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I recently had headers and a catless x-pipe put on my 2014 Stingray, and had it tuned. The exhaust smell is horrible. It smells like the car is running extremely rich. I realize that without catalytic converters there is going to be smell. I had a C6 with the same setup and the fumes weren’t near as noticeable. Is this due to the direct injection of the LT1, or is it a bad tune? I’m almost to the point of putting the stock system back on.
If only you had a way to know if it is running extremely rich or not without smelling it. Oh, wait, there is. Get a scanner on it and see what the upstream O2 sensor readings are. I don't rely on my nose to know. Get the car running hot and then you can scan the data and see if it is low or high. If both sensors are having a higher voltage, it is rich. If they are low, it is lean.
In my opinion, it is the tune. Back in the day before cats and electronic engine controls, we ran modified cars that didn't smell like lighting a match near them would cause an explosion. With electronic ignition and fuel controls, it should be easier to achieve that now than it was before. Without cats, your exhaust pipes should have a tan-colored look if the tune is correct.
In my opinion, it is the tune. Back in the day before cats and electronic engine controls, we ran modified cars that didn't smell like lighting a match near them would cause an explosion. With electronic ignition and fuel controls, it should be easier to achieve that now than it was before. Without cats, your exhaust pipes should have a tan-colored look if the tune is correct.
Bill
How would you know with the exhaust pipe look? The ignition and pulse width has more variance than the carburetors without the electronic controls. Back in the day, we used to put fresh plugs on the jetski,
WOT run and stop then check. Today, it isn't that easy with EFI which is why I suggested checking the O2 sensor voltage and see if it is a figment of the imagination or if it is real. I would think with the increased efficiency of the headers, it would be more likely to run lean than rich. Kinda why I would be getting in closed loop and reading the sensor at different points. It might be rich down at idle but could be lean at the middle to top for all we know.
I believe that the exhaust from unleaded gas smells different than from olden days leaded premium. It does smell bad if not run through cats. I have run catless for a number of years, but on E-85. The smell is much less noticeable.
I believe that the exhaust from unleaded gas smells different than from olden days leaded premium. It does smell bad if not run through cats. I have run catless for a number of years, but on E-85. The smell is much less noticeable.
Why use a subjective scale when you have a more objective means of telling whether it runs rich or lean?
If you have a WB o2 sensor installed, what's it show?
If you have none of the above, you need to find someone that can check it for you.
For it to be the tune, it has to have really been screwed up and/or someone decided to try and run the car open loop all the time. Even with a stock cam, you'll smell it but it shouldn't be eye watering.
If you want to keep the headers, have bullet cats installed. Keep in mind they may or may not clear the tunnel plate. For instance on mine I have 1/8" spacers to gain tunnel plate / bullet cat clearance. Do keep in mind that excellent bullet cats are not cheap. However, having a stock cam you should be able to get buy with some that are ~$300ea.
If you have a scanner, post up fuel trims. If you have a WB o2 sensor installed, what's it show?
Could you just do a preliminary scan of what the O2 sensors are saying so you can at least see if it is really rich before we go any further buying a WB O2 sensor?
Could you just do a preliminary scan of what the O2 sensors are saying so you can at least see if it is really rich before we go any further buying a WB O2 sensor?
Certainly!
Ironically....or maybe not....I've seen more than one person that has a WB o2 installed because they want to watch the pretty gauge mounted on the A-pillar but yet they don't have any sort of scan tool to look at fuel trims.
If you don't, can't you get a voltage off of O2 sensor with a DVOM and get a rough idea?
A pro tuner should probably answer that but... The O2 readings will vary continuously (STFT's), the long term fuel trims (LTFT's) are what you should be checking to determine if it's running rich or lean. If the A/F is incorrect the ECM will set the CEL, so unless you have a check engine light, you should be good to go and the smell is what it is.
A pro tuner should probably answer that but... The O2 readings will vary continuously (STFT's), the long term fuel trims (LTFT's) are what you should be checking to determine if it's running rich or lean.
If the A/F is incorrect the ECM will set the CEL, so unless you have a check engine light, you should be good to go and the smell is what it is.
I believe I did get a voltage reading from the sensor once. THIS article mentioned it. I am THINKING that you can get a rough idea of what you are looking for without buying a scanner to read fuel trims.
I don't like to use smell, sight, touch, etc. I prefer to see objective data to make decisions. My thoughts are that maybe the reading is within programming range but the OP has a nose that doesn't agree? Maybe the sensor is getting old and lazy and doesn't switch as fast as it should but still within range?
I believe I did get a voltage reading from the sensor once. THIS article mentioned it. I am THINKING that you can get a rough idea of what you are looking for without buying a scanner to read fuel trims.
I don't like to use smell, sight, touch, etc. I prefer to see objective data to make decisions. My thoughts are that maybe the reading is within programming range but the OP has a nose that doesn't agree? Maybe the sensor is getting old and lazy and doesn't switch as fast as it should but still within range?
Back in the day before using a wideband, we did try to tune with HPTuners and the readings from the narrow band O2's on my C5 Vette. It didn't work well for us, maybe someone else could do better. I wouldn't try and tune without a scanner and wideband. Just me.
Back in the day before using a wideband, we did try to tune with HPTuners and the readings from the narrow band O2's on my C5 Vette. It didn't work well for us, maybe someone else could do better. I wouldn't try and tune without a scanner and wideband. Just me.
I don't want to play with tuning myself but every tuner wants to do it with a wideband, AFAIK. When Lingenfelter did mine back in the day, obviously he was alive then, I believe he welded a different bung just for that.
If you don't, can't you get a voltage off of O2 sensor with a DVOM and get a rough idea?
You'd have to try and figure out how to correlate the voltage to the fuel trim for that particular cylinder bank. Since there are two banks, you have to do this for both sides. Major PIA to try and power the o2 sensors and log data....you can't just look at a snapshot in time since they vary based on rpm, load, etc. Just sitting at idle, the fuel trims will traverse a dozen cells (+/-) as the engine warms, rpms drop from cold start to hot idle, and so on. For the time and effort it'd take to do this...and then to have no idea if the data is being correlated correctly...is nuts.
Looks like the OP disappeared so we'll never know. If I was in the OPs shoes, I'd take the car to a reputable shop and have them look at the fuel trims and adjust idle and part throttle as necessary.
You'd have to try and figure out how to correlate the voltage to the fuel trim for that particular cylinder bank. Since there are two banks, you have to do this for both sides. Major PIA to try and power the o2 sensors and log data....you can't just look at a snapshot in time since they vary based on rpm, load, etc. Just sitting at idle, the fuel trims will traverse a dozen cells (+/-) as the engine warms, rpms drop from cold start to hot idle, and so on. For the time and effort it'd take to do this...and then to have no idea if the data is being correlated correctly...is nuts.
Looks like the OP disappeared so we'll never know. If I was in the OPs shoes, I'd take the car to a reputable shop and have them look at the fuel trims and adjust idle and part throttle as necessary.
Oh, I totally agree. It might be a pain even at cold and warm idle, never mind if the car is running. I just figured that if he would smell anything, it would be at cold or warm idle. That said, I would and do have a scanner to look at STFT and LTFT and O2 sensor voltage, etc.
Back in the day before using a wideband, we did try to tune with HPTuners and the readings from the narrow band O2's on my C5 Vette. It didn't work well for us, maybe someone else could do better. I wouldn't try and tune without a scanner and wideband. Just me.
Narrow band is fine for idle and part throttle. WB is a must for WOT. I've heard of guys doing WOT with a narrow band but to me that's the ultimate in playing with fire.
Here's mine (all idle and part throttle tuned with the OEM narrow band sensors), with a Stage 3 GPI cam, headers, heads, 103mm throttle body, MSD intake (all of which are ported), etc....
Narrow band is fine for idle and part throttle. WB is a must for WOT. I've heard of guys doing WOT with a narrow band but to me that's the ultimate in playing with fire.
Here's mine (all idle and part throttle tuned with the OEM narrow band sensors), with a Stage 3 GPI cam, headers, heads, 103mm throttle body, MSD intake (all of which are ported), etc....
I got someone to tune my car but I don't think they did the wideband but who cares? We already got the WOT running but the driving around normally wasn't as good as I liked.
Exhaust smell
