Inconsistent hesitation/buck/jerk around half throttle - TCCoA Forums
 
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post #1 of 5 (permalink) Old 10-01-2011, 04:28 PM Thread Starter
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Inconsistent hesitation/buck/jerk around half throttle

Over the last 3 months my mostly stock ’96 Thunderbird LX 4.6 has developed an inconsistent hesitation/buck/jerk when accelerating around half throttle. It doesn't do it at all on light acceleration or at WOT, only in between. This mostly happens in 2nd gear, but also occurs occasionally in 1st and even 3rd. It happens most consistently (but not always) if I ease through 1st gear and then quickly move the throttle position to somewhere around half open after the shift into 2nd. It seems to be independent of ambient temperature and it has happened both when the engine/transmission are cold and after 3 hours of highway driving. Quite the mystery, eh?

I’m not sure how the following maintenance and modifications relate to the problem, I just want to provide as much information as possible. I replaced the original spark plugs and wires in May 2010. The accelerator cable broke in December 2010 and had to be replaced with a full assembly (cable, housing, and TB bracket) from a ’98 Mustang because I couldn’t find the T-bird part anywhere. Around this same time I had a Ford dealership do a transmission service, changing the filter and just topping off the Mercon V instead of a full flush as I did back in '02 and '08. Stupidly, I drove it for a couple days after the service before checking the fluid level. At that point I started to feel a little roughness in shifting. Checking the fluid revealed it was almost a full quart low. That’s the last time that dealership ever saw my Bird! Once the fluid level was correct, the tranny has seemed fine.

This past summer when the hesitation started I had my new mechanic do a full induction/injection system treatment and new fuel filter to no improvement. Then I re-cleaned the MAF, changed the oil, oil filter, air filter and replaced the rear mufflers with Heartbeat muffler tips. Other recent modifications and repairs include 235/55R17 tires on 17x7.5” wheels, Monroe Sensa-Track shocks and struts, alignment, and replacement of a motor mount bolt that had almost worked itself loose.

Any thoughts? Is it as I fear and the torque converter or tranny are starting to go? Chassis/suspension/drivetrain issues? Some other sensor I am not thinking of? I want to troubleshoot as much as possible before taking it in and dropping a bunch of money if I don’t have to. Thanks in advance for reading and considering this ridiculously long post! -J
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post #2 of 5 (permalink) Old 10-01-2011, 04:57 PM
No, Mr. Lemmywinks, No!!!

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Check all vacuum hoses first.

Check the spark plug wells for coolant.

These are the cheaper things that can cause those symptoms...

Most cars are having those issues by now, even if they're well taken care of.

The evap hoses under the front pass. nose come to mind...

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post #3 of 5 (permalink) Old 10-01-2011, 05:37 PM Thread Starter
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That's a system I didn't think of and I have never replaced any hoses with over 115K now. Thanks Grog6, I'll post my findings.
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post #4 of 5 (permalink) Old 10-01-2011, 07:37 PM
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Could be a bad tps as well.
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post #5 of 5 (permalink) Old 10-02-2011, 04:38 PM Thread Starter
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Hoses look alright on visual inspection, will try the old soapy water test when I get a chance. Also looking into a multimeter to check the voltage to and from the Throttle Position Sensor. Will update later in the week with progress...
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