAF code never popped up, it gave us a run for our money.
My car still has mods, only difference is the coolant bypass and the cat delete were removed. I'm thinking the reason I used more fuel was because more cold air was going through the engine, and colder air is more dense than warmer air, meaning dump more fuel, you are right on the money sir. And I realized there are other sensors mainly temp that determines open loop/close loop. I think the secondary air pump was going crazy since there was no cat? (maybe the ecu is triggering the pump to turn on to increase oxidation since o2 sensor is detecting alot of emissions, dunno just a speculation).
You are right with the flashing CEL, most of the time its a misfire, and the computer can try to adjust. I just remember my buddies truck who had a bad MAF and he kept getting misfires/weird fuel trim data and no power. Thing was the MAF code never popped up, it gave us a run for our money.
#20
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The IAT is before the TB so it's curious how this mod effects things both with the Stock setup and the bypass setup.
(FYI I'm using the bypass setup, I'm also boosted just so you understand my perspective on rolling this around in my noodle)
There are two parameters:
1) Load
2) RPM
The vehicle is always in CL until the engine load limit or the RPM limit is reached.
LOL
We've also completely hi-jacked this thread but oh well, it really wasn't a good thread topic anyway.
/start full thread jack mode
#21
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To the OP,
When you put a midpipe on the car, you reduce backpressure and the car will want to run leaner. The O2 sensor will detect this and the ecu will compensate to bring the car back into it's assigned operating perimeters. Without changing these settings in the ecu, you may gain a little horsepower, a lot more sound and little else. You have to tune the ecu to run leaner to get better fuel economy.
For many it's easier and cheaper to modify their driving habits.
When you put a midpipe on the car, you reduce backpressure and the car will want to run leaner. The O2 sensor will detect this and the ecu will compensate to bring the car back into it's assigned operating perimeters. Without changing these settings in the ecu, you may gain a little horsepower, a lot more sound and little else. You have to tune the ecu to run leaner to get better fuel economy.
For many it's easier and cheaper to modify their driving habits.
#22
crazyrussian
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to be honest, your description fits pretty nicely haha anyway is there a midpipe that wont make the car sound ricey..? I like the agency but dang it makes the exhaust hella loud.. I dont know what people are talking about, i haven't gotten any CEL's with the cat off.. limp mode sounds like a personal problem to me
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to be honest, your description fits pretty nicely haha anyway is there a midpipe that wont make the car sound ricey..? I like the agency but dang it makes the exhaust hella loud.. I dont know what people are talking about, i haven't gotten any CEL's with the cat off.. limp mode sounds like a personal problem to me
#25
I have seen a couple 2004's that did not get a cel from removing the cat, I am not sure why. IMO loud exhaust does not = rice. A rotary engine has a distinct sound, nothing like a 1.6 d series Honda with a coffee can strapped to the back. If you do not want the car louder put the cat back on.
Rasp at any volume = Rice
Just my 2
Last edited by Silver_Surfer; 01-11-2012 at 05:12 PM.