Unexplainable lean condition
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Unexplainable lean condition
I’m still tracking down the cause of a code 41 lean condition in my 88 f250 with a 460. It has an ATK short block with rebuilt factory heads. It is supposed to have 10:1 compression which is higher than stock. It has headers and true dual exhaust without cats. The o2 sensor is new and is in the passenger side header collector. I can’t seem to find why its still running lean. It has good fuel pressure and I turned it up a little with an adjustable fuel pressure regulator. I don’t know if its because of the higher compression ratio or not. I only run 91 octane fuel. It doesn’t really have any other mods other than the high compression pistons, headers, and exhaust. What else could I do to remedy this? The CEL doesn’t come on until I’ve driven it awhile and it gets warmed up. Also it is worse in warmer weather.
Tuned
Joined: Sep 2014
Posts: 358
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From: Ky
Is it possible that the oxygen sensor is in a dead spot or similar, or that having it on one pipe serving 4 cylinders, with now less back pressure due to true duel exhaust and no cat, flow past sensor now fast/not as rich?
Just a thought.
Just a thought.
New User
Joined: May 2018
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Same thing happened on my sons 95" F150. It was the fuel filter. The fuel pressure was good while at idle, but as soon as he would drive down the road he would get engine light. The code was for being too lean. He changed the filter and whala.
Cargo Master
Joined: Mar 2010
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From: Laramie, WY
This, and failing pumps, are why I advocate testing fuel pressure under load. No-load test isn't worth much in my experience.
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That is a good thought. I wonder if it would be better off in an h pipe. I will research. Thank you!
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I tested it at the fuel rail at idle. I revved it up a little but didn't test it under load so that might be the next step. I also haven't pulled the plugs yet so I will do that and see!
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I never thought of this so I think it will be worth my time to test it under load. It would make good sense. Thank you!
FTE Legend
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From: Ottawa, Ontario
Originally Posted by TobaccoBarn
Is it possible that the oxygen sensor is in a dead spot or similar, or that having it on one pipe serving 4 cylinders, with now less back pressure due to true duel exhaust and no cat, flow past sensor now fast/not as rich? Just a thought.
No to both of those thoughts. A single sensor is not better off in an H pipe.. that could put it in a dead spot. Your current sensor location is perfectly fine, this isn't your problem.
Mountain Pass
Joined: Jun 2013
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This may sound weird, but....
A buddy of mine just tried to track down a similar lean condition for months, replaced o2 sensor, etc..
The problem ended up being the 02 sensor harness. At some point, the plastic clip broke and enabled someone to plug in the o2 sensor upside down, so none of the proper pins were lined up. Check the voltage at the harness for the appropriate leads.
A buddy of mine just tried to track down a similar lean condition for months, replaced o2 sensor, etc..
The problem ended up being the 02 sensor harness. At some point, the plastic clip broke and enabled someone to plug in the o2 sensor upside down, so none of the proper pins were lined up. Check the voltage at the harness for the appropriate leads.
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