Fuel Trim
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Joined: Mar 2011
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Fuel Trim
I've posted a couple of times about a lean running 5.4. I've got a bunch more information so I'm starting a new thread keying on the problem.
When I start the truck, the Short Trim on both banks behaves reasonably. Mild variation from about -2% to +2%. The Long Trim immediately goes to +25%. Revving the engine to about 1,700RPM reduces the LT to about 12%, but it immediately shoots back up to 25%.
After a few minutes, both banks throw lean codes and the Check Engine light comes on.
This started more than a year ago when the O2 sensor on the right bank failed. The sensor was replaced and all was normal for a couple of months. Then the lean codes started showing up.
I've replaced the fuel pump, filter, and fuel pressure regulator, yet the problem persists.
Any 5.4 guys out there with an idea, I'm all ears. I'm out of ideas.
Thanks,
~Bass
When I start the truck, the Short Trim on both banks behaves reasonably. Mild variation from about -2% to +2%. The Long Trim immediately goes to +25%. Revving the engine to about 1,700RPM reduces the LT to about 12%, but it immediately shoots back up to 25%.
After a few minutes, both banks throw lean codes and the Check Engine light comes on.
This started more than a year ago when the O2 sensor on the right bank failed. The sensor was replaced and all was normal for a couple of months. Then the lean codes started showing up.
I've replaced the fuel pump, filter, and fuel pressure regulator, yet the problem persists.
Any 5.4 guys out there with an idea, I'm all ears. I'm out of ideas.
Thanks,
~Bass
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Joined: Jan 2004
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From: St Louis
When I start the truck,
You have two sets of each trim, one for each bank. You have to monitor both banks and both trims for both banks to get any insight into the mixtures.
Did you ever check the infamous PCV hose and it's various elbows? It accounts for the huge majority of this set of symptoms.
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Joined: Jan 2004
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From: St Louis
Well, there is a way of doing that test that doesn't work (spray and listen) and one that does (spray and watch a scan tool's live data of the O2 voltage or the STFTs).
Depends on which one he did.
Depends on which one he did.
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My guess is that he did the first.
If the weather allows, I'll hook up my tools at the house and rerun the tests this weekend.
Thanks for the suggestion!
If the weather allows, I'll hook up my tools at the house and rerun the tests this weekend.
Thanks for the suggestion!
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Joined: Nov 2011
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From: Eastern WA
Bass, what did you use for spray? Did you find anything? One of my long term trims seems off in comparison to the other.
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Hi RBlac,
I've been on the road (with a different vehicle!) and haven't had a chance to test it yet. If the weather holds, I've already informed the boss (wife) that Sunday is "vehicle maintenance" day. I'll let you know what I find.
I've been on the road (with a different vehicle!) and haven't had a chance to test it yet. If the weather holds, I've already informed the boss (wife) that Sunday is "vehicle maintenance" day. I'll let you know what I find.
I was thinking of something like that.
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Well this went an entirely different direction than I had expected.
I replaced the fuel pressure regulator and all of the lean issues seem to have resolved. I've put about 2 hours on the truck since then, with absolutely no indication of a problem.
Two different Ford mechanics told me that the pressure regulator had tested OKand in good-natured fashion laughed at me when I told them that I was going to change it. "That's a waste of money. The regulator tested out fine". (3 fuel pumps and 3 filters later, I replaced the $30 part.....)
Apparently, they're not just pass/fail as long trim now varies from -3 to +3, where it was locked in at +25 before.
~Bass
I replaced the fuel pressure regulator and all of the lean issues seem to have resolved. I've put about 2 hours on the truck since then, with absolutely no indication of a problem.
Two different Ford mechanics told me that the pressure regulator had tested OKand in good-natured fashion laughed at me when I told them that I was going to change it. "That's a waste of money. The regulator tested out fine". (3 fuel pumps and 3 filters later, I replaced the $30 part.....)
Apparently, they're not just pass/fail as long trim now varies from -3 to +3, where it was locked in at +25 before.
~Bass
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