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2006 Ford Taurus SE, 3.0L Vulcan, AX4N/4F50N transmission
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Discussion Starter · #41 ·
I had a chance to watch some live fuel trim data this morning. For the most part during my drive, LTFT1 hovered around 0… You can see the max/min markers for LTFT 1 & 2 in the upper right corner of the screenshot that's attached. I noticed that LTFT1 didn't drop to ~0 until the engine reached operating temperature, which is also when I began to feel the random surge/bucking. You can also see that neither LTFT reached the 10% mark mentioned above.

With all this said, does this info give any clues where to go from here in an attempt to resolve this very annoying problem?

I will also double check the condition of my air filter later today as soon as I get a chance, and post my findings.

Thanks so much for all the help you guys have offered. It is very much appreciated! The community here is awesome and extremely knowledgeable!
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What is the R THR parameter?

Just collected some live data from my 2000 Vulcan (60 mph, cruise control ON, A/C off):

PID Parameter Value

03 Fuel System CL
04 LOAD_PCT 25 - 40 %
05 ECT 87 C = 189 F
07 LONGFT1 -1 %
09 LONGFT2 -1 %
0A FRP 275 kPa = 40 PSI
0C RPM 2120 /min
0D VSS 98 km/h = 61 mph
0E SPARKADV #1 42 - 48 %
0F IAT 24 C = 75 F
10 MAF 15 - 21 g/s = 2.0 - 2.8 lb/min
11 TP 22 - 24 %

The values of the Throttle Position vary because of the cruise control. The values of the MAF sensor and calculated LOAD percentage vary too. I assume:
  • You find the same MAF values at 60 mph because that is directly related to the amount of gas used at that speed (if the engine is in Closed Loop).
  • The PCM extrapolates Throttle Position and MAF to what the MAF value would be at Wide Open Throttle and thus guesses the LOAD percentage.
  • I could imagine that when the air filter is blocking the flow, you find a higher TP at the same MAF value, but I'm not sure.
 

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2006 Ford Taurus SE, 3.0L Vulcan, AX4N/4F50N transmission
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81 Posts
Discussion Starter · #43 ·
What is the R THR parameter?

Just collected some live data from my 2000 Vulcan (60 mph, cruise control ON, A/C off):

PID Parameter Value

03 Fuel System CL
04 LOAD_PCT 25 - 40 %
05 ECT 87 C = 189 F
07 LONGFT1 -1 %
09 LONGFT2 -1 %
0A FRP 275 kPa = 40 PSI
0C RPM 2120 /min
0D VSS 98 km/h = 61 mph
0E SPARKADV #1 42 - 48 %
0F IAT 24 C = 75 F
10 MAF 15 - 21 g/s = 2.0 - 2.8 lb/min
11 TP 22 - 24 %

The values of the Throttle Position vary because of the cruise control. The values of the MAF sensor and calculated LOAD percentage vary too. I assume:
  • You find the same MAF values at 60 mph because that is directly related to the amount of gas used at that speed (if the engine is in Closed Loop).
  • The PCM extrapolates Throttle Position and MAF to what the MAF value would be at Wide Open Throttle and thus guesses the LOAD percentage.
  • I could imagine that when the air filter is blocking the flow, you find a higher TP at the same MAF value, but I'm not sure.
"R THR" Is Relative Throttle Position"
 

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Now that I think about it, I realize I do not understand why MAF and LOAD% would vary so much during cruising at constant speed and RPM.

Chart, do you happen to have a graph of the MAF signal during highway driving? Any engine, not necessarily a Taurus.
 

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2006 Ford Taurus SE, 3.0L Vulcan, AX4N/4F50N transmission
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Discussion Starter · #45 ·
I've checked the air filter and it isn't collapsed, although I may change it since it's been in for about 18 months, and nearly 10k miles. I don't recall what the OEM change interval is for the air filter -- 15k maybe??

Edit: With the provided information, can anyone see where I might look from here to resolve this surge/bucking/misfire issue? There are some trips where I don't feel it and some trips where the car runs like --- umm, well, you get the picture.
 

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Now that I think about it, I realize I do not understand why MAF and LOAD% would vary so much during cruising at constant speed and RPM.

Chart, do you happen to have a graph of the MAF signal during highway driving? Any engine, not necessarily a Taurus.
PIc. Surprised at how often reach near 100%. In the middle a downshift to gear 3 while going up hill.
-chart-
 

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Did you ever check your TPS to see if it is noisy. Put a ohm meter on it and rotate it to see if it is linear and no noise or ohms jumping around. The TPS won't cause a rough idle but it will cause a buck. Also have you checked the o ring on the runner valve?
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