What other than vacuum causes a lean condition?
09-11-2009, 08:40 PM
#1
Senior Member
Thread Starter
iTrader: (1)
Join Date: Aug 2002
Location: Tennessee
Posts: 529
Likes: 0
Received 1 Like
on
1 Post
Car: 1988 IROC
Engine: L98
Transmission: 700R4 Silver Dart
Axle/Gears: 3.70 posi
What other than vacuum causes a lean condition?
1988 IROC Z 5.7 TPI Auto 2.77 stock engine and exhaust manifolds
It has always stumbled a little on startup but after a couple of seconds it runs fine
Idle is at 900
Timing is 6* BTDC
I have an Autometer air fuel ratio guage installed, at cruising speed it bounces between the bottom lean LED and middle of Stoich LED, at wide open throttle it will go lean off the scale (no lights) and about halfway through the powerband it will creep into the last Stoich light before rich.
It doesn't knock. I thought it was supposed to go deep into the rich range at WOT.
- no codes present
- It failed emissions once in January, I did nothing other than change the oil and then it passed.
- new EGR valve and it was an AC Delco exact replacement
- I have checked my vacuum lines several times and all have been replaced
- All my gaskets are new from intake at the egine to the top of the TPI
- Flowmatched stock injectors from Fuel injector connection
- tune up is getting close to two years old but the past year the car has not been on the road much as I was fixing other stuff.
- IAC is clean, throttle body cleaned, and TPS checked for correct voltage
- CTS for the computer is new
Basically I have slowly replaced most everything that could be replaced on this thing as it was a daily driver before my son was born
I am going top try and run through everything possible again this weekend.
Any ideas as to why it would run lean and what I should add to my checklist?
TIA
It has always stumbled a little on startup but after a couple of seconds it runs fine
Idle is at 900
Timing is 6* BTDC
I have an Autometer air fuel ratio guage installed, at cruising speed it bounces between the bottom lean LED and middle of Stoich LED, at wide open throttle it will go lean off the scale (no lights) and about halfway through the powerband it will creep into the last Stoich light before rich.
It doesn't knock. I thought it was supposed to go deep into the rich range at WOT.
- no codes present
- It failed emissions once in January, I did nothing other than change the oil and then it passed.
- new EGR valve and it was an AC Delco exact replacement
- I have checked my vacuum lines several times and all have been replaced
- All my gaskets are new from intake at the egine to the top of the TPI
- Flowmatched stock injectors from Fuel injector connection
- tune up is getting close to two years old but the past year the car has not been on the road much as I was fixing other stuff.
- IAC is clean, throttle body cleaned, and TPS checked for correct voltage
- CTS for the computer is new
Basically I have slowly replaced most everything that could be replaced on this thing as it was a daily driver before my son was born
I am going top try and run through everything possible again this weekend.
Any ideas as to why it would run lean and what I should add to my checklist?
TIA
09-11-2009, 11:12 PM
#2
Senior Member
iTrader: (1)
Join Date: Jul 2007
Location: MA
Posts: 1,141
Likes: 0
Received 2 Likes
on
2 Posts
Car: '87 IROC/'68 SS
Engine: 5.7L/350
Transmission: 700R4/Muncie 4-spd
Axle/Gears: 3.27 9 bolt / 3.31 12 bolt
Re: What other than vacuum causes a lean condition?
If it's connected to the stock narrow band O2 sensor, it's really not worth worrying about (or looking at for that matter).
09-12-2009, 01:13 PM
#3
Senior Member
Thread Starter
iTrader: (1)
Join Date: Aug 2002
Location: Tennessee
Posts: 529
Likes: 0
Received 1 Like
on
1 Post
Car: 1988 IROC
Engine: L98
Transmission: 700R4 Silver Dart
Axle/Gears: 3.70 posi
Re: What other than vacuum causes a lean condition?
Anyone know what voltmeter readings I should get from a good O2 sensor through the power band?
09-12-2009, 01:56 PM
#4
Junior Member
Join Date: Sep 2008
Location: Jackson, MI
Posts: 95
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Pontiac Firebird
Engine: 3.1L V6
Transmission: 700R4
Axle/Gears: 3.23
Re: What other than vacuum causes a lean condition?
Standard "narrow band" O2 sensors operate between 0 and 1 volts, and are only capable of accurately measuring a stoichiometric air/fuel ratio (e.g. 14.7:1). A richer or leaner condition results in an abrupt voltage change and thus is only useful for qualitative determination.
09-12-2009, 08:12 PM
#5
Senior Member
Thread Starter
iTrader: (1)
Join Date: Aug 2002
Location: Tennessee
Posts: 529
Likes: 0
Received 1 Like
on
1 Post
Car: 1988 IROC
Engine: L98
Transmission: 700R4 Silver Dart
Axle/Gears: 3.70 posi
Re: What other than vacuum causes a lean condition?
I understand that my guage is more a coarse information tool. But what my guage is saying matches the seat of the pants feel and the nose test on my exhaust.
Any other reasons that cause a lean condition? Something you normally would not look for. I am well versed on my car and the up and downs of my equipment.
Any other reasons that cause a lean condition? Something you normally would not look for. I am well versed on my car and the up and downs of my equipment.
Thread
Thread Starter
Forum
Replies
Last Post
