WHY does a car run rich after header install?
#1
TECH Fanatic
Thread Starter
iTrader: (35)
Join Date: Sep 2004
Location: Maryland/Illinois
Posts: 1,660
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
I put header and ory on my car not long ago and I am sure the thing is running to rich. My bud could smell it driving behind me, and in a small garage my eyes will start to sting. I know tuning will take care of that, I am just wondering why it runs so rich. I thought the factory tune could/should compensate for small mods that get more air into the engine. Or is it likely my relocated and/or bad O2 sensors?
#3
11 Second Club
iTrader: (5)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Originally Posted by bowtieman81
I put header and ory on my car not long ago and I am sure the thing is running to rich. My bud could smell it driving behind me, and in a small garage my eyes will start to sting. I know tuning will take care of that, I am just wondering why it runs so rich. I thought the factory tune could/should compensate for small mods that get more air into the engine. Or is it likely my relocated and/or bad O2 sensors?
It's mainly because you took your cats off, as I see you are running an off road y-pipe. The cats were there to burn the excess gas and now they are not. I wouldn't be worried about it.
Originally Posted by bowtieman81
I thought the factory tune could/should compensate for small mods that get more air into the engine.
![Huh](https://ls1tech.com/forums/images/smilies/LS1Tech/huh.gif)
#5
Kleeborp the Moderator™
iTrader: (11)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
I thought I read somewhere that headers actually make your car run leaner. Because of that, the computer tries to compensate by dumping in extra fuel, making the LTrims positive. When you go WOT, and the LTrims are positive, it just dumps in fuel indiscriminately since it goes into open loop.
I probably have that all screwed up, but it makes sense to me.
I probably have that all screwed up, but it makes sense to me.
#6
TECH Fanatic
Thread Starter
iTrader: (35)
Join Date: Sep 2004
Location: Maryland/Illinois
Posts: 1,660
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Originally Posted by MeentSS02
I thought I read somewhere that headers actually make your car run leaner. Because of that, the computer tries to compensate by dumping in extra fuel, making the LTrims positive. When you go WOT, and the LTrims are positive, it just dumps in fuel indiscriminately since it goes into open loop.
I probably have that all screwed up, but it makes sense to me.
I probably have that all screwed up, but it makes sense to me.
Well, I did a couple logging runs at WOT and the O2 sensors were reading a rich condtion the whole way. That might make sense. I have been trying to figure out why it seems to be rich at idle too. Maybe I am idling in open loop for some reason (besides the open loop warm-up period). I will have to take a couple logs at idler and see. Thanks all.
Trending Topics
#8
Launching!
iTrader: (3)
Join Date: Nov 2004
Location: Fairmont, WV
Posts: 299
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
MeentSS02 is correct. Take a carb engine. If you put headers on it and do not rejet you will be lean and depending on your A/F ratio before hand you may be ok or in the danger zone. With a computer controlled car the computer try's to reset the fuel system based on sensor info. Yes if the ltrims are positive that means fuel is being added and you are lean to begin with. If negative then you are rich and fuel is being pulled. So depending on the state of the stock tune will depend if you will have to be mega enriched with fuel or just slightly enriched. I put headers on about 3 weeks ago. My Ltrims are in the +10 range at idle and WOT. I have very little odor. It was worse when I first did the install but now if I am running the car hard or in a lower gear and let the engine pull itself down it will have some odor. Hope that clears it up alittle.
#9
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,604
Likes: 0
Received 6 Likes
on
6 Posts
![](https://ls1tech.com/forums/images/ranks/ls1tech20year.png)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
There are two separate effects.
One is the exhaust extraction, improved scavenging cleans
out the cylinder leaving less spent (neutral) gasses and a
fresher charge on intake is the result. People used to say
headers leaned you out though I suspect this was really
more about pinging from a better charge, which burns
faster.
The other is, headers cool the exhaust gas more (surface
area) and locate the O2s further downstream. A cold O2
that went to sleep looks like a lean O2. So the PCM throws
fuel at the problem.
One is the exhaust extraction, improved scavenging cleans
out the cylinder leaving less spent (neutral) gasses and a
fresher charge on intake is the result. People used to say
headers leaned you out though I suspect this was really
more about pinging from a better charge, which burns
faster.
The other is, headers cool the exhaust gas more (surface
area) and locate the O2s further downstream. A cold O2
that went to sleep looks like a lean O2. So the PCM throws
fuel at the problem.
#10
TECH Resident
iTrader: (4)
Join Date: Nov 2004
Location: Nashville, TN
Posts: 879
Likes: 0
Received 0 Likes
on
0 Posts
![](https://ls1tech.com/forums/images/ranks/ls1tech10year.png)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Originally Posted by bowtieman81
Well, I did a couple logging runs at WOT and the O2 sensors were reading a rich condtion the whole way. That might make sense. I have been trying to figure out why it seems to be rich at idle too. Maybe I am idling in open loop for some reason (besides the open loop warm-up period). I will have to take a couple logs at idler and see. Thanks all.
Jason