Missing / Bucking at 40-45mph

[jmason]

2000 AWD V-8. 107,000....When it gets to 40-45mph, if I give it gas, seemingly putting a load on, prior to it downshifting, it bucks and hesitates. Especially when hot...I did replace the plugs and wires a year ago with taylors. Plugs are Motorcraft Platinums. Now it doesnt do it when i floor it, or at idle, or highway speeds...Only between 40-45, once in a blue moon 45-50mph. I do not see arcing at night, but it doesnt do it at idle..I have a set of OEM wires on order; I am going to take the Taylors off. When it does this behavior, no codes are sent, and the misfire monitor always says OK with the reader...

Any ideas besides the wires? I would think if it was the trans, or mechanical, it would have other bad habits...please advise.

 

[410Fortune]

vapor lock?
Flooding?
Cat converter?

No codes you say...wow

Start with the arcing wires for one.
Before the trans downshifts from OD to 3 it bucks badly? Falls flat on its face?
Does it recover?

 

[exploded99]

My first impression would be a bad thottle position sensor. You can probably duplicate that problem in third or O/D at that rpm (the rpm you are running at 40-45) because of the higher gearing. Might be tougher to duplicate it in 1st or 2nd cause of the lower gearing.

TPS is kind of like the accelerator pump on a carburetor... when you jump the gas its the amount of signal change from the TPS that tells the computer how much extra gas it will need.

No codes from a cheesy TPS. But give the MAF a good cleaning first.

 

[jmason]

Fixed !

I replaced the taylors with a set of bosch OEM wires....While doing this, i noticed the no. 8 boot on the spark plug side had a pinhole burn mark...it was literally a pinhole. i cut it open, the boot was burned through from the inside out. the exit hole was tiny.....why i never got a code is beyond me. thanx for the replies !

 

[exploded99]

Pretty wierd that a spark plug wire problem would only show up at a particular speed!

 

[jmason]

re:

Yea it was wierd. I suspect if I let it go much longer, it would have eventually been all the time. What I am most suprised about it that It wasnt giving me any misfire codes.