Lowering nox/exaust smell from cam overlap
02-09-2018, 09:08 AM
#1
12 Second Club
Thread Starter
Lowering nox/exaust smell from cam overlap Smelling like exhaust fumes is getting old, and my girlfriend won't ride in my car, so I am trying to reduce the smell.
I have a cam with a good bit of overlap, 64° seat to seat, so I realize that I am not going to get rid of all of it, but I would like to improve it as much as I can.
I have adjusted the injector timing and delayed it a little, which seems to have helped a bit. I have also adjusted the afr to read really lean at idle, which also seems to have helped, though the motor really seems to run smoother with a rich idle. I have two magnaflow spun cats in the y-pipe, but I am not sure if they are lighting off. Listed light off temp from magnaflow is around 800°f, but my IR reading of the temp of the cats is only around 350°f. Exhaust temps about an inch down each primary are all around 500°f.
Should I try to get the exhaust temps up a bit?
The mixture would effect the egt, right?
Also, would the idle timing play a role?
Also, It's running open loop MAF tune.
I'm looking for any suggestions that might help tame it down some more.
Thanks
I have a cam with a good bit of overlap, 64° seat to seat, so I realize that I am not going to get rid of all of it, but I would like to improve it as much as I can.
I have adjusted the injector timing and delayed it a little, which seems to have helped a bit. I have also adjusted the afr to read really lean at idle, which also seems to have helped, though the motor really seems to run smoother with a rich idle. I have two magnaflow spun cats in the y-pipe, but I am not sure if they are lighting off. Listed light off temp from magnaflow is around 800°f, but my IR reading of the temp of the cats is only around 350°f. Exhaust temps about an inch down each primary are all around 500°f.
Should I try to get the exhaust temps up a bit?
The mixture would effect the egt, right?
Also, would the idle timing play a role?
Also, It's running open loop MAF tune.
I'm looking for any suggestions that might help tame it down some more.
Thanks
02-09-2018, 09:22 AM
#2
TECH Regular
How do you know your NOx is high? Normally, high NOx is due to combustion temps that are too high. Have you put the car on a sniffer to see what, exactly, is happening? Where is your y-pipe in relation to the rest of the exhaust? If it is a good bit away from the collectors, the cats will not stand a chance of lighting. Your measured temps show this to be the case. Lastly, where does the exhaust exit the car? If you are smelling it inside the vehicle while driving, you've got a leak somewhere. Either in the exhaust or the body of the car - or both. An exhaust leak pre-cat will also cause the PCM to dump in fuel which would add to strong exhaust smell.
All that being said, even sans cats, the exhaust shouldn't be running you out of the car. Something isn't right.
All that being said, even sans cats, the exhaust shouldn't be running you out of the car. Something isn't right.
02-09-2018, 09:32 AM
#3
Village Troll 
iTrader: (2)
Is it exhaust smell or gas? I have an issue with mine when in stop/go traffic smelling up my clothes, but I've heard complaints from others how they are running so rich it burns their eyes from raw fuel.
02-09-2018, 11:24 AM
#4
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Thread Starter
How do you know your NOx is high? Normally, high NOx is due to combustion temps that are too high. Have you put the car on a sniffer to see what, exactly, is happening? Where is your y-pipe in relation to the rest of the exhaust? If it is a good bit away from the collectors, the cats will not stand a chance of lighting. Your measured temps show this to be the case. Lastly, where does the exhaust exit the car? If you are smelling it inside the vehicle while driving, you've got a leak somewhere. Either in the exhaust or the body of the car - or both. An exhaust leak pre-cat will also cause the PCM to dump in fuel which would add to strong exhaust smell.
All that being said, even sans cats, the exhaust shouldn't be running you out of the car. Something isn't right.
All that being said, even sans cats, the exhaust shouldn't be running you out of the car. Something isn't right.
The smell definitely changed with the addition of the cats, but it still stinks.
I might just have to deal with it the way it is.
Maybe I am just overly sensitive to the smell.
02-09-2018, 12:30 PM
#7
TECH Fanatic
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02-09-2018, 01:10 PM
#9
TECH Fanatic
02-09-2018, 01:10 PM
#10
12 Second Club
Thread Starter
The only place I know to adjust the timing of the injectors is "injector offset adder", it has values in microseconds vs bpw?. I'm confused about the table though, and how to adjust it.
02-09-2018, 01:16 PM
#11
TECH Fanatic
Are you in advanced view? Also, this is for gen III pcms. Gen IV's use degrees.
02-09-2018, 01:24 PM
#12
TECH Fanatic
Gen III pcms use "reference periods" for injector timing. Offset is an adder, not timing. There are 8 reference periods. The numbers you see are used to calculate the degrees that the injector will finish spraying.
Stock boundary is 6.5, typically, and normal is set at 5.55. So:
6.5 + 5.55 = 12.05
12.05 * 90 = 1084.5
1084.5 - 784 = 300.5*
Stock boundary is 6.5, typically, and normal is set at 5.55. So:
6.5 + 5.55 = 12.05
12.05 * 90 = 1084.5
1084.5 - 784 = 300.5*
02-09-2018, 02:11 PM
#14
TECH Fanatic
That is definitely different than what I'm talking about. Unfortunately I have no experience with anything OBD I with hp tuners... Only OBD II, Gen III and up. My apologies for confusing you there, but that is definitely not something you hear much about these days. Not too many out there still using OBD I, or so it seems. Props to you for being different... lol.
02-09-2018, 02:31 PM
#15
TECH Fanatic
Learned something new today about that though. I hope you get it figured out. I know there are a lot of differences with the gen II pcms, I'll add that one to the list lol. Sure would be awesome if you did have those tables. Makes this problem much easier to solve.
Looks like if you want to keep the cam and the girlfriend, you might have to upgrade the pcm, and convert to full efi... Maybe she'll pitch in for Valentine's Day? Lol.
Looks like if you want to keep the cam and the girlfriend, you might have to upgrade the pcm, and convert to full efi... Maybe she'll pitch in for Valentine's Day? Lol.
02-09-2018, 02:43 PM
#16
I'll throw it out there- incomplete fuel burn not helping things (?)
What are your mods? i.e. head size, more about the cam (duration/lift/valve events), injector size, verified fuel pressure, approx. compression ratio, what plugs and what's the gap?
One thought is plug heat range too cold and gap too small contributing to incomplete fuel burn, which won't be cured anywhere with trying to lean out the fuel. You just burn less in certain areas with the same inefficiency. If your SCR is less than say 11.2:1 you may as well just run heat range 5 TR55 NGK plugs and gap them only slightly narrower than the stock .050, like maybe .045. Then maybe add a little fuel back where the engine likes it and burn it more efficiently.
What are your mods? i.e. head size, more about the cam (duration/lift/valve events), injector size, verified fuel pressure, approx. compression ratio, what plugs and what's the gap?
One thought is plug heat range too cold and gap too small contributing to incomplete fuel burn, which won't be cured anywhere with trying to lean out the fuel. You just burn less in certain areas with the same inefficiency. If your SCR is less than say 11.2:1 you may as well just run heat range 5 TR55 NGK plugs and gap them only slightly narrower than the stock .050, like maybe .045. Then maybe add a little fuel back where the engine likes it and burn it more efficiently.
02-09-2018, 03:08 PM
#18
12 Second Club
Thread Starter
I'll throw it out there- incomplete fuel burn not helping things (?)
What are your mods? i.e. head size, more about the cam (duration/lift/valve events), injector size, verified fuel pressure, approx. compression ratio, what plugs and what's the gap?
One thought is plug heat range too cold and gap too small contributing to incomplete fuel burn, which won't be cured anywhere with trying to lean out the fuel. You just burn less in certain areas with the same inefficiency. If your SCR is less than say 11.2:1 you may as well just run heat range 5 TR55 NGK plugs and gap them only slightly narrower than the stock .050, like maybe .045. Then maybe add a little fuel back where the engine likes it and burn it more efficiently.
What are your mods? i.e. head size, more about the cam (duration/lift/valve events), injector size, verified fuel pressure, approx. compression ratio, what plugs and what's the gap?
One thought is plug heat range too cold and gap too small contributing to incomplete fuel burn, which won't be cured anywhere with trying to lean out the fuel. You just burn less in certain areas with the same inefficiency. If your SCR is less than say 11.2:1 you may as well just run heat range 5 TR55 NGK plugs and gap them only slightly narrower than the stock .050, like maybe .045. Then maybe add a little fuel back where the engine likes it and burn it more efficiently.
02-09-2018, 03:20 PM
#19
12 Second Club
Thread Starter
02-09-2018, 03:55 PM
#20
Blind guess you're in the 10.8:1 ballpark, low 500s lift on your 1.7s. I don't see injector size or measured fuel pressure and what your injector offset is. Cam seems fine for stock heads for the amount of air it wants, though port velocity is going to be a bit on the low side. If stock 24# injectors with factory injector offsets at 39-43psi of fuel I'd expect you to be just a hair lean and combustion temps to be higher, and exhaust temps higher at the collector (~550-600* at idle, fully warmed up). If you've gone bigger on the injectors or higher on the pressure or lengthened the pulse width those are going to be contributors with your current setup.