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YOUR RESEARCHNegative Fuel Trim (slightly rich) Normal at Higher Elevation?
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Smoke-test intake
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Performed · outcome unconfirmed · Original poster
I smoke tested the intake for the umpteenth time yesterday and everything looks tight.
Negative Fuel Trim (slightly rich) Normal at Higher Elevation?
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Negative Fuel Trim (slightly rich) Normal at Higher Elevation?
Set "baseline"
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Suggestion · Original poster
Ok makes sense, so the MAF is setting the "baseline" for everything downstream and altitude is irrelevant.
Negative Fuel Trim (slightly rich) Normal at Higher Elevation?
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Howdy folks,
Getting the 212k mile 996 sorted after the "out of time" exhaust cam fiasco.
Curious question ... I have slightly below zero FRA and RKAT values on both banks, indicating that the DME is pulling fueling because it thinks it's running rich. I live at about 6000' near Denver. What I'm curious about is if this is normal at higher altitude given the lower O2 saturation? Curious to know what other folks in Colorado experience (assuming they have Durametric).
After a 4 hour drive today, I see the following values:
Bank 1
FRA: 0.93
RKAT: -1.31 %
Bank 2
FRA: 0.91
RKAT: -1.31%
I'll also note that those values seemed to improve slightly throughout the drive. They started at .90 /.89 and -1.36% respectively.
Mostly inquiring to gain some knowledge. If I understand correctly, the car will throw a check engine light at RKAT = +- 6% and an LN Engineering video with Tony Calas indicates that he starts to get concerned around the RKAT +- 3% level.
Thanks for any thoughts on the subject.
Steve
the Mass Air Flow sensor (MAF) senses the Mass/air density along with the air flow...... at high altitude the air is less dense , the MAF will know this as that is it's design and purpose...( if working properly)
That said the MAF is one of the suspects when there is rich running as is the fuel injectors ( leaking) , fuel pressure and fuel pressure regulator. Also there is a vacuum line to the fuel pressure regulator that if the small plastic line is broken or not getting full vacuum will raise the fuel pressure and cause the FRA to reduce injector time..
Your RKAT is fine but the FRA is a bit low to my liking...( but still in spec) ..
Ok makes sense, so the MAF is setting the "baseline" for everything downstream and altitude is irrelevant.
Would the vacuum line to the fuel pressure regulator show a leak during a smoke test? I smoke tested the intake for the umpteenth time yesterday and everything looks tight.
MAF seems ok: 1.32V and 18 kg/h. I do have a new Bosch MAF so maybe I'll throw that in there.
I assume fuel injectors are original so I wouldn't surprised if they're a bit leaky ...
As always, thank you!
SB
One correction on my last comment,,, I remember you have a 996.2 3 chain engine... so disregard the comments on the vacuum line to fuel pressure regulator, you don't have that...
Yours is a "non-return" system, meaning the there is no vacuum line and the regulator is built in the fuel tank...
So on your system the most likely suspect is the MAF or leaky injectors..
"""Ok makes sense, so the MAF is setting the "baseline" for everything downstream and altitude is irrelevant"""".<<< this is correct.....
Right !! That would have been your next question, " Where is my vacuum line and fuel pressure regulator? I can't find it !! ""
But it's your fault for not reminding me of your year model...( I'm old)
