Lean Mixture Code
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Lean Mixture Code
All;
Changed the exhaust last summer to a Banks Power-Pack, including K&N air filter, removed the venturis from the intake plumbing, new 02 sensor etc. This is on an '88 F-250 SC 4x4 460ci.
Am having poor mileage (dropped from 10± to 8±) and a check engine light occasionally, code reads lean mixture, often after a long downhill. The mixture appears rich as there is carbon in the tailpipe, it was cleaner prior to installation of the Banks exhaust, with lighter colored deposits. I assume since the system is flowing more air, and is cooler, that somehow the computer believes the mixture is lean and is making the mixture richer, causing the lower mileage.
Any ideas how to fool the computer or if my assumption is correct?
Thanks, Paul
Changed the exhaust last summer to a Banks Power-Pack, including K&N air filter, removed the venturis from the intake plumbing, new 02 sensor etc. This is on an '88 F-250 SC 4x4 460ci.
Am having poor mileage (dropped from 10± to 8±) and a check engine light occasionally, code reads lean mixture, often after a long downhill. The mixture appears rich as there is carbon in the tailpipe, it was cleaner prior to installation of the Banks exhaust, with lighter colored deposits. I assume since the system is flowing more air, and is cooler, that somehow the computer believes the mixture is lean and is making the mixture richer, causing the lower mileage.
Any ideas how to fool the computer or if my assumption is correct?
Thanks, Paul
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From: Connecticut
Lean Mixture Code
Where did you purchase your oxygen sensor? Some of the aftermarket sensors cause problems. I've seen this occur on my vehicle. I was getting lean codes along with intermittent rough idling. Try the original one if you still have it or get one from Ford.
Mark
Mark
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Lean Mixture Code
So I changed the O2 sensor, no joy. Was wondering if maybe the fuel pressure regulator could be changed out for an adjustable, and if increasing/decreasing the fuel pressure would satisfy the computer? I still think the computer is fooled with the "lean mixture" code, and it's rich, based on exhaust.
Thanks in advance for any ideas.
Paul
Thanks in advance for any ideas.
Paul
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From: Canton, OH
Lean Mixture Code
Although I haven't made the purchase myself, you're in line for a new computer chip from JET Performance. With the mods you've already done the new chip will be set for a less restrictive exhaust and more in air flow.
Take ya for $300. Should solve all problems, though.
Take ya for $300. Should solve all problems, though.
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From: Connecticut
Lean Mixture Code
I believe your vehicle is the "speed density" type control system. They are not very friendly when modifying an engine. "Mass air" is more modification friendly. Your modifications do not seem too severe, but you may have altered the system enough to bring the air fuel ratio out of range. Did the new exhaust relocate the position of the O2 sensor? Do you have any exhaust leaks before the O2 sensor? Any intake leaks? You really need to find out the cause for the lean code before making other changes as you will only introduce more variables. Sounds like the ECM thinks the mixture is lean but it's actually rich. Do you have access to a scan tool? If so, you can monitor the sensor outputs while driving. Also check the fuel pressure to see if it's in spec. with and without the pressure regulator's vacuum hose connected. Turn vehicle off, make sure it holds pressure for a minute or more.
Mark
Mark
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Lean Mixture Code
Paul
I have had similar problems with my speed Density computer, I went a little further than you by putting in larger valves, roller rockers and porting late model heads before i had any problems. Are you still running a cat, it shouldn't make a difference, since 460 computers are coded for motor homes so the o2 sensor is self heated. it sounds like Mark might be on the right track, a vacume leak or something of that nature would get the same result.
I have run w/o cat w/ headers/ K&N and no chip with great success for past two years. You might want to consider converting to mass air, especially if you want to run another cam or bump up your compression with some pistons. Ill let you know how that works if your interested, im in the process of doing it.
I have had similar problems with my speed Density computer, I went a little further than you by putting in larger valves, roller rockers and porting late model heads before i had any problems. Are you still running a cat, it shouldn't make a difference, since 460 computers are coded for motor homes so the o2 sensor is self heated. it sounds like Mark might be on the right track, a vacume leak or something of that nature would get the same result.
I have run w/o cat w/ headers/ K&N and no chip with great success for past two years. You might want to consider converting to mass air, especially if you want to run another cam or bump up your compression with some pistons. Ill let you know how that works if your interested, im in the process of doing it.
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Lean Mixture Code
Thanks for all the replies.
I searched for exhaust leaks, found a slight one at one of the joints between the long tube headers and Y pipe, fixed that one, problem still occurs.
Found a leak at the grommet for the PCV valve, and replaced the grommet, haven't driven it enough to see if that was enough of a vacuum leak to solve the problem. Does anyone know of a good way to look for vacuum leaks? I know how to soap test for pressure leaks, but know of no simple way to test for vacuum leaks.
The cat is still in the vehicle, Washington State visually inspects for the cat, so I could get a high flow cat, but prefer not to spend that kind of money for the minimal performance gain with a stock engine (other than the headers and cat-back).
Am a bit hesitant to do anything with a cam or other mods with the computer, I've heard that the computer thinks the rough idle is a problem, and it causes other driveability problems too. Any experience with that?
Would appreciate hearing from anyone who has replaced the system with a MAF system.
Thanks again,
Paul
I searched for exhaust leaks, found a slight one at one of the joints between the long tube headers and Y pipe, fixed that one, problem still occurs.
Found a leak at the grommet for the PCV valve, and replaced the grommet, haven't driven it enough to see if that was enough of a vacuum leak to solve the problem. Does anyone know of a good way to look for vacuum leaks? I know how to soap test for pressure leaks, but know of no simple way to test for vacuum leaks.
The cat is still in the vehicle, Washington State visually inspects for the cat, so I could get a high flow cat, but prefer not to spend that kind of money for the minimal performance gain with a stock engine (other than the headers and cat-back).
Am a bit hesitant to do anything with a cam or other mods with the computer, I've heard that the computer thinks the rough idle is a problem, and it causes other driveability problems too. Any experience with that?
Would appreciate hearing from anyone who has replaced the system with a MAF system.
Thanks again,
Paul
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Lean Mixture Code
I use a cheap little vacume gauge I bought at the hardware store, just plug in a vacume line and read the reading, pretty simple...helped me track down a upper intake manifold leak I had when I ported my intakes and heads, heh whoops...next time use more orange goopy pcv!
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Lean Mixture Code
WARNING! THE FOLLOWING SUGGESTION CAN BE VERY DANGEROUS! DO AT YOUR OWN RISK!
Ok, now that I've warned you, this is how I detect intake vacuum leaks.
Get out your propane torch and open the valve slightly, but do not ignite the gas. Run the engine and pass the tip of the torch (where the gas is coming out) along any area you think may be leaking. The engine idle speeds up when you pass the torch across the leak due to the extra "fuel" you are providing.
A slightly safer way is to use carb cleaner and spray the hell out of the intake, but i think that just makes a mess.
Don't do it if the engine is very hot or anywhere near an exhaust manifold. It may not work if the area you work in is very windy.
Be careful.
Randy
Ok, now that I've warned you, this is how I detect intake vacuum leaks.
Get out your propane torch and open the valve slightly, but do not ignite the gas. Run the engine and pass the tip of the torch (where the gas is coming out) along any area you think may be leaking. The engine idle speeds up when you pass the torch across the leak due to the extra "fuel" you are providing.
A slightly safer way is to use carb cleaner and spray the hell out of the intake, but i think that just makes a mess.
Don't do it if the engine is very hot or anywhere near an exhaust manifold. It may not work if the area you work in is very windy.
Be careful.
Randy
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Lean Mixture Code
I've always used WD-40 to locate vacuum leaks, much as described above.
I would pay particular attention to the vacuum line that runs to your MAP sensor. I knocked mine off installing my Banks Power Pack... had the computer thinking I had atmospheric pressure in the intake manifold... it could not get enough fuel in there for that... first a lean code... then it would put the computer into limp mode. Milage wasn't very good in limp mode... but, I didn't check it. Reconnected the vac line and the problem went away.
A small leak in that line could throw your milage off as you describe... or, for that matter a defective MAP sensor could do the same.
Hope this helps.
Perry
I would pay particular attention to the vacuum line that runs to your MAP sensor. I knocked mine off installing my Banks Power Pack... had the computer thinking I had atmospheric pressure in the intake manifold... it could not get enough fuel in there for that... first a lean code... then it would put the computer into limp mode. Milage wasn't very good in limp mode... but, I didn't check it. Reconnected the vac line and the problem went away.
A small leak in that line could throw your milage off as you describe... or, for that matter a defective MAP sensor could do the same.
Hope this helps.
Perry
