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5.4 running lean

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Old 12-31-2012, 09:53 PM
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5.4 running lean

I've got a '97 F150 with a 5.4.

The truck started throwing a lean code. Checked the fuel pressure and it was low so I replaced the filter and got 2# back. Not enough so I put a new fuel pump in her.

Now she's throwing lean codes on both banks. Clear the codes, drive the truck for 20 to 30 minutes and the codes return. Run diagnostics while driving and the short and long trim voltages on both banks look normal.

So what's next?


Thanks,
Bass
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Old 01-01-2013, 08:18 AM
projectSHO89 projectSHO89 is offline
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Vacuum leaks. Check/clean MAF.

If the fuel trims were normal, it wouldn't be setting fault codes for the mixture.
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Old 01-01-2013, 09:30 AM
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Thanks. Already checked for vacuum leaks and found none. MAF was next on my list so glad to hear someone back that up....
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Old 01-02-2013, 10:47 PM
4x41977 4x41977 is offline
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Mine threw codes saying it was running lean Nd looked all over for a vacuum leak. Someone on here told mme to clean the MAF sensor and that's all it was. They make a spray for cleaning it. Have been told only to use that and not cleaners such as brake cleaner.
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Old 01-03-2013, 09:05 AM
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Haven't had a chance to pull the MAF sensor yet. Probably this weekend.

The sensor's pretty delicate and costic cleaners would likely damage it, or even leave a deposit on it.
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Old 01-03-2013, 12:42 PM
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Brake cleaner and MAF cleaners work good. Carb cleaner leaves a film. Just spray the filaments, don't touch. Also check the PCV hose elbows front and rear. The rear one tends to get overly soft and cracks.
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Old 01-03-2013, 01:03 PM
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I've always heard to stay away from brake cleaner. No matter though as I've got MAF cleaner and electrical component cleaner on the shelf.

I'm thinking that this won't solve it though. The truck also is a bit hard to start. When the truck is cold, you have to engage the starter for 1.5 - 2 seconds.
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Old 01-04-2013, 08:46 AM
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Just asking a question here...............

Assuming the new pump gives acceptable pressure readings at the test point could this condition be related to worn injectors?

I don't know enough about these systems so forgive me if this is a foolish question!
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Old 01-07-2013, 08:42 AM
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Did cleaning it help?
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Old 01-07-2013, 08:46 AM
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It rained all weekend so I didn't get a chance to do it. Covered space at the house is at a premium.

Still on the radar for ASAP.
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Old 01-22-2013, 05:29 PM
HjalmarOrn HjalmarOrn is offline
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q

Have you cleaned the MAF sensor yet?
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Old 02-01-2013, 02:08 PM
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Sorry for not getting back. The truck's been parked while I worked on other stuff.

Cleaned the MAF sensor, no change. After clearing the codes, the truck runs for about 20 minutes before the Check Engine light comes back on. 20 minutes continuous, two ten-minute trips, with or without complete cooling between trips. 20 minutes.

Both left bank lean and right bank lean are being thrown. Both of the O2 sensor's voltages/patterns look normal and regular on the graph.


~Bass
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