Code 45: Rich air/fuel mixture - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 07-05-2007, 09:03 AM
scrot's Avatar
Registered User
 
Last photo:
Join Date: Apr 2006
Location: In front computer
Posts: 449
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Code 45: Rich air/fuel mixture

Hello, I have an '87 Olds Cutlass 2.5L that sometimes runs very rough only when it's first started, and only in the morning when it's cooler. Not every time, but sometimes.
I've checked the obvious like vacuum leaks and loose spark plug wires, but those problems would make it run bad all of the time.
I thought about a sticking EGR valve, but I think that would be a problem more than what it is.
The manual says code 45 is a rich a/f mixture. It also says it could be the O2 sensor, but I thought the O2 sensor isn't used right after start-up.

Doesn't the car stay in "open loop" until the O2 sensor heats up?

I believe the computer ignores the sensor input and refers back to it's memory for the fuel mixture and timing.
I'm thinking it could be a bad coolant temp sensor.
I believe if it is bad, it will tell the computer the engine is colder than it is, and the computer richens the mixture.
I don't get any trouble codes for the coolant sensor however.

What do you think?
Thanks.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-05-2007, 11:52 AM
Deuce's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Choosing a trailer
Last journal entry: Jan 13 2013
Last photo:
Join Date: Aug 2002
Location: Deuceland USA
Age: 66
Posts: 5,657
Wiki Edits: 6

Thanks: 0
Thanked 9 Times in 9 Posts
I am moving this to the engine area ... hopefully where it will be viewed by a few engine techs ... BUT ... I had the same problem with a 90 Silverado with a 350 and I changed the temperature sensor at the thermostat housing and the problem went away ...

The sensor was giving false readings to the computer.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-05-2007, 01:07 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 6,682
Wiki Edits: 0

Thanks: 3
Thanked 403 Times in 348 Posts
Quote:
Originally Posted by scrot
Hello, I have an '87 Olds Cutlass 2.5L that sometimes runs very rough only when it's first started, and only in the morning when it's cooler. Not every time, but sometimes.
I've checked the obvious like vacuum leaks and loose spark plug wires, but those problems would make it run bad all of the time.
I thought about a sticking EGR valve, but I think that would be a problem more than what it is.
The manual says code 45 is a rich a/f mixture. It also says it could be the O2 sensor, but I thought the O2 sensor isn't used right after start-up.

Doesn't the car stay in "open loop" until the O2 sensor heats up?

I believe the computer ignores the sensor input and refers back to it's memory for the fuel mixture and timing.
I'm thinking it could be a bad coolant temp sensor.
I believe if it is bad, it will tell the computer the engine is colder than it is, and the computer richens the mixture.
I don't get any trouble codes for the coolant sensor however.

What do you think?
Thanks.
It could be a defective thermostat that keeps the engine too cool. It should come out of cold start at 176 degrees. The computer is also doing a time check so it'll look at the mixture at a point after start up where the engineers had established that the engine should be warm enough to suspend "choke" and go into closed loop.

I doubt this is an EGR problem, which usually causes the engine to fall lean when it fails.

It could be a fuel system pressure problem caused by the regulator. Higher pressure will result in a richer mixture.

A leak in the exhaust ahead of the O2 sensor will cause the sensor to drive the computer to richen the mixture.

A faulty O2 sensor, damn there hard to take out, rust being what it is!

If this problem is real, you should see a reduction in fuel economy. In my Franken Mouse powered S-15, I watch every tank full because I have flex couplings in the exhaust ahead of the O2 sensors and they are a known leakage point, when mileage takes a 3-5 miles per gallon drop, I know it's time to replace them.

Bogie
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-05-2007, 01:53 PM
scrot's Avatar
Registered User
 
Last photo:
Join Date: Apr 2006
Location: In front computer
Posts: 449
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
OK, thanks for the replies.
It happens imediately after starting up, so I know it's not the thermostat.
I don't have a flex coupling. Even if I did, the O2 sensor isn't an input to the computer at this time, Correct?
I'm going to check/replace the coolant temp sensor.
I imagine it could also be a sticking idle air control motor.
Any others suggestions?
Thanks.

Last edited by scrot; 07-05-2007 at 03:30 PM.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-05-2007, 01:57 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 56
Posts: 5,084
Wiki Edits: 26

Thanks: 7
Thanked 100 Times in 86 Posts
I would check the O2 to see if it working, check the temperature sensor that talks to the computer, and the Idle air control in that order.
It could also be the MAF or MAP depending on what type of system it has.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-05-2007, 03:19 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 6,682
Wiki Edits: 0

Thanks: 3
Thanked 403 Times in 348 Posts
Quote:
Originally Posted by scrot
OK, thanks for the replies.
It happens imediately after starting up, so I know it's not the thermostat.
I don't have a flex coupling. Even if I did, the O2 sensor isn't an input to the computer, Correct?
I'm going to check/replace the coolant temp sensor.
I imagine it could also be a sticking idle air control motor.
Any others suggestions?
Thanks.
Yes the O2 sensor is an input to the computer, however, it's supposed to be held out till the engine hits 176 degrees F at which point it should go into closed loop operation. But there's also a timer circuit that assumes the engine is warm after a certain period of time that will attempt to put the engine into closed loop regardless of the temp sensor.

The O2 sensor is the device that determines and sends a signal to the CE light by way of the computer if it senses a rich mixture. It should have enough authority to step the mixture leaner, but if it can't it sets code 45 which means it's maxed out.

The question is not only why is the mixture rich but why are you getting a code when the O2 sensor should be ignored by the computer. Assuming the computer hasn't gone south, one has to consider the problem is either a sensor is out of whack, a connector or wire is having problems.

The IAC could be out of adjustment, but the MAP sensor should pick that out as a disparity between idle speed and manifold vacuum.

A failure of the temp sender in the hot position would make the computer think the engine was warm when it wasn't and it would be in closed loop at start up but the engine would show lean characteristics when it was cold, i.e. backfire.

Where I think a good possibility is that a failure of the sensor in the cold position would cause the computer to fuel the engine in "choke" for a rich start up mixture. In addition to the temp sensor, there is a time out circuit for the O2 sensor and if the computer counts down and goes to closed loop, but the engine temp sensor is reading cold, the "choke" condition would prevail into the closed loop function at least long enough to get a code. In that case the O2 sensor would try to lean out the mixture, but since it's still in cold start mode on injector timing, I doubt the O2 has enough command authority to lean the mixture enough for it not to be rich. At that point the computer seeing a continuously rich mixture would set code 45. One has to keep in mind that the O2 sensor is simply a little clean up circuit, in cruise and under certain conditions, it trys to keep the mixture chemically correct for efficient burn, but it's very limited in what it really can do. The engine would act similarly if the cam was falling out of time, the ignition was out of time, a spark plug wasn't firing, or an exhaust valve was burnt. So these conditions also need to be checked out as they would either allow excess unburnt fuel to pass through.

My reference to an exhaust leak ahead of the O2 sensor is to mean that a failure of an exhaust gasket, a loose or holed manifold/pipe would add air in the exhaust which would cause the O2 sensor to correct by richening the mixture, while this usually doesn't set a code, you'll see fuel economy decrease. The same can be said for a leak into the intake side. This also will add excessive air to which the O2 sensor will attempt to correct with more fuel. Again these usually don't cause a code, but mileage suffers. None of these conditions occurring in a carbureted engine would cause a carb to correct the situation so this is new and unique to EFI motors.

Lastly you can't rule out a failure of the O2 sensor, though this usually shows as a specific code. But I've been involved in electronic systems self diagnoses for many years and if one thing is true in complex systems, its each component points to another when a failure occurs (kind of like kids getting into trouble), so the code shown isn't always what the real problem is.

Bogie
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-05-2007, 03:52 PM
scrot's Avatar
Registered User
 
Last photo:
Join Date: Apr 2006
Location: In front computer
Posts: 449
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
OK. Thanks a lot people, and oldbogie. I'll just go ahead and replace the coolant temp sensor and see what happens. It's less than $20.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-10-2007, 05:35 PM
scrot's Avatar
Registered User
 
Last photo:
Join Date: Apr 2006
Location: In front computer
Posts: 449
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Update

I took a shot in the dark and replaced the coolant temp sensor since it's cheap and easy to replace and I believe it's an important sensor. Unfortunately, it didn't change anything. No biggie. It didn't work, but at least I now have a fresh sensor (and a spare) that should last for the life of the car.
I then spent some time looking thru the manual, looking for other possibilities such as the suggested MAP SENSOR, and MANIFOLD TEMP SENSOR.
I went under the hood and decided to remove the EGR valve to check for it sticking open. It was ok, so I cleaned and lubed the shaft with anti seize and reinstalled..
I then jumped the fuel pump relay to pressurize the system without the engine running to look for a leaking TBI injector.
There it was!

The TBI fuel pressure regulator, which is mounted up near the TBI injector, was leaking gas around the diaphragm.
It made the area wet with gas inside the air cleaner, causing the vapors to be sucked into the engine.
I bought a new one ($25). The new diaphragm is a little thicker around the circumference, which I believe is a design change to fix this problem. In the TBI housing the diaphragm is sealed by sandwiching it between a groove in the housing and the stamped dome that is screwed to the TBI.
I installed it and briefly checked, and it's as dry as a
This should fix the symptoms. I'll see in the next few days.
Thanks for everyone for the help.

Last edited by scrot; 07-10-2007 at 05:49 PM.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
this is a saver.... GM build codes TooMany2count General Rodding Tech 24 11-23-2009 09:36 AM
paint code please ( or mixture ) 4x4x4COPPER Body - Exterior 4 11-30-2007 01:56 PM
Air/Fuel mixture and performance orian Engine 13 01-16-2005 09:24 AM
Air/Fuel mixture and performance orian Introduce Yourself 1 01-15-2005 04:32 PM
air/fuel mixture???? FenderGitars Engine 6 08-28-2004 07:59 PM


All times are GMT -6. The time now is 01:15 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.