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Throttle Body Issue


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It's been a few months since I drove mine, but pretty sure it does it too... My best guess, is that it MIGHT be programed into the car to reduce stress on the rods. Might be a far fetched guess, but I've read that the "pull" on the rods from the crank being forced to spin when slowing down in gear can actually weaken them and cause failure if it's excessive, SO, keeping the rpms slightly up might prevent this during shifting to lower the risk of failure over the life of the car... Who knows though... Curious to see what others think about this too.

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If my cruise is ON and I turn it off with my foot on the pedal, the car accelerates. Maybe it's a feature? :headscratch: It probably has to do with the tune; I don't recall it doing that prior to installing the blower and motion delete plates.

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Perhaps it's just the lag time from when the injectors are 'told' to cut supply when you lift off of the accelerator. Little burst of unaccounted for fuel?

I dunno man, when my engine was stock, it help RPM very solid in between shifts, no drop hardly at all (but no spike either). Once I did the cams, the RPM's would drop like 'normal' in between shifts. Hopefully it's nothing to be too concerned about, but you might want to try a custom tune. Good luck.

 

Ken

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Here the thing - It's not on the Decel, it's only on the Excel.. It's as if I put the clutch in and hit the gas at the same time. I have 1000 miles on it and I felt it would go away by now but it's the same.

 

I know when the Shelby arrived at the Dealer they had to replace the throttle body "Kit". May be that it and should ask that it be checked and may be replaced??? May be as Ken said - custom tune!

 

Doc

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Here the thing - It's not on the Decel, it's only on the Excel.. It's as if I put the clutch in and hit the gas at the same time. I have 1000 miles on it and I felt it would go away by now but it's the same.

 

I know when the Shelby arrived at the Dealer they had to replace the throttle body "Kit". May be that it and should ask that it be checked and may be replaced??? May be as Ken said - custom tune!

 

Doc

 

 

If they replaced the electronics in the TB (sensor & servo) they could easily have adjusted it wrong ...that'd be my guess, but dunno.

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If they replaced the electronics in the TB (sensor & servo) they could easily have adjusted it wrong ...that'd be my guess, but dunno.

 

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Back to the Dealer is all I can think of now... If they replace the Throttle body with a "Kit" - it's time to replace the Throttle body. See if I can, get them to up-grade to a better TB. I am stumped!!!

Doc

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Doc, if they replace it with a new TB (electronics already installed & calibrated) and the problem goes away, then they almost certainly screwed up the calibration when they re-fitted the new electronics into the old TB. If that doesn't correct the problem and still not throwing any MILs/codes (I'm assuming you've seen no MILs but could be some transient codes logged -- they'll check), then I'm stumped.

 

Best of luck and let us know how it works out. --Dan

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Doc, if they replace it with a new TB (electronics already installed & calibrated) and the problem goes away, then they almost certainly screwed up the calibration when they re-fitted the new electronics into the old TB. If that doesn't correct the problem and still not throwing any MILs/codes (I'm assuming you've seen no MILs but could be some transient codes logged -- they'll check), then I'm stumped.

 

Best of luck and let us know how it works out. --Dan

 

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Hi Dan,

 

You are correct - No MIL/codes showing... I asked if a Cal'd. needed to be redone. They said no, it's in the Computer.?

Stumped is a good word.

Thanks - Doc

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Hi Dan,

 

You are correct - No MIL/codes showing... I asked if a Cal'd. needed to be redone. They said no, it's in the Computer.?

Stumped is a good word.

Thanks - Doc

 

 

We'll they're sort of right. The computer expects that when the butterfly position sensor returns a certain voltage it means that the butterflies are in a very specific position. Every key-on cycle (before starting even occurs) Ford's ETC has the TB servo push the butterflies 100% closed momentarily (idle is not 100% closed) to validate where the hard-stop is so that offsets can be calculated/validated, then makes certain assumptions (based on a properly calaibrated TB) as to what driver demand (your foot) should translate to what specific torque demand (TB butterfly angle) based on correlating angles and voltages (it doesn't correlate directly to your foot position). On the GT500 (not sure on the MGT/SGT but I assume it's the same) the calibration is set-up at +1.26 volts. So if you buy a TB with the electronics already installed it should have already been calibrated properly so that what the computer expects for a given position is what it sees. I'm oversimplifying the process -- there are many checks and even a separate processor that samples and checks the main processor to eliminate the possiblilty of single-point failures, etc, but all of this assumes the TB is properly calibrated. The fact that the revs are blipping a bit when you get off the gas and push in the clutch to shift makes me think there's a mispatch between sensed butterfly location and actual butterfly location -- something like that. Given that the hard-stop is checked on every key-on the only mismatch I can think of is a miscalibrated TB, and the fact the dealer changed the electronics makes that highly supect, imo.

 

Alternatively I guess it's possible that maybe something was simply reinstalled slightly out of position (seems unlikely), but I would expect that to affect driveability and throw codes -- but maybe not. I've never calibrated a TB myself but maybe one of the tuners in here or someone who has ported over the electronics to an aftermarket TB can shed some light on what could have been done wrong since that would seem to be the only thing different between your car and the many others out there original TB and original electronics ...at least that's what I'm thinking.

 

If interested, check out pages 105-110 or so in the Motorcraft OBD-II Operations Summary to get some insight on how the ETC (electronic throttle control) works on these cars (maybe if Toyota had all those checks they'd not be having the problems they are??)

 

One other thought... recall on late-model carbureted cars two functions: a dashpot to squirt extra fuel on accelerator tip-in so the car didn't stumble and a decel valve so that when you lift off the gas the revs don't drop right away (this was to minimize emissions). Both of these functions also exist on computer controlled fuel-injection cars tho implemented in tables in the tune (and far more accurately). But if the decel function is set to come off very slow, the decel lag might permit the engine revs to blip a bit when the wheel-load is removed when the clutch is pushed-in. I can't think of any reason why yours would be different unless the dealer reloaded the tune with an MGT (or??) tune instead of an SGT tune ...even then the rev blip is odd so I'm stumped if not the electronics.

 

Sorry for the long post... -Dan

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Well - I have some info on the "Throttle Body Kit" It is really called CMCV or Charge Motion Control Valve... Which opens and closes the valve's. Now, I think it should have been Cal'd to the Shelby program or would the Computer in the Shelby program this Valve???

 

Doc - Stumped? - May be! :redcard:

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Well - I have some info on the "Throttle Body Kit" It is really called CMCV or Charge Motion Control Valve... Which opens and closes the valve's. Now, I think it should have been Cal'd to the Shelby program or would the Computer in the Shelby program this Valve???

 

Doc - Stumped? - May be! :redcard:

Buy these: http://www.brenspeed.com/555-3125.html

Problem solved. :)

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Good afternoon,

 

I have noticed that when I shift, i come off the excel. engage the clutch peddle - but what happens is the RPM still increase. I have noticed that the Rev's continue to climb any where from 5 - 10 RPM. Any body have this issue?

Thanks,

Doc

 

 

A few years ago I read that the purpose of this was to reduce emissions and fuel consumption. The sudden drop-off and resumption of the engine in the old days allegedly caused more pollution and fuel consumption.

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Well - I have some info on the "Throttle Body Kit" It is really called CMCV or Charge Motion Control Valve... Which opens and closes the valve's. Now, I think it should have been Cal'd to the Shelby program or would the Computer in the Shelby program this Valve???

 

Doc - Stumped? - May be! redcard.gif

 

 

 

Just saw this ...yeah, CMCV is a totall different animal than the TB. Not sure what effect CMCV would have on this problem or if the SGT tune does anything with it's control.

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