Throttle Lag Summary

2646 Views 11 Replies 5 Participants Last post by  Bob Jusnes
Can someone sum this up for me?

Like what do I need to do to fix it.

And does a higher octane help?
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If you think you are experience excessive throttle lag, you have 2 choices. Go to the dealer and complain, they may have an updated PCM tune for you. Or go with an aftermarket tune.

Higher octane shouldnt really improve anything, since your car isnt tuned for it.
Higher octane fuel will help to alleviate, but not fully eliminate, throttle lag or downshift delay.

More detail on higher octane.

Higher octane allows the engine to operate in a Taller gear ratio at a low(er) RPM without "lugging", knock/ping.

So with a higher octane when you initially re-apply pressure to the gas pedal shortly after/during the lift-throttle upshift the transaxle may (more often) remain, briefly, in the "taller" gear ratio since the ECU "knows" that will not result in a seriously detrimental level of Knock/Ping. The ECU would therefore allow the DBW system to immediately begin raising engine RPM, generating additional drive torque, as a result of the new, re-applied, gas pedal pressure.

So now the engine RPM is no longer at idle and should you continue to increase the pressure on the gas pedal such that a downshift is required to keep the engine in a proper, non-lugging, operating range there is now much more likelihood that there will be be enough ATF pump pressure/flow volume to accommodate the upcoming downshift.

The above might also be an indication that a fairly s..l...o....w re-application of pressure to the gas pedal after a FULL lift-throttle event might often alleviate the downshift delay/hesitation regardless of octane. Whereas a quick/fast/heavy re-application would almost always result in a serious level of knock/ping absent an immediate downshift.

Counter-intuitive, huh..??



Furthermore I suspect that the new variable displacement ATF oil pressure pump just announced for the Ford Edge will be a final solution for this problem once implemented across the product line. Actually it would be even nicer if all manufacturers of FWD vehicles would adopt this solution.
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That would be true if the PCM decided to venture out of its set spark tables. It wont climb in spark just to see if youre using a higher octane fuel. It is tuned for 87, and wont be able to take advantage of the higher octane fuel to prevent "lugging".
[quote author=Bob Jusnes link=topic=61163.msg1044142#msg1044142 date=1162378425]
That would be true if the PCM decided to venture out of its set spark tables.  It wont climb in spark just to see if youre using a higher octane fuel.  It is tuned for 87, and wont be able to take advantage of the higher octane fuel to prevent "lugging".

Actually that is wrong. Your engine/transaxle ECU is like a young child, continually "pushing" the parameters to build a parametric map of what is reasonable/acceptable vs what is not.

The engine/transaxle ECU builds a full "bandwidth" parametric map so it "knows" what regions of the map not to venture into. But then it continually tests the far regions of that map to discover, for instance, if the tolerance level of the MAF/IAT module has wondered off due to someone using a K&N air filter and the module is now becoming slowly covered with oil and dirt, or, 92 octane is NOW being used.

Besides which, COLD, DENSE, wintertime intake airflow will exhibit the same results, insofar as Fuel/air mixture ratio is concerned, as would moving to a higher octane.
wwest, I'm wondering where your getting your info from?
Multiple sets of Ford repair/shop manuals, going all the way back to a 64 T-bird, Same for many Toyota/Lexus vehicles going back to the 92 LS400, annual subscribtion access to, and finally, the entire information bandwidth of the internet.

Oh, over 55 years of DIY shade tree mechanicing, beginning with Farmall, John Deere (poppin jonny) and Ford Ferguson tractors. First car was a 1956 Ford Fairlane, then 58, then 63 T-bird, then...Ran most of my Fords of the late sixties to mid-seventies for well over 200k miles.

No Ford ever let me down.

Current Ford ownership is 93 Ranger PU, 92 & 94 AWD Aerostars (which should have NEVER gone out of production), E-350 V10 based MH.

Shame they didn't have the good sense to build those early Lexus vehicles or at least immediately clone them.

Was just in TN/AR in early October for Tyronza all-year school reunion and the Memphis Blues ball. Pat Kerr Tigrett was a summer sweetheart over in Clinton/Savannah in the late forties.

Maybe Alan Mullay will open the eyes of a few of those moribund Ford design engineers.
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It is spelled Alan Mullaly...
I thought maybe you had some inside info that the rest of us don't.
All I can tell you is I tuned my Fusion and the lag is gone, it has more power and gets better MPG. The results from a custom tune from Bob was great. You should look into it.
And just to add to what WWEST said about the Higher Octane, all I used was Higher Octane from the time I bought the car and it had a bad lag. Using the Higher Octane did nothing for the car until it got a custom tune.
Colder denser air is measured within the MAF with an built in IAT sensor. This reading is fully dynamic, it does not check periodically to see if there is colder air, it is continually measuring the temperature and volume of the incoming air. Unfortunately, within the last 55 years Ford has not implemented the OLS (Octane Level Sensors) to see if SFIPPIHT (Some Fool Is Putting Premium In His Tank.)

Or wait, did I see the SFIPPIHT settings in the SCT Advantage software........
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