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Hesitation while accelerating

(2004 Ford Thunderbird)
in West Chester, PA on November 07, 2010
no codes shown. tps and iacvalve replaced with tuneup. car accelerates ok when not racing to speed. hard acceleration causes hesitation at first. maf and o2sensor not replaced. codes have shown this on my other ford. someone questioned me about the air snorkel??????????? would that be a rare problem?
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Popular Answer
on November 07, 2010
The air snorkel...also known as the air tube and air filter box -- making sure they are secure and not cracked or broken, as unmetered air getting into the engine can cause issues. However, I don't feel like that is the issue.

When you say a tune up was performed -- what in all was done? Did they replace the spark plugs AND the coil boots? You really need to replace those boots during a tune up on this car. Also, the boots should be inspected to determine if there is any oil contamination. The valve cover gaskets on the 3.9L V8 can seep oil into the plug holes and oil soak the rubber coil boots...which deteriorates the boots and causes them to arc under load.

Being that your concern is primarily under load, I'm going to suggest you focus on the coil boots first, if they have not been replaced.

Any way you look at it -- just do not throw parts at this car! A good diagnostic test is in order, which will be cheaper than making an error in parts.

Good luck!
on November 08, 2010
thank you for your reply. this engine is a v6 and i am not sure if it has coil boots? i will do further research. if you have any more suggestions they would be greatly appreciated.
on November 08, 2010
I am sorry - do you have the right year indicated for your Thunderbird? The only engine available for a 2004 Thunderbird is a 3.9L V8.

If your car indeed has a V6, it must be a 1997 or earlier Thunderbird.

If in fact it is a different year and a V6, my thoughts and suggestions would most certainly please - let me know! Thanks.
on November 08, 2010
sorry about the misunderstanding. it is a 1994 t-bird lx with v6. the tune-up did include new plugs, wires, distr cap. iac was replaced. air hoses to egr and pcv and plenum air hose have been replaced but were leaking. could a failing alternator cause a problem at the fuel pump? the alternator was taken to 2 local shops which gave 2 different opinions. it does not have a problem keeping battery charged but headlights flicker slighty at times. it is only when the gas pedal is pushed hard from start that hesitation occurs. idles smooth and accelerates fine on highway cruises.
on November 08, 2010
Thank you for clearing up the model year. It makes a huge difference, as the cars could not be more different. Also, the engine management system is different - OBDI verses OBDII.

The alternator is not likely to be causing an issue. Also, I don't feel that a fuel pump is a likely issue, as fuel pressure does not seem to be an issue once you get going.

Hesitation from the start would make me still lean towards a vacuum leak of some sort, or possibly clogged EGR passages or EGR valve. A 3.8L V6 of this age likely has deposits in the EGR system that can cause some troubles.
on November 09, 2010
thank you for the reply this car did have vacum leaks and we replaced several hoses but some hoses still are a little soft and the egr valve was not checked. i dont have a clue how to check it but probably can figure it out.
on November 13, 2010
can this cars plug in diagnostic plug be "hot wired to flash codes? ocb1 tests are expensive.
on November 13, 2010
Yes, you can obtain flash codes from the check engine light by inserting a jumper wire into the OBDI connector and the tethered single spade terminal that is along with it. In the main trapezoid shaped connector, looking at the row of four spade slots at the bottom, the jumper goes into the third from the left (or second from the right).
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