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High Fuel Trim ONLY Bank 1, on High Rev. Low power under load

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High Fuel Trim ONLY Bank 1, on High Rev. Low power under load

 
  #1  
Old 06-23-2019, 09:12 PM
quantumfield
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High Fuel Trim ONLY Bank 1, on High Rev. Low power under load

5.4 V8. 2006 (in Navigator.)

LTFT1/STFT1 gets +% on higher rpm. (Bank 2 is fine)

I just recently replaced the Exhaust manifold on the passenger side Bank 1. The old was badly cracked and clearly taking in air on high revs. (Was pressure tested and was leaking badly) So it would seem logical that upon replacing a cracked manifold that my STFT and LTFT should stop running high +% on that side.
But NOTHING changed???

The LTFT pushes up to +16.2% @ 1500 rpm and 22%-25% at 2500 rpm.

I'm at a loss.. as after going through the PIG of a job of putting a new Exhaust manifold in to replace a badly cracked and obvious leaking one, I thought the trims would be closer to normal. I thought that was the fault..but no change in trims???

I'm wondering if the O2 sensor has been "poisoned" (if that is possible) by running in a high O2 environment for so long?

Both O2 sensors appear to be functional. I have charted the voltage using my scan tool and it is fluctuating up and down between 0.1 and 0.9 of course there could be a bias I cant see in the charts, not sure how to, or if you even can test for a functional O2 sensor which is potentially skewed?

This is clearly (?) Not a vacuum leak as Fuel trims are within +- 3% on idle. They only shoot up at higher RPM and only bank 1. A vacuum leak would do the opposite (high on idle and lower at high rpm).

Any help? Suggestions?




 
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Old 06-24-2019, 05:22 AM
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I can't offer anything helpful but will be watching this thread--very interesting symptoms.

Could this be possibly related to a cracked or leaking intake manifold? I've heard, read and seen YouTube videos about how awful some OEM Ford intakes deteriorate over time, typically the crossover coolant fitting the first to have problems. Just curious if this might extend to any of the intake runners too?

BTW great diagnostic numbers--what sort of scanner are you using?
 
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Old 06-24-2019, 11:46 AM
quantumfield
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Thanks. A vacuum leak would cause high fuel trims on idle and then the fuel trims improve on higher rpm. I'm getting the exact opposite. Fuel trims fine at idle but get terrible at high rpm.

I use the BlueDriver scantool which connects to my android pad via bluetooth. It's the most expensive ($99) dongle type scantool but it's well worth paying the extra as it will connect with most vehicles, whereas the cheap ones won't connect to Hyundai, Toyota and a few others. Plus I can reset codes and run mode6 and there is a library of actual test and repair procedures for odb codes. And of course live data which I reported above.
 
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Old 06-25-2019, 05:12 AM
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Thanks for the reply---good info on the scanner and especially the dongle. I'm about to begin using FORScan and having already been through a few cheap ELM-devices settled for one that's about twice as much as others---and its working perfectly, connecting and talking to my laptop without any issues.

Best of luck on this---as I said I'm interested to know the outcome.
 
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Old 06-26-2019, 05:14 PM
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I would be looking for an exhaust leak upstream of the O2 sensor.

Have you checked for vacuum leaks using propane?

Mode 6 showing any misfires?
 
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Old 06-30-2019, 07:02 AM
150R
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your going to be looking for a failed O2 sensor or a plugged cat, plus trims at high rpm and not idle are usually a result of one of these two.
If you can do a back pressure test at the o2 sensor port no more than 1.5 lbs. of back pressure.
swap the o2 with the other bank and see if the problem follows, no then cat yes replace o2.
The extra oxygen will burn up a cat and o2 quick, blow on a camp fire and see what happens.
This may help you,
 
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Old 07-02-2019, 11:14 PM
quantumfield
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Originally Posted by freak007 View Post
I would be looking for an exhaust leak upstream of the O2 sensor.

Have you checked for vacuum leaks using propane?

Mode 6 showing any misfires?
Yeh, you must have missed that but I Swappes out the manifold on that side as it was badly cracked. However, nothing changed. The O2 sensor is only about 2 inch down from ball joint on manifold. There is a remote possibility of a tiny leak on the ball joint, but putting my hand around it.on startup and near it on hot I cannot feel any blowing nor hear that typical puut puut puut sound. Of there is a tiny leak, I would have suspected that the fuel trims would at least be lower after removing a cracked manifold which I varied was leaking substantially.
 
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Old 07-02-2019, 11:20 PM
quantumfield
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Originally Posted by 150R View Post
your going to be looking for a failed O2 sensor or a plugged cat, plus trims at high rpm and not idle are usually a result of one of these two.
If you can do a back pressure test at the o2 sensor port no more than 1.5 lbs. of back pressure.
swap the o2 with the other bank and see if the problem follows, no then cat yes replace o2.
The extra oxygen will burn up a cat and o2 quick, blow on a camp fire and see what happens.
This may help you,
Thanks!

I did spray carb cleaner in the intake while watching the O2 sensor voltages on both banks and both O2 sensors jumped up to 0.9 after spraying which I thought would clarify the correct function of both sensors. However is it possible that an O2 sensor can still be fluctuating beyween .1 and .9 "correctly", but maybe a bit skewed to create a false reading? I guess the swap will clarify it. On the back pressure. I will have to buy a gage to do that. Any type of gage OK? Thanks.
 

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