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Rpm drops under lite acceleration
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Gungho
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Jul 17, 2009, 10:10 AM
Post #1 of 9
(5558 views)
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Rpm drops under lite acceleration
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I have an 06 mustang gt auto. When I am traveling at about 40mph and want to increase speed to 45 mph under lite throttle my rpms will drop from 2k to sometimes as low as 1k. When this happens It can take as long as 10 seconds to go from 40 to 45 mph. only way to fix this is to push the pedal to 1/2 throttle to cause a downshift. Any Ideas?
Best way to describe the feeling? Its like starting out in second gear from a stop in a manual. Real boggy!!!!!!!!
Things that I have done to try to fix this?
1. Cleaned throttle body
2. Cleaned the MAF sensor
3. New fuel filter
4. New air filter
5. Seafomed engine
6. disconnected battery
7. Tried performance tuning via sct tuner ( this mad the problem worse so I returned tune to stock)
8. Scanned for codes, non found.
Non of this worked
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Hammer Time
Ultimate Carjunky
/ Moderator
Jul 17, 2009, 10:18 AM
Post #2 of 9
(5555 views)
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Re: Rpm drops under lite acceleration
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I don't think you have a problem at all. The car is just engaging overdrive. It has an overrunning clutch that allows it to coast until you accelerate and then it engages.
Try pulling the shifter down out of overdrive and see if it goes away.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Gungho
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Jul 17, 2009, 11:41 AM
Post #3 of 9
(5550 views)
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Re: Rpm drops under lite acceleration
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It drops when I am accelerating. Grant it its not very much but my foot is on the pedal. The rpms drop even at 1/4 throttle. I did some more testing and it seems that in 4th gear their is a spot around 2k (with o/d on) that the rpms drop. However I did do some testing (today) with o/d off, and here is whats happening.
Example: O/D off in 4th gear
Once I hit 4th gear I am at 1.5k. With a steady 1/4 throttle I gain speed as well as rpms. As soon as I reach 2k (same 1/4 throttle) my rpms drop as well as my speed, not much but enough to notice. This is good news because i am now closer to an accurate description assuming O/D on and off symtoms are related.
With O/D on its a sudden rpm drop without any speed loss, with it off the rpms drop along with speed.
As a side note: My car is all stock but I did try one of thoes cold air intakes and it made the problem above so bad that I took it off.....the recovery from these rpm drops takes almost wide open throttle(with the cai)
(This post was edited by Gungho on Jul 17, 2009, 11:46 AM)
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Gungho
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Jul 17, 2009, 6:29 PM
Post #4 of 9
(5537 views)
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Re: Rpm drops under lite acceleration
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A little more info. This datalog was taken with O/D off. Notice the throttle position and rpms in both attachments
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Attachments:
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Pos1.jpg
(91.4 KB)
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Pos2.jpg
(93.4 KB)
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Hammer Time
Ultimate Carjunky
/ Moderator
Jul 17, 2009, 10:47 PM
Post #5 of 9
(5532 views)
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Re: Rpm drops under lite acceleration
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Your throttle is an electronic "drive by wire" system that is completely controlled by the computer. It has features built in that will act like that.
Here is a little explanation of how it works
TORQUE BASED ELECTRONIC THROTTLE CONTROL (ETC)
Overview
The torque based ETC is a hardware and software strategy that delivers an engine output torque (via throttle angle) based on driver demand (pedal position). It uses an electronic throttle body, the powertrain control module (PCM), and an accelerator pedal assembly to control the throttle opening and engine torque. The ETC system replaces the standard cable operated accelerator pedal, idle air control (IAC) valve, 3-wire throttle position sensor (TPS), and mechanical throttle body.
Torque based ETC enables aggressive automatic transmission shift schedules (earlier upshifts and later downshifts). This is possible by adjusting the throttle angle to achieve the same wheel torque during shifts, and by calculating this desired torque, the system prevents engine lugging (low RPM and low manifold vacuum) while still delivering the performance and torque requested by the driver. It also enables many fuel economy/emission improvement technologies such as variable camshaft timing (VCT) (deliver same torque during transitions).
Torque based ETC also results in less intrusive vehicle and engine speed limiting, along with smoother traction control.
Other benefits of ETC are:
- eliminate cruise control actuators
- eliminate idle air control (IAC) valve
- better airflow range
- packaging (no cable)
- more responsive powertrain at altitude and improved shift quality
It should be noted that the ETC system illuminates a powertrain malfunction indicator (wrench) on the instrument cluster when a concern is present. Concerns are accompanied by diagnostic trouble codes (DTCs) and may also illuminate the malfunction indicator lamp (MIL).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Gungho
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Jul 18, 2009, 6:51 PM
Post #6 of 9
(5519 views)
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Re: Rpm drops under lite acceleration
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So basically I need ford to reflash the pcm with a new strategy?
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Sidom
Veteran
/ Moderator
Jul 19, 2009, 9:55 AM
Post #7 of 9
(5507 views)
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Re: Rpm drops under lite acceleration
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There is a TSB 06-9-9 that refers to a hesitation after a long cruise, basically air getting into the fuel system.
That data stream has a lot of missing info, engine speed, engine load, coolant & air temps, fuel trims, O2 crosscounts, etc.
If you have access to those I would be looking at your fuel trims (both LT & ST trims) & engine load. If you are getting elevated trims (more positive) at higher rpms & load, then you are problably looking at a fuel delivery problem...........
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Gungho
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Jul 19, 2009, 2:52 PM
Post #8 of 9
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Re: Rpm drops under lite acceleration
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Thanks for the info but I am just not too familiar with the datalog variables. I know a lot of ppl have the capability to do these kind of logs. Their just isnt enough info on the web to make much use out of them unless you are a trained professional.
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Sidom
Veteran
/ Moderator
Jul 19, 2009, 3:50 PM
Post #9 of 9
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Re: Rpm drops under lite acceleration
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That pretty much the 1st thing is knowing when the data is good or bad. Fuel trims are a good place to start, I'm sure if you googled it there would have to be some info on it...... One of the many things it will tell you is if you running rich or lean, on which bank & most importantly WHEN.
The snapshots your provide look like they are barely off idle, going by rpm, tps voltages. Get to a screen with some of the primary inputs & take the snapshot during the failure event ( that 40 to 50mph area while driving), that will give you a lot more useful data.
You said there were no codes....On comp systems, everything has parameters it operates within, systems can fail within those parameters and then you will get no codes but a drivability problem. It's definately alot easier when something goes out of specs to set a code & push you in the right direction. Your system has 3 ways to retrieve codes. Memory, KOEO (key on engine off) & KOER (key on, engine running) and they should be retrieved in that order. Doing a KOEO or KOER before going to memory can is some case erase a memory code.....
Maybe take it out for a drive, get the problem to occur, take a couple of snapshots & pull codes again to see if anything comes up......
(This post was edited by Sidom on Jul 19, 2009, 3:51 PM)
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