Lean Mixture - Trouble Codes

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Jul 5, 2004 | 12:34 AM

jvaski

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Lean Mixture - Trouble Codes ??

Whenever I take my 98' F150 5.4 liter truck to lower altitude - I get the check engine lite and trouble codes for lean mixture banks 1 & 2. ( upon returning to altitude) ( I live at 6000ft elevation )
The trouble codes only trigger after I leave altitude - and trigger upon return & pulling a steep hill. MAF tests fine and is clean. Fuel filter is new. IAT is clean and tests fine.
Anyone else have the same problem, or know what might cause this ?

Last edited by jvaski; Jul 5, 2004 at 01:03 AM.

Jul 5, 2004 | 11:18 PM

Racerguy

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Hi jvaski and welcome to the forum

I haven't seen that problem before so I'll just have guess here.
I think you have a MAF problem. It might not set a code but still could have a problem. If you could monitor live data you might find it.
For some interesting reading that might apply take a look at http://www.v8sho.com/SHO/TSB982310Ma...tamination.htm and notice where it talks about BARO.

Jul 5, 2004 | 11:54 PM

jvaski

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Lean Mixture codes

Racerguy - Thanks very much for the reply and the excellent reading on the problem I'm having !
I'm taking my real-time scanner with me the next trip off the hill to watch for the problem. The writeup aslo said to try WOT a few times to reset BARO .
I'll give it a shot . Then maybe it's time to try replacing the MAF or looking for contamination.
Thanks again - you've been a great help !
John A

Jul 5, 2004 | 11:57 PM

Racerguy

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Please let us know what you find.
I'm curious about this one too.

Jul 18, 2004 | 01:13 AM

jvaski

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Lean Mixture trouble codes

Dave, Thanks for the Tech page on MAF sensors and BARO .
I ran a test at idle for Long Term Fuel TRIM and found the MAF sensor was beyond -12 which indicated contamination . I pulled the MAF sensor and used a Q-tip with Chemtool carb cleaner to gently clean the wires . The MAF sensor is now operating in normal range. I will let you know if it also cured the lean mixture codes when I change altitude .
Thanks again for the help. !
John

Jul 18, 2004 | 10:23 AM

Racerguy

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It sounds like you're on the right track there.
We had a MAF problem on one at work the other day. It ended up being that the rubber grommet where the MAF wires go into the air fliter housing was out of it's hole and allowing unmetered air in. It was a simple problem but took a while to find.

Jul 18, 2004 | 12:39 PM

blueharley

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I have a 98 4.6 and have had the same problem. I clear the code and it does fine for a while then get the light. No vacum or manifold leaks so waiting for something to hard fail. Where I live we use the oxygenated gas Oct thruough Mar and that is when I started having the problem. Have not had the light since we switched back to regular fuel.